The potential of phosphorus-solubilizing purple nonsulfur bacteria in agriculture: Present and future perspectives

Phosphorus (P) is one of the essential macronutrients for crops. It is present in soil in two forms: soluble and insoluble. However, plants cannot absorb the insoluble forms, including Al-P, Fe-P, and Ca-P; thus, the phosphorus use efficiency is reduced. Therefore, the biological approaches should focus more on sustainable agriculture to overcome this constraint. This article cites publications relating to the biological P solubilizer group of bacteria, which have a highly potential adaptation to many conditions in soils. Among the biological approaches, purple nonsulfur bacteria (PNSB) are a potent group of bacteria according to their adaptability in acidic, saline, and toxic conditions based on their mechanisms in producing exopolymeric substances and siderophores under such adverse environments like acid-sulfate and saline soils. PNSB can solubilize P in soil to have more P availability for soil microbes and plants. This particular group of bacteria has been widely applied in liquid and solid forms from agricultural waste to promote plant growth under submerged conditions. Moreover, this article summarized the P-solubilizing mechanisms of P-solubilizing bacteria and introduced future research perspectives on patterns of PNSB in aspects of nutrient-providing potency, plant growth-promoting capability, and biological control capacity. However, the specific mechanisms of P solubilization by PNSB have not been well documented since the P-solubilizing mechanisms have been investigated on general P-solubilizing bacteria. Thus, specific pathways and metabolites relating to the P-solubilizing PNSB should be investigated, and attention should be addressed to them soon.