Abstract
Sponges are permanent benthos residents which establish complex associations with a variety of microorganisms that raise interest in the nature of sponge-symbionts interactions. A molecular approach, based on the identification of the 16S rRNA and ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit genes, was applied to investigate diversity and phylogeny of bacterial phototrophs associated with four species of Lubomirskiidae in Lake Baikal. The phylogeny inferred from both genes showed three main clusters of Synechococcus associated with Baikalian sponges. One of the clusters belonged to the cosmopolitan Synechococcus rubescens group and the two other were not related to any of the assigned phylogenetic groups but placed as sister clusters to S. rubescens. These results expanded the understanding of freshwater sponge-associated photoautotroph diversity and suggested that the three phylogenetic groups of Synechococcus are common photosynthetic symbionts in Lubomirskiidae sponges.
Highlights
Sponges are an important component of the marine and freshwater benthos ecosystems that establish associations with a great diversity of unicellular and multicellular organisms [1]
In contrast to marine sponges, there is not a lot of data on photosynthetic symbionts of freshwater sponges, associations with unicellular green algae, including Chlorella spp., Choricystis minor, yellow-green algae, and Chloroflexi have been shown in cosmopolitan sponges [4, 10,11,12,13] and cyanobacterial sequences detected in L. baicalensis [14]
The 16S rRNA and rbcL gene fragments were analysed in L. baicalensis, L. abietina, B. bacillifera and B. martinsoni
Summary
Sponges are an important component of the marine and freshwater benthos ecosystems that establish associations with a great diversity of unicellular and multicellular organisms [1]. Sponges can benefit from phototrophic symbionts which fix carbon using the CalvinBenson cycle and provide products of photosynthesis to the host [2,3,4]. Photosynthetic symbionts are prevalent in marine sponges of coastal regions worldwide where they contribute significantly to net primary production [5, 6]. From onethird to more than half of the sponges of tropical and temperate regions harbor a high level of photosynthetic symbionts [7, 8]. Sponges from the endemic family Lubomirskiidae are widely distributed in Lake Baikal and often harbor photosynthetic symbionts. The identification and diversity of sponge-associated phototrophs in Lake Baikal are undetermined to date
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