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In this study, the influence of cultivation time on xanthan biosynthesis by different Xanthomonas strains, reference strain and crucifers? and pepper leaves? isolates, was examined. Biopolymer was produced by submerged cultivation of fourteen producing strains on medium with glycerol as a sole carbon source. Each experiment was performed at a laboratory level under aerobic conditions at 30?C and 150 rpm for 168 h and 240 h. Bioprocess efficacy was estimated based on the xanthan quantity and its average molecular weight that was selected as quality parameter. According to the obtained results, it can be concluded that all applied strains have a statistically significant effect on xanthan concentration in medium and on its average molecular weight, while cultivation time significantly affect the bioprocess efficacy only when biosynthesis is performed by Xanthomonas strains isolated from crucifers. Further, when only Xanthomonas strains isolated from crucifers are observed, statistically obtained data suggest that the largest amount of the best quality xanthan in applied experimental conditions can be accomplished by the cultivation of CB strain for 240 h. On the other hand, when it comes to Xanthomonas strains isolated from pepper leaves, the highest productivity is shown by PL 2, PL 4 and PL 5 strains regardless of the cultivation time, while the PL 3 strain was responsible for the synthesis of biopolymers with the highest average molecular weight. The results obtained in this study represent valuable information for development of biotechnological process for xanthan production on glycerol containing media using new producing strain.

Apple fruit diseases caused by phytopathogenic species of the genus Alternaria have become current in recent years in Serbia as well as in other parts of the world. Due to the fact that pesticides have a number of side effects on the environment and human health, scientists around the world are concerned with finding alternative ways to control this important food. Usage of microorganisms, optimization of the medium and process conditions for their cultivation and production of biofungicides are the actual research direction. The effect of aeration on biofungicide production by Streptomyces hygroscopicus was studied in a 3 l stirred tank bioreactor using a previously optimized cultivation medium with glycerol as a carbon source. Aeration rates of 0.5, 1.0, and 1.5 vvm with constant agita?tion speed of 100 rpm were studied. It was found that the greatest production of antifungal metabolites effective against two Alternaria alternata isolates occurred with an aeration of 1.5 vvm and an agitation speed of 100 rpm. Statistical analysis showed that the largest inhi?bition zone diameters of A. alternata KA10 (78 mm) and T1Jg3 (78.67 mm) mycelial growth were achieved under the indicated conditions in 96 h of cultivation.

Xanthan is the most important microbial exopolysaccharide used in different branches of food and non-food industry. Due to high consumption of glucose and sucrose, usually utilized carbon sources in many bioprocesses, the most prominent research in xanthan production is related to the isolation of new xanthan producing strains capable to metabolize other carbon sources and to produce xanthan with characteristics appropriate for usage in food industry. The aim of this study was to examine the effect of variation of carbon sources in cultivation media on xanthan production by reference strain Xanthomonas campestris ATCC 13951 and five Xanthomonas strains isolated from infected pepper leaves. Bioprocess efficacy was estimated based on the quantity and quality of biosynthesized xanthan. The obtained results show that both, the selection of the carbon source and selection of producing strain have a statistically significant effect on bioprocess efficacy whereby the influence of carbon sources on the analyzed parameters is more pronounced. It was confirmed that Xanthomonas strains responsible for the production of a large amount of xanthan are not suitable for biosynthesis of good-quality biopolymer. Taking into account all results it can be concluded that the greatest potential in biotechnological xanthan production has strain PFNS PL4 and glucose or starch containing media which is the basis for further research.