Abstract
The role of ammonia-oxidizing bacteria and archaea was evaluated using amoA gene in a freshwater recirculating system. Broken earthen pot pieces (BEP) were used as filter bed material. Five archaeal and four bacterial operational taxonomic units were retrieved from amoA genes. Shannon-Weiner and Simpson indices were higher in archaeal amoA sequence compared with the bacteria. Subtype diversity ratio and subtype diversity variance were 0.522 and 0.008, respectively, for archaea and 0.403 and 0.015, respectively, for bacteria. In archaea, 50% amoA sequences showed 99%–100% similarity with the known sequences of ammonia monooxygenase subunit A of uncultured archaeon clones and thaumarchaeote. In bacteria, 84% sequences showed 99% similarity with amoA sequences of different uncultured bacterial clone and Nitrosomonadaceae. Absolute quantification showed that the abundance of archaea was 12-fold higher compared with bacteria. In this recirculating system, ammonia-oxidizing archaea and bacteria played a major role; BEP supported the growth of these ammonia-oxidizing microorganisms.
Highlights
Recirculating aquaculture system is based on the reutilization of waste water involving microorganisms as a tool that reduces the nitrogenous wastes in the culture system
After the confirmation of their belonging to the ammonia-oxidizing microbes, the sequences were clustered into five operational taxonomic units (OTUs) for ammonia-oxidizing archaea (AOA) and four OTUs for Ammonia-oxidizing bacteria (AOB), based on 97% similarity
The sequence analysis of ammonia monooxygenase (amoA) showed the presence of AOA and AOB in the Broken earthen pot pieces (BEP) that were used in the filter bed of the recirculating system
Summary
Recirculating aquaculture system is based on the reutilization of waste water involving microorganisms as a tool that reduces the nitrogenous wastes in the culture system. The main problem is the accumulation of toxic nitrogenous metabolites derived from excess, uneaten feed and excreta. Removal of these nitrogen metabolites is carried out by the process of biofiltration with the help of ammonia-oxidizing microbes. The treatment is completed by nitrite-oxidizing bacteria; denitrifying bacteria releases the free nitrogen into the atmosphere, else absorbed by the plants as nutrients It is a great challenge for the aquaculturists to remove these toxic metabolites from the culture systems. AOA play an important role in nitrification and their amoA genes serve as marker for diversity and abundance (Pester et al 2012). The amoA gene is a function-specific target for the detection of AOB (Kowalchuk and Stephen 2001)
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