Candidatus Chloracidobacterium thermophilum is a recently discovered aerobic chlorophototroph that belongs to the phylum Acidobacteria. It grows in a highly enriched coculture with Anoxybacillus sp. and was initially isolated from Octopus Spring in Yellowstone National Park. It has unique properties in that it synthesizes type 1 reaction centers, the bacteriochlorophyll (BChl) a-binding protein FMO, BChl c and chlorosomes, but it does so in the presence of oxygen. Here we report the first isolation of chlorosomes from Cab. thermophilum and an initial analysis of their carotenoid content. Unlike the chlorosomes of Chlorobi (green sulfur bacteria) and Chloroflexi, the chlorosomes of Cab. thermophilum contain large amounts of ketocarotenoids, including echinenone and cis and trans isomers of canthoxanthin, which are typically found in aerobic phototrophs. We hypothesize that these carotenoids play an important photoprotective role in the chlorosomes of Cab. thermophilum. Keywords: carotenoids, chlorosomes, acidobacteria, photoprotection