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Abstract Background Malaria is a major cause of death in tropical countries such as Nigeria. Chasmanthera dependens (Hochst) is a wild plant used by traditional healers for the treatment of malaria and other health challenges. This study evaluated the 'Antiplasmodial and in vitro antioxidant potentials of crude aqueous and methanol extracts of leaves, root and stem of Chasmanthera dependens (Hochst)’. Results Methanol extracts of leaves and roots of this plant exhibited higher antimalarial activities than other extracts. The level of parasitemia was significantly (p

The toxicity of phenol, 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, 2-chlorophenol, 4-chlorophenol, 4-bromophenol and 3,5-dimethylphenol on Pseudomonas, Bacillus and Escherichia species isolated from petroleum refinery wastewater was assessed via inhibition of dehydrogenase enzyme activity. At low concentrations, 2-nitrophenol, 2-chlorophenol, 4-chlorophenol, 4-bromophenol and 3,5-dimethylphenol stimulated dehydrogenase activity and at sufficient concentrations, phenolic compounds inhibited dehydrogenase activities. Generally, phenol is less toxic than substituted phenols. Estimations of the degree of inhibition/stimulation of dehydrogenase activities showed significant dose-dependent responses that are describable by logistic functions. The toxicity thresholds varied significantly (P < 0.05) among the bacterial strains and phenolic compounds. The median inhibitory concentrations (IC50s) ranged from 4.118 ± 0.097 mg.L-1 for 4-nitrophenol against Pseudomonas sp. DAF1 to 1407.997 ± 7.091 mg.L-1 for phenol against Bacillus sp. DISK1. This study suggested that the organisms have moderate sensitivity to phenols and have the potential to be used as indicators for assessment of chemical toxicity. They could also be used as catalysts for degradation of phenols in effluents.

Toxicity of zinc to Pseudomonas, Escherichia, Proteus, Bacillus and Arthrobacter species isolated from a tropical river and petroleum refinery effluent was assessed using TTC-dehydrogenase activity (DHA) inhibition test. At sufficient concentrations, zinc is toxic to these bacterial cells, and the exposure of the cells to zinc ion resulted in repression of dehydrogenase activity. The patterns of these toxic effects can be mathematically described with logistic dose-response models and in a manner similar to the non-competitive inhibition of enzymes. The threshold concentration above which toxic effect is observed ranged from 0.008 mM for Pseudomonas sp. DAF1 to 0.364 mM for Proteus sp. PLK2. The coefficients of inhibition Ki correlated with the IC50 and indicate that zinc toxicity is dependent on the organism. The Ki and toxicity threshold values predicted from the equations are comparable and are suitable indicators for kinetic analyses of zinc toxicity against bacteria.

Amylase production by Citrobacter sp. isolated from potato was optimized in batch culture studies under shake flask conditions. Effects and interactions of best sources and levels of carbon and nitrogen estimated by 4 x 5 and 4 x 4 factorial experimental arrangements were significant (P < 0.01) on amylase production. Optimal alpha-amylase yield was obtained in a medium containing sorghum flour (2.0 % w/v) and a mixture of (NH4)2SO4 + soybean meal (1.5% w/v) with an initial medium pH of 8.0. Under optimum conditions, amylase yield was maximal (0.499 U/ml) after 60h incubation at room temperature (28oC ± 2oC). Characterization studies showed that the enzyme had maximum activity at 60oC, retained 100% of its original activities at 60oC for 2h, was maximally active at pH 7.0 and retained 100% of original activities at pH 9.0 for 2h. Enzyme activity was stimulated by urea, Mg2+, Ca2+ and Zn2+ but inhibited by Hg2+.

The impacts of Hg2+, Cd2+ and Zn2+ on the activities of periplasmic nitrate reductase (NAP) and dehydrogenase (DHA) enzymes of three organisms isolated from soil and sediment-water interface were analysed in liquid culture studies. NAP and DHA activities were estimated from nitrite and triphenyl formazan were produced respectively after 4h incubation at 28 ± 2oC. Hg2+ completely inhibited NAP activity in Escherichia and Pseudomonas spp at all the concentrations (0.2 – 1mM) while progressive inhibitions of NAP activity were observed in Escherichia and Pseudomonas spp with increasing concentrations of Zn2+ and Cd2+. Both metals were stimulatory to NAP of Acinetobacter sp at 0.2 – 1mM. Apart from stimulation of DHA activity by Zn2+ (0.2 – 1mM) in Escherichia sp, Cd2+ (0.4 -1.0mM) in Acinetobacter sp and (1.0mM) in Pseudomonas sp, all the metals progressively inhibited DHA activities in the three organisms. In Escherichia sp, the activities of the two enzymes were negatively correlated on exposure to Zn2+ (r = -0.91) and positively correlated (r = >0.90) on exposure to Cd2+ and Hg2+. Based on IC50 values of the metals for the DHA and NAP enzymes, the most resistant of the three organisms were Escherichia sp and Acinetobacter sp respectively. Quantitatively, NAP with its lower IC50 values than DHA was a more sensitive toxicity measure for Hg2+ in all the organisms. The sensitivity of microbial metabolic enzymes to the toxic effects of metals varies with the type of enzyme, metal and the microorganism involved.