MCT13: a newly discovered agarase-producing Sphingomonas sp. Isolated from freshwaters

The yellow-pigmented Gram-negative MCT13 strain was isolated from a drainage ditch within a disused system of constructed wetlands, flowing through uncultivated land. Growth on agar media was associated with clearing and pitting around the colonies, a feature never reported so far among sphingomonads. This trait, together with the unusual biochemical profile, let us to hypothesize that MCT13 belonged to a novel species. The 16S rDNA sequence shared the highest (98%) identity with uncultured sphingomonads. High Throughput DNA Sequencing confirmed the presence of putative agarase-like enzymes, and allowed to perform an Average Nucleotide Identity analysis, by comparing MCT13 with other Sphingomonas sp. deposited in the INSDC databases. The closest homolog (78.3%) is Sphingomonas koreensis NBRC_16723. As the species delineation cut-off is <95%, the hypothesis that MCT13 belongs to a novel species in the genus Sphingomonas is supported. The ability to degrade agar, together with the lack of known antibiotic resistances other than the genus-related resistance to streptomycin, make Sphingomonas sp. MCT13 a potentially interesting strain for the degradation of complex carbohydrates.