AUTHOR=Tank Marcus , Bryant Donald A. 

TITLE=Nutrient requirements and growth physiology of the photoheterotrophic Acidobacterium, Chloracidobacterium thermophilum

JOURNAL=Frontiers in Microbiology

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2015.00226

DOI=10.3389/fmicb.2015.00226

ISSN=1664-302X

ABSTRACT=<p>A novel thermophilic, microaerophilic, anoxygenic, and chlorophototrophic member of the phylum <italic>Acidobacteria</italic>, <italic>Chloracidobacterium thermophilum</italic> strain B<sup>T</sup>, was isolated from a cyanobacterial enrichment culture derived from microbial mats associated with Octopus Spring, Yellowstone National Park, Wyoming. <italic>C. thermophilum</italic> is strictly dependent on light and oxygen and grows optimally as a photoheterotroph at irradiance values between 20 and 50 μmol photons m<sup>-2</sup> s<sup>-1</sup>. <italic>C. thermophilum</italic> is unable to synthesize branched-chain amino acids (AAs), <sc>l</sc>-lysine, and vitamin B<sub>12</sub>, which are required for growth. Although the organism lacks genes for autotrophic carbon fixation, bicarbonate is also required. Mixtures of other AAs and 2-oxoglutarate stimulate growth. As suggested from genomic sequence data, <italic>C. thermophilum</italic> requires a reduced sulfur source such as thioglycolate, cysteine, methionine, or thiosulfate. The organism can be grown in a defined medium at 51<sup>∘</sup>C (T<sub>opt</sub>; range 44–58<sup>∘</sup>C) in the pH range 5.5–9.5 (pH<sub>opt</sub> = ∼7.0). Using the defined growth medium and optimal conditions, it was possible to isolate new <italic>C. thermophilum</italic> strains directly from samples of hot spring mats in Yellowstone National Park, Wyoming. The new isolates differ from the type strain with respect to pigment composition, morphology in liquid culture, and temperature adaptation.</p>