Culturable protease-producing bacteria from sub-Antarctic sediments: diversity and enzyme properties.

NELDA OLIVERA; CYNTHIA CABALLERO

Viena, Austria

Simposio; 11th Symposium on Microbial Ecology ISME-11; 2006

International Society for Microbial Ecology

Microorganisms from cold habitats are adapted to grow and carry out their metabolic processes at low temperature, this includes their extracellular cold-active enzymes which have an important ecological role in the nutrient turnover and also in biotechnological applications. In this study we analyze the diversity of culturable protease-producing bacteria in subantarctic sediments, and determine the thermostability of their extracellular proteases. Coastal marine sediments were collected from Isla de los Estados, Argentina. After incubation at 4°C, 19 morphologically different protease-producing bacteria were isolated from skim milk agar plates prepared with natural seawater. Isolates were characterized by phenotypic methods and 16S rRNA phylogenetic analysis. Thermal stability of the proteases was determined by measuring the rates of inactivation at temperatures between 30 and 70ºC, using casein as substrate. Activation energies were calculated from Arrhenius plots, and thermodynamic activation parameters from the transition state theory. Except for a Planococcus isolate, the microorganisms belonged to the Gram-negative genera Pseudoalteromonas (8), Shewanella (6), Colwellia (3), and Formosa (1). Colwellia isolates showed the lowest optimal growth temperature at about 15°C, while no growth was observed at 25°C. The remaining isolates presented optimal growth between 20-25°C, and none of them was able to grow at 33°C. The Gibbs Free Energy of thermal inactivation (deltaGin*), at a reference temperature of 30 ºC, for proteases of isolates from different genera varied between 97 and 124 kJ mol-1. This reflects a considerable variety in the thermal properties of the proteases that coexist in this environment, showing Colwellia proteases the highest thermosensitivity.