Real-time detection of cofactor availability in genetically modified living Saccharomyces cerevisiae cells — Simultaneous probing of different geno- and phenotypes

A compact multifunctional microfluidic platform for exploring cellular dynamics in real-time using electrochemical detection

Dopamine detection from PC12 cell populations and monitoring of yeast redox metabolism demonstrate the multifunctionality of the compact microfluidic cell culture and electrochemical analysis platform with in-built fluid handling and detection unit.

Probing the redox metabolism in the strictly anaerobic, extremely thermophilic, hydrogen-producing Caldicellulosiruptor saccharolyticus using amperometry

Changes in the redox metabolism in the anaerobic, extremely thermophilic, hydrogen-forming bacterium Caldicellulosiruptor saccharolyticus were probed for the first time in vivo using mediated amperometry with ferricyanide as a thermotolerant external mediator. Clear differences in the intracellular electron flow were observed when cells were supplied with different carbon sources. A higher electrochemical response was detected when cells were supplied with xylose than with sucrose or glucose. Moreover, using the mediated electrochemical method, it was possible to detect differences in the electron flow between cells harvested in the exponential and stationary growth phases. The electron flow of C. saccharolyticus was dependent on the NADH- and reduced ferredoxin generation flux and the competitive behavior of cytosolic and membrane-associated oxidoreductases. Sodium oxamate was used to inhibit the NADH-dependent lactate dehydrogenase, upon which more NADH was directed to membrane-associated enzymes for ferricyanide reduction, leading to a higher electrochemical signal. The method is noninvasive and the results presented here demonstrate that this method can be used to accurately detect changes in the intracellular electron flow and to probe redox enzyme properties of a strictly anaerobic thermophile in vivo.

Electrochemical probing of in vivo 5-hydroxymethyl furfural reduction in Saccharomyces cerevisiae

In this work, mediated amperometry was used to evaluate whether differences in intracellular nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) level could be observed between a genetically modified Saccharomyces cerevisiae strain, engineered for NADPH dependent 5-hydroxymethyl-2-furaldehyde (HMF) reduction, and its control strain. Cells overexpressing the alcohol dehydrogenase 6 gene (ADH6 strain) and cells carrying the corresponding control plasmid (control strain) were each immobilized on Au-microelectrodes. The real-time dynamics of NAD(P)H availability in the two strains, preincubated with HMF, was probed using the menadione-ferricyanide double mediator system. A lower intracellular NADPH level as the consequence of more effective HMF reduction was observed for the ADH6 strain both with and without added glucose, which increases the overall cellular NADPH level. The mediated amperometric signal during real-time monitoring of the concentration dependent HMF reduction in living cells could be translated into the cellular enzyme kinetic parameters: K(M,cell)(app), V(MAX), k(cat,cell), and k(cat,cell)/K)M,cell)(app). The results indicated that the overexpression of the ADH6 gene gave a 68% decrease in K(M,cell)(app) and 42% increase in V(MAX), resulting in a 4-fold increase in k(cat,cell)/K(M,cell)(app). These results demonstrate that the mediated amperometric method is useful for monitoring the short-term dynamics of NAD(P)H variations and determining cellular enzyme kinetic parameters in S. cerevisiae cells.