LAUSR

Tolyporphins are structurally diverse tetrapyrrole macrocycles produced by the cyanobacterial culture HT-58-2. Although tolyporphins were discovered over 25 years ago, little was known about the microbiology of the culture. The studies reported herein expand the description of the community of predominantly alphaproteobacteria associated with the filamentous HT-58-2 cyanobacterium and isolate a dominant bacterium, Porphyrobacter sp. HT-58-2, for which the complete genome is established and growth properties are examined. Fluorescence in situ hybridization (FISH) analysis of the cyanobacterium-microbial community with a probe targeting the 16S rRNA of Porphyrobacter sp. HT-58-2 showed fluorescence emanating from the cyanobacterial sheath. Although genes for the biosynthesis of bacteriochlorophyll a (BChl a) are present in the Porphyrobacter sp. HT-58-2 genome, the pigment was not detected under the conditions examined, implying the absence of phototrophic growth. Comparative analysis of four Porphyrobacter spp. genomes from worldwide collection sites showed significant collinear gene blocks, with two inversions and three deletion regions. Taken together, the results enrich our understanding of the HT-58-2 cyanobacterium-microbial culture.