Investigation of Antibacterial, Cytotoxic and Antioxidant Properties of the Mangrove Plant Xylocarpus mekongensis

The plant (Xylocarpus mekongensis) of the Sundarbans mangrove origin was evaluated for its antibacterial, cytotoxic and antioxidant properties using methanolic and chloroformic leaf, stem and bark extracts, respectively. The methanolic extracts contained higher amount of total phenolics, flavonoids, tannins than the chloroformic extracts and the result was in correlation with their ferric reducing power ability as well. However, the chloroformic bark extract contained more potent DPPH free radical scavenging activity than others. Antibacterial activity of the extracts was determined against both Gram-positive (Micrococcus and Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Vibrio cholerae, Salmonella typhimurium and Salmonella paratyphi) by disc diffusion assay and their zone of inhibitions (ZOI) were measured. Moreover, their minimum inhibitory concentrations (MIC) were determined by tube dilution method. Chloroformic bark and stem extracts showed strong inhibition to growth of P. aeruginosa (ZOI = 19 mm and MIC = 150 μg/ml) and S. aureus (ZOI = 19.5 mm and MIC = 250 μg/ml), respectively. All six extracts were subjected to brine shrimp lethality bioassay for possible measure of cytotoxicity. Concentration dependent increment in percentage mortality of brine Shrimp nauplii produced by the extracts indicated the presence of cytotoxic principles in these extractives. Therefore, Xylocarpus mekongensis showed antioxidant, antibacterial and cytotoxic activities.

Biocontrol of Rhizoctonia solani K1 by Iturin A Producer Bacillus subtilis RB14 Seed Treatment in Tomato Plants

Bacillus subtilis RB14 was used as an antagonist against fungal pathogen Rhizoctonia solani K1 to control damping-off diseases in tomato plants. Tomato seeds were treated with B. subtilis RB14 culture. The concentration of bacterial cells for the treatment was about 108 cfu/ml. Treated tomato seeds showed 99% germination index similar to the untreated seeds. Scanning Electron Microscopic observations showed a clear evidence of the presence of B. subtilis RB14 on tomato seed surface. Clear inhibition zone was observed using treated seed in dual plate assay against R. solani K1. B. subtilis RB14 treated seed showed 80% reduction in disease incidence during in vivo plant experiments. B. subtilis RB14 produces lipopeptide antifungal antibiotic iturin A which could suppress R. solani K1. The phenomenon was supported by our observation where we found significant amount of iturin A from the root zone soil of the seed treated plants.

Production of iturin A through glass column reactor (GCR) from soybean curd residue (okara) by <i>Bacillus subtilis</i>RB14-CS under solid state fermentation (SSF)

The present study was conducted with an aim to scale up the production of iturin A using soybean curd residue (okara). Iturin A was produced by indigenous bacterial strain Bacillus subtilis RB14-CS through glass column reactor (GCR) under solid state fermentation (SSF) was characterized. The enhanced iturin A production was observed with respect to enhanced substrate bed height when SSF was conducted in Erlenmeyer flask. To check the effect of substrate bed height on iturin A production under SSF of okara, GCR was introduced. Substrate bed height of 15 cm was suitable for iturin A production which was about 2700 mg/kg wet substrate. The observed iturin A production by the aerobic bacteria Bacillus subtilis in nearly anaerobic condition in such high substrate bed for SSF is a wonderful finding for development of SSF system in future.