FACTORS INFLUENCING THE LOSS OF BACTERIA IN PRESERVED SEAWATER SAMPLES

Several time course storage experiments with preserved seawater sample s were con ducted to study the loss of bacterial cells as a function o f storage lime. The number of bacteria decreased by 24 to 50% within 7 to 29 d in samples preserved with 2.5% glutaraldehyde (final cone.). A comparison between epifluorescence and electron microscope counts sh owed that the decrease was not due to filtration artefacts. Only 0.4 t o 0.6% of the bacterial cells were found to be attached to the walls o f the sample containers after 1 yr of storage. There was no positive c orrelation between the frequency of virus-infected cells at the start of the storage experiments and the loss of bacteria as a function of s torage time. Numbers of bacteria declined by only 5% the first 9 d in samples preserved in glutaraldehyde and stored at -20 degrees C. By ad ding phenolmethylsulfonylfluoride (PMSF), a protease inhibitor, prior to the addition of glutaraldehyde, the loss of bacterial cells only 17 to 18% over a 30 to 35 d period. Our study shows that protease activi ty may be a major cause of bacterial loss in glutaraldehyde preserved samples.