The (Microbial) Caffeine Diet Explained
Some people seem to live on caffeine, but some bacteria actually do obtain all their carbon and nitrogen from the world’s favorite stimulant. Now Mani Subramanian and colleagues of the University of Iowa, Iowa City, are elucidating the mechanics of caffeine metabolism in the bacterium Pseudomonas putida CBB5, which grows on several purine alkaloids, and which this team previously showed metabolizes caffeine and related methylxanthines via sequential N-demethylation of xanthine. “Mapping all the genes in CBB5 involved in the degradation of caffeine identified N1 (ndmA), N-3 (ndmB), and N-7 (ndmC) specific N-demethylases,” says Subramanian. Xanthine and formaldehyde liberated from caffeine via these genes are further degraded for growth and energy. NADH-dependent conversion of caffeine to xanthine by ndmA, B, and C is absolutely dependent on ndmD, a Rieske protein with three redox centers! This is the first report of N-demethylase reactions catalyzed by Rieske/non-heme iron proteins.” Subramanian notes that “Coffee, tea, and cocoa waste are abundant worldwide,” but that genes identified herein can remove the purine alkaloids in the wastes, so that these can be used as animal fee, a source of high-value alkylxanthines, or for ethanol production. “Scientifically, this work demonstrates for the first time how purine alkaloids are completely degraded via N-demethylation reactions, contributing to the carbon and nitrogen balance on our planet.” (R. M. Summers, T. M. Louie, C.-L. Yu, L. Gakhar, K. C. Louie, and M. Subramanian. 2012. Novel, highly specific N-demethylases enable bacteria to live on caffeine and related purine alkaloids. J. Bacteriol. 194:2041-2049.)
Bacterial Caffeine Addiction
Ryan Summers, a PhD student in Dr. Subramanian’s laboratory, recently presented a paper at the ASM 2011 Annual Meeting entitled: “Purification, Cloning, and Functional Expression of NdmA and NdmB, Two Positional-Specific Methylxanthine N-Demethylases from Pseudomonas Putida CBB5”. His paper was selected by the ASM Communications Committee to be highlighted in the press room during the conference. This resulted in more than 60 citations on popular press with respect to “bacterial addiction to caffeine”.