The potentials of dead neem leaves for the production of the biogas was investigated as key measure to reduce the deforestation mainly caused by firewood cuttings in the Far-North Cameroon. Biomass collected was allowed to undergo biological pretreatment to facilitate its hydrolysis during anaerobic co-digestion with the cow dung. Samplings of dead neem leaves were taken after 0, 5, 10, 15, 20 and 30 days of pretreatment. Collected substrates from the pretreatment unit were used to feed 1.5L micro-bioreactors in three doses namely 5%, 15% and 25%. The gross volume and flammable gas produced was evaluated. The pH of the various treatments was measured. Data on production were analyzed using SPSS 20.0 software at 5% level of significance. It appears from this study that the pretreated leaves supplied biogas just as from 4 days after digestion, while those which did not undergo this pretreatment started producing biogas after more than 3 weeks. In terms of the amount of the generated biogas, the15 days pretreated substrate produced 3158 ml which was 22%, 35% and 94% higher than those of non-pretreated leaves, mechanically pretreated leaves and cow dung respectively. With regard to the change in pH within the bioreactors, pH dropped to 4 during the co-digestion of non-biologically pretreated leaves. At the same time in bioreactors where the substrate was biologically pretreated, the pH was more stable and appropriate for the biogas production and varied around 6 and7.

This work has been led in view to find the influence of sublethal heat (45°C, 50°C, 60°C) on acid resistance of B. subtilis NCTC 3610 and B. stearothermophilus CNCH 5781 spores. Firstly, we have submitted Bacillus spores to 0.4% acetic acid pH 4.5 during the times of 1, 2 and 3 hours. Then another spores group were preheated at various sublethal temperatures, before be treated with acetic acid. The effect of acetic acid before and after preheat was evaluated by the culture of treated spores on agar medium and the number of colony obtained was compared with that of control culture (neither treated with heat nor acid) and control A culture (only treated with acid). We found that acetic acid was effective on the twice Bacillus spores with more effect on B. stearothermophilus CNCH 5781 spores. Furthermore we have noticed a significant increasing in percentages of recovery of colonies obtained from preheated and acid treated spores compared to those of control and control A cultures. This increase of recovery percentages could be demonstrated the manifestation of a "heat-induced acid resistance" phenomenon. Yet, this phenomenon was more accentuated for preheatings at 50 and 60°C during 3 and 2 hours, respectively for B. subtilis and B. stearothermophilus spores. This study suggest that sublethal heats could be play major role in protection of microorganisms to chemicals