Identification of a novel agarolytic γ -Proteobacterium Microbulbifer maritimus and characterization of its agarase

The phenotypic and agar degrading features of an unidentified marine bacteria was investigated. The strain was Gram-negative, obligatory aerobic and non motile. On the basis of several morphological features and a phylogenetic analysis of the genes coding for the 16S rDNA, this strain was identified as Microbulbifer maritimus. On solid agar medium, this isolate produced extracellular agarase which causes agar liquefaction around the colonies. An extracellular agarase was purified by ammonium sulfate precipitation, gel filtration and ion-exchange chromatography on DEAE-cellulose. The purified protein migrated as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and it had a molecular mass of 75.2 kDa. The enzyme exhibited maximal activity at pH 7.5. The kinetic parameters of the enzyme were K(m) = 3 ± 0.19 mM, K(cat) = 160 ± 10 S(-1) and K(cat) /K(m) = 53 ± 10 S(-1) · mM(-1) .