Browsing by Subject "ACC-deaminaasi"

This study was conducted to find suitable methods for the quality control of commercial plant growth-promoting (PGP) microbial products. A commercial bacterial product called TwinN was evaluated for its microbiological quality, physiological features of its bacterial strains, and its ability to promote plant growth. Other bacterial strains which had shown PGP features in earlier studies, were used as reference strains. The microbiological composition of the TwinN bacterial lyophilisate corresponded to the manufacturer's description, as it was composed of bacteria belonging to the genera Azoarcus, Azorhizobium, and Azospirillum. However, the concentrations of some of the bacterial species were lower than reported. If the product was used according to the manufacturer's instructions, the bacterial counts in the plants wouldn't necessarily reach a sufficient level. With the TwinN product, a powdery growth medium was also supplied, which appeared to be highly contaminated with bacteria and moulds. The nature and source of these microbes remained unknown. The bacteria in the TwinN product were isolated as pure cultures, and identified based on the partial sequences of their 16S rRNA genes. Specific plate and broth culturing techniques were used to uncover the potential PGP physiological features of the pure cultures. The bacterial strains were able to produce indole-3-acetic acid, ACC deaminase and siderophore, which suggests that they might also have PGP activity. The ability of the bacteria to promote plant growth was tested in a plant experiment using hydroponic growth pouches. An Azospirillum brasilense strain isolated from the TwinN product was able to increase the dry weight of the shoots of chinese gabbage almost 41 % compared with the uninoculated control plants. Of the five bacterial treatments used, the A. brasilense strain was the only one able to promote plant growth. Chinese cabbage was the only plant species out of six that gave a positive response to the A. brasilense treatment. For some reason, the TwinN product itself didn't show any PGP activity. The plants showed signs of nitrogen deficiency, which indicates that no bacterial nitrogen fixation had taken place. The method used to determine the microbial composition of the TwinN product, was Amplicon sequencing. Combined with the results of traditional culturing techniques, Amplicon sequencing proved to be a useful method for the assessment of the microbiological quality of the product. The physiological tests that could be of use in the quality control of PGP products, are siderophore production test, phosphate solubilization test and the test that measures indole-3-acetic acid production.