Quaternary amines (QAs) such as glycine betaine (GBT) are ubiquitous in marine organisms. GBT is used by marine organisms as a compatible solute in response to changes in environmental conditions, such as increasing salinity, because GBT does not interfere with cell metabolism. QA compounds are frequently released into the ocean ecosystems due to environmental changes, such as viral attack and grazing. The degradation of these compounds, especially in intertidal coastal areas, contributes significantly to the production of climate-active trace gases. These include the potent greenhouse gas methane and volatile methylated amines, which are thought to be involved in cloud formation in the marine environment.
Coastal sediments are estimated to contribute approximately 75% of the global oceanic methane emissions (8-13 Tg per year) and much of this is likely to be derived from the degradation of QAs. Although we know that microorganisms are mainly responsible for the degradation of GBT to methane and volatile methylamines, we know little about the genes and enzymes involved in the degradation pathway. Furthermore, the identity of those microorganisms responsible for the transformation has not yet been determined. Our current knowledge of these two aspects remains speculative, at least partially due to the lack of definitive research.
This NERC-funded project (2012-2016) aims to fill in this major gap in our knowledge of marine carbon cycle. Using cultivated model microorganisms, we aim to define the key genes and the encoding enzymes in the anaerobic degradation of GBT. Using molecular ecology techniques and the resultant data from the study of the model microorganisms, we aim to further determine the key microbial players involved in the anaerobic production of methane and methylamines from GBT in the marine environment.
Methylamines represent a major group of metabolites in human gut. Microbial transformation of dietary precursors to methylated amines is implicated in the development of several human disorders, including insulin resistance, liver disease and cardiovascular diseases. We have continued interest in understanding the transformation of methylamines in gut microbiota. Our group has recently characterized a novel microbial pathway leading to the formation of trimethylamine from dietary carnitine from gut microbiota (Zhu et al., 2014 PNAS). We have also recently shown that trimethylamine formation from choline degradation leads to enhanced growth and swarming of Proteus mirabilis (Jameson et al, 2015 Environ Microbiol).
PhD student: Tiantian Fu, funded by University of Warwick. Postdoctoral research fellow: Dr Eleanor Jameson, funded by BBSRC and WISB.
Selected key publications on microbial methylamine metabolism
- Jameson E, Fu T, Brown IR,Paszkiewicz K, Purdy KJ, Frank S, Chen Y. (2015) Anaerobic choline metabolism in microcompartments promotes growth and swarming of Proteus mirabilis. Environmental Microbiology, in press.
- Zhu, Y., Jameson, E., Crosatti, M., Schafer, H., Rajakumar, K., Bugg, T.D.H., Chen., Y (2014) 'Carnitine metabolism to trimethylamine by an unusual Rieske-type oxygenase from human microbiota', Proceedings Of The National Academy Of Sciences (USA), 111 (11), 4268 - 4273.
- Y Zhu, E Jameson, R A Parslow, I Lidbury, T Fu, T R Dafforn, H Schafer, Y Chen (2014) 'Identification and characterization of trimethylamine N-oxide (TMAO) demethylase and TMAO permease in Methylocella silvestris BL2', Environmental Microbiology, 16 (10), 3318 - 3330.
- Lidbury, I., Murrell, J.C., Chen, Y. (2014) 'Trimethylamine N-oxide metabolism by abundant marine heterotrophic bacteria', Proceedings Of The National Academy Of Sciences (USA), 111 (7), 2710 - 2715
- Lidbury, I. Murrell, J.C., Chen, Y. (2014) 'Trimethylamine and trimethylamine N-oxide are supplementary energy sources for a marine heterotrophic bacterium: implications for marine carbon and nitrogen cycling', ISME Journal, in press
- Y Chen (2012) 'Comparative genomics of methylated amine utilization by marine Roseobacter clade bacteria and development of functional gene markers (tmm, gmaS)', Environmental Microbiology, 14 (9), 2308 - 2322.
- Chen, Y., Patel, N., Crombie, A., Scrivens J., Murrell, J.C. (2011) 'Bacterial flavin-containing monooxygenase is trimethylamine monooxygenase', Proceedings Of The National Academy Of Sciences (USA), 108 (43), 17791 - 17796.
- Chen, Y. et al., (2010) Gamma-glutamylmethylamide is an essential intermediate for the metabolism of methylamine by Methylocella silvestris', Applied and Environmental Microbiology, 76 4530 - 4537.
- Chen, Y., McAleer, K. L. and Murrell, J. C. (2010) 'Monomethylamine as a nitrogen source for a nonmethylotrophic bacterium Agrobacterium tumefaciens', Applied and Environmental Microbiology, 76 (12), 4102 - 4104.