Bioelectrochemical detection of L-lactate respiration using genetically modified Hansenula polymorpha yeast cells overexpressing flavocytochrome b2

In general, L-lactate respiration is difficult to detect in living yeast cells due to the small activity of L-lactate oxidizing enzymes within the mitochondria. Genetically modified cells of methylotrophic yeast Hansenula polymorpha overproducing L-lactate:cytochrome c-oxidoreductase (EC 1.1.2.3, also known as flavocytochrome b2, FC b2) were physically immobilized by means of a dialysis membrane onto various types of electrode materials in order to investigate the possibility of electrochemically detecting L-lactate respiration. It could be shown that in the case of genetically modified Hansenula polymorpha cells in contrast to cells from the parental strain, enhanced L-lactate-dependent respiration could be detected. Due to overproduction of FC b2 the O2 reduction current is decreased upon addition of L-lactate to the electrolyte solution. The electron transfer pathway in the L-lactate-dependent respiration process involves a cascade over three redox proteins, FC b2, cytochrome c and Complex-IV, starting with L-lactate oxidation and ending with oxygen reduction. By means of selective inhibition of Complex IV with CN−, lactate respiration could be proven for causing the decrease in the O2 reduction.