Prosthecate aerobic anoxygenic phototrophs Photocaulis sulfatitolerans gen. nov. sp. nov. and Photocaulis rubescens sp. nov. isolated from alpine meromictic lakes in British Columbia, Canada

Seven Gram-negative flagellated and subsequent prosthecate bacteria were isolated from meromictic Mahoney Lake and Blue Lake in British Columbia, Canada. Each became pink-red after 1-2 weeks of incubation, containing bacteriochlorophyll a incorporated into light harvesting and reaction center pigment-protein complexes. They did not grow anaerobically under illuminated conditions, supporting their identification as obligate aerobic anoxygenic phototrophs (AAP). All isolates preferred high salinity and BL14(T) tolerated up to 6.5% NaCl or 16.0% Na2SO4. In addition to phenotypic differences, analysis of 16S rRNA gene sequences found both strains BL14(T) and ML37(T) were related to Alkalicaulis satelles, G-192(T) by 98.41 and 98.84%, respectively, and distantly associated to members of the non-phototrophic genus Glycocaulis profundi, ZYF765(T) (95.59 and 95.36%, respectively) within the newly recognized Maricaulales order of alpha-Proteobacteria. BL14(T) and ML37(T) contained photosynthetic operons of 46,143 and 46,315 bp, where genes of BL14(T) were uniquely split into two distal operons. Furthermore, A. satelles was not originally published as an AAP, but was also found in this work to contain a similar 45,131 bp fragment. The distinct morphological features, physiological traits and genomic analysis including average nucleotide identity and digital DNA:DNA hybridization of circularized genomes supported the proposal of new genus and species Photocaulis sulfatitolerans gen. nov. sp. nov., type strain BL14(T) and Photocaulis rubescens sp. nov. type strain ML37(T).