Diversity of sediment-associated Planctomycetes in the Arabian Sea oxygen minimum zone

We examined the diversity of Planctomycetes in the sediment sample collected from an oxygen minimum zone (OMZ) in the southeast Arabian Sea. A 16SrRNA gene library was constructed using the forward primer specific for Planctomycetes and a universal reverse primer. The 237 sequences obtained were grouped into 130 operational taxonomic units, and the majority of them were clustered with phylum Planctomycetes (45.0%) and unclassified bacteria (27.0%). There were sequences that clustered with distantly separated monophyletic groups such as Latescibacteria (9%), Actinobacteria (6%), Proteobacteria (5%), and others (8%). Among Planctomycetes, 55.7% belonged to family Planctomycetaceae, followed by unclassified Planctomycetes (25.0%) and family candidatus Brocadiaceae (19.2%). The family Planctomycetaceae included the genera Blastopirellula (11.5%), Rhodopirellula (3.8%), and a large number unclassified Planctomycetaceae sequences (40.4%). The members of family candidatus Brocadiaceae included the genera candidatus Scalindua (11.5%), candidatus Brocadia (1.9%) and unclassified genera (5.8). Our study indicates the relatively large diversity of Planctomycetes in sediments underlying the oxygen minimum zone of Arabian Sea. Also, the sequence data generated in the present study may support the efforts on isolation and purification of Planctomycetes from marine environment for understanding their biogeochemical significance.