Isolation of a methane-oxidizing bacterium that bioremediates hexavalent chromium from a formerly industrialized Suburban River.

Sediment samples were taken from sediment adjacent to a suburban river in Sheffield in Northern England that had suffered heavy metal pollution due to previous activity of the steel industry (between the 17th and 19th centuries). The most abundant heavy metals found in the samples were lead, chromium, nickel, arsenic and cobalt, with maximum concentrations of 412·80, 25·232, 25·196, 8·123 and 7·66 mg kg-1 , respectively. Enrichment cultures were set up using methane as carbon and energy source, as a result of which a strain of methanotroph was isolated that was shown via 16S rRNA gene sequencing to be a strain Methylomonas koyamae and given the designation SHU1. M. koyamae SHU1 removed hexavalent chromium from an initial concentration of 10 ppm, which was inhibited by the metabolic inhibitor sodium azide or the methane monooxygenase inhibitor phenylacetylene. To the authors' knowledge, this is the first description of a strain of the widely environmentally distributed genus Methylomonas that is capable of remediating hexavalent chromium.