Isolation and Molecular Identification Of Lactobacillus Bacteria and Evaluation of Their Efficacy In Inhibiting The Pathogenic Fungus Pythium aphanidermatum

Abstract

Twenty-eight isolates of Lactobacillus were isolated from the rhizosphere of pea cultivated in the fields of five districts in Salah al-Din, which included: Tikrit, Al-Alam, Al-Sharqat, Samarra and Al-Baiji. The isolates identified according to molecular diagnosis using the analysis of the 16S rRNA sequences and were divided into five species: 7 Isolates of L. fermentum, 3 isolates of L. casei, 9 isolates of L. plantarum, 4 isolates of L. herbarum and 5 isolates of L. paralimentarius. Antagonism tests were conducted for these isolates against the pathogen Pythium aphanidermatum, the highest rate of inhibition was by isolates of bacteria L. paralimentarius 1981 reached 2.7 mm, followed by isolate L.plantarum 1982 with an inhibition rate of 2.5 mm. In the antagonism test using bacterial filtrate of L. paralimentarius 1981, the concentration of 30% was the highest in inhibiting the pathogenic fungus, as the fungus colony diameter reached 3.22 cm, followed by the concentration of 20 and 25%, as the colony diameter reached 4.47 and 3.68 cm, respectively. L. paralimentarius 1081 was recorded in the databases of the World Genetic Bank within the accession number MW149434.1. This is the first record of this bacteria in Iraq. L. paralimentarius 1081 showed the highest production of the antibacterial active substances including siderophores, total phenols and bacteriocin reached to 61.24%, 1.05 mg/ml and 18.02 mg/ml, respectively, as well as pH decreased to 4.5. The results also showed there are a strong correlation of pathogenic fungus inhibition with high concentrations of siderophores, total phenols, bacteriocin and low pH in the bacterial filtrate.