Effect of nickel on the mineralization of hydrocarbons by indigenous microbiota in Kuwait soils.

Assessment of nickel contents in soil samples in Kuwait indicated only a minor difference in concentration in hydrocarbon-contaminated (86 mg kg(-1) soil) and non-contaminated soils (84 mg kg(-1) soil). The potential inhibitory effects of nickel on the number of hydrocarbon degraders, and hydrocarbon utilization were investigated over a wide range of nickel concentrations to span concentrations observed in the soil. Nickel addition, as nickel sulphate, to soil samples reduced the number of hydrocarbon degraders in all samples by a wide range (15-96%) depending on concentration and the hydrocarbon substrate utilized. Similarly, the metabolic activities were affected as observed in mineralization (3-60%) of soils amended with various concentrations of nickel. The inhibitive effects of nickel on hexadecane and crude oil utilization were minimal but were significantly higher with naphthalene (P < 0.05) in both hydrocarbon-contaminated and non-contaminated soils. Polarographic determination of hydrocarbons induced oxygen uptake rate demonstrated the tendency of nickel to significantly inhibit (P < 0.05) the oxidation of polyaromatic hydrocarbons compared to aliphatic hydrocarbons.

Sequential hydrophobic partitioning of cells of Pseudomonas aeruginosa gives rise to variants of increasing cell-surface hydrophobicity.

The partitioning of bacterial cells in a dual aqueous-solvent phase system leads to separation into 'hydrophilic' and hydrophobic functions. Sequential multistep partitioning, accompanied by successive enrichment, gives rise to several cycles of hydrophobic and hydrophilic cell populations which possess different cell-surface hydrophobicity characteristics. Characterization of the cell-surface hydrophobicity by several methods (salting-out aggregation test, bacterial adherence to hydrocarbon, polystyrene binding and hydrophobic interaction chromatography) was carried out. The cell-surface hydrophobicity varied in the order: hydrophilic fraction < parental strain < first cycle hydrophobic variant < second cycle hydrophobic variant < third cycle hydrophobic variant. Electron microscopy showed that the most hydrophobic variant was densely covered by hydrophobic structures - fimbriae - whereas the parental strain was covered by a mixture of surface structures. The hydrophilic variant was covered by an amorphous exopolymeric substance, which is a polysaccharide, shown by its reaction with Alcian blue.