Girgis M. G. Z.; Heba M . A. Khalil and M. S. Sharaf( 2008). In Vitro Evaluation Of Rock Phosphate And Potassium Solubilizing
Potential Of Some Bacillus Strains
Australian Journal of Basic and Applied Sciences, 2(1): 68-81, 2008
ISSN 1991-8178
Abstract: The efficacy of 8 rhizobacterial Bacillus strains for potassium and phosphate dissolution from insoluble soil minerals were evaluated in vitro. Aleksandrov's medium (MA) supplemented with either mica (MA-m) or feldspar (MA-f) and Pikovskaya medium (PVK) containing rock phosphate
(PVK-rp) or tri-calcium phosphate (PVK-tcp) at concentration of 0.5% were used to investigate solubilizing ability of tested strains. Final pH, total acidity, soluble K & P, exopolysaccharides (EPS)
& viscosity and released organic acids were determined in their culture media. Somaclonal diversity between the most efficient strains using isozyme analysis and PCR-fingerprinting were also detected. Current data showed that inoculation with the selected strains having a variable degrees of metabolic effectiveness led to partial degradation of minerals, resulting in release of higher amounts of soluble K & P in the culture media compared to controls. Their effects were more obvious in culture media supplemented with insoluble forms of P. Strains UBFBc1, UBFBa7 and UBFBa4, UBFBm2 were the most powerful K mobilizes and P solubilizers detected on MA-f, MA-m and PVK-tcp, PVK-rp culture media, respectively. Relationships were observed between the final pH and total acidity and the amount of soluble P in their culture media and this was accompanied by a decrease in pH causing an increase of total acidity of media, while obtained results from K insoluble culture media took contrary view. However, a relationship between the capacity for P & K dissolution and viscosity of culture media depending on the quantity of EPS produced by Bacillus strains was also noticed. Differences in EPS production amongst the strains were recorded. Strains UBFBc1 and UBFBa7 grown in MA-f and MA-m culture media produced the highest amount of EPS and viscosities compared to other strains. Variations in organic acids quality and quantity were analyzed. Higher amounts of organic acids i.e., oxalic, fumaric, citric and tartaric, were produced by strains UBFBa4 and UBFBm2 in PVK-tcp and PVK-rp culture media accompanied by lowest amount of EPS. On the other hand, strains UBFBc1 and UBFBa7 in MA-f and MA-m culture media, respectively took contrast trend. Protein fractions, phosphatase isozymes and DNA fingerprint analysis were successfully revealed somaclonal and genetic variations among the 4 closely related Bacillus strains. Similarity analysis confirmed the difference in protein pattern and phosphatase confirming the genetic variation between strains.
Keywords: (Bacillus spp., K & P rock minerals, dissolution mechanism, EPS production, organic acids, somaclonal variations. )
