In vitro shoot culture and microtuber induction in the steroid yam Dioscorea composita Hemsl

The individual effects of sucrose, plant growth regulators and basal salt media formulations were investigated on microtuber induction and development in shoot cultures of the steroid yam Dioscorea composita. Sucrose at 8% (w/v) was the single most significant medium constituent for microtuber induction. Of the four cytokinins tested, 6-benzyladenine at 1.25 and 2.5 μM showed strong inhibitory effects on microtuber induction. By contrast, the auxins α-naphthaleneacetic acid and indole-3-butyric acid at 5.0 μM showed striking promotive effects on microtuber induction and growth. In the presence of either one of these auxins at 5.0 μM shoot cultures produced microtubers weighing 300–400 mg fresh weight whilst kinetin, 6-(γ,γ-dimethylallylamino)-purine, 6-benzyladenine and abscisic acid failed to promote microtuber growth (microtubers weighed generally <200 mg). Media formulations Lloyd and MacCown and White supported the lowest frequencies of microtuber induction when kinetin was present at 2.5 μM. Anderson Rhododendron was as effective as Murashige and Skoog overall in promoting both microtuber induction and growth. When removed from cultures and planted in sterilized moist sand, microtubers sprouted readily (60–87% within 2 weeks) and produced vigorous shoot growth and after 5–7 months minitubers of sizes (30–80 g) suitable for direct field planting. This revised version was published online in June 2006 with corrections to the Cover Date.     

Isolation, characterization, and investigation of surface and hemolytic activities of a lipopeptide biosurfactant produced by Bacillus subtilis ATCC 6633

Bacillus subtilis ATCC 6633 was grown in BHIB medium supplemented with Mn2+ for 96 h at 37 degrees C in a shaker incubator. After removing the microbial biomass, a lipopeptide biosurfactant was extracted from the supernatant. Its structure was established by chemical and spectroscopy methods. The structure was confirmed by physical properties, such as Hydrophile-Lipophile Balance (HLB), surface activity and erythrocyte hemolytic capacity. The critical micelle concentration (cmc) and erythrocyte hemolytic capacity of the biosurfactant were compared to those of surfactants such as SDS, BC (benzalkonium chloride), TTAB (tetradecyltrimethylammonium bromide) and HTAB (hexadecyltrimethylammonium bromide). The maximum hemolytic effect for all surfactants mentioned was observed at concentrations above cmc. The maximum hemolytic effect of synthetic surfactants was more than that of the biosurfactant produced by B. subtilis ATCC 6633. Therefore, biosurfactant would be considered a suitable surface-active agent due to low toxicity to the membrane.