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Halomonas glaciei isolated from frazil ice in the Ross Sea (Antarctica) during austral summer 2003 was phenotypically characterized and its capability of degrading organic matter was tested. We evaluated specific bacterial growth rates (mu) to understand at which temperatures bacterial growth shows a linear and direct relationship with the available substrate (4-22 degrees C) and afterwards we tested H. glaciei growth curves and degradative potential at 0, 10 and 37 degrees C using two different media (one enriched and one depleted in PO(4)). The strain grew exponentially only at 10 degrees C. The fastest hydrolysis rates were expressed by enzymes aimed at polysaccharide degradation (alpha-D-glucosidase, beta-D-glucosidase and beta-D-galactosidase) while alkaline phosphatase and aminopeptidase activities were rather low. Our data suggest a preferential demand for carbon derived from carbohydrates rather than from proteins: ectoenzyme activities transformed into carbon mobilization from organic polymers, showed that the total carbon potentially released from polysaccharides can be almost one order of magnitude higher than the protein carbon mobilization. Principal component analysis of the enzyme affinity separated the six experimental conditions, highlighting how different physical (temperature) and chemical (PO(4) enrichment or depletion) features actively lead to a differentiation in the efficiency of the ectoenzymes produced, resulting in preferential degradation of diverse kinds of organic substrates.

A preliminary study was carried out on a picocyanobacterial mixed culture harvested from the Gulf of Trieste (Northern Adriatic) and identified as Synechococcus spp. both by transmission electron microscopy observations, biliprotein composition and molecular analyses. Absorption and fluorescence spectra revealed phycourobilin and phycoerythrobilin chromophores, suggesting the presence of both CU- and C-phycoerythrin, besides phycocyanobilin chromophores typical for phycocyanins and allophycocyanins. Both biliprotein analyses and molecular identification indicated the presence of at least two Synechococcus subgroups presumably differing either in phycoerythrin type or in physiological traits. Among the exoenzymatic activities acting on different substrates, only aminopeptidase showed high hydrolysis rates and the uptake of organic molecules was positive for leucine but not for thymidine. The protein carbon mobilized was high compared with the leucine incorporation rates, resulting in low percentages of newly mobilized carbon utilized by cultures. The organic carbon incorporated as leucine was compared with the photosynthetically produced one, and the balance between the phototrophic- and heterotrophic-like processes was c. 3 : 1. Our findings suggest that the Synechococcus heterotrophy plays an important role in cell's metabolism, and that the photoheterotrophic behavior, together with their chromatic adaptation capability, might represent the key for the absolute dominance of this genus in the Adriatic Sea.

A preliminary study was carried out on a picocyanobacterial mixed culture harvested from the Gulf of Trieste (Northern Adriatic) and identified as Synechococcus spp. both by transmission electron microscopy observations, biliprotein composition and molecular analyses. Absorption and fluorescence spectra revealed phycourobilin and phycoerythrobilin chromophores, suggesting the presence of both CU- and C-phycoerythrin, besides phycocyanobilin chromophores typical for phycocyanins and allophycocyanins. Both biliprotein analyses and molecular identification indicated the presence of at least two Synechococcus subgroups presumably differing either in phycoerythrin type or in physiological traits. Among the exoenzymatic activities acting on different substrates, only aminopeptidase showed high hydrolysis rates and the uptake of organic molecules was positive for leucine but not for thymidine. The protein carbon mobilized was high compared with the leucine incorporation rates, resulting in low percentages of newly mobilized carbon utilized by cultures. The organic carbon incorporated as leucine was compared with the photosynthetically produced one, and the balance between the phototrophic- and heterotrophic-like processes was c. 3 : 1. Our findings suggest that the Synechococcus heterotrophy plays an important role in cell's metabolism, and that the photoheterotrophic behavior, together with their chromatic adaptation capability, might represent the key for the absolute dominance of this genus in the Adriatic Sea.