Evidence of Chemolithoautotrophy in the Bacterial Community Associated withAlvinella pompejana, a Hydrothermal Vent Polychaete

Abstract

The deep-sea polychaete Alvinella pompejana colonizes tubes on the sides of black smoker chimneys along the East Pacific Rise. A diverse, yet phylogenetically constrained episymbiotic community is obligately associated with its dorsal surface. The morphologically and phylogenetically distinct dominant episymbionts have not yet been cultured, and there are no clearly defined roles for these bacteria in this symbiosis. A large insert fosmid library was screened for the presence of the two dominant phylotypes. Two fosmids, 35.2 and 38 kb, containing phylotype-specific 16S ribosmal DNA sequences were fully sequenced. Each fosmid had a gene encoding ATP citrate lyase, a key enzyme in the reverse tricarboxylic acid (rTCA) cycle, a CO 2 fixation pathway. A selection of episymbiont communities from various geographic locations and vent sites were screened for the presence, diversity, and expression (via reverse transcription-PCR) of the ATP citrate lyase gene. Our results indicate that the ATP citrate lyase gene is not only a consistent presence in these episymbiont communities but is also expressed. Phylogenetically distinct forms of ATP citrate lyase were also found associated with and expressed by bacteria extracted from the tubes of A. pompejana. Utilizing PCR with degenerate primers based on a second key enzyme in the rTCA cycle, 2-oxoglutarate:acceptor oxidoreductase, we also demonstrated the persistent presence and expression of this gene in the episymbiont community. Our results suggest that members of both the episymbiont and the surrounding free-living communities display a chemolithoautotrophic form of growth and therefore contribute fixed carbon to other organisms in the vent community.The tube-dwelling polychete Alvinella pompejana inhabits high-temperature hydrothermal vent chimneys from 21°N to 32°S along the East Pacific Rise (EPR) (17,18,21). A morphologically and phylogenetically diverse episymbiotic bacterial community forms a dense layer on the dorsal surface of A. pompejana (12,18,28). This association is specific and obligate, and the dominant epibionts are filamentous and associated with the dorsal epidermal expansions (hair-like projections) of A. pompejana (12,18). The role of these episymbiotic bacteria in the association has been difficult to decipher. The symbionts have previously been hypothesized to be involved in both the nutrition of the host and in the detoxification of sulfide and heavy metals (1,19,43). The ␦ 13 C ratios of the A. pompejana worms and fatty acid profiles of the symbiont community indicate potential chemolithoautotrophy within the community (17,19,53). However, the dominant bacterial filaments associated with the polysaccharide structures on A. pompejana appear not to assimilate CO 2 in any appreciable amount via the Calvin-Benson cycle according to ribulose 1,5-bisphosphate carboxylase-oxygenase, 14 C labeling, and bicarbonate uptake assays (17,19).Molecular characterizations of the A. pompejana symbiont population indicate that the majority of the symbionts group withi...

Living on the edge: single-species dominance at the Pakistan oxygen minimum zone boundary

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Alternative oxidase in animals: unique characteristics and taxonomic distribution

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Culture dependent and independent analyses of 16S rRNA and ATP citrate lyase genes: a comparison of microbial communities from different black smoker chimneys on the Mid-Atlantic Ridge

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