Low frequency ultrasound inactivation of thermophilic bacilli (Geobacillus spp. and Anoxybacillus flavithermus) in the presence of sodium hydroxide and hydrogen peroxide.

The vegetative cells and spores of Geobacillus spp. and Anoxybacillus flavithermus were subjected to 20 kHz ultrasound with a power ∼8 W. Ultrasonication had considerable effect on vegetative cells (5-log reduction in Geobacillus spp. and 1.6-log reduction in A.flavithermus). TEM imaging of the ultrasonicated vegetative cells showed an extensive damage both internally and externally. However, spores showed high resistance towards ultrasound treatment in the absence of NaOH and H2O2, although the outer layers such as the exosporium and the outer coat layer were disrupted, resulting in the reduced resistance of spores towards sonication. The combination of 0.12 M NaOH and 10 min ultrasonication inactivated 6 log spores of Geobacillus spp. A 7 log spore reduction of A.flavithermus was achieved by combining 0.17 M NaOH with 10 min ultrasonication. Ultrasonication combined with 1% H2O2 inactivated ∼7 log Geobacillus spp. spores in 6 min and ∼7 log A.flavithermus spores in 3 min. These ultrasound treatments in the presence of NaOH and H2O2 are synergistic as they showed a greater spore reduction when compared to NaOH combined with high temperature (85 °C), where only 1 and 3 log reduction was achieved in Geobacillus spp. and A.flavithermus spores, respectively.

Diesel biodegradation capacities of indigenous bacterial species isolated from diesel contaminated soil.

Petroleum based products are the major source of energy for industries and daily life. Leaks and accidental spills occur regularly during the exploration, production, refining, transport, and storage of petroleum and petroleum products. In the present study we isolated the bacteria from diesel contaminated soil and screened them for diesel biodegradation capacity. One monoculture isolate identified by 16S rRNA gene sequence analysis to be Acinetobacter baumannii was further studied for diesel oil biodegradation. The effects of various culture parameters (pH, temperature, NaCl concentrations, initial hydrocarbon concentration, initial inoculum size, role of chemical surfactant, and role of carbon and nitrogen sources) on biodegradation of diesel oil were evaluated. Optimal diesel oil biodegradation by A. baumanii occurred at initial pH 7, 35°C and initial hydrocarbon concentration at 4%. The biodegradation products under optimal cultural conditions were analyzed by GC-MS. The present study suggests that A. baumannii can be used for effective degradation of diesel oil from industrial effluents contaminated with diesel oil.