Bundera sinkhole, located in north-western Australia, is the only known continental anchialine system in the Southern Hemisphere. Anchialine environments are characterised by stratified water columns with complex physicochemical profiles spanning hypoxic and anoxic regions, often displaying high levels of endemism. Research on these systems has focused on eukaryotic fauna, however interest in the microbial diversity of these environments is growing, enabled by next-generation DNA sequencing. Here we report detailed analyses of the microbial communities across a depth profile within Bundera sinkhole (from 2 to 28 m), involving parallel physicochemical measurements, cell population counts and 16S rRNA amplicon analyses. We observed clear shifts in microbial cell counts, community diversity, structure and membership across the depth profile, reflecting changing levels of light, organic and inorganic energy sources as well as shifts in pH and salinity. While Proteobacteria were the most abundant phylum found, there was a high degree of taxonomic novelty within these microbial communities, with 13,028 unique amplicon sequence variants (ASVs) identified, belonging to 67 identifiable bacterial and archaeal phyla. Of these ~4,600, more than one third of the total, were unclassified below family level. A small number of ASVs were highly abundant at select depths, all of which were part of the set not classified below family level. The 2 m and 6 m samples had in common two highly abundant ASVs, belonging to the Ectothiorhodospiraceae and Thiotrichaceae families, while the 8 m community contained a single predominant ASV belonging to family Thioglobaceae. At lower depths a different Ectothiorhodospiraceae ASV comprised up to 68% relative abundance, peaking at 26 and 28 m. Canonical correspondence analyses indicated that community structure was strongly influenced by differences in key physicochemical parameters, particularly salinity, dissolved organic and inorganic carbon, phosphate and sulphate concentrations. This work highlights the potential for anchialine systems to house considerable microbial novelty, potentially driven by adaptations to the specific physicochemical makeup of their local environment. As only a small number of anchialine systems have been examined via microbial community studies to date, this work is particularly valuable, contributing new insight regarding the microbial residents of these important and sensitive environments.

Bundera天坑位于澳大利亚西北部，是南半球唯一已知的大陆anchialine系统。Anchialine 环境的特点是分层水柱，其物理化学分布复杂，跨越缺氧和缺氧区域，通常表现出高水平的特有性。对这些系统的研究主要集中在真核动物群上，但是由于下一代 DNA 测序，人们对这些环境的微生物多样性的兴趣正在增长。在这里，我们报告了对 Bundera 天坑内深度剖面（从 2 到 28 m）的微生物群落的详细分析，包括平行的物理化学测量、细胞群计数和 16S rRNA 扩增子分析。我们观察到微生物细胞计数、群落多样性、结构和成员在深度剖面上的明显变化，反映光、有机和无机能源水平的变化以及 pH 值和盐度的变化。虽然变形菌门是发现的最丰富的门，但在这些微生物群落中存在高度的分类学新颖性，鉴定出 13,028 个独特的扩增子序列变体 (ASV)，属于 67 个可识别的细菌和古细菌门。其中约 4,600 人，超过总数的三分之一，未分类低于家庭级别。少数 ASV 在选定的深度非常丰富，所有这些都是不属于家庭级别的集合的一部分。2 m 和 6 m 的样本共有两个高度丰富的 ASV，属于 Ectothiorhodospiraceae 和 Thiotrichaceae 科，而 8 m 群落包含一个属于 Thioglobaceae 的主要 ASV。在较低深度，不同的 Ectothiorhodospiraceae ASV 的相对丰度高达 68%，在 26 和 28 m 处达到峰值。典型对应分析表明，群落结构受到关键物理化学参数差异的强烈影响，特别是盐度、溶解的有机和无机碳、磷酸盐和硫酸盐浓度。这项工作突出了anchialine系统容纳大量微生物新颖性的潜力，这可能是由对其当地环境的特定物理化学组成的适应驱动的。由于只检查了少量的anchialine系统 特别是盐度、溶解的有机和无机碳、磷酸盐和硫酸盐浓度。这项工作突出了anchialine系统容纳大量微生物新颖性的潜力，这可能是由对其当地环境的特定物理化学组成的适应驱动的。由于只检查了少量的anchialine系统 特别是盐度、溶解的有机和无机碳、磷酸盐和硫酸盐浓度。这项工作突出了anchialine系统容纳大量微生物新颖性的潜力，这可能是由对其当地环境的特定物理化学组成的适应驱动的。由于只检查了少量的anchialine系统通过迄今为止的微生物群落研究，这项工作特别有价值，为这些重要和敏感​​环境的微生物居民提供了新的见解。