Cruising the marine halomethane cycle: Microbiology, biochemistry and geochemistry of reference bacteria, new microbial players and underlying processes – MAHABIO

Volatile organohalides are toxic to living organisms. Furthermore, they contribute to the destruction of stratospheric ozone. Seas and oceans are major sources of these compounds, which prominently include halomethanes, produced in significant amounts by microorganisms and algae. Conversely, halomethanes may also represent nutrients for marine bacteria. Hence, the observed steady-state atmospheric concentrations of these compounds do not reflect the magnitude and dynamics of their production and consumption. Moreover, the sources and sinks of halomethanes, as well as their resulting fluxes in the marine environment and the atmosphere, remain poorly characterized. In particular, only one pathway for microbial degradation of chloromethane (CH3Cl) has been elucidated so far, although many studies in the literature clearly suggest that others exist.
The 36-month French-German research project MAHABIO ambitions to gain a comprehensive view on global biogeochemical cycles of volatile halogenated compounds. It proposes a resolutely interdisciplinary, innovative, and tightly focussed approach to explore and characterize bacterial processes associated with production and consumption of chloromethane in the marine environment.
MAHABIO associates two French and two German partners with complementary areas of microbiological, genetic, biochemical and analytical expertises. Experimental approaches combine cultivation of marine microorganisms under oxic and anoxic conditions, chemical and isotopic analysis of halomethanes, biochemical and enzymatic characterization of bacterial dehalogenases, and characterization of pure strains, synthetic communities, microcosms and environmental samples using "omics" techniques.
MAHABIO is organized in 3 experimental workpackages: i) characterization of chloromethane consumption by marine samples, including under hitherto neglected anoxic conditions, and characterization of dehalogenases of reference strains; ii) quantification of bacterial production of chloromethane in marine samples and by reference bacterial strains; and iii) integrative study of concomitant production and consumption of chloromethane by synthetic bacterial communities.
The synergistic expertise of MAHABIO partners on all aspects of the proposed work is a key asset of the project. Many prerequisites for this project have been validated in preliminary experiments. These include cultivation of marine chloromethane-degrading bacteria, stable isotope analysis of chloromethane including all three elements of the molecule (C, H and Cl), and preliminary genetic and proteomic characterization of chloromethane utilization by a marine chloromethane-degrading bacterium with yet uncharacterized pathway.
In-depth analysis of each aspect of the project has also made it possible to explicitly identify associated risks, and to propose fallback solutions. A CNRS EC2CO project, initiated this year and led by the scientific coordinator of MAHABIO, will provide useful complementary input to that proposed in MAHABIO.
Highly promising scientific and technological deliverables are envisaged from MAHABIO: i) biochemical, enzymatic and genetic characterization of novel bacterial enzymes involved in production and consumption of chloromethane, and ii) biomarkers and isotopic signatures associated with chloromethane production and consumption. Taken together, expected results will yield an improved, integrative understanding of biogeochemical cycling of chloromethane in the marine environment, and contribute in developing renewed, state-of-the-art investigations of global biogeochemical cycles essential to the functioning of our planet.