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

Abstract

Background: Monitoring and investigating the ecosystem of the great lakes provide a thorough background when forecasting the ecosystem dynamics at a greater scale. Nowadays, changes in the Baikal lake biota require a deeper investigation of their molecular mechanisms. Understanding these mechanisms is especially important, as the endemic Baikal sponge disease may cause a degradation of the littoral ecosystem of the lake. Methods: The chloroplast genome fragment for the algae endosymbiont of the Baikal sponge was assembled from metagenomic sequencing data. The distributions of the polymorphic sites were obtained separately for the genome fragments from healthy, diseased and dead sponge tissues. Results: The distribution of polymorphic sites allows for the detection of the signs of extensive mutations in the chloroplasts isolated from the diseased sponge tissues. Additionally, the comparative analysis of chloroplast genome sequences suggests that the symbiotic algae from Baikal sponge is close to the Choricystis genus of unicellular algae. Conclusions: Mutations observed in the chloroplast genome could be interpreted as signs of rapid adaptation processes in the symbiotic algae. The development of sponge disease is still expanding in Baikal, but an optimistic prognoses regarding a development of the disease is nevertheless considered.

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

“…The sequencing reads and source codes of scripts sufficient to reproduce the presented results are available from GitHub: https:// github.com/sferanchuk/bsponge_chloroplast Archived source code at time of publication available at: https://doi.org/10.5281/zenodo.1326765 [Feranchuk, 2018].…”

Symbiosis, Selection, and Novelty: Freshwater Adaptation in the Unique Sponges of Lake Baikal

“…In our transcriptomes, 189 L. baikalensis (A8) hits are seen, but only 14 and 21 contigs in L. abietina (A10) and B. bacillifera (A2), respectively. As our genomic and transcriptomic sample for L. baikalensis are derived from the same tissue, we suspect that a member of the Chlorophyta was particularly abundant in that specimen, and could have been performing a symbiotic role, as has been reported previously in freshwater sponges (Sand-Jensen and Pedersen 1994; Feranchuk et al. 2018).…”

“…Many of the best assembled sequences present in our genomic data derive from unicellular algae, which are common symbionts of freshwater sponges (Feranchuk et al. 2018).…”