Extracellular Hydrolytic Enzymes Produced by Moderately Halophilic Bacteria

Abstract

High salinity is the main characteristic of hypersaline habitats, in which the salt concentration is generally higher than that of seawater. Among the beststudied hypersaline environments are the saline lakes (Dead Sea, Great Salt Lake), salterns used for the production of salt and some saline soils. Except for a few eukaryotic organisms such as the brine shrimp (Artemia salina) or the photosynthetic flagellate Dunaliella, most organisms adapted to live in these hypersaline environments are prokaryotic microorganisms belonging to the groups of archaea and bacteria (Rodríguez-Valera 1993). The salt requirements divide these populations of prokaryotic halophilic microorganisms into two predominant physiological groups: extreme halophiles, which grow optimally in media containing 15–30% NaCl, and moderate halophiles, which are able to grow optimally in media containing between 3 and 15% NaCl. Highly saline environments are dominated by extremely halophilic archaea, mostly halobacteria. However, in the intermediate salinities, the most abundant microorganisms are the moderate halophiles, a heterogeneous group which includes very different Gram-negative and Gram-positive bacterial species, as well as some archaea (Ventosa et al.1998).