Anaerobic mineralization of quaternary carbon atoms: Isolation of denitrifying bacteria on dimethylmalonate

The microbial capacity to degrade simple organic compounds with quaternary carbon atoms was demonstrated by enrichment and isolation of five denitrify ing strains on dimethylmalonate as the sole electron donor and carbon sourc e. Quantitative growth experiments showed a complete mineralization of dime thylmalonate. According to phylogenetic analysis of the complete 16S rRNA g enes, two strains isolated from activated sewage sludge were related to the genus Paracoccus within the alpha-Proteobacteria (98.0 and 98.2% 16S rRNA gene similarity to Paracoccus dentrificans(T)), and three strains isolated from freshwater ditches were affiliated with the P-Proteobacteria (97.4 and 98.3% 16S rRNA gene similarity to Herbaspirillum seropedicae(T) and Acidov orax facilis(T), respectively). Most-probable-number determinations for den itrifying populations in sewage sludge yielded 4.6 x 10(4) dimethylmalonate utilizing cells ml(-1), representing up to 0.4% of the total culturable ni trate-reducing population.