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Membranes were prepared from four temperature range variants of Bacillus megaterium: one obligate thermophile, one facultative thermophile, one mesophile, and one facultative psychrophile, covering the temperature interval between 5 and 700C. The following changes in membrane composition were apparent with increasing growth temperatures: (i) the relative amount of iso fatty acids increased and that of anteiso acids decreased, the ratio of iso acids to anteiso acids being 0.34 at 50C and 3.95 at 700C, and the pair iso/anteiso acids thus seemed to parallel the pair saturated/unsaturated acids in their ability to regulate membrane fluidity; (ii) the relative amount of long-chain acids (016 to C18) increased fivefold over that of short-chain acids (014 and C15) between 5 and 700C; (iii) the relative amount of phosphatidylethanolamine increased, and this phospholipid accordingly dominated in the thermophilic strains, whereas diphosphatidylglycerol was predominant in the two other strains; and (iv) the ratio of micromoles of phospholipid to milligrams of membrane protein increased threefold between 5 and 700C. Moreover, a quantitative variation in membrane proteins was evident between the different strains. Briefly, membrane phospholipids with higher melting points and packing densities appeared to be synthesized at elevated growth temperatures. Most microorganisms alter their membrane composition in response to changes in the environmental temperature. The physical properties of the membrane lipid bilayer are believed to be important for this temperature adaptation. Escherichia coli thus maintains a nearly constant fluidity of its membrane lipids over its entire temperature range of growth, a process called "homeoviscous adaptation" (45). The mechanism, in this case, involves the production of membrane lipids containing a higher proportion of saturated fatty acids relative to unsaturated ones at higher temperatures.

Three Lactobacillus plantarum and seven Lactobacillus reuteri strains were studied by using restriction endonuclease analysis (REA) combined with principal-component analysis (PCA) and soft independent modeling of class analogy (SIMCA). Chromosomal DNAs from the strains were extracted and cleaved with restriction enzymes, and the DNA fragments were separated according to size by agarose gel electrophoresis. Band patterns were read by using a laser densitometer. The procedure to obtain reproducible digestion patterns with a suitable number of DNA fragments was optimized. Asp 718, ClaI and EcoRI were the most suitable of the 17 restriction enzymes tested, each giving 30 to 50 DNA fragments down to a molecular weight of 4.2 X lo6. The digestion patterns of all three enzymes, which gave a data set for 10 strains and 80 variables, were used for classification by PCA and SIMCA. All strains were clearly separated, and the separation within each species was in general accordance with data on DNA-DNA homology found in the literature. We concluded that restriction endonuclease analysis, combined with PCA and SIMCA, can be used for the classification of Lactobacillus spp.The genus Lactobacillus comprises about 50 validly described species; for historical reasons, in this genus circumscription of taxa has been based mainly on phenotypic features (e.g., the ability to ferment carbohydrates). Furthermore, the members of the genus Lactobacillus are formally differentiated from members of the genera Leuconostoc, Lactococcus, and Pediococcus on morphological grounds; in several cases this differentiation has caused systematic problems, as it can be diacult to distinguish between rods and cocci (23). Numerical studies have revealed the weakness in the phenotypic foundation (5,19). The systematics of this group have been improved by chemotaxonomy and DNA-DNA homology studies. Thus, the genus consists of deterministically defined taxa, but the relationships among the taxa are vague.Examples of characteristics that indicate the weakness in the present definition of the genus Lactobacillus are (i) the wide range in guanine-plus-cytosine contents of DNAs from different Lactobacillus species (32 to 53 mol%), (ii) the different kinds of cross-linkage of the peptidoglycans in cell walls, and (iii) the mingling in a phylogenetic tree of Lactobacillus, Leuconostoc, and Pediococcus strains as indicated by rRNA sequencing data (25). Thus, there seems to be a need to study the genus Lactobacillus with reclassification in mind. What method should be applied? Sequencing of rRNA is technically difficult and labor intensive. The accuracy of using enzymes as genetic markers (15) can be questioned as long as the majority of the information in the DNA remains unknown. And DNA-DNA homology is, unfortunately, not suitable outside the constraints of highly related species. An alternative method is restriction endonuclease analysis (REA), which, compared with rRNA sequencing, is technically easy to handle and may, in contrast to DNA-DNA homology, have g...

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