Methylobacterium flocculans sp. nov., a Floc-Forming Bacterium Isolated from Aquaculture Ponds

Strain FF17^T, a Gram-negative, obligate aerobic, motile, pink-pigmented, and methylotrophic bacterium, was selected for a polyphasic taxonomic investigation due to its capacity for aggregation, or floc formation. The predominant respiratory quinone observed was Q-10, accounting for 83.36% of the total, while the major fatty acids were summed feature 8 (18:1 w6c and/or 18:1 w7c). The major polar lipids included Diphosphatidylglycerol (DPG), phosphatidylglycerol, phosphatidylethanolamine (PE), phosphatidylinositol (PI), and one unknown polar lipid. Phylogenetic analysis showed that strain FF17^T was hithermost related to Methylobacterium goesingense iEII3^T (99.86%), M. gossipiicola Gh-105 ^T (99.22%), M. adhaesivum AR27^T (98.92%), and M. iners 5317S-33 ^T (97.27%) based on 16S rRNA gene sequence similarity. A 5,735,273-bp chromosome and six plasmids make up the genome, making it larger than the genomes of the other four Methylobacterium species described above. The digital DNA-DNA hybridization and average nucleotide identity values between strain FF17^T and the reference strains were 21.90-28.70 and 77.39-85.04%, respectively. Strain FF17^T had a genome DNA G + C content of 68.5 mol%. The analysis of genomes indicated that cellulose apparently plays an important character in the aggregation of Methylobacterium species. Genome annotation revealed the presence of genes involved in assimilatory/dissimilatory nitrate reduction and ammonia assimilation. In conclusion, Strain FF17^T is identified as a new species in the Methylobacterium genus, based on analyses of genomics, phylogeny, biochemistry, and fatty acids, and the name Methylobacterium flocculans sp. nov. is proposed. The type strain is FF17^T (= MCCC 1K08738^T = KCTC 8320 ^T).