Primi dati sulla caratterizzazione microbiologica delle acque dell'Adriatico Settentrionale

In the general framework of the Prisma 1 project, aimed at studying the biogeochemical cycles, the distribution of heterotrophic bacteria at three sampling stations located in the North Adriatic Sea was analysed during two different seasons (spring and summer 1995). Biochemical assays using 7 fluorogenic substrates were carried out on 794 strains isolated in order to determine the physiological potentiality of the bacterial populations to hydrolyse organic compounds. The highest concentrations of heterotrophic bacteria occurred in the surface layers at inshore stations, more influenced by the allocthonous inputs of the Po river. Viable counts revealed the presence of high percentages of active metabolising bacteria at the station located in front of the delta. During the spring season, at the off-shore station the lowest bacterial abundances were found together with a higher level of potential degradative capability. In spite of the limited increase of densities, in summer months a significative increase of enzymatic activities was recorded at all the stations. Qualitative study of microflora composition showed differences in relation to temperature and water masses: in April a predominance of Gram-negative strains belonging to Pseudomonas and Flavobacterium genera was found in coastal surface waters, whereas Vibrio strains were prevalent in the deepest layers at the off-shore site. The composition of microflora, characterised by a greater diversification in the warm period, strongly influenced the metabolic profiles of the strains isolated. Proteic, lipidic and phosphate substrates were preferentially hydrolysed by heterotrophic strains, whereas a lower percentage of bacteria metabolises polysaccharide compounds. The high levels of enzymatic potentiality recorded in the studied area expressed the high degree of nutritional versatility, caused by shifts in species, which allows the bacterial community to colonise sites with various ecological characteristics.