Eight strains isolated from the stems of Lippia sidoides were identified as belonging to Lactococcus lactis, a bacterial species considered as "generally recognized as safe". Their capacity to solubilize/mineralize phosphate was tested in vitro with different inorganic and organic phosphorus (P) sources. All strains were able to solubilize calcium phosphate as an inorganic P source, and the best result was observed with strain 003.41 which solubilized 31 % of this P source. Rock phosphate, a mined rock containing high amounts of phosphate bearing minerals, was solubilized by five strains. When calcium phytate was the organic P source used, the majority of the strains tested showed phosphate mineralization activity. Moreover, all strains were able to solubilize/mineralize phosphate from poultry litter, a complex P source containing inorganic and predominantly organic P. The presence of genes coding for phytase and alkaline phosphatase was searched within the strains studied. However, only gene sequences related to alkaline phosphatase (phoA and phoD) could be detected in the majority of the strains (excepting strain 006.29) with identities varying from 67 to 88 %. These results demonstrate for the first time the potential of L. lactis strains for phosphate solubilization/mineralization activity using a broad spectrum of P sources; therefore, they are of great importance for the future development of more safe bioinoculants with possible beneficial effects for agriculture.
Keywords: Endophytes; Generally recognized as safe (GRAS); Lactococcus lactis; Lippia sidoides Cham.; Phosphate mineralization; Phosphate solubilization.