Effect Of Carbon And Nitrogen Sources On Phosphate Solubilization By Some Local Isolates From Egyptian Rock Phosphate Deposit

Abstract

One hundred and eight phosphate solubilizing (PS) isolates were isolated from different rhizosphere plants, rock phosphate and soil with the percentage of 36.11%, 45.33% and 18.51%, respectively. Four out of 108 isolates were selected as the most efficient Ps isolates which gave the highest values of phosphate solubilization index (PSI) and phosphate solubilization efficient (PSE%) in Pikovskaye's agar medium containing tri-calcium phosphate as a source of insoluble phosphate (qualitative estimation). These isolates were Rs22, Rs7, Bf6&RPf10which recorded PSE of 320%, 300%, 126% and 125%, respectively. These isolates also recorded the maximum rock phosphate solubilization efficiency (RPSE%) being 4.3%, 3.4%, 1.1% and 0.8% by RPf10, Bf6, Rs22 and Rs7, respectively in Pikovskaye's medium supplemented with 5% RP after 10 days of 30°C using shake flasks as a batch culture. The most efficient bacterial and fungal isolates were phenotypic identified as Serratia and Aspergillus genus. Maximum rock phosphate solubilization(RPS)was recorded in the presence of glucoseas the best carbon source at concentration of 10 gl-1or 12.5-15gl-1andtryptoneor yeast extract as the most favorable nitrogen source with 1.25gl-1 or 1.5-2gl-1concs.after 8 or 10 days of incubation for tested bacterial or fungal isolates, respectively. This modification of Pikovskaye's medium led to increase the RPS about 10%, 19%, 49%&59 % by Serratia sp.Rs22, Serratia sp.Rs7, Aspergillus sp. RPf10 &Aspergillus sp. Bf6, respectively comparing to control. Also, whey and sugar beet waste were the best agro-industrial residues for highest RP solubility by tested bacterial and fungal isolates, respectively when used as a sole carbon sources.