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).