Effect of C/N/P ratio and nonionic surfactants on polychlorinated biphenyl biodegradation

This work investigated whether polychlorinated biphenyl (PCB) removal from a highly contaminated soil (7000-p.p.m.) could be enhanced by manipulating the carbon to nitrogen to phosphorus (C/N/P) ratio, and by nonionic surfactant addition. A Box–Behnken statistical experimental design was used to evaluate the combined effect of surfactant type, surfactant concentration, and C/N/P ratio in a relatively short treatment period (35 days). The variable with the greatest effect on PCB degradation was the type of surfactant used. Higher PCB removal efficiencies (39–60%) were obtained with Tween 80 (compared to Tergitol NP 10 and Triton X-100). This was attributed to its lower critical micelle concentration. Higher C/N/P ratios (increased by biphenyl addition) significantly stimulated the soil heterotrophic activity without enhancing PCB removal. This suggests that nonionic surfactants have a greater potential to enhance bioremediation of PCB-contaminated soil than efforts to enhance the soil heterotrophic activity through nutrient and analogue substrate addition.     

Low concentrations of the non-ionic detergent Nonidet P-40 interfere with sterol biogenesis and viability of the yeast Saccharomyces cerevisiae

Mild non-ionic detergents are used for solubilization of hydrophobic substrates in yeast growth media at concentrations 0.1-1%. Our data show that low concentrations of Nonidet P-40 may significantly affect lipid biogenesis in the yeast Saccharomyces cerevisiae. The uptake and esterification of external [4-14C]-cholesterol is strongly reduced in hem1 mutants treated with low concentrations of Nonidet P-40. Significant inhibitory effect of NP-40 on sterol uptake and esterification was evident both in non-growing and growing cells supplemented with external cholesterol. Increased levels of sterol precursors (squalene, lanosterol) in hem1 cells grown in complex medium with cholesterol indicated general interference of NP-40 with sterol biosynthesis. NP-40 in the growth medium affected also cell viability estimated as the colony forming ability. More attention should be therefore paid to possible effects of mild detergents at low concentrations generally considered to be harmless, especially in cells with disturbed lipid biogenesis.     

Reduction of cytochrome b5 by NADPH-cytochrome P450 reductase

The reduction of mammalian cytochrome b5 (b5) by NADPH-cytochrome P450 (P450) reductase is involved in a number of biological reactions. The kinetics of the process have received limited consideration previously, and a combination of pre-steady-state (stopped-flow) and steady-state approaches was used to investigate the mechanism of b5 reduction. In the absence of detergent or lipid, a reductase-b5 complex is formed and rearranges slowly to an active form. Electron transfer to b5 is rapid within this complex (>30 s(-1) at 23 degrees C), as fast as to cytochrome c. With excess b5 present, a burst of reduction is observed, consistent with rapid electron transfer to one or two b5 molecules per reductase, followed by a subsequent rate-limiting event. In detergent vesicles, the reductase and b5 interact rapidly but electron transfer is slower (approximately 3 s(-1) at 23 degrees C). Experiments with dimyristyl lecithin vesicles yielded results intermediate between the non-vesicle and detergent systems. These steady-state and pre-steady-state kinetics provide views of the different natures of the reduction of b5 by the reductase in the absence and presence of vesicles. Without vesicles, the encounter of the reductase and b5 is rapid, followed by a slow reorganization of the initial complex (approximately 0.07 s(-1)), very fast reduction, and dissociation. In vesicles, encounter is rapid and the slow step (approximately 3 s(-1)) is reduction within a complex less favorable for reduction than in the non-vesicle systems.