Lactic acid-producing bacteria are associated with various plant and animal niches and play a key role in the production of fermented foods and beverages. We report nine genome sequences representing the phylogenetic and functional diversity of these bacteria. The small genomes of lactic acid bacteria encode a broad repertoire of transporters for efficient carbon and nitrogen acquisition from the nutritionally rich environments they inhabit and reflect a limited range of biosynthetic capabilities that indicate both prototrophic and auxotrophic strains. Phylogenetic analyses, comparison of gene content across the group, and reconstruction of ancestral gene sets indicate a combination of extensive gene loss and key gene acquisitions via horizontal gene transfer during the coevolution of lactic acid bacteria with their habitats. evolutionary genomics ͉ fermentation L actic acid bacteria (LAB) are historically defined as a group of microaerophilic, Gram-positive organisms that ferment hexose sugars to produce primarily lactic acid. This functional classification includes a variety of industrially important genera, including Lactococcus, Enterococcus, Oenococcus, Pediococcus, Streptococcus, Leuconostoc, and Lactobacillus species. The seemingly simplistic metabolism of LAB has been exploited throughout history for the preservation of foods and beverages in nearly all societies dating back to the origins of agriculture (1). Domestication of LAB strains passed down through various culinary traditions and continuous passage on food stuffs has resulted in modern-day cultures able to carry out these fermentations. Today, LAB play a prominent role in the world food supply, performing the main bioconversions in fermented dairy products, meats, and vegetables. LAB also are critical for the production of wine, coffee, silage, cocoa, sourdough, and numerous indigenous food fermentations (2).LAB species are indigenous to food-related habitats, including plant (fruits, vegetables, and cereal grains) and milk environments. In addition, LAB are naturally associated with the mucosal surfaces of animals, e.g., small intestine, colon, and vagina. Isolates of the same species often are obtained from plant, dairy, and animal habitats, implying wide distribution and specialized adaptation to these diverse environments. LAB species employ two pathways to metabolize hexose: a homofermentative pathway in which lactic acid is the primary product and a heterofermentative pathway in which lactic acid, CO 2 , acetic acid, and͞or ethanol are produced (3).Complete genome sequences have been published for eight fermentative and commensal LAB species: Lactococcus lactis, Lactobacillus plantarum, Lactobacillus johnsonii, Lactobacillus acidophilus, Lactobacillus sakei, Lactobacillus bulgaricus, Lactobacillus salivarius, and Streptococcus thermophilus (4-11). This study examines nine other LAB genomes representing the phylogenetic and functional diversity of lactic acid-producing microorganisms. The LAB have small genomes encoding a range of biosynthe...

Many strains of Streptococcus thermophilus synthesize extracellular polysaccharides. These molecules may be produced as capsules that are tightly associated with the cell, or they may be liberated into the medium as a loose slime (i.e., "ropy" polysaccharide). Although the presence of exopolysaccharide does not confer any obvious advantage to growth or survival of S. thermophilus in milk, in situ production by this species or other dairy lactic acid bacteria typically imparts a desirable "ropy" or viscous texture to fermented milk products. Recent work has also shown that exopolysaccharide-producing S. thermophilus can enhance the functional properties of Mozzarella cheese, but they are not phage-proof. As our understanding of the genetics, physiology, and functionality of bacterial exopolysaccharides continues to improve, novel applications for polysaccharides and polysaccharide-producing cultures are likely to emerge inside and outside the dairy industry. This article provides an overview of biochemistry, genetics, and applications of exopolysaccharide production in S. thermophilus.

Recent studies have demonstrated that G-protein-linked signal transduction pathways play a significant role in the developmental program of the simple eukaryotic organism Dictyostelium. We have reported previously the isolation of a G-protein 13-subunit and present here a more complete analysis of this gene. Low-stringency Southern blots and RFLP mapping studies suggest that the 13-subunit is a unique gene found on linkage group If. Its deduced amino acid sequence of 347 residues is -60% identical to those of the human, Drosophila, and Caenorhabditis elegans 13-subunits. The carboxy-terminal 300 residues are about 70% identical; the amino-terminal 50 residues are quite divergent, containing only 10 identities. At all stages of growth and development, a single 1.9-kb 13-subunit mRNA is present at a high level, and a specific antibody detects a single 37-kD protein. We propose that G-protein heterotrimers are formed when this 13-subunit couples with each of the eight distinct G-protein a-subunits that are transiently expressed during development. Targeted disruption of the 13-subunit gene had no effect on the viability of haploid cells, but resulted in the inability of cells to aggregate.

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Lactobacillus helveticus CNRZ 32 is recognized for its ability to decrease bitterness and accelerate flavor development in cheese, and has also been shown to release bioactive peptides in milk. Similar capabilities have been documented in other strains of Lb. helveticus, but the ability of different strains to affect these characteristics can vary widely. Because these attributes are associated with enzymes involved in proteolysis or AA catabolism, we performed comparative genome hybridizations to a CNRZ 32 microarray to explore the distribution of genes encoding such enzymes across a bank of 38 Lb. helveticus strains, including 2 archival samples of CNRZ 32. Genes for peptidases and AA metabolism were highly conserved across the species, whereas those for cell envelope-associated proteinases varied widely. Some of the genetic differences that were detected may help explain the variability that has been noted among Lb. helveticus strains in regard to their functionality in cheese and fermented milk.