METABOLIC CONSEQUENCES OF BACTERIAL BETA-GALACTOSIDASE OVERPRODUCTIONBY A RECOMBINANT STRAIN OF HANSENULA-POLYMORPHA

A strain of methylotrophic yeasts Hansenula polymorpha LAC-56, bearing a recombinant pLac56 plasmid with a cloned Escherichia coli gene lacZ (encoding beta-galactosidase), was investigated with respect to its p hysiological and biochemical properties. The cloned gene was controlle d by a promoter of the methanol oxidase gene of H. polymorpha. Upon in duction of this promoter, the recombinant strain overproduced beta-gal actosidase in amounts of up to 12% of the total cellular protein. Stud y of biochemical and physiological parameters of the recombinant strai n of H. polymorpha, grown in a chemostat culture on minimal medium wit h methanol as the carbon and energy source, showed that the overproduc er is characterized by (1) a reduced growth yield with respect to cons umed substrate; (2) a decreased maximal growth rate; (3) an elevated c oncentration of intracellular formaldehyde; (4) an enhanced activity o f formaldehyde dehydrogenase, a key enzyme of methanol dissimilation; (5) a lowered activity of methanol oxidase; and (6) a decreased concen tration of intracellular ATP. It is assumed that the formaldehyde util ization pathway in this recombinant strain has a bottleneck at the lev el of dihydroxyacetone kinase, which eventually leads to reduced value s of the biomass yield and maximal growth rate in the recombinant stra in.