Expression Of Mitochondrial Malate Dehydrogenase In Improves Phosphate Solubilization

C2 was isolated from the rhizosphere of Mexican stonecrop based on its high level of tricalcium phosphate solubilizing activity. A full-length gene encoding mitochondrial malate dehydrogenase (mMDH) was cloned from C2 by RT-PCR and RACE techniques. The cDNA was 1,284 bp in length, with a complete open reading frame of 1,023 bp encoding a protein of 340 amino acids with a predicted molecular mass of 35.7 kDa. The predicted amino acid sequence shared high identity with mMDHs from other organisms. strain BL21(DE3) transformed with the C2 mMDH gene showed an increase in MDH activity of about 5-fold compared to non-transformed cell as measured in cell extracts. It also secreted more malate, lactate, acetate, citrate, oxalate and produced higher clearing halos when grown in plates with tricalcium phosphate as the sole source of phosphate. These results showed that expression of the C2 mMDH gene in could enhance organic acid secretion and improve the phosphate solubilizing ability of the cell.