Microbial utilisation of methanol in seawater

Methylotrophs are aerobic bacteria that use methanol as a carbon and/or energy source. They are widespread but have not been extensively studied in marine environments. Seawater 14C tracer studies were combined with molecular biological cultivation- independent techniques (polymerase chain reactions using 16S rRNA and mxaF gene specific primers, 454 pyrosequencing) to investigate temporal and spatial variability in rates of microbial methanol utilisation and methylotrophic community composition in temperate coastal waters of the western English Channel, UK (WEC) and the Atlantic Ocean (Atlantic Meridional Transect 19). Microbial methanol dissimilation rates were, on average, thirteen times higher in waters of the WEC (0.65–11.2 nmol l-1h-1) than in open ocean waters of the Atlantic (0.01–1.7 nmol l-1h-1), with maximum rates found during winter months in the WEC. Highest methanol dissimilation rates in the Atlantic were measured in the north subtropical gyre of up to eight times higher than other Atlantic regions. Microbial methanol assimilation rates in the Atlantic Ocean (0.01–2.2 x10-2 nmol l-1h-1) were up to four times higher than those from the WEC (0.04–2.6 x10-2 nmol l-1h-1). Methanol assimilation rates from the WEC displayed seasonal maxima during summer, but showed methanol bacterial growth efficiency (BGEM) of <1% all year. Overall, assimilation rates were highest in the equatorial upwelling where BGEM reached 17%. Methanol assimilation rates showed a significant positive correlation with bacterial leucine incorporation in contrast to methanol dissimilation, which showed a negative relationship. Methanol dissimilation rates strongly correlated with the abundance of bacteria of the SAR11 clade, previously shown to utilise methanol as an energy source. The first basin scale approach using 454 pyrosequencing in the Atlantic revealed a remarkable increase in bacterial diversity in the nutrient limited southern gyre. Use of mxaF PCR primers also confirmed the ubiquitous presence of methylotrophic bacteria throughout the top 200m of the Atlantic Ocean.