Distribution, diversity and ecology of aerobic carbon monoxide-oxidizing bacteria in Hawaiian volcanic deposits

Carbon monoxide-oxidizing bacteria are among the first colonists of recently formed volcanic deposits despite environmental conditions that challenge their survival, such as oscillating water regimes and lack of endogenous sources of organic carbon and nitrogen. Activity assessments and molecular surveys of the coxL gene (large subunit carbon monoxide dehydrogenase) across a vegetation gradient on a 1959 volcanic deposit on Kilauea Volcano (Hawai’i) indicated that CO-oxidizing communities continue to expand, diversify and remain competitive during ecosystem development. Distinct compositional shifts occurred across the gradient with Firmicutes-like coxL sequences dominating clone libraries from unvegetated sites (Bare) and Proteobacteria coxL sequences dominating libraries from vegetated sites (Canopy). Water regimes at the Bare and Canopy sites were distinct, with the former experiencing sometimes extreme diurnal oscillations in water potential (i.e. near 0 MPa to -60 MPa) and the Canopy remaining near 0 MPa. However, CO-oxidizing communities at these sites did not exhibit differential adaptations to water stress, which may not be an important factor controlling CO oxidizer distributions in these sites. Of the major taxonomic groups represented in the coxL clone libraries, increased total richness across the transect was most highly correlated with the number of OTUs represented by ?-Proteobacteria sequences, many of which were closely related to Burkholderia coxL. A qPCR approach developed to target Burkholderia coxL indicated that absolute gene copy numbers increased from undetectable quantities in the Bare site to an average of 8.6 x 108 copies gdw soil-1 in the Canopy site. In addition, a 16S rRNA gene phylogenetic analysis of Burkholderia isolates obtained from these sites and their close relatives indicated that CO-oxidation may be a common trait among root-associated Burkholderia species. Their strong association with plants, abundance and ability to consume atmospheric levels of CO, may explain their contribution to CO-oxidizer community expansion during ecosystem development and indicates that they may be an important constituent of active CO-oxidizing communities in situ