Glutamate racemization and catabolism inFusobacterium varium

Abstract

The pathways of glutamate catabolism in the anaerobic bacterium Fusobacterium varium, grown on complex, undefined medium and chemically defined, minimal medium, were investigated using specifically labelled 13C‐glutamate. The metabolic end‐products acetate and butyrate were isolated from culture fluids and derivatized for analysis by nuclear magnetic resonance and mass spectrometry. On complex medium, labels from l‐[1‐13C]glutamate and l‐[4‐13C]glutamate were incorporated into C1 of acetate and equally into C1/C3 of butyrate, while label derived from l‐[5‐13C]glutamate was not incorporated. The isotopic incorporation results and the detection of glutamate mutase and 3‐methylaspartate ammonia lyase in cell extracts are most consistent with the methylaspartate pathway, the best known route of glutamate catabolism in Clostridium species. When F. varium was grown on defined medium, label from l‐[4‐13C]glutamate was incorporated mainly into C4 of butyrate, demonstrating a major role for the hydroxyglutarate pathway. Upon addition of coenzyme B12 or cobalt ion to the defined medium in replicate experiments, isotope was located equally at C1/C3 of butyrate in accord with the methylaspartate pathway. Racemization of d‐glutamate and subsequent degradation of l‐glutamate via the methylaspartate pathway are supported by incorporation of label into C2 of acetate and equally into C2/C4 of butyrate from d‐[3‐13C]glutamate and the detection of a cofactor‐independent glutamate racemase in cell extracts. Together the results demonstrate a major role for the methylaspartate pathway of glutamate catabolism in F. varium and substantial participation of the hydroxyglutarate pathway when coenzyme B12 is not available.

Comparative In silico Analysis of Butyrate Production Pathways in Gut Commensals and Pathogens

“…This pathway (Supplementary Figure S2), involved in fermentation of Glutamate to Acetyl-CoA and finally Butyryl CoA, has been observed in various strains of Fusobacteria (Ramezani et al, 2011). Further analysis in this study on sequenced genomes (data not shown) showed that amongst the butyrate producers, this pathway was observed in Fusobacteria and few pathogenic strains of Clostridium like Clostridium tetani and Clostridium tetanophorum .…”

“…Apart from the above mentioned three pathways, previous studies have also reported involvement of methylaspartate pathway in butyrate production in Fusobacterium varium (Ramezani et al, 2011), a pathogen observed in human ulcerative colitis. This pathway (Supplementary Figure S2), involved in fermentation of Glutamate to Acetyl-CoA and finally Butyryl CoA, has been observed in various strains of Fusobacteria (Ramezani et al, 2011).…”

Infection/inflammation-associated preterm delivery within 14 days of presentation with symptoms of preterm labour: A multivariate predictive model

“…For instance, Fusobacterium sp. which was more prevalent in the women who delivered preterm and within 2 weeks of sampling, ferments glutamate to acetate via the hydroxyglutarate pathway [32, 33]. Such metabolic processes explain our observation that the Ace/Glx ratio was associated with sPTD and delivery within 2 weeks of sampling.…”

In Silico Analysis of Putrefaction Pathways in Bacteria and Its Implication in Colorectal Cancer

“…These two pathways have been referred to as ‘histidine degradation’ and ‘THF production’ pathways throughout the manuscript. Further, for the glutamate fermentation pathway (glutamate → acetate + pyruvate) ( Figure 1C ), the third ammonia releasing pathway considered here, a subset of the constituent genes has been reported to occur in genomic context in Fusobacterium varium ( Ramezani et al, 2011 ). The genes encoding two (EC: 5.4.99.1 and EC: 4.3.1.2) out of the four enzymes of the pathway are located in consecutive positions in the F. varium genome ( Ramezani et al, 2011 ).…”