This pathway was contributed by Rachael Long, Carla Essenberg, Tony Dodge, University of Minnesota and Stephan M. Cameron, University of Minnesota, BioC/MicE 5309.
Caffeine (1,3,7-trimethylxanthine) is found naturally in coffee, tea and cocoa and used as a food and drug additive. When ingested by humans, caffeine stimulates the central nervous system, elevates blood pressure, increases metabolic rate, and acts as a diuretic (Higdon and Frei, 2006). Caffeine consumption may reduce the risk of Parkinson's disease. However, adverse reactions to caffeine consumption can include anxiety, insomnia, heart palpitations, abdominal pain, and nausea, and high caffeine intake has been linked with increased risk of osteoporosis and complications in pregnancy (Dash and Gummadi, 2006). Caffeine is also mildly addictive. Withdrawal symptoms can include headache, fatigue, depressed mood, difficulty concentrating, irritability, nausea, and muscle pain (Higdon and Frei, 2006).
Coffee pulp, a waste product produced during coffee processing, is a major pollutant in water bodies near coffee plants. Despite the fact that it is high in nutrients, it cannot be used as animal feed due to the high levels of caffeine and other unwanted compounds (Pandey et al., 2000). Solvents commonly used to produce caffeine-free products are either very expensive to use or toxic (Dash and Gummadi, 2006). However, a number of bacterial and fungal strains capable of degrading caffeine have been identified (Mazzafera, 2004).
There are multiple possible pathways depending on the genus, species and strain of organism degrading the caffeine. In the bacteria Psuedomonas putida and Serratia marcescens, the major pathway is through theobromine to 7-methylxanthine to xanthine (Mazzafera, 2004). Minor branches produce methyluric acids; it has been proposed that these degrade to uric acid (Dash and Gummadi, 2006), but this has not been confirmed. Another bacterial pathway, found in Rhodococcus and Klebsiella spp., requires oxidation to yield 1,3,7-trimethyluric acid (Madyastha and Sridhar, 1998). Caffeine can also be degraded via alternative pathways found in several fungal and one bacterial species.
The following is a text-format caffeine degradation pathway map. Organisms which can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in graphic (15k) format.
Caffeine Caffeine Serratia marcescens Rhodococcus spp. Pseudomonas putida Klebsiella spp. | | | | | | +---------------------+---------------------+ | | | | | caffeine | caffeine | caffeine | demethylase | demethylase | oxidase | | | | | | v v v Theobromine Paraxanthine 1,3,7-Trimethyl- | | uric acid | | | | | | | | | +--------+------------+ +---------------+-----------+ | | | | | | | xanthine | theobromine | paraxanthine | xanthine | urate | oxidase | demethylase | demethylase | oxidase | oxidase | | | | | | | | | | v v v v v 3,7-Dimethyl- 7-Methylxanthine 1,7-Dimethyl- 3,6,8-Trimethyl- uric acid | uric acid allantoin | | | | | | +----------+----------+ | | | v | xanthine | heteroxanthine | A | oxidase | demethylase | | | | | | | v v v 7-Methyl- Xanthine N,N'-Dimethyl- + N-Methyl- + Glyoxylate uric acid | urea urea | | | | | | | | | v v Intermediary Intermediary Metabolism Metabolism (KEGG) (KEGG)
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