Linking ecology and systematics of acidobacteria: Distinct habitat preferences of the Acidobacteriia and Blastocatellia in tundra soils

The Acidobacteria is one of the major bacterial phyla in soils and peatlands. The currently explored diversity within this phylum is assigned to 15 class-level units, five of which contain described members. The ecologically relevant traits of acidobacteria from different classes remain poorly understood. Here, we compared the patterns of acidobacterial diversity in sandy soils of tundra, along a gradient of increasing vegetation–unfixed aeolian sand, semi-fixed surfaces with mosses and lichens, and mature soil under fully developed plant cover. The Acidobacteria-affiliated 16S rRNA gene sequences retrieved from these soils comprised 11 to 33% of total bacterial reads and belonged mostly to members of the classes Acidobacteriia and Blastocatellia, which displayed opposite habitat preferences. The relative abundance of the Blastocatellia was maximal in unfixed sands and declined in soils of vegetated plots, showing positive correlation with soil pH and negative correlation with carbon and nitrogen availability. An opposite tendency was characteristic for the Acidobacteriia. Most Blastocatellia-affiliated reads belonged to as-yet-undescribed members of the family Arenimicrobiaceae, which appears to be characteristic for dry, depleted in organic matter soil habitats. The pool of Acidobacteriia-affiliated sequences, apart from Acidobacteriaceae- and Bryobacteraceae-related reads, had a large proportion of sequences from as-yet-undescribed families, which seem to specialize in degrading plant-derived organic matter. This analysis reveals sandy soils of tundra as a source of novel acidobacterial diversity and provides an insight into the ecological preferences of different taxonomic groups within this phylum.

酸杆菌门（Acidobacteria）是土壤与泥炭地中的主要细菌类群之一。目前已探明的该门类多样性可划分为15个纲级单元，其中仅5个单元包含已被正式描述的成员。不同纲级酸杆菌的生态相关性状仍未得到充分解析。本研究针对苔原沙质土壤，沿植被梯度设置了三类生境：未固定风积沙、覆盖苔藓与地衣的半固定地表，以及具备完整植被覆盖的成熟土壤，并对比了其中酸杆菌的多样性分布模式。从上述土壤中获取的隶属于酸杆菌门的16S rRNA基因序列，占细菌总测序读段的11%至33%，且主要归类于酸杆菌纲（Acidobacteriia）与芽囊杆菌纲（Blastocatellia），二者展现出完全相反的生境偏好。芽囊杆菌纲的相对丰度在未固定沙中达到峰值，随植被覆盖土壤的发育逐渐降低，与土壤pH值呈正相关，与碳、氮可利用性呈负相关；酸杆菌纲则呈现出截然相反的分布趋势。绝大多数隶属于芽囊杆菌纲的测序读段，属于暂未被描述的Arenimicrobiaceae科成员，该类群似乎是干燥、有机质贫乏土壤生境的标志性类群。除了与酸杆菌科（Acidobacteriaceae）和Bryobacteraceae相关的序列外，酸杆菌纲的序列库中还包含大量暂未被正式描述的科的序列，这些类群似乎专性降解植物来源的有机质。本研究揭示苔原沙质土壤是新型酸杆菌多样性的重要资源库，并为解析该门类内不同分类群的生态偏好提供了关键见解。