Microlunatus phosphovorus gen. nov., sp. nov., a New Gram-Positive Polyphosphate-Accumulating Bacterium Isolated from Activated Sludge

Researchers isolated two gram-positive, coccus-shaped polyphosphate-accumulating bacterial strains (NM-1T and NM-2) from activated sludge used in wastewater phosphorus removal. These aerobic bacteria exhibited respiratory metabolism with oxygen as the terminal electron acceptor, accumulating over 10% phosphorus by dry weight under aerobic conditions. Chemotaxonomic analysis revealed the major quinone was MK-9(H4), cell wall peptidoglycan contained LL-diaminopimelic acid, and DNA G+C content was 67.9 mol%. The predominant fatty acids were branched-chain types (anteiso-C15:0, iso-C15:0, iso-C16:0). Although phenotypically similar to Luteococcus japonicus, the new isolates differed in fatty acid composition and phylogenetic position. 16S rRNA sequence analysis showed the isolates formed a distinct lineage most closely related to Aeromicrobium erythreum and Nocardioides species, warranting classification as a new genus and species. The authors proposed the name Microlunatus phosphovorus gen. nov., sp. nov., with strain NM-1 designated as the type strain.

Key findings

• Microlunatus phosphovorus is a new gram-positive coccus that accumulates large amounts of polyphosphate (>10% of dry weight) under aerobic conditions
• 16S rRNA phylogenetic analysis demonstrated the organism forms a distinct lineage separate from all known gram-positive genera, most closely related to Aeromicrobium erythreum and Nocardioides species
• Fatty acid composition (predominantly branched-chain anteiso-C15:0, iso-C15:0, iso-C16:0) and reduced nitrate to nitrite distinguish these strains from the phenotypically similar Luteococcus japonicus
• The organism is an obligate aerobe with slow growth (13-hour doubling time) and can utilize diverse carbon sources including various sugars, amino acids, and organic acids