Table_1_Abundant Taxa and Favorable Pathways in the Microbiome of Soda-Saline Lakes in Inner Mongolia.XLSX

Soda-saline lakes are a special type of alkaline lake in which the chloride concentration is greater than the carbonate/bicarbonate concentration. Due to the high pH and a usually higher osmotic pressure than that of a normal soda lake, the microbes may need more energy to thrive in such a double-extreme environment. In this study, we systematically investigated the microbiome of the brine and sediment samples of nine artificially separated ponds (salinities from 5.5% to saturation) within two soda-saline lakes in Inner Mongolia of China, assisted by deep metagenomic sequencing. The main inorganic ions shaped the microbial community in both the brines and sediments, and the chloride concentration exhibited the most significant effect. A total of 385 metagenome-assembled genomes (MAGs) were generated, in which 38 MAGs were revealed as the abundant species in at least one of the eighteen different samples. Interestingly, these abundant species also represented the most branches of the microbiome of the soda-saline lakes at the phylum level. These abundant taxa were close relatives of microorganisms from classic soda lakes and neutral saline environments, but forming a combination of both habitats. Notably, approximately half of the abundant MAGs had the potential to drive dissimilatory sulfur cycling. These MAGs included four autotrophic Ectothiorhodospiraceae MAGs, one Cyanobacteria MAG and nine heterotrophic MAGs with the potential to oxidize sulfur, as well as four abundant MAGs containing genes for elemental sulfur respiration. The possible reason is that reductive sulfur compounds could provide additional energy for the related species, and reductions of oxidative sulfur compounds are more prone to occur under alkaline conditions which support the sulfur cycling. In addition, a unique 1,4-alpha-glucan phosphorylation pathway, but not a normal hydrolysis one, was found in the abundant Candidatus Nanohaloarchaeota MAG NHA-1, which would produce more energy in polysaccharide degradation. In summary, this work has revealed the abundant taxa and favorable pathways in the soda-saline lakes, indicating that efficient energy regeneration pathway may increase the capacity for environmental adaptation in such saline-alkaline environments. These findings may help to elucidate the relationship between microbial metabolism and adaptation to extreme environments.

苏打盐湖（soda-saline lakes）是一类特殊的碱性湖泊，其氯化物浓度高于碳酸盐/碳酸氢盐浓度。由于其pH值偏高且渗透压通常高于常规苏打湖，微生物在这种双重极端环境中繁衍往往需要消耗更多能量。本研究依托深度宏基因组测序（deep metagenomic sequencing）技术，对中国内蒙古两处苏打盐湖内9个人工分隔池塘（盐度范围5.5%至饱和状态）的卤水与沉积物样本的微生物组（microbiome）展开了系统性调研。主要无机离子塑造了卤水与沉积物中的微生物群落结构，其中氯化物浓度的影响最为显著。研究共构建得到385个宏基因组组装基因组（metagenome-assembled genomes, MAGs），其中38个MAGs被鉴定为18个不同样本中至少一个样本内的优势物种。有趣的是，这些优势物种同时也代表了苏打盐湖微生物组在门水平上的主要演化分支。这些优势类群与经典苏打湖及中性盐环境中的微生物为近缘类群，但兼具两类生境的特征组合。值得注意的是，约半数优势MAGs具备驱动异化硫循环（dissimilatory sulfur cycling）的潜力。这些MAGs包括4个自养性外硫红螺菌科（Ectothiorhodospiraceae）MAGs、1个蓝细菌门（Cyanobacteria）MAG以及9个具备硫氧化潜力的异养MAGs，此外还有4个携带元素硫呼吸相关基因的优势MAGs。其潜在机制为：还原性硫化合物可为相关类群提供额外能量，而氧化性硫化合物的还原过程在碱性条件下更易发生，这一过程支撑了硫循环的进行。此外，在优势类群候选纳米嗜盐古菌门（Candidatus Nanohaloarchaeota）MAG NHA-1中，发现了一条独特的1,4-α-葡聚糖磷酸化通路（1,4-alpha-glucan phosphorylation pathway），而非常规的水解通路，该通路可在多糖降解过程中产生更多能量。综上，本研究揭示了苏打盐湖中的优势类群与优势代谢通路，表明高效的能量再生通路或许可提升微生物在这类盐碱环境中的环境适应能力，相关结果或有助于阐明微生物代谢与极端环境适应之间的关联机制。