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Biotechnology and Applied Biochemistry (2003) 38, (157–167) (Printed in Great Britain)

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Enhancement of nisin production by Lactococcus lactis in periodically re-alkalized cultures

Nelson Pérez Guerra and Lorenzo Pastrana Castro¹

Departamento de Bioquímica, Xenética e Inmunoloxía, Facultade de Ciencias de Ourense, Universidade de Vigo, As Lagoas, 32004 Ourense, Spain

Key words: antibacterial, fed-batch cultures, mixed acid products, nisin, re-alkalized cultures, wastes.

Abbreviations used: AU, bacteriocin activity unit(s); Cb 1.01, Carnobacterium piscicola CECT (Colección Española de Cultivos Tipo) 4020; CDW, cell dry weight; MPW, mussel-processing waste; CMPW, concentrated mussel-processing waste; DW, deproteinized whey; CW, concentrated whey; Lc 1.04, Lactococcus lactis subsp. lactis CECT 539; MRS, de Man, Rogosa and Sharpe medium.

¹To whom correspondence should be addressed (e-mail pastrana@uvigo.es).

Synthesis of nisin as well as biomass production by Lactococcus lactis subsp. lactis CECT (Colección Española de Cultivos Tipo) 539 on both hydrolysed mussel-processing waste and whey medium were followed in three fixed volume fed-batch fermentations, with re-alkalization cycles. The two cultures on mussel-processing waste (MPW) were fed with a 240 g/l concentrated glucose and with a concentrated MPW (about 100 g of glucose/l). The culture on whey was fed with a mixture of concentrated whey (48 g of total sugars/l) and a 400 g/l concentrated lactose. The three cultures were mainly characterized with higher nisin titres [49.7, 109.6 and 124.7 bacteriocin activity units (AU)/ml respectively] compared with the batch process on de Man, Rogosa and Sharpe [(1960) J. Appl. Bacteriol. 23, 130–135] medium (49.6 AU/ml), MPW (9.5 AU/ml) and whey (22.5 AU/ml) [1 AU/ml is the amount of antibacterial compound needed to obtain 50% growth inhibition (LD₅₀) compared with control tubes]. In the three fed-batch cultures a shift from homolactic to mixed-acid fermentation was observed, and other products (acetic acid, butane-2,3-diol or ethanol) in addition to lactic acid were detectable in the medium. However, their contributions to the total antibacterial activity of the post-incubates (the cell-free culture supernatant obtained at the end of the fermentation process) of L. lactis CECT 539 against Carnobacterium piscicola CECT 4020 were very low.

Received 3 April 2003/27 May 2003; accepted 9 June 2003

Published as Immediate Publication 9 June 2003, DOI 10.1042/BA20030059

© 2003 Portland Press Ltd