The use of Bacillus species in maintenance of water quality in aquaculture: A review

Aquaculture effluent is often associated with increased organic carbon, suspended solids, phosphates, nitrogenous species (nitrates, nitrites, and ammonia), chemical oxygen demand and biological oxygen demand. This is regarded as a global threat to aquatic ecosystems due to its influence on surrounding waters as well as groundwater. The threat of aquaculture effluent is not confined to the aquatic ecosystems as high levels of phosphorus and nitrogen may become poisonous to plants and change their protein synthesis, enzyme activities, photosynthesis, oxidative stress response, membrane permeability, and respiratory processes. Other forms of water pollution such as the presence of heavy metals as well as pathogenic microbes are issues of concern since they can be transferred through the food chain. Bacillus species have demonstrated great ability in the maintenance of water quality in aquaculture which is simple and cost-effective. This review highlights that Bacillus modulates a wide range of water quality parameters including physical (transparency and total dissolved solids) and chemical (pH, conductivity, chemical oxygen demand, dissolved oxygen, biological oxygen demand, alkalinity, phosphates, nitrogenous species, hardness) water quality parameters, heavy metals, oil spillage as well as maintenance of microbial balance; hence reduction in pathogenic microbes. The efficiency of Bacillus in modulating water quality is greatly dependent on factors such as mode of application, dissolved oxygen, pH, temperature, source of nutrients, strain type, and metal ions. This review further highlights aquaculture activities that lead to pollution and the possible mechanisms used by Bacillus for improving water quality. It is recommended that a range of optimum conditions be established to increase the efficiency of Bacillus in modulating water quality. A better understanding of Bacillus to the genetic level and the development of new genetic tools is also recommended since the ability of microorganisms to modulate water quality is related to their genetic makeup.