Initial Characterization of the Photosynthetic Apparatus of “ Candidatus Chlorothrix halophila,” a Filamentous, Anoxygenic Photoautotroph

Abstract

"Candidatus Chlorothrix halophila" is a recently described halophilic, filamentous, anoxygenic photoautotroph (J. A. Klappenbach and B. K. Pierson, Arch. Microbiol. 181:17-25, 2004) that was enriched from the hypersaline microbial mats at Guerrero Negro, Mexico. Analysis of the photosynthetic apparatus by negative staining, spectroscopy, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that the photosynthetic apparatus in this organism has similarities to the photosynthetic apparatus in both the Chloroflexi and Chlorobi phyla of green photosynthetic bacteria. The chlorosomes were found to be ellipsoidal and of various sizes, characteristics that are comparable to characteristics of chlorosomes in other species of green photosynthetic bacteria. The absorption spectrum of whole cells was dominated by the chlorosome bacteriochlorophyll c (BChl c) peak at 759 nm, with fluorescence emission at 760 nm. A second fluorescence emission band was observed at 870 nm and was tentatively attributed to a membrane-bound antenna complex. Fluorescence emission spectra obtained at 77 K revealed another complex that fluoresced at 820 nm, which probably resulted from the chlorosome baseplate complex. All of these results suggest that BChl c is present in the chlorosomes of "Ca. Chlorothrix halophila," that BChl a is present in the baseplate, and that there is a membrane-bound antenna complex. Analysis of the proteins in the chlorosomes revealed an ϳ6-kDa band, which was found to be related to the BChl c binding protein CsmA found in other green bacteria. Overall, the absorbance and fluorescence spectra of "Ca. Chlorothrix halophila" revealed an interesting mixture of photosynthetic characteristics that seemed to have properties similar to properties of both phyla of green bacteria when they were compared to the photosynthetic characteristics of Chlorobium tepidum and Chloroflexus aurantiacus.

New phylotypes of mesophilic filamentous anoxygenic phototrophic bacteria enriched from sulfide‐containing environments

“…White bars show a 10 mm scale. not shown) suggested that this pigment was nearly absent in chlorosomes from both cultures as previously reported for other filamentous anoxygenic phototrophic bacteria (Gich et al, 2003;van de Meene et al, 2007).…”

Diversity, Distribution and Hydrocarbon Biodegradation Capabilities of Microbial Communities in Oil-Contaminated Cyanobacterial Mats from a Constructed Wetland

“…4A ). About 85% of the sequences of the Chloroflexi group belonged to Candidatus chlorothrix , a filamentous anoxygenic photoautotroph isolated from Guerrero Negro hypersaline mats in Mexico [37] whereas most of the Planctomycetes sequences belonged to the genus Phycisphaera . The remaining less dominant groups (≤3% of total sequences) were distributed among several other groups ( Fig.…”

The enigmatic SAR202 cluster up close: shedding light on a globally distributed dark ocean lineage involved in sulfur cycling

“…Phylogenetic analysis of 16S rRNA genes in general provides little information regarding metabolic traits. This is particularly true for Chloroflexi , which display a broad spectrum of lifestyle characteristics, e.g., anoxygenic photosynthesizers [ 16 , 17 ], obligate aerobic/anaerobic heterotrophs [ 18 – 21 ], thermophiles [ 18 , 20 , 22 ], halophiles [ 23 ], nitrite oxidizers [ 24 , 25 ], predators with gliding motility [ 26 ], some with capacity for reductive dehalogenation [ 27 , 28 ] and even endospore-forming Gram-positive bacteria in a largely Gram-negative phylum [ 29 , 30 ]. The only genomic information from the SAR202 group at present is from an incomplete single cell amplified genome (SAGs), Pac-SCGC-AAA240-N13, obtained from a depth of 770 m from the ALOHA station in the Pacific Ocean north of Hawaii [ 31 ] but no genomic analyzes have been reported.…”