Journal
FRONTIERS IN MICROBIOLOGY
Volume 12, Issue -, Pages -Publisher
FRONTIERS MEDIA SA
DOI: 10.3389/fmicb.2021.704168
Keywords
Acidobacteriota; Chloracidobacterium; thermophile; chlorophototrophy; genome
Categories
Funding
- NASA Exobiology program [NNX16AJ62G, DE-FG02-94ER20137]
- Photosynthetic Systems Program, Division of Chemical Sciences, Geosciences, and Biosciences (CSGB), Office of Basic Energy Sciences of the U.S. Department of Energy [DE-FG02-94ER20137]
- Institute of Fermentation, Osaka (IFO), Japan
- Tokyo Metropolitan Government, Tokyo, Japan via a Tokyo Human Resource Funds for City Diplomacy scholarship
- NASA [901703, NNX16AJ62G] Funding Source: Federal RePORTER
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Chloracidobacterium is the only genus in the phylum Acidobacteriota that performs chlorophyll-dependent phototrophy, with multiple strains isolated from different hot spring locations exhibiting consistent characteristics such as obligate photoheterotrophic, microaerophilic, non-motile behavior.
Chloracidobacterium is the first and until now the sole genus in the phylum Acidobacteriota (formerly Acidobacteria) whose members perform chlorophyll-dependent phototrophy (i.e., chlorophototrophy). An axenic isolate of Chloracidobacterium thermophilum (strain B-T) was previously obtained by using the inferred genome sequence from an enrichment culture and diel metatranscriptomic profiling analyses in situ to direct adjustments to the growth medium and incubation conditions, and thereby a defined growth medium for Chloracidobacterium thermophilum was developed. These advances allowed eight additional strains of Chloracidobacterium spp. to be isolated from microbial mat samples collected from Mushroom Spring, Yellowstone National Park, United States, at temperatures of 41, 52, and 60 degrees C; an axenic strain was also isolated from Rupite hot spring in Bulgaria. All isolates are obligately photoheterotrophic, microaerophilic, non-motile, thermophilic, rod-shaped bacteria. Chloracidobacterium spp. synthesize multiple types of (bacterio-)chlorophylls and have type-1 reaction centers like those of green sulfur bacteria. Light harvesting is accomplished by the bacteriochlorophyll a-binding, Fenna-Matthews-Olson protein and chlorosomes containing bacteriochlorophyll c. Their genomes are approximately 3.7 Mbp in size and comprise two circular chromosomes with sizes of approximately 2.7 Mbp and 1.0 Mbp. Comparative genomic studies and phenotypic properties indicate that the nine isolates represent three species within the genus Chloracidobacterium. In addition to C. thermophilum, the microbial mats at Mushroom Spring contain a second species, tentatively named Chloracidobacterium aggregatum, which grows as aggregates in liquid cultures. The Bulgarian isolate, tentatively named Chloracidobacterium validum, will be proposed as the type species of the genus, Chloracidobacterium. Additionally, Chloracidobacterium will be proposed as the type genus of a new family, Chloracidobacteriaceae, within the order Blastocatellales, the class Blastocatellia, and the phylum Acidobacteriota.
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