Survival and viability of Vibrio vulnificus in seawater incubated at 4°C was analysed by flow cytometry and with a fluorescent dye that stained only living cells. Although evidence was obtained that a proportion of the cells became non‐culturable, resuscitation experiments suggested that this was a transient state leading to cell death and that raising the incubation temperature from 4° to 20°C allowed numbers to increase by growth and division rather than by conversion of dormant cells to active culturable forms.

. 1999. Denitrification is a globally important process leading to loss of fertiliser efficiency and the production of the greenhouse gas nitrous oxide and nitric oxide, an ozone depleter. Membrane inlet mass spectrometry (MIMS) was employed to study the effect of different variables on the process of denitrification by Pseudomonas stutzeri in a defined salts medium. MIMS was used for concomitant measurements of nitrous oxide, nitrogen and oxygen and showed that denitrification occurred in the presence of dissolved oxygen. A nitrate concentration of 15 mmol l −1 and a nitrite concentration of 5 mmol l −1 were found to be optimum for complete denitrification of nitrate or nitrite to nitrogen and varying these concentrations had a marked effect on the ratio of gaseous products released. Denitrification products were also dependant on pH with neutral or alkaline conditions being best for production of gaseous end products. Our results suggest that under nutrient rich conditions the most important factor in the regulation of denitrification by Ps. stutzeri is the amount of nitrite generated at the first enzymatic stage of the process. This appears to cause inhibition of the denitrification pathway above 5 mmol l −1 and at high enough concentrations (15 mmol l −1 ) restricts growth.

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Membrane inlet mass spectrometry (MIMS) was used to investigate denitrification by Pseudomonas stutzeri in a static lake water column. Continuous real‐time measurement of gases enabled the dynamics of the process to be investigated. Concentrations of 17 mmol l−1 nitrate and 10 mmol l−1 nitrite were identified as optimal for denitrification under nutrient‐limited conditions (i.e., produced the highest concentrations of N2). Available carbon was the major rate‐limiting factor in lake water when nitrate or nitrite was present. No stratification of the process with depth was observed, and aerobic denitrification was apparent under all the conditions employed. The rate of denitrification was dependent on cell concentration, and possible limitations of the usefulness of MIMS under environmentally modelled conditions were identified for environments containing low numbers of bacteria.

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