<正> A wide variety of different types of microorganisms are known to produce intracellular energy and carbon storage products

which have been generally described as being poly （β-hydroxybutyrate）

PHB

but which are

more often than not

copolymers containing different alkyl groups at the β-position. Hence

PHB belongs to the family ofpoly （β-hydroxyalkanoastes）

PHA

all of which are usually formed as intracellular inclusions in bacteria under unbalanced growth conditions. Recently

it became of industrial interest to evaluate these PHA polyesters as natural biodegradable and biocompatible plastics for a wide range of possible applications

such as surgical sutures or packaging containers. For industrial applications

the controlled incorporation of repeating units with different chain lengths into a series of copolymers is desirable in order to produce polyesters with a range of material properties because physical and chemical characteristics depend strongly on the polymer composition. Such "tailor-made" copolymers can be produced under controlled growth conditions in that

if a defined mixture of substrates for a certain type of microorganisms is supplied

a well defined and reproducible copolymer is formed.