Evaluation of the Virulence and Plant Growth-Promoting Potential of Endophytic Bacteria for Improving Vegetable...

Beneficial microbes, including endophytic bacteria, are widely used in bioformulation to improve crop productivity. However, the microbes are rarely assessed for their virulence properties. Thus, this study evaluates bacterial endophytes from vegetables for their hemolytic, antibiotic, cytotoxic activity, and ability to colonise and promote spinach (Spinacia oleracea) growth. Colonisation was assessed by visualising mCherry plasmid-tagged endophytic bacteria within plant tissues using a confocal microscope. Results showed that endophytic Pseudomonas azotoformans, Enterobacter bugandensis, Bacillus cereus and Serratia marcescens were non-hemolytic, sensitive to antibiotics, with high antibacterial and very slow cytotoxic activity, suggesting their nonvirulence and biocontrol potential. These bacteria had the highest and fastest rate of promoting seed germination and colonised the spinach leaves in a greenhouse experiment, as revealed by the visualised red fluorescence of the mCherry-plasmid transformed endophytes. Spinach inoculated with E. bugandensis and S. marcescens had higher total chlorophyll, but lower growth parameters compared to P. azotoformans and B. cereus. The root length, fresh weight and dry weight were higher in plants inoculated with P. azotoformans compared to the control and other endophytes. While endophytes with virulence potential may present health implications when consumed by humans, the nonvirulent and plant growth-promoting endophytes have applications in microbial formulation. Overall, beneficial endophytes present valuable resources in inoculum production for sustainable crop production.