Characterization And Optimization Of Antifungal Compounds And Evaluation Of Iron Acquisition Mechanism Of Paenibacillus Polymyxa SQR-21

The tested Paenibacillus polymyxa (SQR-21) was provided by Microbe-Plant Interaction Laboratory, Nanjing Agricultural University. Antifungal compounds were extracted with n-butanol and purified by size exclusion and reverse phase chromatography. The structural information was obtained by mass spectroscopy and Edman degradation. The purified antifungal compounds were members of the fusaricidin group of cyclic depsipeptides having molecular masses of 883,897,947, and 961 Da with an unusual 15-guanidino-3-hydroxypentadecanoic acid moiety. The strain SQR-21 was not able to produce antifungal volatile compounds but it was able to produce cellulase, mannase, pectinase, protease,β-1,3-glucanase and lipase. It also showed phosphatase activity, however, did not show any chitinase activity. Metal ions are known for their effect on antibiotic production but fusaricidins production by Paenibacillus polymyxa lacked this information. The effect of different factors on antifungal compounds production and growth of Paenibacillus polymyxa SQR-21 was evaluated. King’s B modified medium was found best medium while n-butanol was best extractant for antifungal compounds extraction. The medium containing C sources glycerol and lactose showed maximum antifungal activity while maximum growth was obtained from glucose, starch, sucrose, galactose, mannose and fructose. Among all tested N sources rapeseed cake + cow manure extract and mixture of this with rapeseed cake + pig manure extract gave maximum growth. While maximum antifungal activity was obtained from yeast extract, however, it was non-significant with rapeseed cake + cow manure extract and mixture of this with rapeseed cake + pig manure extract. Maximum growth was obtained on second day while increase in antifungal activity was observed from third to sixth days. All metal ions alone increased the antifungal activity and growth except Ca2+, which decreased the growth. The combined interactive study experiments data showed that Mg2+ in first experiment and Ni2+ and Mn2+ in the second experiment, were most effective metal ions in combined cultures. This information will help in the optimum production of antifungal compounds. To evaluate the behavior of the biocontrol agent P. polymyxa SQR-21 under differential iron availability, P. polymyxa was grown under three differential iron conditions. Iron starvation slowed bacterial growth. At all iron levels, pH of liquid culture was decrease but maximum reduction was observed at highest iron level. Cell surface ferrireductase activity decreased as culture aged, while Fe3+-reducing activity of low molecular reductants and hydroxamates type of siderophores production constantly increased. Our research gives useful information about the biochemical characteristics of P. polymyxa SQR-21 and the effects of metal ions on the overall metabolic processes of P. polymyxa mainly fusaricidin production which can help in the fermentation technology for maximum antibiotic production. This work also reports the kinetic study of P. polymyxa under differential iron availability and the information provided here gives initial information about the iron uptake mechanism of P. polymyxa.