Abstract: Chimeric alpha-amylases are disclosed of the formulaQ--R--Lin which Q is a N-terminal polypeptide residue of from 55 to 60 amino acid residues which is at least 75 percent homologous to the 55 N-terminal amino acid residues in the Bacillus amyloliquefaciens alpha-amylase as described in Takkinen et al., J. Biol. Chem. 258 (1983) 1007-1013,R is a polypeptide residue of the general formula ##STR1## L comprises a C-terminal polypeptide of from 390 to 400 amino acid residues which is at least 75 percent holologous to the 395 C-terminal amino acid residues in the Bacillus licheniformis 584 (ATCC 27811) alpha-amylase.

Abstract: A method for stabilization of extra-chromosomal elements in bacteria during cultivation which comprises transformation of a host bacterium having a defect in a chromosomal gene needed for the synthesis or maintenance of the cell envelope with an extra-chromosomal element capable of complementing the chromosomal gene defect of the host bacterium, the extra-chromosomal element also including an expressible DNA-sequence coding for a desired product.