Meganema perideroedes gen. nov., sp. nov., a filamentous alphaproteobacterium from activated sludge

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Abstract
An industrial wastewater treatment plant at Grindsted, Denmark, has suffered from bulking problems for several years caused by filamentous bacteria. Five strains were isolated from the sludge by micromanipulation. Phylogenetic analysis of the 16S rRNA gene sequences showed that the strains formed a monophyletic cluster in the Alphaproteobacteria, and they were phenotypically different from their closest relatives and from all hitherto known filamentous bacteria described (closest relative Brevundimonas vesicularis ATCC 11426T, 89.8 % sequence similarity). In pure culture, the cells (1.5–2.0 μm) in filaments are Gram-negative and contain polyphosphate and polyhydroxyalkanoates. The optimum temperature for growth is 30 °C and the strains grow in 2 % NaCl and are oxidase- and catalase-positive. Ubiquinone 10 is the major quinone. The major fatty acid (C18 : 1 ω7c) and smaller amounts of unsaturated fatty acids, 3-hydroxy fatty acids with a chain length of 16 and 18 carbon atoms and small amounts of 10-methyl-branched fatty acids with 18 carbon atoms (C19 : 0 10-methyl) affiliated the strains with the Methylobacterium/Xanthobacter group in the Alphaproteobacteria. The G+C content of the DNA is 42.9 mol% (for strain Gr1T). The two most dissimilar isolates by 16S rRNA gene comparison (Gr1T and Gr10; 97.7 % identical) showed 71.5 % DNA–DNA relatedness. Oligonucleotide probes specific for the pure cultures were designed for fluorescence in situ hybridization and demonstrated that two filamentous morphotypes were present in the Grindsted wastewater treatment plant. It is proposed that the isolates represent a new genus and species, Meganema perideroedes gen. nov., sp. nov. The type strain of Meganema perideroedes is strain Gr1T (=DSM 15528T=ATCC BAA-740T).