Ultrastructural description of development and cell composition of primmorphs in the endemic Baikal sponge Lubomirskia baicalensis

International audienceThe morphological description of morphogen-esis accompanying primmorph formation from cell aggre-gates in the endemic Baikal sponge Lubomirskia baicalensis as well as the description of cell composition of these primmorphs was investigated. Development of small sponges from dissociated cells in L. baicalensis is a stepwise process that can be separated into three stages: 1—primary aggregates; 2—early-stage primmorphs; and 3—primmorphs or young sponges. Primary aggregates are irregular in shape and consist of loosely packed cells. Early-stage primmorph development is characterized by cell sorting, aggregate compactization, surface epitheliza-tion and cell differentiation. Primmorphs or young sponges have developed elements of the aquiferous system. The main morphogenesis occurring during primmorph devel-opment in L. baicalensis is the epithelization of the cell aggregate surface accompanied by the flattening of poorly connected spherical cells. The main sources of new exopinacoderm development during L. baicalensis prim-morph formation are choanocytes and amoebocytes that transdifferentiate into exopinacocytes. The cellular com-position of L. baicalensis primmorphs does not differ sig-nificantly when compared to intact sponges. The most abundant cells in both primmorphs and in intact sponges are amoebocytes and choanocytes. Our results provide a morphological basis for future investigations using prim-morphs of this species as models in biotechnology, evo-devo, cytology and molecular biology approaches

<i>Janthinobacterium</i> sp. Strain SLB01 as Pathogenic Bacteria for Sponge <i>Lubomirskia baikalensis</i>

Sponges (phylum Porifera) are ancient, marine and inland water, filter feeding metazoans. In recent years, diseased sponges have been increasingly occurring in marine and freshwater environments. Endemic freshwater sponges of the Lubomirskiidae family are widely distributed in the coastal zone of Lake Baikal. The strain Janthinobacterium sp. SLB01 was isolated previously from the diseased sponge Lubomirskia baikalensis (Pallas, 1776), although its pathogenicity is still unknown. The aim of this study was to confirm whether the Janthinobacterium sp. strain SLB01 is the pathogen found in Baikal sponge. To address this aim, we infected the cell culture of primmorphs of the sponge L. baikalensis with strain SLB01 and subsequently reisolated and sequenced the strain Janthinobacterium sp. PLB02. The results showed that the isolated strain has more than 99% homology with strain SLB01. The genomes of both strains contain genes vioABCDE of violacein biosynthesis and floc formation, for strong biofilm, in addition to the type VI secretion system (T6SS) as the main virulence factor. Based on a comparison of complete genomes, we showed the similarity of the studied bacterial strains of Janthinobacterium spp. with the described strain of Janthinobacterium lividum MTR. This study will help expand our understanding of microbial interactions and determine one of the causes in the development of diseases and death in Baikal sponges