Zinc concentrations ranging between 0.1 and 1 mM only slightly reduced maximal growth of wild-type Pseudomonas aeruginosa 7NSK2 in iron-limiting casamino acid medium, but had a clear negative effect on the growth of mutant MPFM1 (pyoverdin negative) and especially mutant KMPCH (pyoverdin and pyochelin negative). Production of pyoverdin by wild-type strain 7NSK2 was significantly increased in the presence of 0.5 mM zinc and could not be repressed by iron even at a concentration of 100 microM. Siderophore detection via isoelectrofocusing revealed that mutant KMPCH did not produce any siderophores, while mutant MPFM1 overproduced a siderophore with an acidic isoelectric point, most likely pyochelin. Pyochelin production by MPFM1 was stimulated by the presence of zinc in a similar way as pyoverdin for the wild-type. Analysis of outer membrane proteins revealed that three iron regulated outer membrane proteins (IROMPs) (90, 85 and 75 kDa) were induced by iron deficiency in the wild-type, while mutants were found to have altered IROMP profiles. Zinc specifically enhanced the production of a 85 kDa IROMP in 7NSK2, a 75 kDa IROMP in MPFM1 and a 90 kDa IROMP in KMPCH.

The plant growth-promoting rhizobacterium Pseudomonas aeruginosa 7NSK2 produces three siderophores when iron is limited: the yellow-green fluorescent pyoverdin, the salicylate derivative pyochelin, and salicylic acid. This Pseudomonas strain was shown to be an efficient antagonist of Pythium-induced damping-off. The role of pyoverdin and pyochelin in the suppression of Pythium splendens was investigated by using various siderophore-deficient mutants derived from P. aeruginosa 7NSK2 in a bioassay with tomato (Lycopersicon esculentum). To provide more insight into the role of pyochelin in antagonism, mutant KMPCH, deficient in the production of pyoverdin and pyochelin, was complemented for pyochelin production. The complementing clone was further characterized by subcloning and transposon mutagenesis and used to generate a pyochelinnegative, pyoverdin-positive mutant by marker exchange. All mutants were able to reduce Pythium-induced preemergence damping-off to some extent. Production of either pyoverdin or pyochelin proved to be necessary to achieve wild-type levels of protection against Pythium-induced postemergence damping-off. Mutant KMPCH inhibited P. splendens but was less active than the parental strain. This residual protection could be due to the production of salicylic acid. Since pyoverdin and pyochelin are both siderophores, siderophore-mediated iron competition could explain the observed antagonism and the apparent interchangeability of the two compounds. We cannot, however, exclude the possibility that both siderophores act in an indirect way.

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A 10‐week trial was conducted to determine the response of juvenile jade perch Scortum barcoo on the replacement of dietary fish oil (FO) in a fishmeal free diet. Three iso‐nitrogenous, isocaloric and isolipidic diets were formulated, each containing a different primary fat source: FO, linseed oil (LO), and a mixture of Schizochytrium and LO. The substitution of FO with the mixture of Schizochytrium and LO did not cause a difference in growth. However, there was an 8% reduction in weight gain in fish fed dietary LO, indicating that juvenile jade perch do require a minimal concentration of dietary n‐3 highly unsaturated fatty acids (HUFA). Fish fed the Schizochytrium diet stored more efficient n‐3 HUFA and in particular DHA in their flesh, and retained a higher fillet recovery compared to fish fed FO. In addition, we demonstrated that jade perch are able to produce both n‐3 HUFA and n‐6 HUFA when dietary PUFA are present. Fish fed the LO diet for 10 weeks contained the lowest amount of n‐3 HUFA in fillets among dietary treatment groups. However, feeding these fish the Schizochytrium diet for an additional 4 weeks increased the n‐3 HUFA content towards the same concentration of n‐3 HUFA found in the flesh of fish fed FO, without affecting the sensory properties of the fillets. In contrary, feeding the Schizochytrium diet for a continuous period of 14 weeks lowered overall sensory property scores.

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Node cultures of Gypsophila paniculata showed vitrified growth when cultured under standard conditions, resulting in poor survival of tissue culture derived plants. The deviant growth pattern appeared to be determined in the lag phase of the cultures. A limited evaporation period in this stage induced normal growth. Re-establishment of high relative humidity and poorer gas exchange thereafter did not lead to vitrified growth. Vitrification was also depressed when evaporation was continued during the whole culture period, but shorter plantlets resulted. A simple adaptation of the plastic lid that is commonly used in micropropagation, allowed controlled and contamination-free evaporation.