Comparative evaluation of pectolytic and proteolytic enzyme production by free and immobilized cells of some strains of the phytopathogenic Erwinia chrysanthemi.

Whole cells of the phytopathogenic Erwinia chrysanthemi strains were immobilized in k-carrageenan and grown in high-calcium Xanthomonas campestris medium containing sodium polypectate as carbon source. All the strains used survived immobilization into k-carrageenan beads. Immobilized E. chrysanthemi strains displayed higher pectolytic and proteolytic enzyme activities than free cells in liquid suspension. Carrageenan immobilization techniques could provide a system to mimic the conditions of E. chrysanthemi cells in the infected plant tissue. This could prompt a thorough study of the factors governing the biosynthesis of virulence factors by this bacterium.

Comparative evaluation of the antimicrobial activities of essential oils of Artemisia afra, Pteronia incana and Rosmarinus officinalis on selected bacteria and yeast strains.

Essential oils are frequently used for flavour and fragrance in the perfume, pharmaceutical, cosmetic and food industries. The antimicrobial activities of the essential oils of Artemisia afra, Pteronia incana and Rosmarinus officinalis were tested against 41 microbial strains. The test organisms were selected on the basis of their significance as food spoilage and/or poisoning, common human and plant pathogens. The agar diffusion assay was performed using nutrient agar and antibiotic medium. All the oils tested displayed some antimicrobial activities. However, the efficiency differed and depended both on the type and concentration of the oil, as well as the test microbial strain. Artemisia afra and R. officinalis showed similar and higher antimicrobial activity than P. incana. Due to their broad antimicrobial activities, the essential oils of the above plants growing in Eastern Cape may have preservative potential for the food and cosmetic industries.

Phosphate uptake by immobilized Acinetobacter calcoaceticus cells in a full scale activated sludge plant.

An in situ study of the P-uptake ability of Acinetobacter calcoaceticus was carried out using the alginate immobilization technique. Immobilized A. calcoaceticus cells displayed a high P-uptake ability (> 97% P-accumulating cells) when immersed in the aerobic zone of an activated sludge system for 30-240 min. The overall P-accumulation pattern of the anaerobic zone depicted a typical P-release mechanism. However, limited P-accumulation was also observed at this stage. Growth and anaerobiosis were not prerequisites for P-uptake. The immobilized cell retention time in the anaerobic zone did not affect remarkably the inherent P-uptake ability of immobilized A. calcoaceticus when exposed to the aerobic stage. P-uptake and release were reversible and depended on the environmental conditions to which immobilized cells were exposed. Immobilization of A. calcoaceticus using alginate can be regarded as a reliable method of studying pure cultures in the activated sludge process.