VTT has produced various organic acids (e.g. lactic, glycolic, xylonic, mucic acids) with yeast and filamentous fungi. In addition to developing conversion routes of xylose and glucose to acids and studying oxidative pathways for 5 carbon sugars, we have addressed pectin-derived galacturonic acid as a raw material for acid production, while characterising the catabolic pathway. Suitable enzyme catalysts for the conversions were identified by bioinformatic data mining and several were characterised. NMR has been used to monitor the kinetics of pathway enzymes and in vivo reactions. Site-directed mutagenesis and structure determinations have been carried out. Studies of xylonic acid production have highlighted global transcriptomic responses and intracellular accumulation of xylonic acid. Iintracellular acid accumulation was shown at the single cell level to result in acidification and loss of viability, and thus we are investigating the design of a control circuit to overcome the obstacle. Our efforts have led to the development of efficient production hosts for several organic acids, in the best cases reaching titres up to 170 g/L. Choice of host, gene, pathway and production process (typically batch or fed batch) have all been found to be important in achieving high levels of organic acid production.
