Amperometric detection of the bacterial metabolic regulation with a microbial array chip

A microbial array chip with collagen gel spots entrapping living bacterial cells has been applied to investigate the metabolic regulation in Paracoccus denitrificans. Scanning electrochemical microscopy (SECM) was used to monitor the ferrocyanide production that reflects the electron flow in the respiratory chain located within the internal membrane of P. denitrificans. The ferrocyanide production from P. denitrificans largely depends on the types of the carbon source (glucose or lactate), suggesting that the electron flow rate in the respiratory chain depends on the activity of the metabolic pathway located up-stream of the respiratory chain. More importantly, it was found that the enzymes affecting glucose catabolic reactions were significantly up-regulated in cultures with a nutrient agar medium containing d-(+)-glucose as a sole carbon source. Enzyme assays using crude extracts of P. denitrificans were carried out to identify the enzymes expressed at a higher level in cultures supplemented with d-(+)-glucose. It was confirmed that the pyruvate kinase and enzymes of the overall Entner-Doudoroff pathway were highly induced in cultures containing d-(+)-glucose.