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The effect on nisin production of increasing nisin immunity/resistance genes in Lactococcus lactis subsp. lactis MG1363 was investigated. The 60-kb nisin immunity/resistance plasmid pND300, which was isolated from a non-nisin-producing strain, encodes five genes involved in nisin immunity/resistance, which are very similar to those of the immunity/resistance system encoded by the nisin-production transposon. The introduction of pND300 into MG1363(TnNip) resulted in the construct being able to produce significantly more nisin than the parent MG1363(TnNip). The introduction of pND314, which contains the nisin immunity/resistance genes subcloned into pSA3, into MG1363(TnNip) allowed the strain to grow more rapidly than the parent MG1363(TnNip) with a concomitant increase in the rate of nisin production. This work illustrates that introduction of pND300 and a derivative containing the nisin immunity/resistance system of pND300 into MG1363 (TnNip) can result in significant alterations to the kinetics of nisin production. These observations indicate approaches that may be used successfully to improve the economics of nisin production.

The kinetics of nisin production was studied in batch cultures using a construct of Lactococcus lactis subsp. lactis C2SmPrt-, containing a transposon (TnNip) that encodes nisin production. The introduction of TnNip into C2SmPrt- significantly lowered the specific growth rate and the maximum A620 reached was reduced from 15.2 to 11.0. The effect of nisin concentration and nutrient depletion on nisin production of the construct, C2SmPrt-(TnNip), was examined. Nisin production was found to be inhibited by high concentrations of nisin, when grown in excess nutrient, even though growth of the culture continued because nutrient limitation was not operating. However, in low nutrient concentrations nisin production was limited by nutrient depletion. The specific growth rate of C2SmPrt-(TnNip) was altered, by using different nutrient concentrations and different sugars, in order to examine the relationship between nisin production and growth. Nisin production was shown to be growth-associated for most of growth, but near the end of growth, when the specific growth rate was 0.05 h-1 or less, the production ceased.

Kinetics of nisin production have been investigated in terms of endogenous features of the producer organism, Lactococcus lactis. Nisin-producing transposons (Tn Nip) were transferred to different hosts by conjugation. Constructs were cultivated in batch cultures and nisin produced was measured. The proteinase function of C2Prt (Tn Nip)-1 was eliminated by plasmid curing, resulting in the construct C2Prt - (Tn Nip)-1. C2Prt - (Tn Nip)-1 produced nisin to a higher concentration compared to C2Prt (Tn Nip)-1 and was able to maintain the maximum concentration till the end of cultivation. The final concentration of nisin produced was host-specific, because when different constructs carrying the same Tn Nip were cultivated they produced nisin to different concentrations. However, when the same host carried Tn Nip transposons derived from different donors the concentration of nisin produced was similar, suggesting that the two Tn Nip transposons may be similar.

A dynamic model of a continuous glucose-fed digester is presented, including hydrogen inhibition of acetogenesis and pH inhibition of methanogens. Unionised volatile fatty acids are not considered toxic. Hydrogen concentration could be a useful stability parameter.

SINCE the first observations by Mikkelsen and Toth1 it has been well established that the reaction between magnesium ions and titan yellow (the sodium salt of methylbenzothiazole (1,3)-4,4′-diazoamino benzene (2,2′)-disulphonic acid) can be extremely variable due to differences in the composition of the dye. In an attempt to overcome difficulties in the determination of magnesium in plant samples due to such variations Bradfield2 recommended a technique for assessing the sensitivity of the dye and later reported the presence of a component which was intensely fluorescent3.

THE introduction of a fluoride sensitive specific electrode1 has greatly simplified the determination of fluoride iou and recently its use has been proposed for the determination of urinary fluoride2–5. This article draws attention to an interesting and important anomaly which has been observed in using the electrode for the routine screening of workers engaged in the manufacture of hydrofluoric acid.

This study indicates that supplying stimulus changes (flickering on-off light) to the visual field following initial stimulation of the retina can prolong the duration of visual after images. Although most current research on after images has focused on the biochemical and neural basis of this phenomena, it is suggested that post stimulation conditions in the visual field as well as such simple ’changes’ as blinking may also be significant parameters.

IT was reported by Peters, Hall, Ward and Sheppard1 that the seeds of Dichapetalum toxicarium contain at least two fluorinated long-chain fatty acids. The acid present in by far the larger amount was identified as ω-fluoro-oleic acid; but the other acid which is solid at room temperature was not properly identified because of the difficulty of isolating it in a sufficiently pure state.