Patterns of Microorganisms Inhabiting Antarctic Freshwater Lakes with Special Reference to Aquatic Moss Pillars

Abstract

The Antarctic continent has ice-free areas with many freshwater lakes that support life. These lakes are generally ultra-oligotrophic and possess simplified food chains dominated by microorganisms with algal and cyanobacterial mats often occurring in the lake bottoms. In association with such mats, aquatic mosses sometimes form unique towerlike structures called “moss pillars.” Previous microflora analysis revealed the presence of several key groups (e.g., Leptolyngbya and Bradyrhizobium species) and uncultivated novel lineages in the pillars and the fact that the bacterial communities differ among the pillar sections. A wide range of eukaryotic phylotypes associated with algae, ciliates, fungi, nematodes, rotifers, and tardigrades, as well as unclassified phylotypes, were detected in the pillars. Moss pillars colonizing the nutrient-limited lakes are likely formed by a synergistic association of diverse organisms including both primary producers and decomposers. Indeed, a potential functional zonation, possibly reflected by different redox conditions within the pillar structure, was identified during the analyses of functional genes (e.g., CO2 fixation-coding genes). Interestingly, multiple sequences related to moss pillar-derived sequences were also observed in other Antarctic habitats. These findings provide clues toward solving a conundrum pertaining to Antarctic lake ecosystems: biomass-rich communities existing in the nutrient-poor conditions.