Isolation and screening of phosphate solubilizing bacteria on tricalcium phosphate containing media

C.B.Tripura* and A.R.Podile

Department of Plant Sciences, University of Hyderabad. Hyderabad-500046, INDIA.

* chaturvedulat@yahoo.com 

Phosphate solubilizing bacteria (PSB) are used as biofertilizers in phosphate deficient soils for enhanced crop yields. PSB were isolated on media containing tri calcium phosphate (TCP) as the source of inorganic phosphate based on the zone of clearance around the colony after 2-3 day incubation at 30⁰C and preserved. Phosphate solubilizing ability of the PSB was evaluated on NBRIP medium (1) with TCP as sole source of inorganic phosphate. After incubation at 28⁰C for 2 weeks the zone of solubilization (clearance) was measured around each colony.

Ten selected bacterial strains that showed solubilization, in terms of zone of clearance were further tested in liquid NBRIP medium after incubation for 48 h. The cell free supernatant was analyzed for change in pH and the amount of phosphate released into the medium (2). At least 4 cultures showed drop in the pH from 7 to 3.5 within the first 48h, suggesting that these cultures were possibly secreting some acids rapidly into the medium, which in turn facilitated solubilization of insoluble phosphate. The culture supernatant of these four strains (Gram-negative) are being analyzed both qualitatively and quantitatively to detect the composition of acid(s) particularly gluconic acid using HPLC. We intend to use one of these strains for isolation of genes involved in mineral phosphate solubilization. 

References: -

1.C.Shekhar Nautiyal, (1999) FEMS Microbiol.Lett. 170, 265-270.

2.Ames, B.N., (1960) Methods in Enzymology 8, 115-118.