This document discusses plant growth promoting rhizobacteria (PGPR) and their ability to solubilize inorganic phosphate. Some key points: - PGPR are bacteria that live in the rhizosphere and provide benefits to plants. An important function is solubilizing insoluble phosphate minerals making phosphorus available for plant uptake. - Common insoluble phosphates include tricalcium phosphate, dicalcium phosphate, and hydroxyapatite. Bacteria secrete organic acids like lactic acid and acetic acid to solubilize these minerals. - Successful phosphate solubilizing bacteria include species from Bacillus, Pseudomonas, and Rhizobium genera. Screening methods involve checking for clearing zones

1. Solubilize inorganic phosphorus from
insoluble compounds

2.  A number of bacterial species provide beneficial effects to a plant and these
are mostly present in rhizosphere and hence called rhizobacteria.
 This group of bacteria has been termed plant growth promoting
rhizobacteria.
 Phosphorus is an essential element for plant development and growth
making up about 0.2 % of plant dry weight.
 Plants acquire P from soil solution as phosphate anions.
 However, phosphate anions are extremely reactive and may be
immobilized through precipitation with cations such as Ca 2+ , Mg 2+ , Fe
3+ and Al 3+.
 In these forms, P is highly insoluble and unavailable to plants.
 Different bacterial species has ability to solubilize insoluble inorganic
phosphate compounds, such as tricalcium phosphate, dicalcium phosphate,
hydroxyapatite, and rock phosphate

3.  The principal mechanism for mineral phosphate solubilization is the production of organic acids,
and acid phosphatases
 phosphate solubilization is the action of organic acids synthesized by soil microorganisms

4.  Bacillus were found to produce mixtures of lactic, isovaleric, iso-butyric and acetic acids.
 Other organic acids, such as glycolic, oxalic, malonic, and succinic acid, have also been
identified among phosphate solubilizers.
 Strains from the genera Pseudomonas, Bacillus and Rhizobium are among the most
powerful phosphate solubilizers
Chelating substances
and inorganic acids
are other
mechanisms but less
effective than organic
acid production.

5. Possible using plate screening
methods.
Phosphate solubilizers produce
clearing zones around the microbial
colonies in media.
 Insoluble mineral phosphates such
as tricalcium phosphate or
hydroxyapatite are contained in the
media.
Bromophenol blue method produce
yellow halos following pH drop
through the release of organic acids`

6.  Potential materials that are able to support good growth and survival of bacteria are needed in
inoculant production such as - coals, bentonite, corn oil, mineral soils, peat, peat moss,
vermiculite, and perlite
 STEP -1 (CULTIVATION)
Bacteria are cultivated on suitable medium in suitable conditions.
 STEP-2 (COLLECTION)
After incubation period collect microbial cells by centrifuge.
Wash cells with distilled water or diluted saline solution.
 STEP-3(FORMULATION OF INOCULANTS USING CARRIE MATERIAL)
Mix cells using carrier materials such as peat, vermiculite, perlite etc.
Centrifuged
Culture