Abstract
Greenwater technology is based on integrating finfishes inside pens for zero water exchange system of shrimp aquaculture. Nitrogen transformation could be improved by rearing euryhaline finfishes like grey mullet, milkfish which have a broad diet and tolerate poor water quality. The abundance of four denitrifying functional genes coding for nitrate reductase (narG and napA), nitrite reductase (nirS), nitricoxide reductase (qnorB) and nitrousoxide reductase (nosZ) has been examined in the greenwater system through a metagenomic approach. Phylogeny revealed homology of narG clones with uncultured environmental clones, whereas napA clone sequences were found to have homology with cultured (Stappia aggregata) and uncultured microorganisms. The nirS clones show uniqueness with Marinobacter hydrocarbonoclasticus, Aromatoleum aromaticum, and Ruegeria pomeroyi. The qnorB gene has been reported for the first time from culture systems along the Indian coast and clone exhibited 84–87 % identity with different uncultured bacteria. The nosZ clones are closely affiliated with S. aggregate and alpha bacterium. This study revealed denitrifying diversity from a greenwater system which could eventually be used in planning the future strategy for comprehending nitrogen fluxes, greenhouse gases and their mitigation in coastal aquaculture systems.
Highlights
Nitrates are a by-product of excess feed and decayed organic wastes from animals in aquaculture ponds and can be toxic to animals at higher concentrations
This study revealed denitrifying diversity from a greenwater system which could eventually be used in planning the future strategy for comprehending nitrogen fluxes, greenhouse gases and their mitigation in coastal aquaculture systems
Denitrifying bacterial community was detected in greenwater-bioaugmentation system using PCR amplification of functional genes such as narG napA, nitrite reductase (nirS), qnorB and nosZ gene
Summary
Nitrates are a by-product of excess feed and decayed organic wastes from animals in aquaculture ponds and can be toxic to animals at higher concentrations. Denitrification is a reductive process which converts nitrate (NO3) into atmospheric nitrogen (N2) through nitrite (NO2), nitric oxide (NO), and nitrous oxide (N2O). Different functional genes are involved that encode for enzyme to use nitrogenous metabolites by targeting conserved regions. Complete denitrification needs the sequential action of four enzymes: nitrate reductase (narG and napA), nitrite reductase (nirK/nirS), nitric oxide reductase (nor), and nitrous oxide reductase (nosZ) (Chen et al 2011). They can be used to remove excess nitrogen from wastewater treatment plants (Throback et al 2004). Analysis of functional diversity and its dynamics in the environment could help to understand the microbial ecology and biogeochemistry of aquatic systems (Taroncher-Oldenburg et al 2003)
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