Exploring and exploiting starch-modifying amylomaltases from thermophiles

Starch is a staple food present in water-insoluble granules in many economically important crops. It is composed of two glucose polymers: the linear α-1,4-linked amylose and amylopectin with a backbone of α-1,4-glycosidic bonds and α-1,6-linked side chains. To dissolve starch completely in water it needs to be heated; when it cools down too much the starch solution forms a thermo-irreversible gel. Amylomaltases (EC 2.4.1.25) are enzymes that transfer a segment of an α-1,4-D-glucan to a new 4-position in an acceptor, which may be glucose or another α-1,4-D-glucan. Acting upon starch, amylomaltases can produce cycloamylose or a thermoreversible starch gel, both of which are of commercial interest.

Isolation and analysis of mutants of the methylotrophic actinomycete Amycolatopsis methanolica blocked in aromatic amino acid biosynthesis

Mutants of the actinomycete Amycolatopsis methanolica blocked in aromatic amino acid biosynthesis were isolated using brief ultrasonic treatments to obtain single cells. After UV irradiation, auxotrophic mutants were selected as pinpoint colonies on mineral agar with only 1 mg l-1 of amino acid supplements. Mutant characterization provided unambiguous evidence that L-tyrosine is synthesized via arogenate and that L-phenylalanine is synthesized via phenylpyruvate. The efficiency of chromosomal DNA marker exchange was highest in matings with mutant strains that lacked the previously characterized 13.3-kb integrative plasmid pMEA300.