Abstract
Nitrogen species such as ammonia and nitrite are considered as major stressors in modern aquaculture practices. We developed enrichments of ammonia oxidising bacteria (AOB) and nitrite oxidising bacteria (NOB) for effective mitigation of nitrogenous wastes in the shrimp culture operations. The objective of this study was to understand the microbial community composition of AOB and NOB enrichments using the V3-V4 region of the 16S rDNA gene by Illumina MiSeq sequencing. The analysis revealed 2948 and 1069 OTUs at 97% similarity index and Shannon alpha diversity index of 7.64 and 4.85 for AOB and NOB enrichments, respectively. Comparative analysis showed that a total of 887 OTUs were common among AOB and NOB enrichments. The AOB and NOB enrichment were dominated by Eubacteria at 96% and 99.7% respectively. Proteobacterial phylum constituted 31.46% (AOB) and 39.75% (NOB) and dominated by α-Proteobacteria (20%) in AOB and γ-Proteobacteria (16%) in NOB. Among the species in AOB enrichment (2,948) two sequences were assigned to ammonia oxidising bacterial group belonging to Nitrosomonas, and Nitrosococcus genera and two belonged to archaeon group comprising Nitrosopumilus and Candidatus Nitrososphaeraea genera. The NOB enrichment was predominated by Nitrospiraceae and Thermodesulfovibrionaceae. Further, the data revealed the presence of heterotrophic bacteria contributing to the process of nitrification and form microcosm with the AOB and NOB. PICRUSt analysis predicted the presence of 24 different nitrogen cycling genes involved in nitrification, denitrification, ammonia and nitrogen transporter family, nitrate reduction and ammonia assimilation. The study confirms the presence of many lesser known nitrifying bacteria along with well characterised nitrifiers.
Highlights
Nitrogen species such as ammonia and nitrite are considered as major stressors in modern aquaculture practices
ammonia oxidising bacteria (AOB) and nitrite oxidising bacteria (NOB) cultures were enriched from the pond sediments under autotrophic conditions with ammonia and nitrite as a sole energy source
The AOB enrichment efficiently oxidised ammonia to nitrite in 10 days while NOB consortium oxidized nitrite to nitrate in 14 days (Fig. 1)
Summary
Nitrogen species such as ammonia and nitrite are considered as major stressors in modern aquaculture practices. We developed enrichments of ammonia oxidising bacteria (AOB) and nitrite oxidising bacteria (NOB) for effective mitigation of nitrogenous wastes in the shrimp culture operations. Nitrification is the biological oxidation of ammonia (NH3) to nitrite (NO2−) and to nitrate (NO3−), is a major oxidative process involved in maintenance of global nitrogen cycle in aquatic systems[8] and soil[9]. This process is predominantly carried out by two different classes of lithoautotrophic microbes, namely the ammonia-oxidising bacteria (AOB) (e.g., Nitrosomonas and Nitrosospira) and the ammonia-oxidising archaea (AOA) (e.g., Nitrososphaerea, Nitrosopumilus) as one guild that convert ammonia to nitrite. The objective of this paper is to understand the microbial diversity of the enrichments developed in the laboratory using 16S rDNA sequencing analysis
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