Microvirgula aerodenitrificans gen. nov., sp. nov., a new Gram-negative bacterium exhibiting co-respiration of oxygen and nitrogen oxides up to oxygen-saturated conditions

Researchers isolated a novel Gram-negative bacterium, designated Microvirgula aerodenitrificans (strain SGLY2T), from an upflow denitrifying filter inoculated with activated sludge. The bacterium exhibits atypical respiratory metabolism, simultaneously utilizing oxygen and nitrogen oxides as terminal electron acceptors even under oxygen-saturated conditions. Morphologically, it appears as motile curved rods with a GC content of 65 mol%. Although phenotypic tests initially suggested similarity to Comamonas testosteroni, phylogenetic analysis using 16S rRNA gene sequencing revealed that SGLY2T shares less than 89% sequence similarity with known genera, establishing it as phylogenetically distinct. The organism grows heterotrophically on various organic compounds including acetate, succinate, and ethanol, but not sugars. Optimal growth occurs at 35°C and pH 7 under both aerobic and anoxic conditions. The researchers designed a specific oligonucleotide probe targeting a unique 16S rRNA sequence region for detection via fluorescent in situ hybridization, enabling identification of this strain in environmental samples without cultivation.

Key findings

• Microvirgula aerodenitrificans is a newly described genus and species exhibiting co-respiration of oxygen and nitrogen oxides simultaneously up to oxygen-saturated conditions, unlike classical denitrifiers.
• 16S rRNA sequence analysis demonstrated the strain belongs to the β-subclass of Proteobacteria but shares less than 89% sequence identity with all previously recognized genera, phylogenetically distinguishing it from phenotypically similar Comamonas testosteroni.
• The bacterium grows aerobically with a doubling time of 1.87 hours and anoxically with 6.3 hours doubling time, utilizing diverse carbon sources except sugars, with optimal growth at 35°C and pH 7.
• A specific oligonucleotide probe (S-*-Mae-0636-a-A-18) was designed and validated for rapid cultivation-independent detection of M. aerodenitrificans using fluorescent in situ hybridization with 90-98% cell detection efficiency.