Characterization and species recognition of Lactobacillus plantarum strains by restriction fragment length polymorphism (RFLP) of the 16S rRNA gene

Twenty-one strains, labelled Lactobacillus plantarum or Lact. plantarum -like, and isolated from different natural sources, were characterized by restriction fragment length polymorphism (RFLP) of the 16S rRNA gene using Hin dIII and Eco RI cleaved chromosomal DNA, together with Lact. plantarum ATCC 14917^T, Lact. pentosus ATCC 8041^T, Lact. plantarum ATCC 10776 and Lact. plantarum ATCC 8014. The fermentation patterns on API 50CH were recorded at 30°C and 37°C for all strains. The phenotypes were heterogeneous, and the ability to ferment 17 of the 49 carbohydrates varied. The fermentation of some carbohydrates, for example D-raffinose and D-arabitol, was temperature-dependent. Strains having identical API profiles were separated by the plasmid profile. All strains but one (affiliated to Lact. casei ) had identical 16S ribosomal DNA sequences ( Lact. plantarum/Lact. pentosus ). The RFLP study resulted in identical ribopatterns for 17 of the strains, including the type strain of Lact. plantarum (pattern A1). Four strains had related fragment patterns to that of Lact. plantarum sensu stricto; three of these strains had more than 60% DNA: DNA homology to the type strain of Lact. plantarum , and one had less than 50% DNA: DNA homology to Lact. plantarum ATCC 14917^T. Two strains had fragment patterns similar to the type strain of Lact. pentosus , and they had more than 80% DNA: DNA homology to Lact. pentosus ATCC 8041^T. One of the Lact. pentosus strains shared one band with the A1 pattern. The ribopatterns of Lact. plantarum were homogeneous (identical for 85% of the strains), irrespective of phenotype and source of isolation. RFLP of the 16S rRNA genes using Eco RI and Hin dIII might be used for species recognition of Lact. plantarum , but seems less suitable for strain typing.     

Electrotransformation of meat lactobacilli. Effect of several parameters on their efficiency of transformation

Intact cells of several lactobacilli isolated from Spanish dry fermented sausages ( Lactobacillus curvatus, Lact. sake, Lact. plantarum and Lact. bavaricus ) were transformed by electroporation. With pNZ12 as a vector, transformation efficiencies of 2.4 times 10⁵, 3.8 times 10³ and 8.8 times 10² transformants μg^-1 DNA were observed for Lact. curvatus CTC435, Lact. sake CTC335 and Lact. bavaricus CTC232, respectively.
Effects of variation in experimental parameters on transformation efficiency were evaluated. Strains, vectors and buffers were the determinant parameters. The growth phase of the culture, cell concentration, voltage, use of cell wall weakening agents and the purity of the vector influenced the transformation efficiency in most strains.     

The antimicrobial effect of organic acids, sour dough and nisin against Bacillus subtilis and B. licheniformis isolated from wheat bread

Prevention of growth in wheat bread for more than 6 d of approximately 10⁶ rope-producing Bacillus subtilis spores per gram of dough was achieved by addition of propionic or acetic acids at levels of 0·10% v/w (based on flour weight), or by addition of 15% sour dough fermented with Lactobacillus plantarum C11, Lact. brevis L62, Lact. plantarum ('vege-start 60'), Lact. plantarum (ch 20), Lact. maltaromicus (ch 15), or the commercial sour dough starter culture, Lact. sanfrancisco L99. These cultures resulted in an amount of total titratable acids above 10 in the sour dough and a pH value below 4·8 in the final bread. Bacteriocin-producing lactic acid bacteria added as starter cultures in wheat dough and nisin (Nisaplin) at levels up to 100 p.p.m. g⁻¹ flour had no effect against B. subtilis and B. licheniformis strains, despite the fact that nisin-producing strains of Lactococcus lactis ssp. lactis among 186 strains of lactic acid bacteria had demonstrated inhibitory activity against B. subtilis and B. licheniformis in an agar spot assay.     

Growth of Bacillus cereus in fermenting tempeh made from various beans and its inhibition by Lactobacillus plantarum

Counts of Bacillus cereus reached ca 10⁸ cfu/g within 40 h in fermenting unacidified horsebean tempeh and resulted in complete spoilage of the product. In fermenting unacidified pea, chickpea and soybean tempeh, B. cereus counts reached 10⁶–10⁷ cfu/g, although the products were not spoiled. Inoculation of these unacidified beans with Lactobacillus plantarum decreased the final count of B. cereus by 2 log units, but had no effect on its growth in unacidified horsebean tempeh and its subsequent spoilage. Acidification of the beans during soaking resulted in a lower rate of B. cereus growth during fermentation. Inoculation of acidified beans with Lact. plantarum resulted in a markedly lower growth rate of B. cereus . In an associative broth culture study, B. cereus was completely inhibited by Lact. plantarum at pH values of about 5·5. Lactobacillus plantarum may be used to control the growth of B. cereus during tempeh production.     

Electrotransformation of Lactobacillus manihotivorans LMG 18010T and LMG 18011

An electroporation procedure was developed for the genetic transformation of intact cells of Lactobacillus manihotivorans , a new Lactobacillus species isolated from cassava sour starch fermentation in Colombia. Transformation efficiency of Lact. manihotivorans strains LMG 18010^T and LMG 18011 was measured and compared with electroporability of Lact. plantarum strains NCIMB 8299 and LMG 9211, by investigating the effect of changes in various parameters. For Lact. manihotivorans strain LMG 18010^T, the composition of the culture medium, such as the type of peptone and the presence of Tween-80, was found to be the most critical parameter, as well as the aeration conditions of the culture; better electroporation was obtained without air. The presence of MgCl₂ in the recovery medium was favourable to regeneration of electroporated cells. Plasmid-curing of the cells did not improve their electroporability. Transformants were obtained with Lact. manihotivorans strain LMG 18010^T and the plasmids pLZ12 and pGK13, whereas Lact. manihotivorans strain LMG 18011 was transformable with plasmids pLP825 and pLZ12, with different electroporation conditions.     

The effect of temperature and Lactobacillus amylovorus and Lact. plantarum, applied at ensiling, on wheat silage

The effects of applying Lactobacillus plantarum and Lact. amylovorus at ensiling on wheat silage stored at 25 and41 °C was studied under laboratory conditions. The inoculants were applied at 10⁶ cfu g⁻¹.Silages with no additives served as controls. Three jars per treatment were sampled on days 2, 8 and 60 after ensiling, for chemical and microbiological analyses. After the ensiling period, the silages were subjected to an aerobic stability test. The control and Lact. plantarum inoculated wheat fermented faster at 25 than at 41 °C, whereas silages inoculated with Lact. amylovorus fermented faster at 41 °C. This was apparent from the rate of pH decrease and from the contents of residual sugars and lactic acid in the final silages. The numbers of lactobacilli in the control and Lact. plantarum silages at 41 °C after 2 and 8 days of ensiling were lower than in the corresponding silages at 25 °C. For the Lact. amylovorus silage the opposite held true. The control silages at both temperatures and the Lact. plantarum silage at 41 °C were the most stable silages under aerobic exposure.     

Selenium and Lactobacillus species

Selenium (Se) is an essential element for man and animal. Supplementation of Se has been done with Se-enriched yeast and inorganic Se compounds. In the present study a quantitative and qualitative evaluation was made of whether lactobacilli are able to concentrate Se. A high correlation was found between the bacterial Se concentration and the concentration of Se in the medium. The Se concentration in biomass was respectively 253 ± 50, 375 ± 33 and 407 ± 108 μg g⁻¹ dry weight for Lactobacillus delbrueckii subsp. bulgaricus, Lact. plantarum and Lact. casei subsp. casei when 1 mg 1⁻¹ Se⁴⁺ was present in the medium. Manganese (Mn) was concentrated in Lact. plantarum and Lact. casei subsp. casei but not in Lact. delbrueckii subsp. bulgaricus. The Mn concentration in biomass was higher compared to the Se concentration but this difference decreased when the concentration of Mn/Se increased in the culture medium. Copper, zinc and iron were also concentrated in biomass of Lact. delbrueckii subsp. bulgaricus. Characterization of the bacterial selenocompound revealed that ⁷⁵Se was generally incorporated, as selenocysteine, into protein of Lact. delbrueckii subsp. bulgaricus. Addition of L-cysteine to the medium decreased the bacterial Se content. It was concluded that Lact. delbrueckii subsp. bulgaricus incorporated Se non-specifically into bacterial protein. The application of Se-enriched lactobacilli (Se-Lb) in Se supplementation would be an interesting approach since selenomethionine, which is the major selenocompound in commercialized Se-yeast, was not detected in Se-Lb and because lactobacilli are already widely used in human nutrition.     

Expression of novobiocin resistance genes in the novobiocin-producing organism Streptomyces niveus

RNA isolated at intervals during fermentation from the novobiocin-producing wild-type strain of Streptomyces niveus and from a series of novobiocin-non-producing (Nov^-) mutants was hybridized to DNA probes containing sequences which specify novobiocin resistance. The probes were made from inserts contained in the clones pGL101 and pGL103 which increase the level of novobiocin resistance of S. lividans transformants from 10 μg ml^-1 to 50 μg ml^-1 and 150 μg ml^-1, respectively. No hybridization was detected with the pGL101 probe. The pGL103 probe hybridized to RNA extracted during the later stages of growth—a pattern corresponding to the transition from low to high level novobiocin resistance during growth of S. niveus wild-type cultures. Neither probe hybridized to RNA extracted from four Nov^- mutants. These mutants showed variable levels of novobiocin resistance but none expressed the high wild-type levels. The authors conclude that expression of the DNA sequence in pGL103 is associated with high level novobiocin resistance.     

DNA probe and PCR-specific reaction for Lactobacillus plantarum

A 300 bp DNA fragment of Lactobacillus plantarum isolated by randomly amplified polymorphic DNA (RAPD) analysis was cloned and sequenced. This fragment was tested using a dot-blot DNA hybridization technique for its ability to identify Lact. plantarum strains. This probe hybridized with all Lact. plantarum strains tested and with some strains of Lact. pentosus , albeit more weakly. Two internal primers of this probe were selected (LbPl1 and LbPl2) and polymerase chain reaction (PCR) was carried out. All Lact. plantarum strains tested amplified a 250 bp fragment contrary to the other LAB species tested. This specific PCR for Lact. plantarum was also performed from colonies grown on MRS medium with similar results. These methods enabled the rapid and specific detection and identification of Lact. plantarum .     

Monitoring the fate of genetically engineered bacteria sprayed on the phylloplane of bush beans and grass

Abstract The fate of a Bacillus amyloliquefaciens with the recombinant plasmid pSB20 sprayed on the phyllosphere of grass, and of a Tn 5 marked Pseudomonas syringae sprayed on the phyllosphere of bush beans was studied in planted soil microcosms. B. amyloliquefaciens showed a decline from 1.5×10⁸ to 3.1×10² cfu g⁻¹ on the phylloplane of grass in the course of the experiment. B. amyloliquefaciens was easy to follow by selective cultivation due to the complete absence of bacterial background growth. Southern blot hybridization of Hin dIII digested genomic DNA showed plasmid restriction patterns identical with pSB20 indicating high plasmid stability. In total DNA extracts from phyllosphere bacteria the recombinant plasmid was detectable by Southern blot hybridization up to 6×10⁴ cfu g⁻¹ (wet weight). Counts of hybridizing colonies showed that P. syringae established on the phyllosphere of bush beans at between 5×10³ and 4×10⁶ cfu g⁻¹ fresh weight. During senescence of the bean plants the strain was no longer detectable by selective cultivation and subsequent colony hybridization. In contrast, Tn5 marked DNA was detected after PCR amplification over the whole period of the experiment.     

The effect of hydroxycinnamic acids on the growth of wine-spoilage lactic acid bacteria

Hydroxycinnamic acids and their derivatives occur naturally in grape juice and wine. To assess their potential as natural preservatives the effect of caffeic, coumaric and ferulic acids on the growth of three wine-spoilage strains of Lactobacillus collinoides and one of Lact. brevis was studied in acid tomato broth containing 5% ethanol at pH 4.8. At concentrations of 500 and 1000 mg l^-1, all three compounds markedly inhibited growth; coumaric and ferulic acids were more effective than caffeic acid. At a concentration of 100 mg l^-1, all compounds stimulated growth. In general, the strains of Lact. collinoides were more susceptible both to inhibition and stimulation by the hydroxycinnamic acids than was the strain of Lact. brevis. The possible influence of hydroxycinnamic acids on the malolactic fermentation of wine is discussed.     

Comparative study on cell envelope-associated proteinases in natural isolates of mesophilic lactobacilli

Lactobacilli isolated from different natural sources were screened for the presence of cell envelope-associated proteinases (Prt⁺ strains). Among them 17 of 75 tested isolates were Prt⁺. All Prt⁺ strains were producers of a serine-type proteinase, since their proteolytic activity was inhibited by phenylmethylsulfonyl fluoride. Most of the natural isolates of mesophilic lactobacilli degraded only β-casein such as Lactobacillus paracasei subsp. paracasei strains BGLI17 and BGLI18 and Lact. rhamnosus BGEN1. Only Lact. divergens BG742 cleaved all three, α-, β- and κ-caseins, even in the presence of Ca²⁺ ions. Total DNA isolated from Lact. paracasei subsp. paracasei strains BGLI17 and BGLI18 hybridized to the lactococcal proteinase gene probes originated from Lactococcus lactis subsp. cremoris Wg2. Hybridization could not be linked to the plasmid DNA, and pulse-field gel electrophoresis analysis suggested that the proteinase genes of these two strains are most probably chromosomally located.     

Growth-inhibitory effects of Galla Rhois-derived tannins on intestinal bacteria

The growth-inhibitory activity of Galla Rhois-derived materials towards 17 intestinal bacteria was evaluated using an impregnated paper disc method. The biologically active components of Galla Rhois were characterized as the tannins methyl gallate (MG) and gallic acid (GA) by spectral analysis. The growth responses varied with bacterial strain tested. In the test using 10 mg disc⁻¹, MG and GA produced a clear inhibitory effect on harmful bacteria such as Clostridium perfringens , Cl. paraputrificum , Eubacterium limosum , Bacteroides fragilis , Staphylococcus aureus and Escherichia coli . Methyl gallate showed no growth-inhibitory activity towards Bifidobacterium adolescentis or B. longum whereas the growth of B. bifidum , B. breve , B. infantis , B. animalis , B. thermophilum , Lactobacillus acidophilus , Lact. plantarum and Streptococcus faecalis was slightly affected. However, GA did not adversely affect the growth of the bifidobacteria and lactobacilli. At 5 mg disc⁻¹, MG significantly inhibited the growth of Cl. perfringens and Cl. paraputrificum but did not affect the growth of the bifidobacteria and lactobacilli. At 1 mg disc⁻¹, MG greatly inhibited the growth of Cl. perfringens alone. These results may be an indication of at least one of the pharmacological actions of Galla Rhois.     

Bacillus tianmuensis sp. nov., isolated from soil in Tianmu Mountain national natural reserve, Hangzhou, China

In a project aiming to isolate strains with the ability to produce nonribosomal peptides, a Gram-negative, endospore-forming, rod-shaped strain, designated B5^T, was isolated from a soil sample collected from Tianmu Mountain national natural reserve in Hangzhou, China. Strain B5^T contained meso -diaminopimelic acid in the cell wall peptidoglycan. The major cellular fatty acids were anteiso-C_15:0 and iso-C_15:0. The DNA G+C content was 42.5 mol%. The phylogenetic analysis based on 16S rRNA gene sequence indicated that strain B5^T fell within the genus Bacillus , with highest sequence similarity values to Bacillus barbaricus DSM 14730^T (96.4%) and Bacillus macauensis JCM 13285^T (95.5%). The isolate, however, could be distinguished from Bacillus strains with validly published names by low 16S rRNA gene sequence similarity values, distinct phenotypic and chemotaxonomic characteristics. On the basis of these polyphasic evidences, it is demonstrated that the isolate B5^T represents a novel species of the genus Bacillus , for which the name Bacillus tianmuensis sp. nov. is proposed. The type strain is B5^T (=DSM 22111^T=CGMCC 1.8879^T).     

Citrate metabolism by Lactobacillus plantarum isolated from orange juice

The behaviour of Strains of Lactobacillus plantarum isolated from fermented orange juice and Lact. plantarum DSM 20174 was studied in the presence of citrate. When used as sole carbon source, citrate scarcely supported the growth of the bacteria. It was shown to enhance the growth of Lact. plantarum in glucose media. Under acid conditions (pH 4·0–5·0), 1 mol of citrate yielded 1·7 mol of acetate as sole major final metabolite with release of CO₂ in the gas phase.     

Conjugative transfer of the transposon Tn919 to lactic acid bacteria

Abstract The streptococcal transposon Tn 919 was transferred from Streptococcus faecalis GF590 to selected Group N Streptococcus strains and to one strain each of Lactobacillus plantarum and Leuconostoc cremoris , using the filter mating method. An S. lactis MG1363 Rif^r Tc^r transconjugant also acted as a donor, but was less efficient than GF590. Frequencies of transfer varied between 4.0 × 10⁻⁸ and 5.29 × 10⁻⁵ per recipient. Further analysis of S. lactis MG1363 Sm^r Tc^r transconjugants showed that insertion of Tn 919 into the chromosome was site-specific.     

Malolactic fermentation of wine: study of the influence of some physico-chemical factors by experimental design assays

The ability of selected lactic acid bacteria to carry out malolactic fermentation depends on the level of numerous wine characteristics. A Hadamard's experimental matrix was used to determine the main effects of 11 physico-chemical factors on malolactic activity of three Leuconostoc œnos strains and one Lactobacillus plantarum strain. Ethanol had the greatest inhibitory effect on the achievement of malolactic fermentation for all Leuc. œnos strains. An inhibitory effect of the L-malic acid was also found in the operating conditions. These strains show different degrees of sensitivity to pH. One of these strains was inhibited by SO₂. Malolactic activity of the Lact. plantarum strain is mainly affected by a low pH, and this strain is often less efficient than Leuc. œnos strains. This methodology could be used for the selection of strains for malolactic starters. Further work is in progress using factorial design in order to determine the interactions between influential factors.     

The normal Lactobacillus flora of healthy human rectal and oral mucosa

The Lactobacillus flora of the rectal and oral mucosa was sampled from 42 healthy volunteers. Species identification was carried out by numerically comparing API 50CH fermentation patterns with type strains, using an S_J-similarity cut-off level of 79%. For the largest groups, identity was further confirmed by DNA-DNA hybridizations against the type strain of the species. Seventeen lactobacilli clusters were defined, of which most were found both on rectal and oral mucosa. The largest taxa were Lactobacillus plantarum , Lact. rhamnosus and Lact. paracasei ssp. paracasei , which were isolated from 52%, 26% and 17% of the individuals, respectively. Most isolates were tested for their capacity to adhere to the human colonic cell line HT-29 in the absence and presence of methyl-α- D -mannoside. Mannose-sensitive adherence to HT-29 cells was encountered in two-thirds of the Lact. plantarum isolates, but infrequently among isolates of other taxa. The results suggest that Lact. plantarum is a major colonizer of the human gastrointestinal mucosa, and that its capacity to adhere to mannose-containing receptors may be of some ecological importance.     

Characterization of the bacterial flora of Sudanese sorghum flour and sorghum sourdough

The microflora of a Sudanese sorghum flour, a spontaneously fermented sourdough and along-term sourdough produced in a Sudanese household by consecutive re-inoculations, wasstudied. The dominant contaminants of sorghum flour were Gram-negative, catalase-positive,rod-shaped bacteria with counts of about 10⁵ cfu g⁻¹. Thespontaneously fermented sorghum sourdough showed a bacterial succession from Gram-negative,catalase-positive contaminants to Enterococcus faecalis , Lactococcus lactis , Lactobacillus fermentum and Lact. reuteri . The total bacterial countreached about10¹⁰ cfu g⁻¹ and the pH dropped from6·4 to 3·35 in about 42 h. In this phase, only the latter two species remaineddominant in a ratio of 1:1. From the Sudanese long-term dough, seven strains of Lactobacillus were isolated, representing the dominant flora. Sequence comparison ofpartial 16S rRNA gene sequences were used to clarify their phylogenetic positions. Five strainswere classified as Lact.vaginalis and could be regarded as heterogenous biovars of thisspecies. The other two strains could be assigned to Lact. helveticus .RAPD-PCR and sugar fermentation patterns were useful in differentiation of these strains.     

Duplication of DNA regions carrying repetitive sequence RSα in Bradyrhizobium japonicum 110

L. D. Kuykendall, M. E. Barnett and J. N. Mathis. 1997. RSα is a repeated DNA sequence found within the nitrogen-fixation gene cluster of Bradyrhizobium japonicum , a symbiotic nitrogen-fixing bacterium that nodulates soybean. Bradyrhizobium japonicum strain 110 spc 4 contains 12 repeats, each located on a separate Xho I DNA restriction fragment between 1.2 and 14 kb in length. Although Fix⁺ and Fix⁻ derivatives of B. japonicum USDA 110 were first reported more than two decades ago, genotypic differentiation, on the basis of RSα hybridization pattern, was reported only recently. Bradyrhizobium japonicum strain USDA 110 had only single copies of the RSα-hybridizing bands, but a particular Fix⁻ derivative, MSDJGl, carried doublets of two distinct Xho I fragments that carry RSα3 and RSα4. In this study, RSα hybridization patterns were analysed further in both Fix⁺ and Fix⁻ derivatives of strain 110 to test for duplication of these particular genomic regions. It was concluded that the duplication, or not, of genetic regions carrying RSα3 and RSα4 in strain USDA 110 derivatives is unrelated to symbiotic nitrogen-fixation ability. Like Fix⁻ MSDJGl, Fix⁺ strain 110 derivatives I-110 and MN-110 had duplications of the Xho I DNA restriction fragments carrying RSα3 and RSα4, but Fix⁻ strain 110 derivative L2–110 lacked these duplications. Thus, it is now clear that Fix⁻ derivatives MSDJG1 and L2–110 arose via distinct genetic mechanisms. Interestingly, Fix⁺ derivatives of strain 110 from the laboratories of Elkan and Hennecke differed in RSα hybridization profile.