Abundance of denitrifying genes coding for nitrate (narG), nitrite (nirS), and nitrous oxide (nosZ) reductases in estuarine versus wastewater effluent-fed constructed wetlands

Abstract

Constructed and estuarine wetlands, influenced by wastewater treatment plants, were investigated, with respect to microbial activity in terms of functional genes. The density and abundance of three denitrifying genes coding for nitrate (narG), nitrite (nirS), and nitrous oxide (nosZ) reductases, in sediment soil samples from wastewater effluent-fed and estuarine wetlands, were quantified using the SYBR green-based real-time polymerase chain reaction (PCR). To assess seasonal effects (i.e., winter (average temperature similar to 2 degrees C) versus spring (average temperature similar to 20 degrees C)), the densities of denitrifying genes, with respect to the abundance of functional genes, for the two different wetlands were determined. The three functional genes for all the sampling sites ranged from 1.0 x 10(6) to 1.0 x 10(9) copies/g of soil. Without considering seasonal variation, the nitrite-reducing functional genes were dominant over the other two genes in the effluent-fed wetland samples. However, nitrate and nitrite-reducing functional genes were dominant in relatively cold and warm seasons, respectively, in the estuarine wetland samples. Even though robust patterns and conclusions could not be obtained from the limited investigations, patterns with certain trends and needs for potential future research directions were obtained. (C) 2009 Elsevier B.V. All rights reserved