Isolation and identification of the microalgal symbiont from primmorphs of the endemic freshwater spongeLubomirskia baicalensis(Lubomirskiidae, Porifera)

Abstract

The first reports on the presence of zoochlorellae within the organelles of mesenchymal cells from freshwater sponges were published in the 19th century. Today, it is well-known that freshwater sponges can be found in association with different endosymbiotic algae. However, until now there has been no detailed information about the endosymbiotic chlorophyll-containing algae in the remarkable endemic green sponges from Lake Baikal. In our study we were able for the first time to isolate and identify endosymbionts from primmorphs cultivated in vitro, and to compare them with those from naturally occurring Lubomirskia baicalensis sponges. Structural as well as molecular biological investigations show that the endosymbiotic alga is a Mychonastes species closely related to M. huancayensis. Another novel aspect of our work was to show that it is possible to use primmorphs of endemic sponges for isolation and subsequent cultivation of their endosymbiotic algae. We employed a simple cold-water (3-4°C) approach for cultivating Mychonastes sp., both within sponge primmorphs and in culture.

Microevolution processes in Baikal are detected in symbiotic microbiomes of Baikal sponges by the methods of fractal theory

“…Endemic sponges in Lake Baikal are clearly vulnerable in this crisis (Bormotov, 2011;Timoshkin et al, 2016;Khanaev et al, 2018). The sponges in Baikal, like all species of the phylum Porifera, always develop in symbiosis with bacterial and micro-algae species (Taylor et al, 2007;Chernogor et al, 2013;Webster and Thomas, 2016). So, the experiments intended to evaluate the composition of microbial communities in sponges from Baikal is one of the most direct ways to investigate processes in the whole lake.…”

“…Precedents where disease of sponges or corals were investigated using modern methods of molecular biology are known (Stabili et al, 2012;Prinzón et al, 2015). And there is a number of studies when a single pathogen which caused the disease was identified (Webster et al, 2002;Luter et al, 2010;Choudhury et al, 2015). But the investigations of microbial communities of diseased sponges in Lake Baikal using similar approaches just demonstrated the complexity of the problem under study (Denikina et al, 2016;Kulakova et al, 2018).…”

“…These integral description of these phylotypes are presented in Table 2; the Genbank ID of the 16S rRNA gene sequence selected as a reference for a most abundant OTU within each phylotype, is included in the Table 2. The phylotype annotated to Trebouxiophyceae class represents 16S rRNA gene of chloroplast from unicelluar algae, endosymbiont of L. baicalensis sponges (Chernogor et al, 2013). The phylotypes identified at the genus level as Sediminibacterium (Chitinophagaceae, Chitinophagales, Chitinophagia, Bacteroidetes) and Synechococcus (Synechococcaceae, Synechococcales, Cyanobacteria), as well as the phylotype identified at the level of family and belonged to Rhodospirillaceae (Rhodospirillales, Alphaproteobacteria, Proteobacteria) are typical for microbiomes of Baikal sponge.…”

The signs of adaptive mutations identified in the chloroplast genome of the algae endosymbiont of Baikal sponge.

“…In healthy condition sponges have a green color, mainly explained by the presence of a photosynthetic symbiont, an intracellular coccoid green algae. This algae belongs to the Cholorophyta division, and is close in taxonomy to the Choricystis genus [Chernogor et al, 2013]. It is natural to assume, that the photosynthetic symbiont is the source of feeding for sponge cells.…”

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“…Flavobacteriaceae was significantly more abundant with 13% to 62% in diseased sponges and 470 primmorphs ( (Bil et al, 1999). We previously showed that the primary photosynthetic 500 algae belonging to green algae of the order Chlorophyta dominate in healthy L. baicalensis 501 sponges and cell cultures of primmorphs (Chernogor et al, 2013). These unicellular eukaryotes 502 entering the complex symbiotic communities of Baikal sponges produce a significant amount of 503 carbohydrates, chlorophyll, fatty acids and secondary metabolites (Bil et al, 1999;Latyshev et 504 al., 1992).…”