Vittorio Bottazzi

High frequency of conjugation in Lactobacillus mediated by an aggregation-promoting factor

Summary: Lactobacillus plantarum strain 4B2, which exhibits a strong autoaggregating phenotype, receives the broad-host-range plasmid pAMβ1 with conjugation efficiencies as high as 10-2 transconjugants per donor using solid matings; broth matings also occur, but at low transfer frequencies. Filter-sterilized spent supernatant of this strain contains a 32 kDa protein that promotes aggregation, and consequently a high frequency of conjugation, in lactic acid bacteria containing α-1,2-glucose-substituted lipoteichoic or teichoic acids. It appears, therefore, that the substituted lipoteichoic or teichoic acids act as receptors for the aggregation-promoting protein.

Deoxyribonucleic Acid Homology Among Lactobacillus Species of the Subgenus Streptobacterium Orla-Jensen

The deoxyribonucleic acid (DNA) relationship among Lactobacillus species of the subgenus Streptobacterium Orla-Jensen was assessed by means of DNA/DNA hybridization experiments. High genetic homologies were found among Lactobacillus casei subsp. casei, L. casei subsp. alactosus, L. casei subsp. pseudoplantarum, and L. casei subsp. tolerans; however, there was only a low level of homology between the DNA of L. casei subsp. rhamnosus and the DNA of other subspecies of L. casei. The DNAs of Lactobacterium zeae ATCC 15820 and L. casei subsp. casei ATCC 393 were nearly completely homologous. Although the latter strain has been proposed as the neotype for L. casei, it is not related to any of the other strains within the subspecies of L. casei. Lactobacillus plantarum and strains identified as belonging to L. plantarum subsp. rudensis and L. plantarum subsp. arabinosus formed a fairly homogeneous and easily recognized group. The DNA of Lactobacillus pentosus was unrelated to that of any known streptobacteria, and we therefore advocate the recognition of this organism as an independent species. There is a high degree of homology between Lactobacillus sake and Lactobacillus homohiochi; the name L. sake has priority, and L. homohiochi is very probably a synonym; for the same reason, Lactobacillus yamanashiensis has priority over its later subjective synonym, Lactobacillus mali. The general DNA/DNA homology relationships among Lactobacillus casei, L. plantarum, L. coryniformis, L. curvatus, L. xylosus, L. alimentarius, L. farciminis, and Sporolactobacillus inulinus justify their status as separate species.

Use of RAPD and 16S rDNA sequencing for the study of Lactobacillus population dynamics in natural whey culture.

The development of communities of the thermophilic microflora of natural whey culture for Parmigiano Reggiano cheese production was studied by means of molecular techniques. RAPD analysis facilitates the identification of the Lactobacillus strains involved in this microbial association and permitted the study of population dynamics during two cycles of whey fermentation. Analysis of RAPD fingerprints revealed the presence of four biotypes that dominate the whey fermentation process. Sequence analysis of 16S rDNA demonstrated that the strains isolated from whey belong to Lact. helveticus and Lact. delbrueckii ssp. lactis species.

Plasmid-encoded ropiness production inLactobacillus casei SSP.casei

SummaryGenetic determinants of the Muc+ character were investigated in two ropy strains,Lactobacillus delbrueckii ssp.bulgaricus 201 andL. casei ssp.casei NCIB 4114, which secrete a large amount of slime in culture media. Plasmid DNA analysis revealed the presence of two plasmids (4.5 and 2.3 Mdal) inL. casei ssp.casei, whileL. delbrueckii ssp.bulgaricus was plasmid free, suggesting a chromosomal location of Muc+ character in this strain. Curing experiments carried out onL. casei ssp.casei NCIB 4114 indicated a correlation between the Muc+ phenotype and the 4.5 Mdal plasmid.

An introduction to rod-shaped lactic-acid bacteria

The genus Lactobacillus is mainly found in the intestinal tract of healthy humans and animals as well as in fermenting vegetables or plant materials, such as silage. It has a moderate diffusion in meat products and is rarely found in wines and beers. On the other hand, rod-shaped lactic-acid bacteria are largely used in the preparation of a variety of foods and feed products. As starter cultures, they are omnipresent in cheeses and dairy manufacturing. Specific fermentation processes have been developed in order to encourage the growth of the desired species, some of which are fastidious organisms such as L. delbrueckii ssp. bulgaricus, L. helveticus and L. sanfrancisco. In addition, a promising and interesting perspective is the use of rod-shaped lactic-acid bacteria, primarily L. acidophilus, L. reuteri and L. salivarius as probiotic starters to preserve the natural biological equilibrium of the intestinal tract.

Aggregation-promoting factor in pig intestinal Lactobacillus strains

V. KMET, M.L. CALLEGARI, V. BOTTAZZI AND L. MORELLI. 1995. Autoaggregation was frequently encountered among intestinal lactobacilli isolated from weaned pigs. The aggregation mechanism was shown to be mediated by the production of a proteinaceous aggregation‐promoting factor in two strains of Lactobacillus reuteri. A 32 kDa aggregation‐promoting protein was detected in these strains by cross‐reaction with rabbit polyclonal antibodies for Aggregation‐Promoting Factor produced by the human isolate Lact. plantarum 4B2. Coaggregation reactions of Lact. reuteri strains with pathogenic and non‐pathogenic Escherichia, coli were detected.

Single-stranded DNA plasmid, vector construction and cloning of Bacillus stearothermophilus α-amilase in Lactobacillus

Vector plasmids were constructed by ligating chloramphenicol and erythromycin resistance genes to TaqI-digested DNA of a cryptic plasmid from Lactobacillus plantarum. The minimal region of Lactobacillus plasmid DNA that was required for DNA replication was defined and a single-stranded DNA intermediate replication system was observed. Homologies with other origins of replication of plasmids from Gram-positive bacteria, replicating via rolling circle mechanism, were found. It was shown that the constructed vectors, named pPSC20 and pPSC22, were transformable into L. plantarum, Lactobacillus acidophilus, Lactobacillus reuteri, Lactobacillus fermentum, Lactobacillus helveticus, Lactococcus lactis subsp. lactis, Bacillus subtilis, and Escherichia coli. Using plasmid pPSC22, the alpha-amylase gene of Bacillus stearothermophilus was cloned and expressed in several Lactobacillus species.

The Lactic Microflora of Fowl

Most of the literature on fowl lactic acid bacteria is concerned with isolates obtained from the lower part of the alimentary tract and from the crop (Barnes, 1979). The presence of lactobacilli in other intestinal areas has not been so thoroughly investigated.

Genotypic and phenotypic correlationships among some strains ofLactobacillushelveticus

SummaryEvidence for the presence of extrachromosomal elements inLactobacillushelveticus ATCC 15009 and the absence of plasmid DNA in two other strains ofL.helveticus is reported. These three strains did not show any difference in regard to lactose metabolism, proteolytic activity, and antibiotic resistance or in N-acetyl-D-glucosamine fermentation. The only difference found is a higher resistance to arsenate forL.helveticus ATCC 15009, suggesting linkage of this resistance to plasmids present in this strain.

Detection of permanent Lactobacillus casei subsp. casei strains in weaned infants' gut

The Lactobacillus microflora in the faeces of two infants was followed in the days after weaning. All colonies isolated at the highest dilution were Lactobacillus casei subsp. casei. They were identified to strain level by plasmid profile, total soluble cell protein and surface cell protein pattern. Two dominant strains of L. casei subsp. casei were identified on successive days, which suggests that these were permanent members of the infant bowel microflora.