Investigation of the effects of rhodobacter capsulatus and rhodobacter sphaeroides on plant growth of a medicinal aromatic plant

Soil fertility and efficiency has been decreased all over the world due to applications such as chemical fertilizer use. Purple non sulfur bacteria are among the plant growth promoter microorganisms with a limited studies to be used as microbial fertilizer. In this study, the effects of Rhodobacter capsulatus and Rhodobacter sphaeroides which are among purple no sulfur bacteria on the development of the medicinal aromatic plant Melissa officinalis L. in a pot experiment. Plants were transferred to pots after germination in viols. Aboveground parts of the plants were dried and elemental analysis was carried out by ICP-OES, and later the dried material was used to obtain ethanol and acetone extracts followed by the antibacterial activity testing of the extracts. The analyses of our results were made in Minitab13 program. R. sphaeroides was found to significantly support plant development, while R. capsulatus hindered plant development but supported root length. R. sphaeroides significantly increased the concentration of P, K, Ca, Cu and Mn. On the other hand, R. capsulatus significantly increased Fe and Zn and decreased the concentrations of these elements in the plant growth material compared to the other bacterial application and the control condition. Agar well diffusion method was used for the determination of antimicrobial activity. The acetone extract of the plant grown upon R. capsulatus application was effective on Gram negative bacteria used in this study more than that grown by R. sphaeroides application. The results revealed that R. sphaeroides had plant growth promoter activity on M. officinalis under the study conditions.