In the context of global warming, understanding how ecosystems contribute to the cycling of carbon compounds and how these systems will react to changing climatic conditions is becoming more and more important. At present, knowledge about the microbial contributions to carbon and sulfur transformations, especially in terrestrial ecosystems, is limited. While tallying up contributions to carbon sequestration or cycling is relatively easy for bacteria that must metabolize either inorganic compounds (autotrophic bacteria) or organic compounds (heterotrophic bacteria), the situation becomes much more complex when the heterotrophic lifestyle is merely an alternative (facultative heterotrophs). This group of microorganisms has the potential to either consume carbon dioxide or to produce it, and it is often unknown what triggers the conversion between the two types of carbon metabolism or how they are linked to the metabolic conversion of other compounds.
Starkeya novella is a soil bacterium that belongs to the facultatively heterotrophic microbes. It is able to utilize a variety of single-carbon compounds, sugar alcohols, amino acids, carboxylic acids, and fatty acids as primary sources of cell carbon. In addition to this extensive carbon metabolism, S. novella is able to grow using a variety of inorganic and organic sulfur compounds such as thiosulfate, tetrathionate, dimethylsulfide (DMS), and dimethylsulfoxide. Thus it is clear that, in addition to carbon cycling, S. novella is also involved in the cycling of sulfur compounds, especially the cycling of DMS, a volatile greenhouse-active gas that is involved in cloud formation. Atmospheric DMS degradation gives rise to methanesulfonic acid, one of the major components of ‘acid rain’. Although Starkeya novella has been studied in some detail in the past, only very few studies so far have attempted to address the question of how this organism interfaces the different ‘pure’ types of metabolism outlined above with growth under mixed conditions. Moreover, these studies are at least 25 years old and were carried out based on carbon source utilization patterns and physiological traits alone. Data on gene regulation and regulatory networks are entirely absent but will be indispensable for an investigation of how carbon and sulfur metabolism are integrated in S. novella.
Principal Investigators: Ulrike Kappler and Scott Beatson (Univ. of Queensland)