Microalgae-Bacteria Consortia: A Review on the Degradation of Polycyclic Aromatic Hydrocarbons (PAHs)

Polycyclic aromatic hydrocarbons (PAHs) are considered as import contaminants portraying diverse ecological and public health apprehension due to their properties such as water solubility, toxicity, bioaccumulation potential and recalcitrant nature. Due to their contrary impact on the human wellbeing and other organisms in the biosphere, research is in progress to remove PAHs from the environment. Several physicochemical methods can be used for the removal of PAHs; however, its bioremediation using microorganisms is a benign and ecofriendly approach. Various strains of bacteria and microalgae are capable to potentially degrade or transform PAHs through their indigenous metabolic pathways. However, their biodegradability potential hindered by the cytotoxic effect of petroleum hydrocarbons, unfavorable environmental conditions, metabolic constrains, hydrocarbon composition, concentration, type and number of microorganisms. During the last decade, different microalgae species have been reported capable of biodegrading PAHs. Moreover, the interaction between microalgae and bacteria PAH metabolic pathways overcomes some rate limiting step(s) observed in single species. Thus, an alternative paradigm "Microalgae-Bacteria Consortia" is emerging as a new strategy to be adopted for the efficient detoxification and removal of the PAH pollutants. This review article aimed to provide an update of the current knowledge on the toxic effects of PAHs in various organisms as well as the symbiotic interactions between different bacteria and microalgae species in the degradation/transformation of PAHs. In addition, environmental factors are highlighted to elucidate how PAHs influence the growth of microalgae within a symbiotic framework with bacteria counterpart. The ultimate outcome of this paper can be beneficial to expedite the progress of new research into the bioremediation of PAHs from the contaminated environments.