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

Abstract

In recent years, a large scale ecological crisis has been observed in the Lake Baikal ecosystem. It is clearly shown by several signs, including the mass disease of sponges in the coastal zone. To investigate the causes of the crisis, the composition of symbiotic communities in sponges was investigated in 2015 by sequencing of the 16S rRNA gene in three locations of the lake. The methods of fractal theory were adopted in order to detect a fractal structure in the distribution of the sequencing reads, being considered as fragments of the 16S rRNA gene for individual bacteria within the collected samples. The fractal-like distributions were constructed for the seven most abundant phylotypes, and the observed properties of the distributions reflect microevolution processes within the selected genera and species. The values of the fractal dimension, evaluated for the distributions, are observed to correlate with an anthropogenic load at the place of sample collection, for the Flavobacterium and Synechococcus genera. The sampling sites were also observed to be associated with the properties of the distributions for chloroplasts of Trebouxiophyceae algae, the endosymbiont of Lubomirskia baicalensis sponge.The long-scale time dependency of fractal dimension was also evaluated for the data from temperature detectors in four locations of Lake Baikal. The values of the fractal dimension for fluctuations of temperature are also observed to be associated with an anthropogenic load in the place of measurement. The consistency of both approaches validates the usefulness of fractal-based methods in the interpretation of the experiments designed to study the ecological crisis in Lake Baikal.

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

“…The average proportion of polymorphic positions in all genes was 98.4%, which is comparable with the previously reported 97.8% for bacterial genomes [Truong et al, 2017]. These values are also consistent with the results reported by Feranchuk et al [2018]. It was shown that on limiting the selection of 16S rRNA fragments of the chloroplast, sequenced by 454 technology, to 95% identity, variation was at most 2% between any of the fragments.…”

“…Baikal and it's sponges Chernogor et al, 2013;Pile et al, 1997 Crisis on Baikal Bormotov, 2012; Khanaev et al, 2018;Kravtsova et al, 2014;Timoshkin et al, 2016 Disease of sponges Belikov et al, 2019;Feranchuk et al, 2018;Kulakova et al, 2018 Evolution of Algae Cai et al, 2017;Fucíková et al, 2014;Lemieux et al, 2014;Lemieux et al, 2015;Sun et al, 2016 Adaptation andEvolution Rosenberg, 2001;Wright, 2004 The algal symbiont of sponge is as conservative as other major constituents of the sponge hologenome in a healthy state. This alga is annotated by taxonomy as a Chlorophyta symbiont of Lubomirskia sp.…”

“…The 16S rRNA reference sequences from the Greengenes gg_13_7 database were used to clarify the relations between subspecies of the algae in Lake Baikal. These sequences were identified in the studies of Belikov et al [2019] and Feranchuk et al [2018] as the 16S rRNA templates which are extensively represented in the sponge microbiomes collected in different locations of the lake. Both templates, 4365343 (gb|JF495289.1) and 1118847 (gb|GU936925.1), were directed to the C. parasitica rRNA (SAG:17.98, gb|KM462878) as the closest annotated species, by a blast search at NCBI site (98% and 96%).…”