青藏高原纳木错夏季沿岸水体可培养细菌多样性及其与理化因子的相关性

Diversity of culturable bacteria and its correlation with physicochemical factors in summer coastal waters of Nam Co, Tibetan Plateau

纳木错位于青藏高原中南部,是该地区独具特色的咸水湖泊。对纳木错夏季沿岸水体可培养细菌物种多样性进行研究,并揭示细菌群落多样性及物种分布与水质理化指标间的相关性。运用直接涂布平板法与稀释涂布平板法来分离湖水中的可培养细菌,细菌菌株的鉴定采用16S rDNA基因序列分析结合经典分类方法,并使用R 4.1.1、SPSS 20.0等软件分析细菌群落多样性。结果显示,从纳木错夏季沿岸水体20个样点中共分离得到681株可培养细菌,鉴定分为16属43种,其中优势种为Acinetobacter johnsonii。Spearman相关系数显示,总磷与总氮均为影响细菌群落多样性的主要理化指标,总磷显著影响细菌总丰度(P<0.05),总氮显著影响Simpson多样性指数(P<0.05)。RDA结果显示,氨氮是影响细菌群落分布的主要理化指标(P<0.05)。本研究初步揭示了纳木错夏季沿岸水体可培养细菌群落多样性,并获得较丰富的细菌菌株资源。

Nam Co, located in the central and southern part of the Tibetan Plateau, is a unique saline lake in the region. To carry out the study on the composition and diversity of culturable bacterial species in coastal water bodies in the summer season in Nam Co and to reveal the response pattern of bacterial species diversity and community distribution to physicochemical factors will not only be able to provide valuable resources and references for the study of microbial diversity and the development and utilization of special bacterial resources under extreme environment, can provide a theoretical basis for the conservation of lake ecosystems on the Tibetan Plateau. In this study, 20 sampling sites were selected based on lake water distribution combined with geographical differences in coastal areas of Nam Co in the summer of 2020. Water samples were collected with sterile samplers at approximately 15 m from the shore and 50 cm from the water surface, the collected water samples were packed in sterile plastic buckets and brought back immediately to the laboratory to isolate the culturable bacteria inside. The direct coating plate method combined with the dilution coating plate method was used to isolate culturable bacteria from lake water, and the plate four zone streaking method was used to purify the whole bacterial strains, and bacterial strains were stored by freezing in glycerol tubes at-20 °C. The medium used in the experiment was beef extract peptone medium, when isolated the cultivable bacteria strains from water samples, the water added in the medium was Nam Co lake water: sterile water=1∶1, when purified the bacterial strains, all the added water in the medium was sterile water. The identification of bacterial strains was performed by the combination of classical taxonomy and 16S rDNA gene sequence analysis, and relevant statistical software, such as R 4.1.1 and SPSS 20.0, etc., was used to analyze the community distribution and species diversity of bacteria and their correlation with aquatic physicochemical factors. A total of 681 cultivable bacteria were isolated from 20 sampling sites of coastal water in the summer season in Nam Co, and all strains identified were classified into 43 species in 16 genera, of which the dominant species was Acinetobacter johnsonii and the dominant genus was Acinetobacter, and Acinetobacter johnsonii was a common bacterial species among 20 sampling sites. Among the 20 sampling sites, number 12 had the highest number of species, and it had 18 species;the second is number 4, which had 14 species, and number 11, which had the lowest number of species, which had only six species.The Shannon-Wiener diversity indexes, Simpson diversity indexes, and Pielou evenness indexes showed generally consistent trends among 20 sampling sites, the three indexes synthetically indicated that number 10 had the highest species diversity and the most even distribution, whereas the number 9 had the lowest species diversity and the most uneven distribution. Spearman correlation coefficient showed that both total nitrogen and total phosphorus were the main physicochemical factors affecting the diversity of cultivable bacterial species in water bodies in summer in Nam Co, and there was a significant correlation between total bacterial abundance and total phosphorus(P<0.05), and the Simpson diversity indexes was also significantly correlated with total nitrogen(P<0.05). Redundancy analysis results showed that ammonia nitrogen was the main environmental factor affecting the distribution of cultivable bacterial communities in water body during summer in Nam Co(P<0.05). This study initially revealed the species diversity and community distribution of culturable bacteria in coastal water bodies and their correlations with environmental factors in the summer season in Nam Co, and obtained a relatively rich resource of bacterial strains, in the hope of providing a theoretical basis for the conservation of lake ecosystems in the Tibetan Plateau and the exploitation and utilization of special bacterial resources.