Depth variability in microbial methanol use Fine scale variability in methanol uptake and oxidation in the micro-layer and near-surface waters of the Atlantic Depth variability in microbial methanol use Depth variability in microbial methanol use

Abstract

The aim of this research was to make the first depth profiles of the microbial assim-ilation of methanol carbon, and its oxidation to carbon dioxide and use as an energy source from the micro-layer to 1000 m. Some of the highest reported methanol oxi-dation rate constants of 0.5–0.6 d −1 were occasionally found in the micro-layer, and 5 immediately underlying waters (10 cm depth), albeit these samples also showed the greatest heterogeneity compared to other depths down to 1000 m. Methanol uptake into the particulate phase was exceptionally low in micro-layer samples, suggesting that any methanol utilised by microbes in this environment is for energy generation. The sea surface micro-layer and 10 cm depth also showed a higher proportion of bacteria with 10 a low DNA content, and bacterial leucine uptake rates in surface micro-layer samples were either less than, or the same as those in the underlying 10 cm layer. The average methanol oxidation and particulate rates were however statistically the same through-out the depths sampled, although the later were highly variable in the near surface 0.25–2 m compared to deeper depths. The statistically significant relationship demon-15 strated between uptake of methanol into particles and bacterial leucine incorporation suggests that heterotrophic bacteria use methanol carbon for cellular growth, but the lack of relationships observed with methanol oxidation, perhaps suggest that a wider group of marine microbes use methanol for energy generation. Whilst the statistically significant relationship observed between the uptake of methanol into cell particles and 20 the numbers of Prochlorococcus during diel experiments could also suggest that this abundant group of marine cyanobacteria are capable of mixotrophy, using methanol as a carbon source for growth. We conclude that microbial methanol uptake rates, i.e., loss from seawater are highly variable, particularly close to the seawater surface, which could significantly impact upon seawater concentrations and hence the air-sea flux. 25 4514 BGD 9, 4513–4542, 2012