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. 2020 Oct 30;21(21):8128.
doi: 10.3390/ijms21218128.

Cooperative Interaction of Janthinobacterium sp. SLB01 and Flavobacterium sp. SLB02 in the Diseased Sponge Lubomirskia baicalensis

Ivan Petrushin  1   2 , Sergei Belikov  1 , Lubov Chernogor  1
Affiliations

Cooperative Interaction of Janthinobacterium sp. SLB01 and Flavobacterium sp. SLB02 in the Diseased Sponge Lubomirskia baicalensis

Ivan Petrushin et al. Int J Mol Sci. .

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.

Keywords: Flavobacterium sp.; Janthinobacterium sp.; Lubomirskia baicalensis; bioinformatics; floc formation; genomes; opportunistic pathogens; symbiosis.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Phylogenetic tree of Janthinobacterium sp. SLB01 (a) and Flavobacterium sp. SLB02 (b) with closely related species. Trees are built based on approximately 400 universal marker genes by PhyloPhlAn (a maximum-likelihood method). GenBank accession numbers are given in Tables S1a and S1b. Strains of Flavobacterium with an aquatic niche are highlighted with a bold font.
Figure 2
Figure 2
Diagram of the violacein production loci in the Janthinobacterium sp. SLB01 genome. Genes are displayed with arrows. A conserved sequence motif within the promoter region is displayed with the gray bar.
Figure 3
Figure 3
Schematic diagram of the genetic organization of the type VI secretion system main gene cluster in the Janthinobacterium sp. SLB01 genome.
Figure 4
Figure 4
Schematic diagram of the genetic organization of Janthinobacterium sp. SLB01 gene clusters required for floc formation: exopolysaccharides (EPS) synthesis, PEP-CTERM, and exosortase. Genes are indicated by arrows and the direction of the arrows represents the direction of transcription of the genes in the genome.
Figure 5
Figure 5
Visual observance of floc formation and violacein synthesis by Janthinobacterium sp. SLB01.
Figure 6
Figure 6
Polysaccharide utilization loci (PULs) of the Flavobacterium sp. SLB02 genome that have homologous PULs in the Flavobacterium johnsoniae UW101 genome.
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