THE PROTEOME OF THE NODULE-FORMING FILAMENTOUS CYANOBACTERIUM, CANDIDATUS CALOTHRIX PAVILIONENSIS, PROVIDES A FUNCTIONAL LINK TO MICROBIALITE FORMATION

Filamentous cyanobacteria are a driving force behind modern microbialite formation through photosynthetically induced alkalinization. However, many of these cyanobacteria have not been cultivated and lack functional characterization. Pavilion Lake is a dimictic oligotrophic microbialite-forming ecosystem in southwestern British Columbia that harbors microstromatolitic forming nodular filamentous cyanobacteria. Previous studies have suggested that these purple nodular cyanobacteria, while not having laminated microstromatolites, are active in carbonate precipitation. The proposed mechanism of carbonate precipitation is by photosynthetically induced alkalinization¹; however, the taxonomic identity of the cyanobacterium and the genes that are functionally expressed in these cyanobacteria is unknown. Phylogenetics based on 16S rRNA classifies the organism as a deep-branching relative of Calothrix spp., which has been assigned the name Candidatus Calothrix pavilionensis. High-throughput liquid chromatography-tandem mass spectrometry revealed >70 expressed proteins relating to photosynthetically induced alkalinization, including carbon fixation (e.g. Rubisco), photosystems (e.g. type II), pigment formation (e.g. phycocyanin and zeta-carotene desaturase) and filamentous sheath formation (e.g. beta-Ig-H3/fasciclin homolog). The proteome also contained proteins related to energy metabolism (e.g. ATP synthase), urea metabolism (e.g. urea binding protein) and phage-related infection (e.g. CRISPR-helicase and phage tail proteins). The microstromatolithic Candidatus Calothrix pavilionensis proteome provides a functional link between photosynthetically induced alkalinization and microbialite formation.

¹Brady et al. 2010. Chemical Geology 274, 56-67.