Willem Meindert De Vos

Discovering lactic acid bacteria by genomics

This review summarizes a collection of lactic acid bacteria that are now undergoing genomic sequencing and analysis. Summaries are presented on twenty different species, with each overview discussing the organisms fundamental and practical significance, nvironmental habitat, and its role in fermentation, bioprocessing, or probiotics. For those projects where genome sequence data were available by March 2002, summaries include a listing of key statistics and interesting genomic features. These efforts will revolutionize our molecular view of Gram–positive bacteria, as up to 15 genomes from the low GC content lactic acid bacteria are expected to be available in the public domain by the end of 2003. Our collective view of the lactic acid bacteria will be fundamentally changed as we rediscover the relationships and capabilities of these organisms through genomics.

Genetics and protein engineering of nisin.

Of the bacteriocins produced by lactic acid bacteria, nisin (Fig. 1) is the best-characterized representative. Nisin is a 34 amino acid Polypeptide (Gross & Morell, 1971) produced by a number of, usually atypical, Lactococcus lactis subsp. lactis strains (Hirsch, 1953; De Vos et al., 1993). Two natural variants of nisin are known, nisin A (Gross & Morell, 1971) and nisin Z (Mulders et al., 1991), which differ in a single amino acid residue at position 27 (aspartic acid in nisin A and histidine in nisin Z; Fig. 1). The structural genes for nisin A and nisin Z (nisA and nisZ, respectively) have been found to differ by a single mutation (see section 3.1). The two nisin variants appear to have the same biological activities, but nisin Z appears to have different diffusion properties from nisin A (De Vos et al., 1993). Nisin is the most prominent member of the group of bacteriocin-like peptides called lantibiotics (Schnell et al., 1988). Lantibiotics are ribosomally synthesized antimicrobial Polypeptides, produced by Gram-positive bacteria, which contain the thioether amino acids lanthionine and 3-methyl-lanthionine (see Jung (1991a, b) for recent reviews). On the basis of their different types of ring structures and their differences in molecular weights, they have been classified into the two subgroups, type A and type B, nisin being a type A lantibiotic. Other members of this group include subtilin (Gross & Kiltz, 1973) produced by Bacillus subtilis, epidermin (Allgaier et al., 1985, 1986) and Pep5 (Kellner et al., 1989), both produced by Staphylococcus epidermidis, and the L. lactis subsp. lactis bacteriocin lacticin 481 (see Chapter 7, this volume; Piard et al., 1992; 1993).

Control of Folate Production in Lactic Acid Bacteria by Using Metabolic Engineering

Folates are essential components in the human diet. They are involved as cofactor in many metabolic reactions, including the biosynthesis of nucleotides, the building blocks of DNA and RNA. Folates are produced in different (green) plants (folium (Latin) = leaf) and by some micro-organisms. Therefore, vegetables and dairy products are the main source of folates for humans. The daily recommended intake for an adult is 200 µg. For pregnant women a double dose is recommended, since folates are known to prevent neural-tube defect in newborns (1). Moreover, folates are reported to protect against some forms of cancer (2). A low folate level in the diet is associated with high homocysteine levels in the blood and, consequently with coronary diseases (3, 4).

Chapter 4 The role of cold-shock proteins in low-temperature adaptation

Publisher Summary This chapter discusses the role of cold-shock proteins in low-temperature adaptation. Research on cold adaptation has mainly focused on the synthesis of so-called “cold-shock proteins” (CSPs), a specific response that is shared by nearly all bacteria. These small (7 kDa) proteins are involved in gene expression, mRNA folding, transcriptional initiation and regulation and/or freeze-protection. Using primarily electrophoresis techniques other (non-7 kDa) low-temperature induced proteins are also identified, which will be referred to as “cold-induced proteins” (CIPs). Such proteins are involved in a variety of cellular processes. The chapter discusses novel aspects concerning the structure, function, and control of CSPs and CIPs, including a model for bacterial cold adaptation and possible mechanisms for low-temperature sensing. The chapter discusses the way bacteria sense low-temperature signals. The putative cellular thermosensors that have been proposed correlate to the major biochemical changes upon low-temperature exposure in bacterial cells, such as DNA topology, ribosomal structure and membrane composition. The sensing of heat shock interlinks with a number of two-component regulatory systems within the bacterial cell.