Lacticaseibacillus jixiensis sp. nov., Isolated from Traditional Chinese Pickle

A novel lactic acid bacterial strain (designated N163-3-2T), isolated from traditional Chinese pickle ('Suan cai'), was characterized using a polyphasic approach. Strain N163-3-2T was most closely related to the type strains of Lacticaseibacillus baoqingensis, Lacticaseibacillus manihotivorans, and Lacticaseibacillus porcinae, having 97.9-98.4% 16S rRNA gene, 82.0-85.1% pheS, 87.5-87.8% rpoA, and 85.8-86.7% concatenated pheS and rpoA sequence similarities. Strain N163-3-2T had 74.4-81.7% ANI, 22.6-23.9% dDDH, and 74.0-75.1% AAI values with L. baoqingensis 47-3T, L. manihotivorans DSM 13343T and L. porcinae JCM 19617T, less than the threshold for species demarcation (95-96%, 70% and 95-96%, respectively), indicating that strain N163-3-2T represented a novel species of the genus Lacticaseibacillus. Based upon the data obtained in the present study, a novel species, Lacticaseibacillus jixiensis sp. nov., is proposed, and the type strain is N163-3-2T (= CCTCC AB 2024125T = JCM 36999T).

Role of Nrf2/HO-1 pathway on inhibiting activation of ChTLR15/ChNLRP3 inflammatory pathway stimulated by E. tenella sporozoites

The aim of this study is to explore whether Nrf2 antioxidant pathway negatively regulates the ChTLR15/NLRP3 inflammatory pathway stimulated by Eimeria tenella infection. Firstly, levels of molecules in the Nrf2/HO-1 pathway in DF-1 cells pre-treated with an optimized dose of Corilagine or probiotics Levilactobacillus brevis 23017 were quantified using real-time PCR (qRT-PCR) and Western blot. Then, DF-1 cells pre-treated with Corilagine or L. brevis 23017 were stimulated with E. tenella sporozoites, and mRNA levels of molecules in Nrf2/HO-1 and ChTLR15/NLRP3 pathways, protein levels of p-Nrf2, Nrf2, HO-1, ChTLR15 and ChNLRP3, levels of malondialdehyde (MDA) and reactive oxygen species (ROS) were quantified. Further, expression level of Nrf2 and ChTLR15 in DF-1 cells was knocked down by RNA interfering (RNAi) method, and target cells were pre-treated with Corilagine or L. brevis 23017, followed by stimulation with E. tenella sporozoites, and the expression levels of key molecules in Nrf2/HO-1 and ChTLR15/NLRP3 pathways were quantified. The results showed that mRNA and protein levels of key molecules in the Nrf2/HO-1 pathway in DF-1 cells was significantly upregulated after pretreating with 15 μM Corilagine and supernatant of L. brevis 23017. After stimulating with E. tenella sporozoites, levels of molecules in the ChTLR15/NLRP3 pathway, levels of MDA and ROS in DF-1 cells pre-treated with 15 μM Corilagine or bacterial supernatant were all significantly down-regulated. The results from the knock-down experiment also displayed that Corrigine and L. brevis 23017 inhibited the activation of the ChTLR15/ChNLRP3 inflammatory pathway stimulated by E. tenella sporozoites through activating Nrf2/HO-1 antioxidant pathway. This study provides new ideas for the development of novel anticoccidial products.

Lactiplantibacillus paraxiangfangensis sp. nov., isolated from traditional Chinese pickle

Three Gram-stain-positive bacterial strains (designated 231-9T, 142-6 and 463-4) were isolated from traditional Chinese pickle, and were characterized using a polyphasic taxonomic approach. Results of 16S rRNA gene sequence analysis indicated that strains 231-9T, 142-6 and 463-4 were phylogenetically related to the type strains of Lactiplantibacillus xiangfangensis, Lactiplantibacillus garii, Lactiplantibacillus carotarum, Lactiplantibacillus plajomi and Lactiplantibacillus modestisalitolerans, having 98.6-99.9 % 16S rRNA gene sequence similarities. Strains 231-9T, 142-6 and 463-4 were most closely related to the type strain of L. xiangfangensis, having 99.9 % 16S rRNA gene, 95.6 % pheS, 99.4 % rpoA and 98.2 % concatenated pheS and rpoA sequence similarities. Relatively low pheS (95.6 %) sequence similarity indicated that strain 231-9T should be further identified. Strain 231-9T shared 99.7-99.9 % average nucleotide identity (ANI) and 98.8-98.9 % digital DNA-DNA hybridization (dDDH) values with strains 142-6 and 463-4, indicating that they belonged to the same species. The ANI and dDDH values between strain 231-9T and L. xiangfangensis LMG 26013T were 92.4-92.9 and 49.6 %, respectively, less than the threshold for species demarcation (95-96% ANI and 70 % dDDH values, respectively), indicating that strains 231-9T, 142-6 and 463-4 represented a novel species within the genus Lactiplantibacillus. Acid production from d-ribose, d-adonitol, d-galactose and lactose, activity of β-galactosidase and β-glucosidase, Voges-Proskauer reaction, hydrolysis of hippurate, resistance to 5 µg ml-1 erythromycin, 100 µg ml-1 tetracycline hydrochloride, 50 µg ml-1 bacitracin, 300 µg ml-1 each of gentamicin sulphate, streptomycin sulphate and neomycin sulphate, tolerance to 6 % NaCl could distinguish strains 231-9T, 142-6 and 463-4 from L. xiangfangensis 3.1.1T. Based upon the data of polyphasic characterization obtained in the present study, a novel species, Lactiplantibacillus paraxiangfangensis sp. nov., is proposed and the type strain is 231-9T (=JCM 36258T=CCTCC AB 2023133T).

Lactiplantibacillus brownii sp. nov., a novel psychrotolerant species isolated from sauerkraut

A Gram-stain-positive, rod-shaped, facultatively anaerobic and homofermentative strain, named WILCCON 0030T, was isolated from sauerkraut (fermented cabbage) collected from a local market in the Moscow region of Russia. Comparative analyses based on 16S rRNA gene sequence similarity and whole genome relatedness indicated that strain WILCCON 0030T was most closely related to the type strains Lactiplantibacillus nangangensis NCIMB 15186T, Lactiplantibacillus daoliensis LMG 31171T and Lactiplantibacillus pingfangensis LMG 31176T. However, the average nucleotide identity and digital DNA-DNA hybridization prediction values with these closest relatives only ranged from 84.6 to 84.9 % and from 24.1 to 24.7 %, respectively, and were below the 95.0 and 70.0% thresholds for species delineation. Substantiated by further physiological and biochemical analyses, strain WILCCON 0030T represents a novel species within the genus Lactiplantibacillus for which we propose the name Lactiplantibacillus brownii sp. nov. (type strain WILCCON 0030T=DSM 116485T=LMG 33211T).

Optimization of a cultivation procedure to selectively isolate lactic acid bacteria from insects

AIMS

Natural niches and transmission routes of lactic acid bacteria (LAB) are highly versatile. Proposed routes of transmission to food fermentations are from plant material via insects or vice versa. This study aimed to establish a method for the selective isolation of LAB from insects.

METHODS AND RESULTS

Varied parameters that influence growth and selectivity are temperature, type of carbohydrate and atmosphere. Additionally, effects of antibiotics to suppress non-LAB species were evaluated. A model consortium consisting of 12 species representing different lifestyles was inoculated in growth medium to identify conditions for highest diversity and recovery rate. The method was applied to isolate LAB from Drosophila melanogaster, Sitotroga cerealella, Tribolium castaneum and Tenebrio molitor. Isolated species were Leuconostoc mesenteroides, Paucilactobacillus vaccinostercus and Lactiplantibacillus plantarum from D. melanogaster and L. mesenteroides, Pediococcus pentosaceus and Latilactobacillus curvatus from T. molitor. No LAB could be isolated from T. castaneum and S. cerealella. 16S rDNA amplicon sequencing of DNA obtained from insects corroborated part of our results.

CONCLUSION

A combination of different enrichment conditions ensures a high probability to isolate LAB species from insects and can be helpful above already known non-cultivation methods.

SIGNIFICANCE AND IMPACT OF THE STUDY

The novel method allows to selectively isolate LAB from insects and the strategy of the method is of interest to study other niches.

Lacticaseibacillus absianus sp. nov., isolated from the cecum of a mini-pig

A rod-shaped, facultative anaerobic, Gram-stain-positive bacteria, isolated from the cecum of a mini-pig, was designated as strain YH-lac23^T. Analysis of 16S rRNA gene sequences revealed that the strain was closely related to Lacticaseibacillus daqingensis JCM 33273^T (97.9 %), Lacticaseibacillus porcinae KCTC 21027^T (96.2 %) and Lacticaseibacillus manihotivorans KCTC 21010^T (95.7 %). Analysis of housekeeping gene sequences (pheS and recA) revealed that the strain formed a sub-cluster with L. daqingensis. The average nucleotide identity value for YH-lac23^T and its most closely related strain (L. daqingensis) is 80.7 %. The main fatty acids are C_18 : 1ω9c and C_16 : 0. The cell wall contains the peptidoglycan of meso-diaminopimelic acid. The G+C content of the genomic DNA is 59.8 mol%. In view of the chemotaxonomic, phenotypic and phylogenetic properties, YH-lac23^T (=KCTC 25006=JCM 33998) represents a novel taxon. The name Lacticaseibacillus absianus sp. nov. is proposed.

The Potential of Lactobacillus spp. for Modulating Oxidative Stress in the Gastrointestinal Tract

The gastrointestinal (GI) tract is crucial for food digestion and nutrient absorption in humans. However, the GI tract is usually challenged with oxidative stress that can be induced by various factors, such as exogenous pathogenic microorganisms and dietary alterations. As a part of gut microbiota, Lactobacillus spp. play an important role in modulating oxidative stress in cells and tissues, especially in the GI tract. Oxidative stress is linked with excessive reactive oxygen species (ROS) that can be formed by a few enzymes, such as nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs). The redox mechanisms of Lactobacillus spp. may contribute to the downregulation of these ROS-forming enzymes. In addition, nuclear factor erythroid 2 (NFE2)-related factor 2 (Nrf-2) and nuclear factor kappa B (NF-κB) are two common transcription factors, through which Lactobacillus spp. modulate oxidative stress as well. As oxidative stress is closely associated with inflammation and certain diseases, Lactobacillus spp. could potentially be applied for early treatment and amelioration of these diseases, either individually or together with prebiotics. However, further research is required for revealing their mechanisms of action as well as their extensive application in the future.

Proposal of Lactobacillus kosoi Chiou et al. 2018 as a later heterotypic synonym of Lactobacillus micheneri McFrederick et al. 2018, elevation of Lactobacillus plantarum subsp. argentoratensis to the species level as Lactobacillus argentoratensis sp. nov., and Lactobacillus zhaodongensis sp. nov., isolated from traditional Chinese pickle and the intestinal tract of a honey bee (Apis mellifera)

Lactobacillus kosoi Chiou et al. 2018 and Lactobacillus micheneri McFrederick et al. 2018 are closely related, and they share 100 % 16S rRNA gene sequence similarity, 99.6 % pheS gene sequence similarity, 100 % rpoA gene sequence similarity, 97.3 % average nucleotide identity (ANI) value and 76.6 % in silico DNA-DNA hybridization (isDDH) value, indicating that they represent the same species. Fatty acid methyl esters (FAME) analysis and phenotypic characterization also indicated that L. kosoi and L. micheneri are very similar. We propose L. kosoi Chiou et al. 2018 as a later heterotypic synonym of L. micheneri McFrederick et al. 2018. The taxonomic position of Lactobacillus plantarum subsp. argentoratensis in the L. plantarum group was re-examined using a polyphasic approach, including sequence analyses of 16S rRNA, pheS, rpoA and recA genes, average nucleotide identity analysis, in silico DNA-DNA hybridization, fatty acid methyl ester analysis and phenotypic characterization. Results of 16S rRNA gene sequence analysis indicated that L. plantarum subsp. argentoratensis was closely related to L. plantarum subsp. plantarum, L. pentosus and L. paraplantarum in the L. plantarum group, sharing 99.6-99.7 % 16S rRNA gene sequence similarities. Results of pheS, rpoA and recA gene sequence analyses indicated that L. plantarum subsp. argentoratensis was most closely related to L. plantarum subsp. plantarum, having 91.8 % pheS gene sequence similarity, 98.9 % rpoA gene sequence similarity and 93.1 % recA gene sequence similarity. L. plantarum subsp. argentoratensis DSM 16365^T shared 95.6 % ANI value and 62.9 % isDDH value with L. plantarum subsp. plantarum ATCC 14917^T. The low isDDH value confirmed that L. plantarum subsp. argentoratensis and L. plantarum subsp. plantarum represent two different species, rather than two different subspecies in the L. plantarum group. On the basis of the data from polyphasic characterization obtained in the present study and in previous studies, L. plantarum subsp. argentoratensis is elevated to the species level and represents a novel species of the genus Lactobacillus, for which the name Lactobacillus argentoratensis sp. nov. is proposed and the type strain is DKO 22^T (=CIP 108320^T=DSM 16365^T=JCM 16169^T). Two novel Gram-stain-positive bacterial strains, designated 1206-1^T and F027-1-2, were isolated from traditional pickle in Heilongjiang Province, PR China, and from the intestinal tract of a honey bee (Apis mellifera) in Hubei Province, PR China, respectively. The two bacteria were characterized by a polyphasic approach, including 16S rRNA gene sequence analysis, pheS gene sequence analysis, rpoA gene sequence analysis, fatty acid methyl ester analysis, average nucleotide identity analysis, in silico DNA-DNA hybridization analysis and an analysis of phenotypic features. The results of 16S rRNA gene sequence analysis indicated that strains 1206-1^T and F027-1-2 were distantly related to Lactobacillus sharpeae, Lactobacillus hulanensis, Lactobacillus songhuajiangensis, Lactobacillus pantheris, Lactobacillus thailandensis, Lactobacillus camelliae, Lactobacillus jixianensis, Lactobacillus nasuensis, Lactobacillus baoqingensis, Lactobacillus manihotivorans and Lactobacillus porcinae. Strain 1206-1^T exhibited 94.2-96.4 % 16S rRNA gene sequence similarities, 69.5-83.3 % pheS gene sequence similarities and 73.1-90.3 % rpoA gene sequence similarities to type strains of phylogenetically related species. ANI and isDDH values between strain 1206-1^T and the type strains of phylogenetically related species were 52.7-73.7 % and 21.1-30.1 %, respectively. On the basis of the data obtained in the present study, a novel species, Lactobacillus zhaodongensis sp. nov. is proposed and the type strain is 1206-1^T (=CCM 8981^T=CCTCC AB 2019200^T=LMG 31620^T).

Complete Genome Sequence of Lactobacillus nenjiangensis SH-Y15, Isolated from Sauerkraut

We isolated a strain of Lactobacillus nenjiangensis named SH-Y15 from traditional suan-cai used in northeastern China because it has a high capacity for degrading nitrites at low temperatures. The complete genome of SH-Y15 contains a single circular chromosome and a plasmid. The complete length is 2,249,893 bp, and the G+C content is 39.68%.

We isolated a strain of Lactobacillus nenjiangensis named SH-Y15 from traditional suan-cai used in northeastern China because it has a high capacity for degrading nitrites at low temperatures. The complete genome of SH-Y15 contains a single circular chromosome and a plasmid. The complete length is 2,249,893 bp, and the G+C content is 39.68%.

A taxonomic note on the genus Lactobacillus: Description of 23 novel genera, emended description of the genus Lactobacillus Beijerinck 1901, and union of Lactobacillaceae and Leuconostocaceae

The genus Lactobacillus comprises 261 species (at March 2020) that are extremely diverse at phenotypic, ecological and genotypic levels. This study evaluated the taxonomy of Lactobacillaceae and Leuconostocaceae on the basis of whole genome sequences. Parameters that were evaluated included core genome phylogeny, (conserved) pairwise average amino acid identity, clade-specific signature genes, physiological criteria and the ecology of the organisms. Based on this polyphasic approach, we propose reclassification of the genus Lactobacillus into 25 genera including the emended genus Lactobacillus, which includes host-adapted organisms that have been referred to as the Lactobacillus delbrueckii group, Paralactobacillus and 23 novel genera for which the names Holzapfelia, Amylolactobacillus, Bombilactobacillus, Companilactobacillus, Lapidilactobacillus, Agrilactobacillus, Schleiferilactobacillus, Loigolactobacilus, Lacticaseibacillus, Latilactobacillus, Dellaglioa, Liquorilactobacillus, Ligilactobacillus, Lactiplantibacillus, Furfurilactobacillus, Paucilactobacillus, Limosilactobacillus, Fructilactobacillus, Acetilactobacillus, Apilactobacillus, Levilactobacillus, Secundilactobacillus and Lentilactobacillus are proposed. We also propose to emend the description of the family Lactobacillaceae to include all genera that were previously included in families Lactobacillaceae and Leuconostocaceae. The generic term 'lactobacilli' will remain useful to designate all organisms that were classified as Lactobacillaceae until 2020. This reclassification reflects the phylogenetic position of the micro-organisms, and groups lactobacilli into robust clades with shared ecological and metabolic properties, as exemplified for the emended genus Lactobacillus encompassing species adapted to vertebrates (such as Lactobacillus delbrueckii, Lactobacillus iners, Lactobacillus crispatus, Lactobacillus jensensii, Lactobacillus johnsonii and Lactobacillus acidophilus) or invertebrates (such as Lactobacillus apis and Lactobacillus bombicola).

Lactobacillus hegangensis sp. nov., Lactobacillus suibinensis sp. nov., Lactobacillus daqingensis sp. nov., Lactobacillus yichunensis sp. nov., Lactobacillus mulanensis sp. nov., Lactobacillus achengensis sp. nov., Lactobacillus wuchangensis sp. nov., Lactobacillus gannanensis sp. nov., Lactobacillus binensis sp. nov. and Lactobacillus angrenensis sp. nov., isolated from Chinese traditional pickle and yogurt

Fourteen Gram-stain-positive bacterial strains were isolated from Chinese traditional pickle and yogurt. The strains were characterized using a polyphasic taxonomic approach, including 16S rRNA gene sequence analysis, pheS gene sequence analysis, rpoA gene sequence analysis, fatty acid methyl ester analysis, determination of DNA G+C content, determination of average nucleotide identity (ANI), in silico DNA–DNA hybridization (isDDH) and an analysis of phenotypic features. The data demonstrated that the 14 strains represented ten novel species belonging to the genus Lactobacillus , strains 73-4T, 247-3T, 143-4(a)T, 33-1T, 143-6T, 247-4T, 17-4T, 143-1T, 735-2T and M1530-1T were designated as the type strains. Strains 73-4T and 247-3T were phylogenetically related to the type strains of Lactobacillus camelliae and Lactobacillus jixianensis , having 97.0–98.9 % 16S rRNA gene sequence similarities, 83.9–87.2 % pheS gene sequence similarities and 86.8–93.3 % rpoA gene sequence similarities. Strains 143-4(a)T and 33-1T were phylogenetically related to the type strains of Lactobacillus rhamnosus , Lactobacillus paracasei and Lactobacillus casei , having 93.6–96.5 % 16S rRNA gene sequence similarities, 73.9–77.2 % pheS gene sequence similarities and 76.1–77.6 % rpoA gene sequence similarities. Strains 143-6T, 247-4T, 17-4T and 143-1T were phylogenetically related to the type strains of Lactobacillus concavus , Lactobacillus dextrinicus and Lactobacillus bayanensis , exhibiting 95.5–99.9 % 16S rRNA gene sequence similarities, 76.5–83.1 % pheS gene sequence similarities and 83.6–98.3 % rpoA gene sequence similarities. Strain 735-2T was phylogenetically related to the type strains of Lactobacillus zhaoyuanensis , Lactobacillus jiayinensis and Lactobacillus coryniformis , having 98.2–99.1 % 16S rRNA gene sequence similarities, 82.8–84.1 % pheS gene sequence similarities and 93.0–93.9 % rpoA gene sequence similarities. Strain M1530-1T was phylogenetically related to the type strains of Lactobacillus suantsaiihabitans and Lactobacillus brevis , having 99.5 and 99.0 % 16S rRNA gene sequence similarities, 90.3 and 81.7 % pheS gene sequence similarities and 97.7 and 91.1 % rpoA gene sequence similarities. The ANI and isDDH values between strains 73-4T, 247-3T, 143-4(a)T, 33-1T, 143-6T, 247-4T, 17-4T, 143-1T, 735-2T, M1530-1T and type strains of phylogenetically related species were less than 86.8 % and 33.9 % respectively, confirming that they represent ten novel species within the genus Lactobacillus . Based upon the data of polyphasic characterization obtained in the present study, ten novel species, Lactobacillus hegangensis sp. nov., Lactobacillus suibinensis sp. nov., Lactobacillus daqingensis sp. nov., Lactobacillus yichunensis sp. nov., Lactobacillus mulanensis sp. nov., Lactobacillus achengensis sp. nov., Lactobacillus wuchangensis sp. nov., Lactobacillus gannanensis sp. nov., Lactobacillus binensis sp. nov. and Lactobacillus angrenensis sp. nov., are proposed and the type strains are 73-4T (=NCIMB 15177T=CCM 8912T=CCTCC AB 2018407T), 247-3T (=NCIMB 15176T=JCM 33275T), 143-4(a)T (=NCIMB 15173T=CCM 8948T=JCM 33273T=CCTCC AB 2018390T), 33-1T (=NCIMB 15169T=CCM 8947T=JCM 33272T=CCTCC AB 2018405T), 143-6T (=NCIMB 15162T=CCM 8951T=JCM 33274T=CCTCC AB 2018411T), 247-4T (=NCIMB 15155T=CCM 8897T=LMG 31059T=CCTCC AB 2018410T), 17-4T (=NCIMB 15161T=CCM 8946T=JCM 33271T=CCTCC AB 2018406T), 143-1T (=NCIMB 15157T=CCM 8937T=CCTCC AB 2018409T), 735-2T (=NCIMB 15190T=CCM 8925T=LMG 31186T) and M1530-1T (=NCIMB 15150T=CCM 8893T=LMG 31046T=CCTCC AB 2018402T), respectively.

Applications of plant-based fermented foods and their microbes

Plant-based fermentations and their microbes provide an underexplored source for novel biotechnological applications. Recent advances in DNA sequencing technologies and analyses of sequencing data highlight that a diverse array of lactic acid bacteria (LAB) frequently dominate these plant fermentations. Because of the long history of safe LAB use in fermented foods, we argue here that various novel probiotic, synbiotic and a range of other industrial applications can be produced based on new insights in the functional and genetic potential of these LAB. To aid in this quest, comparative genomics tools are increasingly available enabling a more rational design of wet-lab experiments to screen for the most relevant properties. This is also true for the exploration of useful enzymatic and (secondary) metabolic production capacities of the LAB that can be isolated from these plant-based fermentations, such as the recent discovery of a cellulase enzyme in specific Lactobacillus plantarum group members.

Comparative genome analysis of Lactobacillus mudanjiangensis, an understudied member of the Lactobacillus plantarum group

The genus Lactobacillus is known to be extremely diverse and consists of different phylogenetic groups that show a diversity that is roughly equal to the expected diversity of a typical bacterial genus. One of the most prominent phylogenetic groups within this genus is the Lactobacillus plantarum group, which contains the understudied Lactobacillus mudanjiangensis species. Before this study, only one L. mudanjiangensis strain, DSM 28402^T, had been described, but without whole-genome analysis. In this study, three strains classified as L. mudanjiangensis were isolated from three different carrot juice fermentations and their whole-genome sequence was determined, together with the genome sequence of the type strain. The genomes of all four strains were compared with publicly available L. plantarum group genome sequences. This analysis showed that L. mudanjiangensis harboured the second largest genome size and gene count of the whole L. plantarum group. In addition, all members of this species showed the presence of a gene coding for a cellulose-degrading enzyme. Finally, three of the four L. mudanjiangensis strains studied showed the presence of pili on scanning electron microscopy (SEM) images, which were linked to conjugative gene regions, coded on a plasmid in at least two of the strains studied.

Evaluation of Plantaricin Genes Expression During Fermentation of Raphanus sativus Roots with a Plantaricin-Producing Lactobacillus plantarum Starter

The aim of the present study was to assess the transcription of the plnE/F, plnN, plnG, plnD and plnI genes during lactic acid fermentation of radish (Raphanus sativus) roots by Lactobacillus plantarum strain LQC 740 at 20 and 30 °C. At both temperatures, this strain dominated the fermentation process, as indicated by (GTG)₅ analysis. A total of five pln genes were detected in the genome of this strain, namely plnE/F, plnN, plnG, plnD and plnI. Regarding plantaricin genes expression, no regulation was observed in the majority of the samples at both temperatures, therefore, the transcription of the pln genes was not affected by the experimental conditions, i.e. radish fermentation vs. growth in MRS broth. Although transcription of the pln genes was similar between the two conditions, bacteriocin activity was different. The maximum plantaricin activity was 87.5 AU/mL during radish fermentation and 700 AU/mL during growth in MRS broth. Thus, no apparent correlation between bacteriocin activity and transcription level of the five pln genes could be established.

Microbial Ecology and Process Technology of Sourdough Fermentation

From a microbiological perspective, sourdough is to be considered as a specific and stressful ecosystem, harboring yeasts and lactic acid bacteria (LAB), that is used for the production of baked goods. With respect to the metabolic impact of the sourdough microbiota, acidification (LAB), flavor formation (LAB and yeasts), and leavening (yeasts and heterofermentative LAB species) are most noticeable. Three distinct types of sourdough fermentation processes can be discerned based on the inocula applied, namely backslopped ones (type 1), those initiated with starter cultures (type 2), and those initiated with a starter culture followed by backslopping (type 3). A sourdough-characteristic LAB species is Lactobacillus sanfranciscensis. A sourdough-characteristic yeast species is Candida humilis. Although it has been suggested that the microbiota of a specific sourdough may be influenced by its geographical origin, region specificity often seems to be an artefact resulting from interpretation of the research data, as those are dependent on sampling, isolation, and identification procedures. It is however clear that sourdough-adapted microorganisms are able to withstand stress conditions encountered during their growth. Based on the technological setup, type 0 (predoughs), type I (artisan bakery firm sourdoughs), type II (industrial liquid sourdoughs), and type III sourdoughs (industrial dried sourdoughs) can be distinguished. The production of all sourdoughs, independent of their classification, depends on several intrinsic and extrinsic factors. Both the flour (type, quality status, etc.) and the process parameters (fermentation temperature, pH and pH evolution, dough yield, water activity, oxygen tension, backslopping procedure and fermentation duration, etc.) determine the dynamics and outcome of (backslopped) sourdough fermentation processes.

Lactobacillus oligofermentans glucose, ribose and xylose transcriptomes show higher similarity between glucose and xylose catabolism-induced responses in the early exponential growth phase

BACKGROUND

Lactobacillus oligofermentans has been mostly isolated from cold-stored packaged meat products in connection with their spoilage, but its precise role in meat spoilage is unknown. It belongs to the L. vaccinostercus group of obligate heterofermentative lactobacilli that generally ferment pentoses (e.g. xylose and ribose) more efficiently than hexoses (e.g. glucose). However, more efficient hexose utilization can be induced. The regulation mechanisms of the carbohydrate catabolism in such bacteria have been scarcely studied. To address this question, we provided the complete genome sequence of L. oligofermentans LMG 22743(T) and generated time course transcriptomes during its growth on glucose, ribose and xylose.

RESULTS

The genome was manually annotated and its main functional features were examined. L. oligofermentans was confirmed to be able to efficiently utilize several hexoses and maltose, which is, presumably, induced by its repeated cultivation with glucose in vitro. Unexpectedly, in the beginning of the exponential growth phase, glucose- and xylose-induced transcriptome responses were more similar, whereas toward the end of the growth phase xylose and ribose transcriptomes became more alike. The promoter regions of genes simultaneously upregulated both on glucose and xylose in comparison with ribose (particularly, hexose and xylose utilization genes) were found to be enriched in the CcpA- binding site. Transcriptionally, no glucose-induced carbon catabolite repression was detected. The catabolism of glucose, which requires initial oxidation, led to significant overexpression of the NAD(P)H re-oxidation genes, the upstream regions of which were found to contain a motif, which was highly similar to a Rex repressor binding site.

CONCLUSIONS

This paper presents the second complete genome and the first study of carbohydrate catabolism-dependent transcriptome response for a member of the L. vaccinostercus group. The transcriptomic changes detected in L. oligofermentans for growth with different carbohydrates differ significantly from those of facultative heterofermentative lactobacilli. The mechanism of CcpA regulation, putatively contributing to the observed similarities between glucose- and xylose-induced transcriptome responses and the absence of stringent carbon catabolite control, requires further studies. Finally, the cell redox balance maintenance, in terms of the NAD(P)+/NAD(P)H ratio, was predicted to be regulated by the Rex transcriptional regulator, supporting the previously made inference of Rex-regulons for members of the Lactobacillaceae family.

Lactobacillus herbarum sp. nov., a species related to Lactobacillus plantarum

Strain TCF032-E4 was isolated from a traditional Chinese fermented radish. It shares >99% 16S rRNA sequence identity with L. plantarum, L. pentosus and L. paraplantarum. This strain can ferment ribose, galactose, glucose, fructose, mannose, mannitol, N-acetylglucosamine, amygdalin, arbutin, salicin, cellobiose, maltose, lactose, melibiose, trehalose and gentiobiose. It cannot ferment sucrose, which can be used by L. pentosus, L. paraplantarum, L. fabifermentans, L. xiangfangensis and L. mudanjiangensis, as well as most of the L. plantarum strains (88.7%). TCF032-E4 cannot grow at temperature above 32 °C. This strain shares 78.2–83.6% pheS (phenylalanyl-tRNA synthetase alpha subunit) and 89.5–94.9% rpoA (RNA polymerase alpha subunit) sequence identity with L. plantarum, L. pentosus, L. paraplantarum, L. fabifermentans, L. xiangfangensis and L. mudanjiangensis. These results indicate that TCF032-E4 represents a distinct species. This hypothesis was further confirmed by whole-genome sequencing and comparison with available genomes of related species. The draft genome size of TCF032-E4 is approximately 2.9 Mb, with a DNA G+C content of 43.5 mol%. The average nucleotide identity (ANI) between TCF032-E4 and related species ranges from 79.0 to 81.1%, the highest ANI value being observed with L. plantarum subsp. plantarum ATCC 14917T. A novel species, Lactobacillus herbarum sp. nov., is proposed with TCF032-E4T ( = CCTCC AB2015090T = DSM 100358T) as the type strain.

Lactobacillus plajomi sp. nov. and Lactobacillus modestisalitolerans sp. nov., isolated from traditional fermented foods

Three Lactobacillus-like strains, NB53T, NB446T and NB702, were isolated from traditional fermented food in Thailand. Comparative 16S rRNA gene sequence analysis indicated that these strains belong to the Lactobacillus plantarum group. Phylogenetic analysis based on the dnaK, rpoA, pheS and recA gene sequences indicated that these three strains were distantly related to known species present in the L. plantarum group. DNA–DNA hybridization with closely related strains demonstrated that these strains represented two novel species; the novel strains could be differentiated based on chemotaxonomic and phenotypic characteristics. Therefore, two novel species of the genus Lactobacillus, Lactobacillus plajomi sp. nov. (NB53T) and Lactobacillus modestisalitolerans sp. nov. (NB446T and NB702), are proposed with the type strains NB53T ( = NBRC 107333T = BCC 38054T) and NB446T ( = NBRC 107235T = BCC 38191T), respectively.

Complete genome sequence and analysis of Lactobacillus hokkaidonensis LOOC260(T), a psychrotrophic lactic acid bacterium isolated from silage

Background

Lactobacillus hokkaidonensis is an obligate heterofermentative lactic acid bacterium, which is isolated from Timothy grass silage in Hokkaido, a subarctic region of Japan. This bacterium is expected to be useful as a silage starter culture in cold regions because of its remarkable psychrotolerance; it can grow at temperatures as low as 4°C. To elucidate its genetic background, particularly in relation to the source of psychrotolerance, we constructed the complete genome sequence of L. hokkaidonensis LOOC260^T using PacBio single-molecule real-time sequencing technology.

Results

The genome of LOOC260^T comprises one circular chromosome (2.28 Mbp) and two circular plasmids: pLOOC260-1 (81.6 kbp) and pLOOC260-2 (41.0 kbp). We identified diverse mobile genetic elements, such as prophages, integrated and conjugative elements, and conjugative plasmids, which may reflect adaptation to plant-associated niches. Comparative genome analysis also detected unique genomic features, such as genes involved in pentose assimilation and NADPH generation.

Conclusions

This is the first complete genome in the L. vaccinostercus group, which is poorly characterized, so the genomic information obtained in this study provides insight into the genetics and evolution of this group. We also found several factors that may contribute to the ability of L. hokkaidonensis to grow at cold temperatures. The results of this study will facilitate further investigation for the cold-tolerance mechanism of L. hokkaidonensis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1435-2) contains supplementary material, which is available to authorized users.