Selection and Characterization of Exoelectrogenic Denitrifying Bacteria from Environmental Soil and Water Samples

Abstract

Global pollution problems have prompted the need of cleaner wastewater treatment strategies; the use of biological processes such as denitrification for this purpose has been increasingly studied as an environmentally friendly alternative. Denitrification can be used to target nitrate-rich wastewaters. The process converts harmful nitrate in water systems into nitrogen gas, this process may be conducted in bioelectrochemical systems by exoelectrogenic bacteria with added benefits. In nature, certain bacteria are able to carry out the denitrification process, for this, the presence of specific genes is required. The genes nirK and/or nirS encoding nitrite reductase are key as the presence of this enzyme characterizes the ability of the bacteria to carry out partial denitrification. The presence of nosZ means that these bacteria are able to carry out the full reaction sequences, converting nitrate to nitrogen gas as the final product. In this study, environmental samples were collected from agricultural soils and sediments from water reservoirs in West Java and East Jakarta, Indonesia. Nine species spread into two genera, Pseudomonas and Acinetobacter, were identified. The screening stages: nitrate removal capacity, denitrification genes characterization, denitrification rate assessment, and exoelectrogenic activity analysis yielded two exoelectrogenic species, Pseudomonas guangdongensis and Pseudomonas entomophila isolated in this study. Denitrification rates and removal of the isolates in this study were comparable with Pseudomonas aeruginosa and Pseudomonas nitroreducens as controls. Moreover, this study presents the first report on exoelectrogenic activity of Pseudomonas entomophila. However, further studies are needed to assess possible denitrification improvement in a system based on the possible consortium formation of microorganisms found in this study.