Recent Progress in Understanding the Molecular Genetics and Biochemistry of Calcium Phosphate Solubilization by Gram Negative Bacteria

Abstract

For most of this century agricultural microbiologists and microbial ecologists have been interested in the ability of some bacteria to efficiently dissolve "insoluble" calcium phosphates. This phenotype has been termed mineral phosphate solubilizing (Mps). This minireview discusses recent work suggesting that the direct oxidation pathway for glucose dissimilation forms the metabolic basis for the strongly Mps+ phenotype observed in many species of gram negative bacteria. In the past, the physiological significance of the direct oxidation pathway for a given species was often considered obscure, giving rise to the term "dissimilatory bypass" to describe the apparent inefficient utilization of reducing power. The Mps function may provide a reason for the expression of this pathway in many bacteria whose bioenergetic needs are satisfied by the Embden-Meyerhof, Entner-Doudoroff or pentose phosphate pathways. The direct oxidation of glucose results in the production of gluconic acid and (often) 2-ketogluconic acid in the periplasmic space which, in turn, results in acidification of the region adjacent to the cell or colony. Calcium phosphates in the medium (soil) are dissolved by these acidic protons. It is proposed that extracellular acidification via the direct oxidation pathway may play an ecological role in some environments including soils where calcium phosphates provide a significant pool of unavailable mineral P. Specific strategies for testing this hypothesis including the use of DNA and antibody probes are discussed.

Assessment of Rice Associated Bacterial Ability to Enhance Rice Seed Germination and Rice Growth Promotion

“…Phosphate-solubilizing microorganisms, in addition to provide phosphorus for plants, provide growth promoting substances like hormones, vitamins and amino acids. It is reported that mechanism of solubilizing phosphate is associated with release of low molecular weight organic acids which chelate the cation bound to phosphate and convert it into soluble form 16,24,25 . According to our result from phosphate solubilizing ability of studied bacteria on NBRIP medium, almost all of them could solubilize phosphate but in different amount.…”

Glucose dehydrogenase of a rhizobacterial strain of Enterobacter asburiae involved in mineral phosphate solubilization shares properties and sequence homology with other members of enterobacteriaceae

“…In Gram-negative bacteria this mineral phosphate solubilization (MPS) phenotype is attributed predominantly to the secretion of low molecular weight organic acids such as gluconic and 2-ketogluconic acids in the periplasmic space 9 .…”

Analysis of the Peltigera membranacea metagenome indicates that lichen-associated bacteria are involved in phosphate solubilization

“…Acidification is a key step in the dissolution of many poorly soluble mineral phosphates, and hence, as proposed by Goldstein (1996), the direct oxidation of glucose to gluconic acid is a key step in some of the major mechanisms for MPS in Gram-negative bacteria, which are suggested to be more efficient at MPS than Gram-positive bacteria owing to secretion of organic acids from sugar metabolism (Sashidhar & Podile, 2009). The pathway is mediated by a membrane-bound glucose dehydrogenase and requires pyrroloquinoline quinone (PQQ) as a cofactor (Goldstein, 1995). Bacteria belonging to the genera Achromobacter, Agrobacterium, Bacillus, Enterobacter, Erwinia, Escherichia, Flavobacterium, Mycobacterium, Pseudomonas and Serratia have been found to be efficient in phosphate solubilization (Goldstein, 2001).…”