Abstract

Phosphorus is critical to the growth and yield of plants, because it stimulates growth, initiates nodule formation as well as influences the efficiency of rhizobium-legume symbiosis.  Deficiency of phosphorus in plants is manifested in terms of stunted growth, reduced yield and delayed maturity. Application of organic or inorganic chemical fertilizers or combinations of both in order to increase fertility, over a period of time builds up total and available phosphorus in the soil. However, this high level of total phosphorus added to the soil is rapidly fixed as insoluble forms soon after application and becomes unavailable to the plants regardless of the fertilizer brand or chemical composition. Excessive application of phosphorus to soil increases phosphorus fixation and the long-term effect is the gradual loss of phosphorus from such soil into underground waters, leading to contamination. A large number of microorganisms present in the rhizosphere are known to solubilize and make available the insoluble phosphorus in the available form to the plants. This study presents insights into the screening and morphological properties of some phosphate solubilizing microorganisms, which are organisms that can solubilize these fixed forms of phosphorus and make it available to plants.  A total of 35 Phosphate Solubilizing Microbial colonies were isolated on Pikovskaya agar medium, containing insoluble tricalcium phosphate (TCP) from agricultural soil. Among these, 3 isolates with strong halo zone formation were studied. The 3 isolates, AFS-A, AFS-B, and AFS-M were subjected to molecular identification, based on the 16SrRNA gene amplification and sequencing technique. The molecular identification showed isolate AFS-A as Enterobacter hormaecheii with a percentage identity of 96.57 (accession number CP017180.1). AFS-B was identified as Enterobacter cloacae, with a percentage identity of 96.57 (accession number CP026850.1). AFS-M was identified as Clostridium beijerinckii, with 97.88 percentage identity (accession no.MK522142.1). Studies on their PSI and PSE showed that E. cloacae solubilized TCP more with a PSI of 3.22 + 0.1 and a PSE of 2.39.0 + 1.0. E. hormaecheii had a PSI of 1.36 + 0.0 and a PSE of 149.3 + 1.0. C. beijerinckii had a PSI of 0.25 + 0.0 and PSE of 146 + 1.0. All isolates lowered the pH of PVK broth. Highest IAA produced was recorded by E. cloacae (44.0 + 0.0). This was followed by C. beijerinckii (19.1 + 0.0) and E. hormaecheii (12.3 + 0.2). This serves as a foundation for future exploration of the bio-prospective potential of rhizosphere bacteria in this unique ecological niche. This could lead to the eventual replacement of chemical fertilizers in agricultural practice by increasing the bioavailability of phosphorus already present in soils. This will lend support to food security and equally protect the environment as a natural practice and health of various life forms.

Key Words: Phosphate Solubilizing Microorganisms, Accession number, Pikovskaya, C. beijerinckii, E. hormaecheii, E. cloacae