Azotobacter, Pseudomonas and Bacillus isolates stimulate the germination and seedling growth of Mellisa officinalis

The objective of this study was the isolation and characterization of Azotobacter, Pseudomonas and Bacillus species from the rhizospheric soil of Mellisa officinalis and to examine the effect of isolates application on the seed germination and seedling growth. Isolation, physiological, biochemical, and plant-growth-promoting activity characterization of isolates were done. Monitoring the effects of isolates application on seed germination and seedling growth were evaluated in controlled conditions. The number of germinated seeds, the shoot and root length of seedlings, vigour index and biochemical stress markers (lipid peroxidation intensity and total phenols) were measured. From the rhizosphere of plant 2 Azotobacter (denoted as A5 and A6), 5 Pseudomonas (denoted as P27, P28, P29, P55 and P56) and 6 Bacillus (denoted as B64, B65, B66, B67, B68 and B69) bacteria were isolated. Azotobacter isolates showed the ability to live in the condition of low (5) and high (9) pH. The isolates varied in terms of the utilization of carbon sources. Both isolates produced pectinase, hydrogen cyanide (HCN) and utilized organic and inorganic phosphorus. Pseudomonas isolates had optimal growth at 10 ºC and 37 ºC, and on medium with pH 5 and 9. All Pseudomonas isolates could produce pectinase, lipase, amylose, IAA, siderophores and HCN. All Bacillus isolates could grow on a medium containing 7% NaCl.