Effects of peanut root exudates on pqqe gene and pqq promoter expression of phosphate solubilizing strain Serratia sp. S119

LUDUEÑA, FABRA, A., TAURIAN, T.

Pucón

Congreso; 3er Taller Latinoamericano de Bacterias Promotoras del Crecimiento Vegetal; 2016

The mineral phosphate solubilization phenotype from some microorganisms is attributed predominantly to the secretion of organic acids such as gluconic acid. The glucose dehydrogenase (GDH) enzyme catalyzes the oxidation of glucose to gluconic acid and requires pyrroloquinoline quinone (PQQ) cofactor for its activity. The genes involved in PQQ synthesis are organized in an operon formed by at least 5 genes (pqqA,B,C,D,E). The transcriptional regulation of pqq operon has been poorly studied and there is preliminary information about this topic in a few bacterial strains. The aim of this study was to evaluate if specific molecules secreted in peanut root exudates modify the expression of phosphate solubilization related genes in the native peanut phosphate solubilizing bacterium Serratia sp. S119. The expression of pqqE gene and the promoter region of pqq operon were analyzed in the presence of peanut root exudates obtained from plants grown under P limiting conditions.PqqE gene expression was analyzed by qRT-PCR in bacterial cultures supplemented with 10 µg/ml root exudates at exponential and stationary growth phases. The expression of pqq promoter region fused to the coding region of fluorescent protein m-Cherry was evaluated. Several concentrations of root exudates were added to bacterial cultures and fluorescence was recorded every 2 hours for 24 h. Finally, the profiles of root exudates were analyzed by HPLC.Results obtained indicated that pqqE gene expression decreases when Serratia sp. S119 grows in medium supplemented with peanut root exudates from plants grown in P-limiting conditions. The expression levels of pqq promoter region varied depending on the concentration of root exudate and the bacterial growth phase. Two promoters, one upstream pqqA (PpqqA) and a second between pqqA and pqqB (PpqqA-pqqB), were identified in the pqq operon in Serratia sp. S119. HPLC analysis of root exudates obtained from peanut plants growing under P-available and P-limiting conditions indicated differences in their composition. In conclusion, these results suggest that molecules exudated by peanut root may modify the expression of specific bacterial genes like those related to phosphate solubilization during plant-bacteria interaction and under P-limiting conditions.