Citrate Metabolism by Enterococcus faecalis FAIR-E 229

Citrate metabolism by Enterococcus faecalis FAIR-E 229 was studied in various growth media containing citrate either in the presence of glucose or lactose or as the sole carbon source. In skim milk (130 mM lactose, 8 mM citrate), cometabolism of citrate and lactose was observed from the first stages of the growth phase. Lactose was stoichiometrically converted into lactate, while citrate was converted into acetate, formate, and ethanol. When de Man-Rogosa-Sharpe (MRS) broth containing lactose (28 mM) instead of glucose was used, E. faecalis FAIR-E 229 catabolized only the carbohydrate. Lactate was the major end product, and small amounts of ethanol were also detected. Increasing concentrations of citrate (10, 40, 70, and 100 mM) added to MRS broth enhanced both the maximum growth rate of E. faecalis FAIR-E 229 and glucose catabolism, although citrate itself was not catabolized. Glucose was converted stoichiometrically into lactate, while small amounts of ethanol were produced as well. Finally, when increasing initial concentrations of citrate (10, 40, 70, and 100 mM) were used as the sole carbon sources in MRS broth without glucose, the main end products were acetate and formate. Small amounts of lactate, ethanol, and acetoin were also detected. This work strongly supports the suggestion that enterococcal strains have the metabolic potential to metabolize citrate and therefore to actively contribute to the flavor development of fermented dairy products

BIOPROCESS DEVELOPMENT FOR SERINE ALKALINE PROTEASE PRODUCTION: A REVIEW

This work is the result of the convergence of the research in biochemical reaction engineering and metabolic flux analysis for serine alkaline protease (SAP) production. The genus Bacillus includes a variety of industrially important species that are known to secrete a large number of extracellular proteases and are used among many species as producer of SAP enzyme. Therefore, in the first part of the present article an overview to serine alkaline protease and regulation of its synthesis and secretion in Bacillus is presented. In the second part, a detailed review of the published information on the bioprocess medium design and bioreactor operation parameters are discussed in relation to the concentrations of the byproducts, i.e. neutral protease, amylase, amino acids, organic acids and alcohols. In the third part, papers on metabolic flux analysis for SAP are reviewed with the emphasis on SAP overproduction potential of the Bacillus licheniformis, the effect of oxygen transfer on the bioreaction-network fluxes and the need for oxygen transfer strategies. The metabolic bottlenecks and strategies for increasing the yield and selectivity of SAP fermentation process are discussed