Quantification of Burkholderia coxL Genes in Hawaiian Volcanic Deposits

Isolation of multiple carbon monoxide (CO)-oxidizingBurkholderia strains and detection by culture-independent approaches suggest thatBurkholderia may be an important component of CO-oxidizing communities in Hawaiian volcanic deposits. The absolute and relative abundance of the bacteria in these communities remains unknown, however. In this study, a quantitative PCR (Q-PCR) approach has been developed to enumerateBurkholderia coxL genes (large subunit of carbon monoxide dehydrogenase). This represents the first attempt to enumeratecoxL genes from CO oxidizers in environmental samples.coxL copy numbers have been determined for samples from three sites representing a vegetation gradient on a 1959 volcanic deposit that included unvegetated cinders (bare), edges of vegetated sites (edge), and sites within tree stands (canopy). Q-PCR has also been used to estimate copy numbers ofBetaproteobacteria 16S rRNA gene copy numbers and totalBacteria 16S rRNA.coxL genes could not be detected in the bare site (detection limit, ≥4.7 × 103 copies per reaction) but average 1.0 × 108 ± 2.4 × 107 and 8.6 × 108 ± 7.6 ×107 copies g−1 (dry weight) in edge and canopy sites, respectively, which differ statistically (P = 0.0007). AverageBurkholderia coxL gene copy numbers, expressed as a percentage of totalBacteria 16S rRNA gene copy numbers, are 6.2 and 0.7% for the edge and canopy sites, respectively. Although the percentage ofBurkholderia coxL is lower in the canopy site, significantly greater gene copy numbers demonstrate that absolute abundance ofcoxL increases in vegetated sites and contributes to the expansion of CO oxidizer communities during biological succession on volcanic deposits.