Role of bacterial pyrroloquinoline quinone in phosphate solubilizing ability and in plant growth promotion on strain <i>Serratia</i> sp. S119

Abstract

The aim of this study was to analyze if cofactor pyrroquinoline quinone from <i>Serratia</i> sp. S119 is involved in the inorganic phosphate solubilization mechanism and in its ability to promote the plant growth. Site directed mutagenesis was performed to obtain a pqqE- minus mutant of strain <i>Serratia</i> sp. S119. The phosphate solubilization ability, gluconate and PQQ production of the mutant <i>Serratia</i> sp. RSL (pqqE-) was analyzed. Mutant RSL (pqqE-) showed significant decrease in P soluble and gluconic acid levels produced and undetectable levels of PQQ cofactor compared with wild-type strain. Complementation with synthetic PQQ cofactor restored P solubilization and gluconate production reaching the levels produced by wild-type strain. PqqE gene sequence indicated that it is highly conserved within <i>Serratia</i> strains and its product shows conserved motifs found in other PqqE proteins of several bacteria. The effect of the inoculation of the PQQ- mutant on peanut and maize plants was evaluated in pot assays. Plants growth parameters showed no differences among the different treatments indicating that PQQ from <i>Serratia</i> sp. S119 is not involved in the growth promotion of these plants. PQQ cofactor is essential for phosphate solubilization ability of <i>Serratia</i> sp. S119 but is not required for growth promotion of peanut and maize plants.