Abstract
Lactic acid bacteria (LAB) are a heterogenous group of acid-tolerant, salt-tolerant, phosphate solubilizing microbes being able to produce lactic acid on carbohydrate fermentation. Since the advancements in plant-microbe interactions research have enhanced the significance of microbial communities in promoting soil productivity, therefore, our current study aims to isolate and characterize those LAB strains that possess antimicrobial, phosphate-solubilizing potential and plant growth promoting properties in vitro. Isolation of LAB was done from milk, meat, rice, fruits, vegetables and soil and the isolated strains were identified up to genus level by catalase test and Gram staining. The isolated strains were screened for antibacterial potential against Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus subtilis, and Streptococcus faecalis. Antifungal activity was determined against predominant phytopathogens, Aspergillus niger, Fusarium oxysporum, Macrophomina phaseolina and specie belonging to genus Penicillium. Phosphatase activity of the promising strains was demonstrated on National Botanical Research Institute's phosphate growth medium (NBRIP). The most promising isolate Lactobacillus MBV41 was grown in the presence of 5% NaCl to assess its salt tolerance capabilities. Finally, fresh tomato seeds were coated with the most promising strain MBV41 to analyze the potential of LAB in plant growth promotion. Twenty-five strains were successfully isolated among which 21% species of Lactococci and 27% Lactobacilli species showed significant antibacterial activity against Pseudomonas aeruginosa and Streptococcus faecalis and effective antifungal activity was also observed against the tested phytopathogens. Significant phosphatase production in vitro was demonstrated by 12% Lactobacilli species giving a maximum halo of 30mm. Our isolated strain, MBV41 exhibited strong tolerance to 5% NaCl and was able to increase the root and shoot length of the tomato plant giving a germination percentage of 51% and seedling vigor index of 558.4. Our findings justify the use of the LAB strains as plant growth promoters. Also, the strong antagonism of our LAB strains towards phytopathogens makes them effective against preventing plant diseases which could minimize the use of hazardous pesticides. Still elaborate studies are needed until they can be utilized to enhance the soil fertility and plant growth.
