Abstract
Endemic freshwater sponges (demosponges, Lubomirskiidae) dominate in Lake Baikal, Central Siberia, Russia. These sponges are multicellular filter-feeding animals that represent a complex consortium of many species of eukaryotes and prokaryotes. In recent years, mass disease and death of Lubomirskia baicalensis has been a significant problem in Lake Baikal. The etiology and ecology of these events remain unknown. Bacteria from the families Flavobacteriaceae and Oxalobacteraceae dominate the microbiomes of diseased sponges. Both species are opportunistic pathogens common in freshwater ecosystems. The aim of our study was to analyze the genomes of strains Janthinobacterium sp. SLB01 and Flavobacterium sp. SLB02, isolated from diseased sponges to identify the reasons for their joint dominance. Janthinobacterium sp. SLB01 attacks other cells using a type VI secretion system and suppresses gram-positive bacteria with violacein, and regulates its own activity via quorum sensing. It produces floc and strong biofilm by exopolysaccharide biosynthesis and PEP-CTERM/XrtA protein expression. Flavobacterium sp. SLB02 utilizes the fragments of cell walls produced by polysaccharides. These two strains have a marked difference in carbohydrate acquisition. We described a possible means of joint occupation of the ecological niche in the freshwater sponge microbial community. This study expands the understanding of the symbiotic relationship of microorganisms with freshwater Baikal sponges.
Highlights
Endemic freshwater sponges dominate in Lake Baikal in the littoral zone
We found genes associated with the quorum sensing in the Janthinobacterium sp
SLB01 can colonize the space and suppress the other bacteria with violacein. This pigment production was observed in cell culture (Figure 5) and all required genes are present in its genome
Summary
Endemic freshwater sponges (demosponges, Lubomirskiidae) dominate in Lake Baikal in the littoral zone. They cover up to 50% of available surfaces [1] and represent a complex consortium of many species of eukaryotes and prokaryotes, including diverse chlorophyll-containing microalgae [2,3,4]. The first appearance of anomalously pink-colored Lubomirskia baicalensis (Pallas, 1776) sponges was reported in 2011. Mass disease and death of freshwater sponges of the family Lubomirskiidae, have been noted as leading to significant negative changes in biota. Diseased and dying sponges have been observed in many areas of the lake [5,6,7]. The etiology and ecology of these events remains unknown
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