Structure of Microbial Mats in the Mramornaya Bay (Crimea) Coastal Areas

Abstract

The structure of microbial mats from the Mramornaya Bay (Crimea) was investigated. Light microscopy in combination with transmission and scanning electron microscopy revealed the base of bacterial mats to be interwoven thin filaments (100 to 500 nm in diameter) consisting mainly of sulfur. Numerous bean-shaped single microbial cells (~1.6 × 0.7 µm), some of which were attached to sulfur filaments, were also revealed. High-throughput sequencing of the 16S rRNA genes revealed predominance of bacteria of the genera Arcobacter (27%), Alcaligenes (17%), and Desulfuromonas (8.5%) as well as of uncultured members of the family Lachnospiraceae (4.9%). No clearly predominant microbial taxa were revealed in the detritus sample below the mats. Similar to the bacterial mat, bacteria of the genera Arcobacter and Desulfuromonas were predominant in the detritus, but their relative abundance was significantly lower (4.1 and 6%, respectively). Analysis of the 16S rRNA gene sequences specific for the genus Arcobacter revealed considerable phylogenetic diversity of this group in the samples from both the upper bacterial mats and the detritus sediment. Most of obtained sequences formed common clusters with the sequences of various uncultured members of the genus Arcobacter, while an insignificant share of them was related to the recently described sulfide-oxidizing bacterium “Candidatus Arcobacter sulfidicus.” Thus, members of the phylogenetically heterogeneous group of epsilonproteobacteria of the genus Arcobacter were the dominant component of the Mramornaya Bay microbial communities.