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The artificial stimulation of biological purification of sea-pollutant hydrocarbons requires phosphorus supply. The concentrations, corresponding to the optimal bacterial growth, depend, in particular on ionic strength. They range between 2 and 8 X 10(-4) M for waters in which the salinity is close to the mean salinity of an oceanic environment and between 1.5 and 3 X 10(-3) M when these waters receive a significant supply of freshwater or when salinity is naturally weak. Inhibition of bacterial development has been observed either with a microflora, or with pure strains for concentrations higher than the upper limits of concentrations so defined.

We have tried in this study to reproduce in germfree mice a bacterial equilibrium observed previously in the gastrointestinal tract of child "L.N.", reared in a plastic isolator. Eight bacterial strains were studied. Seven had been fortuitously introduced: Acinetobacter lwoffi LN1, Staphylococcus epidermidis LN2, Clostridium perfringens LN3, Plectridium anatum LN4, Streptococcus bovis LN5, Enterobacter cloacae LN6, Corynebacterium sp LN7. The eighth strain was purposely administered to the child in order to take advantage of an antagonism between this strain and spontaneously acquired flora. This strain is Bacillus licheniformis FD1. The gnotoxenic mice proved to be a good experimental model because we found their bacterial equilibrium comparable to that observed in child L.N. In addition, we studied the decontamination procedures of the gastrointestinal tract of mice by observing both the antagonism of B. licheniformis with bacitracin, and the action of a suitable mixture of antibiotics. Conditions for the realization of this decontamination are discussed in this study.

Water of the best protected mineral sources always contains a small number (often less than 10/ml) of "authochtonous" bacteria which multiply and subsist infinitely in the underground sheets. These bacteria are psychrotrophic, able to multiply in the absence of detectable traces of organic matter, but grow better in the presence of organic matter. They are very sensitive to the antiseptic agents currently used to purify drinking water. For reasons that are still unknown, these bacteria rapidly multiply in bottled water. However, this multiplication never leads to appearance of a sufficiently great number of populations to affect the limpidity of the water. It has been demonstrated that these autochtonous bacteria are not able to become established., i.e. to multiply and subsist in a great number in the digestive tract of axenic mice receiving mineral water. The conclusion of this is that there are no risks for multiplication of this bacteria in the organism of the consumer. The absolute number of these bacteria in bottled water has therefore no sanitary significance for the consumer and it seems not to be justified to establish strandard recommendations with respect to this. In the water sheet, only an abrupt rise in the number of autochtonous bacteria beyond the usual level, which varies much according to sheets, represents an unfavourable indication. Indeed, this might correspond to an accidental infiltration of organic matter and consequently of pathogenic bacteria into the water sheet. Search for bacteria as indicators of fecal pollutions therefore remains the most reliable method for estimating the hygienic quality of mineral water or of any other food products.

Three bacterial strains, isolated on gas-oil from seawater, have a variously changed growth on hexadecane with supply of two organic substances. Acetate reduces growth of all tested strains and particularly the hexadecane degradation by Acinetobacter sp. On the contrary, trypticase-phytone promotes the degradation by the three strains.