Diversity and Quantitative Detection of Clade I Type nosZ Denitrifiers in the Arabian Sea Oxygen Minimum Zone

Abstract

A significant amount of nitrous oxide (N2O) is effluxed into the atmosphere as a result of marine denitrification in the Arabian Sea (AS) oxygen minimum zone (OMZ). An assessment of temporal variations in the diversity and abundance of nosZ denitrifiers was performed to establish the relative importance of these bacteria in denitrification. Sampling was conducted at the Arabian Sea Time Series (ASTS) location and a quantitative PCR (qPCR) analysis was performed. We detected a high abundance of the nosZ gene at core OMZ depths (250 m and 500 m), indicating the occurrence of denitrification in the AS-OMZ. The maximum abundance of the nosZ gene was observed during the Spring Intermonsoon (SIM) at 250 m (1.32×106 copies L–1) and 500 m (1.50×106 copies L–1). Sequencing analysis showed that nosZ denitrifiers belonged to the classes Alpha-, Beta-, and Gammaproteobacteria. Taxonomic analysis revealed that most OTUs were affiliated with Pseudomonas, Rhodopseudomonas, and Bradyrhizobium. Diversity indices and richness estimators confirmed a higher diversity of nosZ denitrifiers at 250 m than at 500 m during all three seasons. The present results also indicated that dissolved oxygen (DO) and total organic carbon (TOC) are critical factors influencing the diversity and abundance of the nosZ-denitrifying bacterial community.