Production of Bacillus subtilis soil isolate as biocontrol agent under bioreactor conditions.

This study aimed to investigate the biomass production of Bacillus subtilis in flask and bioreactor conditions. It is necessary to carry the culture from the shake flask to the pH, air, temperature and stirring controlled bioreactor in order to reduce the working time and increase the production efficiency and product quality. In this study, Bacillus was isolated from soil and grown under flask and bioreactor conditions as biocontrol agent against Botrytis cinerea and Fusarium oxysporum. In this process, a pH value of 7.5, 100% O2 saturation, 30% dissolved O2, at the temperature of 37 °C, total flow of 0.1 Lmin-1 and mixing speed of 150 min-1 were preferred for optimal concerning high production yield of B. subtilis in bioreactor. To test whether B. subtilis has antifungal activity on the growth of B. cinerea and F. oxysporum, a dual culture assay in a PDA medium was carried out. Ultimately, high biomass production in a short incubation period by reaching 2.2 µg/mL after 9 h in the bioreactor. It was observed that the bacteria produced in the bioreactor cultivation grew stronger and showed high antifungal activity which resulted 33.33% inhibition percentage against B. cinerea. It was concluded that B. subtilis can be used as a green-fungicide against B. cinerea and F. oxysporum, and bacterial metabolites from B. subtilis could pave the way for the development of next generation green/biopesticides.

Optimization of Growth Conditions for the Production of Bacillus subtilis Using Central Composite Design and Its Antagonism Against Pathogenic Fungi.

Today, the enhancement of spore yields of Bacillus subtilis has considerable interest and has been widely investigated. In this context, studies have been carried out to improve the spore yield as well as the production amount. In order to perform this, optimization studies are conducted for large-scale production of B. subtilis in bioreactors. The prokaryotic structure, high extracellular production potential, lack of pathogenic activity, well-known fermentation technology and short fermentation time are the prominent advantages for the production of B. subtilis in a bioreactor. The Bacillus species produce a wide variety of antifungal and antimicrobial compounds, making them ideal biological control agents. In this study, first, the growth conditions of the medium were investigated and then optimized using the central composite design approach to achieve the highest productivity for the growth of B. subtilis. In the experiments, the effect of temperature of 25, 30 and 35 °C and pH level of 6.0, 7.0 and 8.0 on spore yield was studied. Moreover, the antifungal activity of the B. subtilis culture was investigated against pathogenic fungi: Colletotrichum gloeosporioides, Botrytis cinerea and Aspergillus brasiliensis.

Antimicrobial and bacteriostatic activity of surfactants against B. subtilis for microbial cleaner formulation.

Cleaning products containing live bacteria that form spores of Bacillus spp. as active substances are becoming increasingly common in probiotic cleaner formulation. The quality of cleaning performance for the production of probiotic cleaners does not only depend on the potential of the bacterial strains used, but also on the chemical components of the formulations. In this study, the surfactants and other additives were investigated as biocidal or bacteriostatic against B. subtilis, and the viability of B. subtilis was examined at different pH ranges for microbial cleaner formulation. As a result, it was discovered that the B. subtilis, which can be used in the microbial cleaner formulation, shows higher growth and viability at the neutral pH, and it passes into the death phase at pH 3. According to antagonistic activity results, the Gram-positive S. aureus and K. pneumoniae were the most sensitive bacteria while B. cereus was the most resistant bacteria. The anionic surfactants such as linear alkylbenzene sulfonic acid and sodium lauryl ether sulfate act as bacteriostatic on Bacillus spp. and do not cause cell death. In the view of these results, the usage of appropriate bacterial cultures and the correct stabilization of the formulations are also critical elements in the development of microbial cleaner formulations.

Investigation of the antifungal effects of algal extracts on apple-infecting fungi.

It is known that cell extracts of various algae have antifungal activity against microorganisms in vitro. Antifungal activities of Ulva lactuca, Chlorella vulgaris, Chlorella minutissima, and Chlorella protothecoides were investigated against: Aspergillus niger, Alternaria alternata, and Penicillium expansum fungi to present their fungicide potentials. Aspergillus niger, Alternaria sp., and Penicillium expansum are typical soft-rotting fungi and cause important loss of apple fruit in the storage. In vitro antifungal activity was evaluated by agar disc diffusion assay against pathogenic apple rot fungi. As a result, almost all of the extracts obtained from algae species were revealed to have antifungal activity against selected fungal pathogens. Free radical-scavenging activity of the extracts was determined with 1,1-diphenyl-2 picryl hydrazyl (DPPH) free radical-scavenging method. Extract of C. protothecoides was determined to have a stronger antioxidant activity than other algae extracts. This study reveals that the potential of algae should be investigated for the production of natural fungicide for pharmaceutical and food industries.