Metabolic Studies of Fusobacterium varium Using NMR Spectroscopy
Abstract
A complex relationship exists between intestinal microorganisms and the human
host; further knowledge of the microbial contributions is important to understand human
health and disease. The metabolism of F. varium, a genome-sequenced constituent of the
gut microbiota was investigated using NMR spectroscopy. The diverse amino acid
requirements of F. varium were determined; while some amino acids were biosynthesized
and utilized readily, others were required in the growth medium. The individual amino
acid requirements were used to develop a chemically defined minimal medium for the
determination of end products in lyophilized culture fluids by 1H NMR spectroscopy. Six
carboxylate fermentation products (acetate, butyrate and smaller amounts of succinate,
propionate, formate and D-lactate) were detected in the exometabolome of F. varium.
Glucose, glycerol and metabolic intermediates were identified as energy sources, and
their addition to the defined growth medium led to variations in the composition of the
exometabolome, attributed to the availability of substrates and the need to maintain redox
balance through regeneration of reduced coenzymes. For example, the oxidative steps
required for glucose catabolism resulted in higher concentrations of reduced products
(butyrate and lactate), whereas propionate was formed exclusively from threonine.
Substrate-product relationships were established using isotopically labeled substrates.
The pathway of glutamate catabolism was dramatically influenced by the presence of
coenzyme B12, one of the B vitamins. Replacing the amino acid component of the
defined medium resulted in meso-2,3-butanediol formation, a metabolite not previously
identified in fusobacteria that may contribute to the pathogenesis of bowel disease.