Microaerobic and anaerobic metabolism of a Methylocystis parvus strain isolated from a denitrifying bioreactor

Abstract

An obligate methanotrophic bacterium, strain MTS, was isolated from a methane-fed microaerobic denitrifying bioreactor. 16S rRNA and DNA-DNA hybridization analysis revealed that this organism was most closely related to Methylocystis parvus, a Type II methanotroph, belonging to the α-subclass of the Proteobacteria. The metabolism of the bacterium under microaerobic and anaerobic conditions was studied by (13) C-NMR. (13) C-labelled poly-β-hydroxybutyrate (PHB) formation occurred in cell suspensions incubated with (13) C-labelled methane at low (5-10%) oxygen concentration. Under these conditions low levels of succinate, acetate and 2,3-butanediol were formed and excreted into the culture medium. Intracellular PHB degradation was observed in intact cells under anaerobic conditions in the absence of an exogenous carbon source during a long-term incubation of 90 days. Multiple (13) C-labelled β-hydroxybutyrate, butyrate, acetate, acetone, isopropanol, 2,3-butanediol and succinate were identified as products in in vivo(13) C-NMR spectra and in the spectra of culture medium during the dynamic PHB degradation. The isolated obligate methanotroph clearly shows a fermentative metabolism of PHB under anaerobic conditions. The excreted products may serve as substrates for denitrifying bacteria.

Pyrosequencing-Based Assessment of the Bacteria Diversity in Surface and Subsurface Peat Layers of a Northern Wetland, with Focus on Poorly Studied Phyla and Candidate Divisions

“…In particular, type II methanotrophs of the family Methylocystaceae were detected in both oxic and anoxic peat. These are known to have the ability to tolerate long periods of oxygen starvation and also to thrive in anoxic conditions by fermenting their characteristic storage compound, poly-β-hydroxybutyrate [45]. By contrast, type I methanotrophs of the family Methylococcaceae were detected only in the oxic surface layer.…”

Genome Sequence of the Methanotrophic Alphaproteobacterium Methylocystis sp. Strain Rockwell (ATCC 49242)

“…are ubiquitous methanotrophic inhabitants of many ecosystems (3,4,7,8,12), likely due to metabolic versatility within this genus. For instance, Methylocystis parvus ferments poly-beta-hydroxybutyrate anaerobically (16), some isolates grow on multicarbon compounds (2,6), and Methylocystis sp. strain SC2 expresses two particulate methane monooxygenases (pMMO) with different methane oxidation kinetics (1).…”

Complete Genome Sequence of Methylocystis sp. Strain SC2, an Aerobic Methanotroph with High-Affinity Methane Oxidation Potential

“…Apart from their ability to oxidize methane, several strains have been reported to possess additional metabolic capabilities. These include their facultative nature (2,10), ability to utilize different nitrogen sources (14,15), and anaerobic fermentation of poly-␤-hydroxybutyrate (18). Methylocystis sp.…”