Halomethane production by vanadium-dependent bromoperoxidase in marine Synechococcus

To investigate the role of vanadium-dependent bromoperoxidase (VBPO) for the production of halogenated methanes in marine prokaryotes, we measured VBPO activity and halomethane production in two strains of Synechococcus; one with VBPO (strain CC9311) and one without VBPO (strain WH8102). A mutant strain of CC9311, VMUT2, in which the gene for VBPO is disrupted, was also tested. A suite of halomethanes was measured in the headspace above cultures as well as in the culture medium with a purge-and-trap method. Monohalomethanes were the most consistently produced molecules among the three strains tested. Additionally, CC9311 produced 301 +/- 109 molecules cell(-1) d(-1) of bromoform (CHBr3) when VBPO activity was detected, while production was not significantly different from zero when VBPO activity was not detected. VBPO activity and CHBr3 production were only detected when cultures of CC9311 were stirred, which may contribute to the often moderate to weak correlations between CHBr3 concentration and biological markers in the ocean. No production was seen by VMUT2 or WH8102. These data show that CHBr3 production rates are dramatically increased with or exclusive to the presence of VBPO, supporting its involvement in CHBr3 synthesis. This study thus provides genetic evidence that certain strains of marine Synechococcus, under particular conditions, can be a natural source of marine CHBr3, which contributes to ozone depletion in the stratosphere.