*5.2.1 Enzyme production*

The content of organic phosphorus in the soil can reach 30–50% of the total amount, which is represented by compounds such as phosphonates, phytic acid, polyphosphonates, sugar phosphates [3, 56], phosphomonoesters, phosphodiesters, phosphotriesters [8], phospholipids and nucleic acids [3, 8]. Generally, these high molecular weight organic compounds are resistant to chemical hydrolysis and need to be converted into soluble ionic phosphate or low-molecular-weight organic phosphates for plant uptake [56].

PSM produce and secrete the enzymes to solubilise the organic phosphates [8]. There are several groups of enzymes are secreted by PSM as [3, 8, 54–56],


NSAPs are a class of enzymes secreted extracellularly or bound to the lipoprotein membranes of PSM. NSAP are generally known as phosphomonoesterases, which dephosphorylate a wide variety of phosphoesters, solubilising around 90% of organic phosphate in soils. The proportion of phosphatases and abundance of P in the soil has a direct relationship, which influences the availability of phosphates to plants.

#### *Managing Soil and Plant Nutrients: Role of Microbial Phosphate Solubilisation DOI: http://dx.doi.org/10.5772/intechopen.112640*

According to the authors, the activity of NSAPs is more concentrated in the rhizosphere than in other parts of soil and phosphatase activity, P uptake by plants and nodule weight has a positive correlation [56].

Phytase enzymes are phosphatases produced by PSM, which have the capability to hydrolyse phytic acid by acting on the phosphomonoester bonds present in the compound, originating two subgroups, myo-inositol hexaphosphate or phytate. In addition to P, this process makes biologically available other nutrients such as zinc and iron [65].

Phosphatases (phosphonate hydrolases) are enzymes, which promote the breaking of C-P bonds of phosphonates by catalysing this reaction from a group carbonyl electron scavenger that allows heterologous cleavage between nutrients. Phosphonatases act on several substrates, including phosphoenolpyruvate, phosphonoacetate, and phosphoenol-acetaldehyde and make biologically available P for plants [56, 65].

Carbon–phosphorus lyases are a complex of membrane enzymes released by PSM that also allow the making available of P, cleaving the C–P bonds of phosphonates, producing hydrocarbons and inorganic Phosphate. This complex is the leading mechanism for the utilisation of phosphonates by PSM. The enzymes and proteins of C–P lyases are complex and specific to their substrates. *Escherichia coli* and *Enterobacter cloacae* K7 are commonly involved with solubilisation of phosphates by using C–P lyases [65].
