Phosphate Solubilizing Bacteria and Fungi Isolated from Rubber (Hevea brasiliensis) Root Rhizosphere, Their Biofilm Formation and Phosphate Solubilizing Abilities

Abstract

The ability of some soil microorganisms and their biofilm combinations to convert insolubleforms of phosphorus to an accessible form is an important trait associated with plant Pnutrition. The phosphorus solubilizing potential of bacteria and fungi isolated from Hevearhizosphere and their effective biofilm communities were evaluated using solid and liquidmedia under in vitro conditions. Phosphate solubilization ability of them were tested oncalcium phosphate media by analysing the soluble P content after incubation at 28±2°C. Outof the microbial isolates, 10 bacterial colonies and one fungal colony formed haloes (clearzones) around the isolate growing on solid media containing calcium phosphate as the solephosphate source. Spectrophotometric quantification of phosphorus solubilization in theliquid media showed that the ten bacterial isolates, and ten fungal isolates solubilizedinsoluble calcium phosphate in to the liquid media in the range of 200 – 450 and 200 – 300mg P L-1 respectively. Biofilm showed significantly higher P solubilization (853.3±25.17 mgP L-1) than their bacteria and fungi counterparts alone. Phosphate solubilization of bacteria,fungi and their biofilm could be attributed to the secretion of organic acids. A significant dropin the pH of the broth media (4.7 to 5.6) compared to the pH of the control treatment (6.8-7.0)was observed. pH change in the media could be due to secretion of organic acids bymicroorganisms and/or utilisation of compounds in the broth media. Although there was asignificant synergistic effect on P solubilization due to biofilm formation, pH in the liquidmedia of their mono cultures and biofilm were not significantly different. This observationwarrants further investigation.