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The -amylase gene amyH of the moderate halophile Halomonas meridiana: cloning and molecular characterization

Department of Microbiology and Parasitology, Faculty of Pharmacy, University of Seville, 41012 Seville, Spain¹
Sector of Organic Chemistry and Biochemistry, Department of Chemistry, University of Ioannina, 45110 Ioannina, Greece²

Author for correspondence: Antonio Ventosa. Tel: +34 95 455 67 65. Fax: +34 95 462 81 62. e-mail: ventosa{at}cica.es

Two types of Tn1732-induced mutants defective in extracellular amylase activity were isolated from the moderate halophile Halomonas meridiana DSM 5425. Type I mutants displayed amylase activity in the periplasm, and were unable to use any of the carbon sources tested, including starch and its hydrolysis product maltose. The type II mutant was affected in the gene responsible for the synthesis of the extracellular -amylase. This gene (amyH) was isolated by functional complementation of mutant II and sequenced. The deduced protein (AmyH) showed a high degree of homology to a proposed family of -amylases consisting of enzymes from Alteromonas (Pseudoalteromonas) haloplanktis, Thermomonospora curvata, streptomycetes, insects and mammals. AmyH contained the four highly conserved regions in amylases, as well as a high content of acidic amino acids. The amyH gene was functional in the moderate halophile Halomonas elongata and, when cloned in a multicopy vector, in Escherichia coli. AmyH is believed to be the first extracellular-amylase-encoding gene isolated from a moderate halophile, a group of extremophiles of great biotechnological potential. In addition, H. meridiana and H. elongata were able to secrete the thermostable -amylase from Bacillus licheniformis, indicating that members of the genus Halomonas are good candidates for use as cell factories to produce heterologous extracellular enzymes.

Keywords: -amylase, halophile, Halomonas

The EMBL accession number for the sequence reported in this paper is AJ239061.

This article has been cited by other articles:

				B. N. Mijts and B. K. C. Patel Cloning, sequencing and expression of an {alpha}-amylase gene, amyA, from the thermophilic halophile Halothermothrix orenii and purification and biochemical characterization of the recombinant enzyme Microbiology, August 1, 2002; 148(8): 2343 - 2349. [Abstract] [Full Text] [PDF]