Metabolism of microbial communities in the environment: A compound-specific stable hydrogen isotope approach

Abstract

Microorganisms are key players in all elemental cycles, their metabolic activity and potential impacts the environment on a local and global scale. In order to understand this significant role in the environment, microbial communities, their diversity and metabolic activity have to be studied in situ. In recent years the hydrogen isotopic composition of fatty acids have been shown to be a potentially useful tool to study the metabolic activity from individual microbial species to entire microbial communities. While first results are promising, further research has to be down in order to understand in which magnitude metabolism influences the deuterium to hydrogen ratio in fatty acids. In this work, culture studies have been done in order to understand the impact of other biological and physical parameters on the D/H ratio of fatty acids and compare those results to the influence of metabolism. These culture studies confirmed that the D/H ratio of fatty acids allows for a differentiation between photoautotrophic, chemoautotrophic and heterotrophic growth. Additionally, it was shown that both salinity and growth phase have a minor effect on the D/H ratio of fatty acids in comparison with metabolism. Environmental studies were conducted in two different aquatic settings in the Netherlands. The pelagic microbial communities of the coastal North Sea and the sedimentary microbial communities of Lake Grevelingen were studied. At both sites it was shown that it is possible to study the general metabolism of microbial communities in situ by measuring the D/H ratio of fatty acids. While in the coastal North Sea changes in the community metabolism due to different phytoplankton blooms were observed via the D/H ratio of fatty acids, in Lake Grevelingen it was possible to differentiate between sedimentary and pelagic communities.