Temporal and spatial variations in the bacterial community composition in lake bosten, a large, brackish lake in china

ABSTRACT The bacteria inhabiting brackish lake environments in arid or semi-arid regions have not been thoroughly identified. In this study, the 454 pyrosequencing method was used to study

the sedimentary bacterial community composition (BCC) and diversity in Lake Bosten, which is located in the arid regions of northwestern China. A total of 210,233 high-quality sequence reads

and 8,427 operational taxonomic units (OTUs) were successfully obtained from 20 selected sediment samples. The samples were quantitatively dominated by members of _Proteobacteria_ (34.1% ± 

11.0%), _Firmicutes_ (21.8% ± 21.9%) and _Chloroflexi_ (13.8% ± 5.2%), which accounted for more than 69% of the bacterial sequences. The results showed that (i) Lake Bosten had significant

spatial heterogeneity, and TOC(total organic carbon), TN(total nitrogen) and TP(total phosphorus) were the most important contributors to bacterial diversity; (ii) there was lower taxonomic

richness in Lake Bosten, which is located in an arid region, than in reference lakes in eutrophic floodplains and marine systems; and (iii) there was a low percentage of dominant species in

the BCC and a high percentage of unidentified bacteria. Our data help to better describe the diversity and distribution of bacterial communities in contaminated brackish lakes in arid

regions and how microbes respond to environmental changes in these stable inland waters in arid or semi-arid regions. SIMILAR CONTENT BEING VIEWED BY OTHERS BACTERIAL DIVERSITY IN SURFACE

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Open access 22 February 2023 INTRODUCTION Heterotrophic bacteria are major constituents of pelagic aquatic ecosystems, where they play a prominent role in the breakdown of organic compounds

and the remineralization of nutrients as well as in trophic coupling to eukaryote predators1. Recently, lakes, especially lakes in arid and semi-arid regions, have been described as early

indicators of both regional and global environmental change. Microorganisms are some of the most important factors in the nutrient cycling and decomposition of organic matter in lake

sediments2, and bacteria are thought to be a sensitive sentinel of those environmental changes3. Sediments are some of the most diverse microbial habitats and play a key role in the

biogeochemical cycles of organic matter decomposition and of major elements, including carbon, nitrogen and phosphorus. Sediment is now an major topic in the investigation of bacterial

communities because analysis of the community in sediments can provide clues to understanding benthic ecosystem processes, particularly in saline and eutrophic aquatic environments. Sediment

bacteria, due to their high population density (>108 cells/g), play an important ecological role in the biogeochemical cycle in lake ecosystems4. The biomass and community structure of

sediment bacteria change due to changes in the physical, chemical and biological factors in water and sediment, so they can also be considered representative organisms indicating

environmental changes5. The combination of abiotic factors and microorganisms in sediments has an important effect on nutrient balance in water. Arid and semi-arid regions account for almost

one-third of the world’s land area6, and lakes in these areas provide sparse but valuable water resources for fragile environments and humans. However, these water resources are also

inevitably affected by human activities. Studies have shown that many water resources in arid and semi-arid regions have been contaminated by eutrophication or salinity7,8,9. Lake Bosten is

the largest inland brackish lake in the arid regions of northwestern China, and it plays an important role in the surrounding terrestrial ecosystems. Surprisingly, the lake was a freshwater

lake before the 1960s, but climate change and human activities over the past 50 years have developed it into a brackish lake with moderate nutrient levels10,11. Salinization and

eutrophication continue to affect Lake Bosten. Therefore, Lake Bosten provides us with an exclusive opportunity to carefully study the potential response mechanisms of bacterial communities

in the early stages of salinization and eutrophication. At the same time, due to anthropogenic agricultural and tourism activities, it also forms a nutritional gradient from malnutrition to

eutrophication12, and this complex ecosystem is an ideal model for studying the response of bacterial communities to salinity and nutrient gradients13. This work is particularly important

for the restoration of polluted dry lakes, as changes in microbial communities may be some of the more rapid agents of biological change. Although a small number of studies have reported

temporal changes in community composition in the sediments of the Lake Bosten, these studies have concentrated on a single sample from a single season14. There is little research on the

variations over the four seasons across the whole lake. In this study, we used high-throughput sequencing technology and redundancy analysis to explore the association between

spatial-temporal changes in Lake Bosten bacterial communities and environmental factors. The research objectives are to identify (1) Whether there is spatial-temporal heterogeneity in the

bacterial communities of lake sediments under the dual effects of eutrophication and salinity and (2) Which environmental factors control the assembly of bacterial communities in the

sediments of Lake Bosten. MATERIALS AND METHODS STUDY AREA AND SAMPLING Lake Bosten (86°19′~87°28′E, 41°46′~42°08′N, 1046 m above sea level) is located in the southern part of Bohu County,

Xinjiang Province, in the lower reaches of the Kaidu River. The basin is located in the center of Eurasia. The combination of sunlight and heat, the annual average precipitation is 64.3 mm,

and the annual average evaporation is 1,881.2 mm, resulting in an inland desert climate15. The lake covers an area of approximately 1,100 km2 16 with an average water depth of 7 meters and a

maximum depth of more than 16 meters3. The annual average temperature is about 7.9 °C, and the coldest temperature occurs in January (−12.7 °C). There is a four-month freeze season at Lake

Bosten from December to March every year15. Mountain Tian in Xinjiang, which is the lowest point of the Basin Yan. Additionally, the lake covers a vast area of more than 1,100 km2 and has a

maximum water depth of more than 16 m. Originating from the snow-covered Mountain Tian, the Kaidu River, with an annual average runoff volume of 34 × 108 m3, supplies 85% of the water volume

of Lake Bosten17. Moreover, as Lake Bosten is located in the centre of Eurasia, a good level of light and heat provide extremely favourable natural conditions for the development of the

lake, allowing the basin to be rich in animal and plant resources. The Kaidu River is divided into two branches at the Baolang Sumu Water Diversion Project, which are respectively injected

into two lakes of Lake Bosten. The Large Lake Area is 55 km from east to west and 20 km wide from north to south. At an altitude of 1,048.75 m, the water surface area is 1,002. 4 km2, volume

is 88 × 108 m3, average water depth is 7.38 m, the maximum depth is 16 m. The centre of lake area (HX) is located in the centre of the Large Lake Area and is highly disturbed by

hydrodynamic forces, but is less affected by external influences. Huangshuigou area (HS) located in the northwest of the Large Lake Area and is enriched with nutrients (nitrogen and

phosphorus) and salinity from agricultural irrigation and industrial wastewater discharged from the surrounding rivers. There are the highest nutrients and salinity in the area of Lake

Bosten4. The Large Lake Area is regularly monitored by the Environmental Protection Bureau of Bayinguoleng Mongolian Autonomous Prefecture and has been continuously monitored for over ten

years. Small Lake Area, also known as macrophyte-dominated area (SC), covers an area of about 300 km2, and is an important reed production base in China. From 8 May 2013 to 18 January 2014,

20 samples were collected from the centre of Lake area (HX, 87°08′00″E, 42°00′00″N), Huangshuigou area (HS, 86°50′30″E, 42°06′00″N), estuary of the Kaidu River (KD, 86°44′30″E, 41°53′40″N)

and its nearby area (KF, 86°46′20″E, 41°57′00″N) and macrophyte-dominated area (SC, 86°38′5″E, 41°47′24″N). We avoided extreme weather when sampling and sampled when it was fine. Undisturbed

duplicate sediments (0–5 cm deep) were collected seasonally using a Petersen grab sampler from 8 May 2013 to 18 January 2014 (Fig. 1). The sediment samples were transferred into sterile

plastic containers, and immediately frozen at −80 °C for storage until analysis. PHYSICOCHEMICAL ANALYSIS The sediment samples were dried to constant weight using a freeze dryer (Alpha 1–2

LD, Martin Christ Instrument Co, Germany). Total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC) content in the sediments were determined according to standard methods

(Jin and Tu 1990). The temperature, salinity, dissolved oxygen (DO), Salinity (TDS), and pH of the lowest water layer covering the sediment were measured using a multi-parameter water

quality detector (YSI 6600V2, USA). After DAPI (4′, 6-diamidino-2-phenylindole) staining direct counting, the bacterial abundance in the deposited samples was determined by epifluorescence

microscopy12,15. We used one-way ANOVA to test the correlation between environmental factors. DNA EXTRACTION, PURIFICATION AND PCR AMPLIFICATION Total DNA was extracted from twenty 0.25 g

freeze-dried pellets using the Soil Rapid DNA Rotation Kit (MP Biomedicals, Fountain Pkwy. Solon, OH, USA). Genomic DNA concentration and purity were determined by an ultraviolet

spectrophotometer. According to the concentration test results, the integrity of the DNA sample was detected by 0.8% agarose gel electrophoresis. The test conditions were as follows: voltage

120 V, electrophoresis time was about 20 minutes. The extracted DNA stock was diluted to 20 ng.μl−1 and used as a PCR template. The V1–V3 region of the bacterial 16S rRNA gene was amplified

using PCR amplification of universal primers 8 F (5′-AGAGTTTGATCCTGGCTCAG-3′) and 533 R (5′-TTACCGCGGCTGCTGGCAC-3′)18. PCR amplification was carried out using a 50 μL reaction system under

the following conditions: predenaturation at 94 °C for 5 minutes, and denaturation at 50 °C. Anneal at 94 °C for 30 seconds, 55 °C for 45 seconds, 72 °C for 1 minute, 27 cycles, 72 °C for 8 

minutes, and stored at 4 °C, the experiment was repeated 3 times. The PCR product was purified and concentrated using E.Z.N.A. ®Cycle-Pure Kit. The PCR products from each sample were then

mixed in a single tube in equimolar ratios. 454 PYROSEQUENCING AND DATA ANALYSIS Amplicon pyrosequencing was performed on a Roche Genome Sequencer GS FLX Titanium platform using a 454/Roche

A sequencing primer kit. Each read file produced by a pyrosequencing run is associated with one quality file, which contains the quality score for each base. After sequencing, the QIIME

software package19 was used to exclude sequences with a length of less than 200 bases, an average mass fraction of less than 25, or no primers and barcode sequences. The rest of the

sequences were trimmed and compared against the Bacterial Silva database (SILVA version 106; http://www.arb-silva.de/documentation/background/release-106/) via QIIME. Similar sequences were

clustered into Operational Taxonomic Units (OTUs) using a minimum identity of 97% by UCLUST software20. Good’s coverage, abundance-based coverage estimator (ACE), Chao 1 richness estimator,

Shannon and Simpson diversity indices were also calculated by QIIME pipeline. RESULTS PHYSICAL AND CHEMICAL FACTORS The environmental characteristics of the studied lake are presented in

Fig. S1. The overlying water temperatures showed a characteristic annual cycle, with a higher temperature in the HS sample (26.9 °C, summer) and lower temperatures in the KF and SC samples

(1.0 °C, winter). In the overlying water, the concentration of TDS increased from 278 mg L−1 in the KD sample (winter) to 2,238 mg L−1 in the HS sample (spring). The average concentrations

of TN and TP in the seasonal sediment samples remained stable at approximately 1.74 (KD, winter) to 4.08 (SC, winter) mg·g−1 and 0.15 (KD, winter) to 0.52 (HS, winter) mg·g−1, respectively.

The average concentration of TOC among the seasonal sediment samples ranged from 3.07 (HX, summer) to 12.4 (HS, summer) mg·g−1. BACTERIAL DIVERSITY The seasonal variation in the bacterial

community structure in Lake Bosten was determined using 454 pyrosequencing technology. From all sediment samples, sequencing analysis yielded a total of 210,233 high-quality sequence reads

with an average length of approximately 400 bp effective sequence, 8,427 OTUs, and 97% sequence identity threshold. The effective sequence length for each sediment sample ranged from 8,729

to 12,909, and the number of OTUs ranged from 1,319 to 2,209 (Table 1). The sparse curve with a cluster distance of 0.03 was still not saturated and increased (Fig. 2), indicating that new

bacterial populations may continue to appear after 10,000 reads and sequencing. However, the values of the Shannon index (4.68–6.64) for all sediment samples in this study stabilized,

suggesting that more sequencing may be required, but most of the bacterial diversity of the sample has been captured. In addition, good reports showed that these libraries represent the

majority of bacterial 16S rRNA sequences present in each sediment sample, ranging from 0.902 to 0.951 (Table 1). BACTERIAL COMMUNITY COMPOSITION In the filtered high-quality sequences, the

dominant bacterial phylum or sub-phylum in each sediment sample was identified by the SILVA database using the QIIME algorithm (the top 10 most abundant phyla or sub-phyla in each sample).

The most abundant bacterial phyla were _Proteobacteria_ (34.1% ± 11.0%), _Firmicutes_ (21.8% ± 21.9%) and _Chloroflexi_ (13.8% ± 5.2%), representing more than 69.0% of the bacterial

sequences (Fig. 3). In addition, a large number of bacteria were detected at lower numbers (<4% relative abundance per phyla) in the sediment samples, such as _Planctomycetes_, _TA06_,

_Candidate division WS3_, _Bacteroidetes, Spirochaetae_, _Chlorobi_, _OD1_, _OP8_ and _Deferribacteres_ (Fig. 3). _Firmicutes_ (10.9%–65.7%) dominated in the spring and summer samples. In

contrast, the autumn and winter samples were mainly dominated by _Deltaproteobacteria_ (0.19%–27.2%) and _Chloroflexi_ (0.18%–22.1%) (Fig. 3). Figure 4 shows the 56 dominant genera in the

sediment samples. At the genus level, the differences between the sediment samples are more pronounced. Microorganisms from the genera Uncultured _Neisseriaceae_ (21.62%) and

_Lysinibacillus_ (22.63%) predominated in the BS1 and BS2 samples but were less abundant in the other samples. The genus _Clostridium_ (27.94%) and unclassified _Peptostreptococcaceae_

(16.47%) had higher proportions in the HS (summer) sample. Unclassified _Anaerolineaceae_ (2.42%–16.38%) and _Sva0485_ (0.77%–16.33%) were more abundant in SC (spring) and KD (summer)

samples. Therefore, the main bacterial populations in the twenty sediment samples are slightly different. REDUNDANCY ANALYSIS OF SEDIMENT BACTERIA AND ENVIRONMENTAL FACTORS Microorganisms

are highly sensitive to environmental changes, and the relationship between different environmental factors and the microflora structure can be determined according to the size of the angle

between bacterial and environmental factors and the length of the connection in a redundancy analysis (Fig. 5). _Betaproteobacteria_, _Firmicutes_, and _Gammaproteobacteria_ were negatively

correlated with TDS and DO, whereas _Chloroflexi_ and _Bacteroidetes_ were positively correlated with TDS and DO. _Deltaproteobacteria_ was positively correlated with each indicator. In the

RDA analysis diagram, combining the sediments showed that the levels of the physical and chemical indicators phylum flora structure, TN, TOC and TP were the main factors that influenced the

growth of bacteria, but other environmental factors also had certain effects. DISCUSSION The five sampling points selected from the Large Lake area and Small Lake area in Lake Bosten are

representative areas for studying the sediment bacterial community structure of Lake Bosten. Based on the results of the physical and chemical analyses, the physical and chemical indicators

of the 20 samples showed certain similarities and differences due to factors such as time and geographical location. There was no significant change in the pH value among the 20 samples, but

the other indicators had significant differences (Fig. S1). Most obviously, the values of TDS at the Huangshuigou and central lake areas were significantly higher than those at the other

sampling points (P < 0.05). According to previous research, agricultural production around Lake Bosten discharges a large amount of farmland drainage with high salinity that includes

chloride ions, sulfate ions, ammonia nitrogen and so on. This discharge was the main reason for the increased salt content in Lake Bosten, as 71% and 29% of the lake water flows into the

Large Lake Area and Small Lake Area, respectively21. In addition, the TDS of the summer and autumn samples from the estuary of Lake Bosten and nearby areas was higher than the TDS in other

seasons. Weberscannell _et al_.22 noted that changes in the concentrations of TDS in natural waters are often attributed to the discharge of industrial effluent, increased precipitation, or

saltwater intrusion. In the summer and autumn, the Kaidu River glaciers melted and created abundant snow and ice water resources, which caused the water volume to increase rapidly23, leading

to a significant increase in TDS content. However, the specific causes of this difference in TDS could be complex, and other potential reasons for this difference still deserve further

investigation. Interestingly, the contents of TD, TP and TOC in the Huangshuigou and macrophyte-dominated area were higher in winter than in summer (Fig. S1), which may be because the

continuous low temperature in winter inhibits microbial activity and reduces the effect of microorganisms on the removal of nitrogen and phosphorus24. On the other hand, TN and TP

concentrations were reduced due to dilution and biological blocking25. In addition, a large number of aquatic plants in the aquatic grass area can enrich N and P and desalinize water by

adsorbing, decomposing, oxidizing and precipitating the water, salt, and N and P26. This also explained why the value of pollution indicators in the macrophyte-dominated area was higher than

that in the Huangshuigou area. A large number of studies have shown that temperature is an important factor affecting the structure of bacterial communities27. High temperatures can

increase the metabolic rate, thus causing the cycle of organic matter to increase in speed; a drop in temperature will lower the growth rate of bacteria and lower productivity27. This trend

has also been confirmed in the laboratory28. Therefore, the bacterial community composition of the samples in autumn and winter was more complicated than that in the samples in spring and

summer (Fig. 3). This may be due to the relative abundance of the dominant bacteria _Firmicutes_ in spring and summer decreasing greatly under the influence of temperature. Temperature

changes improve the competitive advantage of other bacteria and increase the relative abundance of other bacteria, leading to a higher diversity of bacteria in autumn and winter. The

competitive advantage between microorganisms changes under conditions such as temperature changes29,30, and some studies on bacteria also illustrate this point. In aquatic ecosystems, in

addition to temperature, the most relevant factor to bacterial growth and reproduction is inorganic salt nutrition (such as TN, TP) and algae biomass31. Shiah′s study also suggests that in

the Chesapeake at temperatures below 20 °C, temperature, more than nutrient levels, functions as the main control factor of planktonic bacteria. At temperatures above 20 °C, the nutrient

control became dominant5. In the whole bacterial community, the three most abundant phyla were _Firmicutes_ (21.8% ± 21.9%), _Proteobacteria_ (_Deltaproteobacteria_ and

_Gammaproteobacteria_) (34.1% ± 11.0%) and _Chloroflexi_ (13.8% ± 5.2%), accounting for more than 69.0% of the bacterial community. This community structure is largely in accordance with

those found in other sediments and soils worldwide32,33 (Fig. 3). _Firmicutes_ (10.9%–65.7%) dominated sediment samples in spring and summer but was present at less than 1% abundance in

autumn and winter. The RDA suggested that the members of _Firmicutes_ were not particularly dependent on the nutrients in the seasonal samples (Fig. 5). This finding was consistent with that

from a previous study in Lake Dongping, a shallow lake34. Under anaerobic conditions, nitrate can be used to achieve denitrification35. DO in spring and summer was lower than that in autumn

and winter, suggesting that the increase in DO would restrain the growth of _Firmicutes_. Related studies have shown that DO controls the _Firmicutes_ community structure more than other

main factors, which is consistent with the results of RDA analysis (Fig. 5). The genus _Clostridium_ are specialized anaerobic bacteria that mainly exist in anaerobic environments and have

strong degradation ability and high metabolic activity36. The genus _Bacillus_ was the primary component of _Firmicutes_, and the group was abundant in the spring and summer samples (Fig. 

4). A previous study observed significant variations in the composition of the genus _Bacillus_ in different estuary sediments from Lake Taihu37, and their presence caused the production of

high amounts of ammonia, nitrite and other hazardous substances38. The genus _Lysinibacillus_, which includes facultative bacteria, can reduce macromolecular organic matter to low molecular

weight acids, dissolve nutrients in the soil sediment39, degrade crude compounds40, fix nitrogen from the air41 and prevent plant diseases and insect pests39, and therefore has certain

environmental benefits. _Proteobacteria_ (13.5%–55.0%) were the dominant bacteria in all sediment samples. However, in samples from different seasons, the relative abundances of different

kinds of _Proteobacteria_ were very different (Fig. 3). In this study, _Deltaproteobacteria_ were the main group of _Proteobacteria_, followed by _Gammaproteobacteria_ and

_Betaproteobacteria_ (Fig. 3). In the sediment samples from autumn and winter, _Deltaproteobacteria_ dominated. In freshwater sediments, _Deltaproteobacteria_ were also abundant6,42.

_Deltaproteobacteria_ was mainly represented by unclassified _Desulfarculaceae_ in the present study (Fig. 4). As sulfate-reducing bacteria, the family _Desulfarculaceae_ has been detected

as being dominant in the salt marsh sediments of the North Atlantic and on the East Coast of the US. These bacteria are important participants in the sulfur biogeochemical cycle43,44 and can

degrade organic matter. The resultant compensatory nutrition and energy sources play an important ecological role, especially in the anaerobic degradation of organic matter and the

conversion process45,46. In the past 20 years, the chemicals in Lake Bosten have come to include high levels of sodium sulfate47; a high concentration of SO42− and TDS provide good nutrient

conditions, thereby promoting the growth of bacteria. Therefore, its dominant position in the sample may be related to nutrients in the lake. As a second group of _Proteobacteria_48,49,

_Gammaproteobacteria_ play an important role in the degradation and absorption of organic compounds50, ammonia51 and sulfide52,53 (Fig. 3). The relative abundance of _Gammaproteobacteria_

(1.27–16.40%) in the estuary and its vicinity was significantly higher than that in the other samples. Several previous studies have revealed that _Gammaproteobacteria_ usually exist in

sediments in areas contaminated with agricultural pollution or organic matter15,54. The agricultural activities around Lake Bosten have increased the amounts of organic pollutants in the

estuary55, and the organic content of the sediments has increased56. Therefore, it was not surprising that _Gammaproteobacteria_ were abundant in the estuarine sediments of Lake Bosten, and

a high relative abundance of _Gammaproteobacteria_ has also been observed in other aquatic systems57,58. Additionally, the genus _Pseudomonas_ was found to be representative of

_Gammaproteobacteria_. The group appeared as the dominant genus in the estuarine sediment samples, especially in the spring sample (Fig. 4). A high relative abundance of the genus

_Pseudomonas_ has been observed in the estuarine sediments of Lake Poyang59. In addition, the genus _Acinetobacter_ was a minor proportion of the _Gammaproteobacteria_ (Fig. 4). A previous

study indicated that the genus _Acinetobacter_ is commonly detected as phosphorus-accumulating microorganisms in sediments60 and that the presence of the genus _Acinetobacter_ might explain

the phosphorus-accumulating microorganism concentration in the phosphorus-containing sediment samples from summer (Fig. S1)59. In this study, _Betaproteobacteria_ appeared as the predominant

phylum in all sediment samples (Fig. 3). This finding was consistent with that of a previous study in which _Betaproteobacteria_ was found to be the predominant group in the upper sediments

of Lake Taihu61. _Betaproteobacteria_ (0.87–40.56%) are a dominant bacterial group widely distributed in freshwater lakes around the world. They are present in surface waters and are one of

the most studied groups to date62, but they are rarely found on the open seas or in salt lakes2,63. The presence and success of _Betaproteobacteria_ in freshwater lakes are related to their

ability to respond quickly to changes in bioavailable nutrient content, e.g., they have a rapid response to dissolved organic carbon64. However, the results of the RDA analysis in this

study showed that nutrients such as TOC, TP and TN did not exhibit positive correlations with the relative abundance of _Betaproteobacteria_ (Fig. 5). Interestingly, the most abundant OTU in

_Betaproteobacteria_ was the genus _Thiobacillus_. The genus _Thiobacillus_ is a dominant genus in habitats polluted with mine wastewater65, and they are very abundant in all four seasons.

_Thiobacillus_ was the dominant genus in the HS samples. This indicates that there may be substantial mineral pollution in the HS area. _Chloroflexi_ (3.94–22.13%) was evenly distributed

among the various sediment samples. A previous study indicated that members of _Chloroflexi_ are active not only in deep subsurface sediments on the ocean floor66 but also in various

wastewater treatment systems67. In this study, the RDA showed a positive correlation between the concentration of TOC and the relative abundance of _Chloroflexi_ (Fig. 5). This finding was

consistent with that of a previous study that reported on riparian sedimentary ecosystems34. _Chloroflexi_ can biodegrade organic pollutants68, giving it a better growth advantage in

eutrophic environments69. In addition, _Chloroflexi_ efficiently degrades chlorides. Zanaroli _et al_.70 found that the genus does not produce O2 by photosynthesis and cannot fix nitrogen

but has a dechlorination function. Unclassified _Anaerolineaceae_ was dominant in _Chloroflexi_, and the group dominated in all seasonal sediment samples (Fig. 4). The family

_Anaerolineaceae_ has previously been found to be dominant in the estuarine sediments of Lake Taihu69, and members of this family are often involved in the anaerobic degradation process of

alkanes71,72, as well as in the biodegradation process of organic pollutants59,73. Bacteroidetes were dominant in samples from all seasons (Fig. 3). A previous study revealed that

Bacteroidetes has the capacity to decompose complex molecules in freshwater sediments74. Furthermore, our results indicated that the genus Flavobacterium and unclassified vadinHA17 were the

two primary components of Bacteroidetes, of which the genus Flavobacterium was the most abundant OTU. A similar study revealed that the genus Flavobacterium functions in heterotrophic

nitrification and metabolizes refractory organic compounds75. Therefore, the enrichment of the genus Flavobacterium may indicate widespread organic pollution in Lake Bosten. It is noteworthy

that there was a substantial percentage of unclassified bacterial groups detected in these seasonal samples (Fig. 4). In addition to those mentioned above, there were still several dominant

unclassified bacteria found in the samples, such as unclassified _Caldilineaceae_, unclassified _KD4–96_, and some incertae cedis bacteria (Fig. 4). Numerous studies have observed the

abundance of unclassified bacteria in various lake systems76,77, especially in sulfur-rich and anoxic environments18,78. The existence of abundant unclassified species in the estuarine

sediments of Lake Bosten indicates that new bacterial communities inhabit Lake Bosten and that the bacterial diversity, taxonomy and phylogenetics of the location deserve further attention.

CONCLUSION In this study, 454 pyrosequencing technology was used to study the bacterial community structure of the sediments in Lake Bosten. We found that the bacterial community of Lake

Bosten sediments is spatially specific. For example, the genus _Thiobacillus_, which is mainly found in mine wastewater and had a relatively high abundance in other areas, was found in the

HS area; enrichment in the HS area may indicate that the area is rich in minerals. In addition, there are obvious seasonal changes in the bacterial community of sediments. For example, the

relative abundance of the Firmicutes in the SC samples in the spring sampling was 53.3%, but only 0.14% in winter. The discharge of agricultural sewage caused the TN and TP of the HS area to

be higher than those of other samples, and the adsorption and decomposition of aquatic plants led to the enrichment of pollutants in the SC area. Furthermore, temperature and nutrient

status are key factors driving the bacterial community structure in sediments. We have discovered nitrifying bacteria with a large amount of degradable pollutants in Bosten Lake, and our

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the Environmental Monitoring Station of the Environmental Protection Bureau of Bayingolin Mongolia Autonomous Prefecture for helping with sample collection and water chemical analysis. This

work was supported by the National Science Foundation of China (41601573), the Key University Science Research Project of Anhui Province (KJ2019A0641), the Linkage Project of Anhui Public

Welfare Technology Application Research (1704f0804053) and the Science and the Technology Innovation Strategy and Soft Science Research Special Project of Anhui Province (1706a02020048).

Anonymous reviewers are acknowledged for their constructive comments and helpful suggestions. AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * School of Civil Engineering and Architecture,

Chuzhou University, Chuzhou, 239000, China Lei Zhang, Tingting Shen, Yu Cheng, Tingting Zhao & Li Li * State Key Laboratory of Pharmaceutical Biotechnology, Nanjing University, Nanjing,

China Pengfei Qi Authors * Lei Zhang View author publications You can also search for this author inPubMed Google Scholar * Tingting Shen View author publications You can also search for

this author inPubMed Google Scholar * Yu Cheng View author publications You can also search for this author inPubMed Google Scholar * Tingting Zhao View author publications You can also

search for this author inPubMed Google Scholar * Li Li View author publications You can also search for this author inPubMed Google Scholar * Pengfei Qi View author publications You can also

search for this author inPubMed Google Scholar CONTRIBUTIONS L.Z.: wrote the manuscript. T.T.S.: provided materials. Y.C.: proof read the manuscript. T.T.Z.: data analysis. L.L.: laboratory

analysis. F.P.Q.: collection of the sedmients samples. All authors read and approved the final manuscript. CORRESPONDING AUTHOR Correspondence to Lei Zhang. ETHICS DECLARATIONS COMPETING

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spatial variations in the bacterial community composition in Lake Bosten, a large, brackish lake in China. _Sci Rep_ 10, 304 (2020). https://doi.org/10.1038/s41598-019-57238-5 Download

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