Bacterial functional diversity in the Global Ocean

Abstract

Bacterioplankton plays a key role in decomposing organic matter and recycling nutrients in the ocean. Although we have advanced in the last decades in the knowledge of the diversity of microbial communities, still little is know on the metabolic abilities of bacterioplankton, and even less of bacteria living in the deep ocean. During the circumnavigation expedition Malaspina we took samples in the Atlantic, Indic and Pacific oceans in order to assess functional diversity of bacterioplankton in vertical profiles from surface to 4,000 m. We tested the utilization of 95 carbon sources (belonging to the main categories: carbohydrates, amino acids, carboxylic acids) included in the Biolog plates, and 8 additional sources selected by their relevance in marine environments. Samples were inoculated in the microplates, incubated in the dark at in situ temperature and the absorbance of the plates was measured. The results show a generally higher utilization of carbohydrates and amino acids in the upper layers of all the oceans, above 100m, with the highest values in the southern Pacific Ocean. The utilization of carbon sources in the deep ocean was lower, with the exception of an area in the southern Pacific Ocean where utilization of carbohydrates, amino acids and carboxylic acids at 4000m exceeded even that found in upper layers of the ocean