Chloracidobacterium thermophilum gen. nov., sp nov.: an anoxygenic microaerophilic chlorophotoheterotrophic acidobacterium

A novel anoxygenic photoheterotrophic member of the phylum Acidobacteria, Chloracidobacterium thermophilum strain B sp. nov., was isolated from a cyanobacterial enrichment culture derived from microbial mats associated with Octopus Spring, Yellowstone National Park, WY. C. thermophilum sp. nov. was a Gram-stain-negative rod (diameter, approximately 0.8-1.0 mu m; variable length, approximately 2.5 mu m), which formed greenish-brown liquid suspension cultures. It was a moderately thermophilic microaerophile and grew in a defined medium at 51 degrees C (T-opt; range 44 to 58 degrees C) and in the pH range 5.5 to 9.5 (pH(opt)=similar to 7.0). The DNA G+C content was 61.3 mol%, and phylogenetic analysis, based on the 16S rRNA sequence, showed that C. thermophilum sp. nov. belongs to subdivision 4 (Acidobacteriaceae) of the Acidobacteria. C. thermophilum sp. nov. was unable to synthesize branched-chain amino acids, L-lysine, and vitamin B-12, which were required for growth. Although the organism lacked genes/enzymes for autotrophic carbon fixation, bicarbonate was required. Growth was stimulated by other amino acids and 2-oxoglutarate. Cells produced chlorosomes containing a diverse mixture of bacteriochlorophyll (BChl) c derivatives, and additionally, synthesized BChl a(P), Chl a(PD), and Zn-BChl a'(P), which occurred in type-1 homodimeric reaction centres. The carotenoids included echinenone, canthaxanthin, lycopene, gamma-carotene and beta-carotene. C. thermophilum sp. nov. produced iso-diabolic acid as its major fatty acid and synthesized three hopanoids (diploptene, bacteriohopanetetrol and bacteriohopanetetrol cyclitol ether). Based upon its phenotypic and genotypic properties, the name Chloracidobacterium thermophilum gen. nov., sp. nov. is proposed for this isolate; the type strain is C. thermophilum strain B-T (ATCC BAA-2647=JCM 30199).