Organic-matter degradative potential of Halomonas glaciei isolated from frazil ice in the Ross Sea (Antarctica)

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 (m) to understand at which temperatures bacterial growth shows a linear and direct relationship with the available substrate (4–22 °C) and afterwards we tested H. glaciei growth curves and degradative potential at 0, 10 and 37 °C using two different media (one enriched and one depleted in PO4). The strain grew exponentially only at 10 °C. The fastest hydrolysis rates were expressed by enzymes aimed at polysaccharide degradation (a-D-glucosidase, b-D-glucosidase and b-Dgalactosidase) 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 (PO4 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.