Cold-active α-l-rhamnosidase from psychrotolerant bacteria isolated from a sub-Antarctic ecosystem

Psychrotolerant bacteria obtained from sea water and alimentary tracts of benthonic organisms from the sub-Antarctic environment of Tierra del Fuego (Argentina) were screened for cold-active α-l-rhamnosidase production. Only 10 of a total of 140 isolates were positive for α-l-rhamnosidase activity as determined by a qualitative assay; and five of them showed substantial activity at 5 °C. Molecular identification (16S rDNA) of five selected isolates revealed that four of them were closely related to the genus Pseudoalteromonas while the other was identified as Ralstonia pickettii. The Pseudoalteromonas sp. 005NJ strain was selected for further characterization based on the higher relative α-l-rhamnosidase activity at 4 °C. It showed specific growth rates of 0.12–0.19 h−1 in the temperature range of −1 to 8 °C, and the α-l-rhamnosidase activity was mainly intracellular. The reaction showed optimal pH and temperature values of 6 and 40 °C respectively and maintained 6% activity at 4 °C. The enzyme was found to be thermo-sensitive, presenting a half-live of 4 min at 50 °C. In presence of 12% (v/v) ethanol the activity decreased by approximately 48%. Cold-active α-l-rhamnosidase might be useful for food processing technologies.