Biochemical Engineering Journal 28 (2006) 220–230 Computational prediction of impact of rerouting the carbon flux in metabolic pathway on cell growth and nisin production by Lactococcus lactis Agustin Krisna Wardani a , Sunao Egawa a , Keisuke Nagahisa b , Hiroshi Shimizu b , Suteaki Shioya a,∗ a Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan b Department of Bioinformatic Engineering, Graduate School of Information Science and Technology, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan Received 16 June 2005; received in revised form 20 September 2005; accepted 19 October 2005 Abstract The detrimental effect of a low pH due to the accumulation of lactate on cell growth and nisin production by Lactococcus lactis is well known. To avoid such an inhibitory effect of lactate and to enhance nisin production, a new strategy by rerouting the carbon flux was considered. This strategy will be conducted in two ways: (i) rerouting the carbon flux to ethanol, or (ii) rerouting the carbon flux to alanine. To confirm the feasibility of both compounds as targets to reroute the carbon flux, their inhibitory effects on cell growth and nisin production were investigated. For this purpose, a mathematical model was developed to investigate the nisin production during the cultivation of L. lactis subsp. lactis ATCC11454 with addition of the compounds. The constructed model then was applied to estimate the optimum redirection ratio of the carbon flux to ethanol. The model described that nisin production with rerouting the carbon flux to ethanol was 1.7 times higher than that without rerouting the carbon flux. Investigation of inhibitory effect of alanine was also carried out and the result confirmed that alanine gave no significant inhibitory effect on both cell growth and nisin production. Based on the calculation, the optimum of nisin production was estimated twice higher than that without rerouting the carbon flux. The proposed model here provided a reasonable description to estimate and to evaluate quantitatively the feasibility of rerouting the carbon flux to ethanol or alanine to achieve a high nisin production. © 2005 Elsevier B.V. All rights reserved. Keywords: Carbon flux; Mathematical modeling; Batch culture; Lactate; Nisin; Lactococcus lactis 1. Introduction Nisin belongs to a group of bacteriocins called lantibiotics (lanthionine-containing antimicrobial peptides) produced by Gram-positive bacteria. Nisin is the most prominent lantibi- otic produced by some strains of Lactococcus lactis [1,2]. The importance of nisin as an effective preservative is the fact that its spectrum of inhibitory activity includes almost all Gram- positive and spoilage bacteria, such as clostridia, listeria, bacilli and staphylococci [3–5]. In addition, this compound is non toxic to humans, active in a wide pH range and sensitive to prote- olytic enzymes, including gastric proteinases. It is stable after high-heat treatment and stable over several months of drying, ∗ Corresponding author. Tel.: +81 6 6879 7444; fax: +81 6 6879 7444. E-mail address: shioya@bio.eng.osaka-u.ac.jp (S. Shioya). freezing and refrigeration storage [6]. With these character- istics, nisin is very promising as a natural food biopreserva- tive. It has been widely used as a food preservative, notably in cheese and other dairy products, meat products, alcoholic beverages and canned vegetables [7]. Nisin has been approved by the United States Food and Drug Administration (FDA) as a natural food preservative [8] and it is permitted for use as a food additive in 50 countries [9]. Since consumer concern for more natural and minimally processed food has recently been increasing, there has been considerable interest in nisin, owing to its effectiveness and potential as a food biopreserva- tive [10]. Because bacteriocin production by lactic acid bacteria (LAB) is growth-associated, it usually occurs throughout the growth phase and ceases at the end of the exponential growth [11–13]. Therefore, an increase in growth rate is expected to increase nisin production rate. Many growth and environmental factors 1369-703X/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.bej.2005.10.003