Summary Various bacterial species accumulate intracellular polyhydroxyalkanoates (PHAs) granules as energy and carbon reserves inside their cells. PHAs are biodegradable, environmentally friendly and biocompatible thermoplastics. Varying in toughness and flexibility, depending on their formulation, they can be used in various ways similar to many nonbiodegradable petrochemical plastics currently in use. They can be used either in pure form or as additives to oil‐derived plastics such as polyethylene. However, these bioplastics are currently far more expensive than petrochemically based plastics and are therefore used mostly in applications that conventional plastics cannot perform, such as medical applications. PHAs are immunologically inert and are only slowly degraded in human tissue, which means they can be used as devices inside the body. Recent research has focused on the use of alternative substrates, novel extraction methods, genetically enhanced species and mixed cultures with a view to make PHAs more commercially attractive.

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Aims:  To synthesize silver‐loaded zeolite X and establish the extent to which it persist in its antimicrobial action against strains of Escherichia coli K12W‐T, Pseudomonas aeruginosa NCIMB8295 and Staphylococcus aureus NCIMB6571. Methods and Results:  The antimicrobial action and efficacy of silver‐loaded zeolite X on Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa were investigated. Zeolite X was synthesized and loaded with Ag+ by ion exchange. This resulted in 2·0% (w/w) loading of Ag+ in the zeolite framework and 5·8% (w/w) on the zeolite. Escherichia coli and Pseudomonas aeruginosa and Staphylococcus aureus suspended in tryptone soya broth were exposed to 0·15, 0·25, 0·5 or 1·0 g l−1 of silver‐loaded zeolite X for a period up to 24 h. No viable cells were detected for any of the three micro‐organisms within 1 h. Silver‐loaded zeolite X, retrieved three times from the first exposure cultures, was washed with de‐ionized water and added to fresh bacterial suspensions. The results showed that the silver‐loaded zeolite X retained its antimicrobial action. Conclusions:  Silver‐loaded zeolite X persisted in its antimicrobial action against all three micro‐organisms. Significance and Impact of the study:  The results are significant for the longevity of antimicrobial action of silver‐loaded zeolite X.

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Polyhydroxyalkanoates (PHAs) are biopolymers, which can replace petrochemical plastics in many applications. However, these bioplastics are currently far more expensive than petrochemical plastics. Many researchers are investigating the use of inexpensive substrates derived from waste streams. Waste frying oil is abundant and can be used in PHA production without filtration.Cupriavidus necator (formerly known as Ralstonia eutropha) is a versatile organism for the production of PHAs. Small-scale batch fermentation studies have been set up, using different concentrations of pure vegetable oil, heated vegetable oil and waste frying oil. These oils are all rapeseed oils.It has been shown that Cupriavidus necator produced the homopolymer polyhydroxybutyrate (PHB) from the rapeseed oils. The achieved PHB concentration from waste frying oil was 1.2 g/l, which is similar to a concentration that can be obtained from glucose. The PHB harvest from pure oil and heated oil was 0.62 g/l and 0.9 g/l respectively. A feed of waste frying oil could thus achieve more biopolymer than pure vegetable oil. While the use of a waste product is beneficial from a life-cycle perspective, PHB is not the only product that can be made from waste oil. The collection of waste frying oil is becoming more widespread, making waste oil a good alternative to purified oil or glucose for PHB production.