Biotechnology and Bioinformatics (1+1)

6.1.5.2. Bioremediation of Nitrogenous compounds

Nitrogen applications in excess of pond assimilatory capacity can lead to deterioration of water quality through the accumulation of nitrogenous compounds (e.g., ammonia and nitrite) with toxicity to fish and shrimp.

• Bacteriological nitrification is the most practical method for the removal of ammonia from closed aquaculture systems and it is commonly achieved by setting of sand and gravel bio-filter through which water is allowed to circulate.
• The ammonia oxidizers are placed under five gene ra, Nitrosomonas, Nitrosovibrio, Nitrosococcus, Nitrolobus and Nitrospira, and nitrite oxidizers under three genera, Nitrobacter, Nitrococcus and Nitrospira.
• There are also some heterotrophic nitrifiers that produce only low levels of nitrite and nitrate and often use organic sources of nitrogen rather than ammonia or nitrite.
• Nitrifiers in contaminated cultures have been demonstrated to nitrify more efficiently.
• Nitrification not only produces nitrate but also alters the pH slightly towards the acidic range, facilitating the availability of soluble materials.
• The vast majority of aquaculture ponds accumulate nitrate, as they do not contain a denitrifying filter.
• Denitrifying filters helps to convert nitrate to nitrogen. It creates an anaerobic region where anaerobic bacteria can grow and reduce nitrate to nitrogen gas. Nitrate may follow several biochemical pathways following production by nitrification.

                      NO₃ →NO₂ → NO N₂O →N₂

Unlike the limited species diversity of bacteria mediating nitrification, at least 14 genera of bacteria can reduce nitrate. Among these, Pseudomonas, Bacillus and Alkaligenes are the most prominent numerically.