Characterization and electrotransformation of Lactobacillus crispatus isolated from chicken crop and intestine

Changes in the intestinal microbiota of broiler chicken induced by dietary supplementation of the diatomite-bentonite mixture

BACKGROUND

Diatomite is a source of biologically available silicon but in feed industry its insecticide and anti-caking properties have been also widely recognized. The aim of the study was to evaluate the effect of dietary diatomite-bentonite mixture (DBM) supplementation on the quantitative and qualitative composition of the bacterial microbiome of the broiler chicken gut. The trial was carried out on 960 Ross 308 broiler chickens divided into 2 experimental groups throughout the entire rearing period lasting 6 weeks. The birds were fed complete granulated diets without (group C) or with DBM (group E) in an amount of 1% from the 11 day of life. Two nutritionally balanced diets were used, tailored to the age of the broilers: a grower diet (from day 11 to 34) and a finisher diet (from day 35 to 42 of life).

RESULTS

Diatomite used in a mixture with bentonite significantly altered the microbiome. Restricting the description to species that comprise a minimum of 1% of all analyzed sequences, 36 species in group E (with diatomite) and 30 species in group C (without diatomite) were selected. Several bacteria species were identified in intestinal contents of chickens for the first time. Thirteen species occurred only in group E: Agathobaculum butyriciproducens, Anaerobutyricum hallii, Anaerobutyricum soehngenii, Blautia producta ATCC 27,340 = DSM 2950, Gordonibacter pamelaeae 7-10-1-b, Helicobacter pullorum NCTC 12,824, Lactobacillus crispatus, L. helveticus DSM 20,075 = CGMCC 1.1877, Mucispirillum schaedleri, Phascolarctobacterium faecium, Phocaeicola coprocola DSM 17,136, P. massiliensis, and Ruthenibacterium lactatiformans.

CONCLUSIONS

The findings highlight the intricate and potentially consequential relationship between diet, specifically diatomite-bentonite mixture supplementation, and gut microbiota composition.

Modified vaginal lactobacilli expressing fluorescent and luminescent proteins for more effective monitoring of their release from nanofibers, safety and cell adhesion

Electrospun nanofibers offer a highly promising platform for the delivery of vaginal lactobacilli, providing an innovative approach to preventing and treating vaginal infections. To advance the application of nanofibers for the delivery of lactobacilli, tools for studying their safety and efficacy in vitro need to be established. In this study, fluorescent (mCherry and GFP) and luminescent (NanoLuc luciferase) proteins were expressed in three vaginal lactobacilli (Lactobacillus crispatus, Lactobacillus gasseri and Lactobacillus jensenii) and a control Lactiplantibacillus plantarum with the aim to use this technology for close tracking of lactobacilli release from nanofibers and their adhesion on epithelial cells. The recombinant proteins influenced the growth of the bacteria, but not their ability to produce hydrogen peroxide. Survival of lactobacilli in nanofibers immediately after electrospinning varied among species. Bacteria retained fluorescence upon incorporation into PEO nanofibers, which was vital for evaluation of their rapid release. In addition, fluorescent labelling facilitated efficient tracking of bacterial adhesion to Caco-2 epithelial cells, while luminescence provided important quantitative insights into bacterial attachment, which varied from 0.5 to 50% depending on the species. The four lactobacilli in dispersion or in nanofibers were not detrimental for the viability of Caco-2 cells, and did not demonstrate hemolytic activity highlighting the safety profiles of both bacteria and PEO nanofibers. To summarize, this study contributes to the development of a promising delivery system, tailored for local administration of safe vaginal lactobacilli.

Engineered reporter phages for detection of Escherichia coli, Enterococcus, and Klebsiella in urine

The rapid detection and species-level differentiation of bacterial pathogens facilitates antibiotic stewardship and improves disease management. Here, we develop a rapid bacteriophage-based diagnostic assay to detect the most prevalent pathogens causing urinary tract infections: Escherichia coli, Enterococcus spp., and Klebsiella spp. For each uropathogen, two virulent phages were genetically engineered to express a nanoluciferase reporter gene upon host infection. Using 206 patient urine samples, reporter phage-induced bioluminescence was quantified to identify bacteriuria and the assay was benchmarked against conventional urinalysis. Overall, E. coli, Enterococcus spp., and Klebsiella spp. were each detected with high sensitivity (68%, 78%, 87%), specificity (99%, 99%, 99%), and accuracy (90%, 94%, 98%) at a resolution of ≥10³ CFU/ml within 5 h. We further demonstrate how bioluminescence in urine can be used to predict phage antibacterial activity, demonstrating the future potential of reporter phages as companion diagnostics that guide patient-phage matching prior to therapeutic phage application.

Engineering of Vaginal Lactobacilli to Express Fluorescent Proteins Enables the Analysis of Their Mixture in Nanofibers

Lactobacilli are a promising natural tool against vaginal dysbiosis and infections. However, new local delivery systems and additional knowledge about their distribution and mechanism of action would contribute to the development of effective medicine. This will be facilitated by the introduction of the techniques for effective, inexpensive, and real-time tracking of these probiotics following their release. Here, we engineered three model vaginal lactobacilli (Lactobacillus crispatus ATCC 33820, Lactobacillus gasseri ATCC 33323, and Lactobacillus jensenii ATCC 25258) and a control Lactobacillus plantarum ATCC 8014 to express fluorescent proteins with different spectral properties, including infrared fluorescent protein (IRFP), green fluorescent protein (GFP), red fluorescent protein (mCherry), and blue fluorescent protein (mTagBFP2). The expression of these fluorescent proteins differed between the Lactobacillus species and enabled quantification and discrimination between lactobacilli, with the longer wavelength fluorescent proteins showing superior resolving power. Each Lactobacillus strain was labeled with an individual fluorescent protein and incorporated into poly (ethylene oxide) nanofibers using electrospinning, as confirmed by fluorescence and scanning electron microscopy. The lactobacilli retained their fluorescence in nanofibers, as well as after nanofiber dissolution. To summarize, vaginal lactobacilli were incorporated into electrospun nanofibers to provide a potential solid vaginal delivery system, and the fluorescent proteins were introduced to distinguish between them and allow their tracking in the future probiotic-delivery studies.

The Composition and Concordance of Lactobacillus Populations of Infant Gut and the Corresponding Breast-Milk and Maternal Gut

The maternal gut is the principal source of commensal bacteria in the infant gut during the lactation stage, where breast milk acts as an intermediary for the transfer of potential probiotic bacteria consortia, including Lactobacillus. This study aimed to characterize the bacterial communities in human milk, maternal, and infant feces in a small yet very homogeneous cohort of 25 healthy mother–infant pairs in northwestern China (n = 25, infant age from 7 days to 2 years), with special emphasis on the cooccurrence and vertical transfer of Lactobacillus phylotypes at the species or strain level in mother-breast milk-infant triads. Accurate sequencing analysis revealed that among 73 Lactobacillus zero-radius operational classification units (ZOTUs) identified, 58 belonging to 18 recognized species or species groups were distributed in all three types of samples. Lactobacillus ruminis, L. mucosae and L. gasseri-johnsonii as true residents were the most represented in all three ecosystems, whereas the content of Lactobacillus phylotypes commonly developed as probiotics was not dominant. While the numbers of Lactobacillus species in breast milk and infant feces were greater than that in maternal feces, principal coordinates analysis (PCoA) based on beta diversity, coupled with the frequency of isolates determined by culture methods, showed that the Lactobacillus community in the infant gut was more similar to that in the maternal gut than to that in breast milk, suggesting that the gut is niche selective for Lactobacillus populations. In addition, identical strains of L. ruminis, L. paracasei, L. mucosae and L. salivarius were isolated from multiple mother–infant pairs, supporting the hypothesis that vertical transfer of bacteria via breastfeeding contributes to the initial establishment of the microbiota in the developing infant intestine.

Critical Anti-CRISPR Locus Repression by a Bi-functional Cas9 Inhibitor

Bacteriophages must rapidly deploy anti-CRISPR proteins (Acrs) to inactivate the RNA-guided nucleases that enforce CRISPR-Cas adaptive immunity in their bacterial hosts. Listeria monocytogenes temperate phages encode up to three anti-Cas9 proteins, with acrIIA1 always present. AcrIIA1 binds and inhibits Cas9 with its C-terminal domain; however, the function of its highly conserved N-terminal domain (NTD) is unknown. Here, we report that the AcrIIA1^NTD is a critical transcriptional repressor of the strong anti-CRISPR promoter. A rapid burst of anti-CRISPR transcription occurs during phage infection and the subsequent negative feedback by AcrIIA1^NTD is required for optimal phage replication, even in the absence of CRISPR-Cas immunity. In the presence of CRISPR-Cas immunity, full-length AcrIIA1 uses its two-domain architecture to act as a "Cas9 sensor," tuning acr expression according to Cas9 levels. Finally, we identify AcrIIA1^NTD homologs in other Firmicutes and demonstrate that they have been co-opted by hosts as "anti-anti-CRISPRs," repressing phage anti-CRISPR deployment.

Comparative Genomics of Lactobacillus crispatus from the Gut and Vagina Reveals Genetic Diversity and Lifestyle Adaptation

Lactobacillus crispatus colonizes the human feces, human vagina, and the crops and ceca of chicken. To explore the genetic characteristics and evolutionary relationships of L. crispatus isolated from different niches, we selected 37 strains isolated from the human vagina (n = 17), human feces (n = 11), and chicken feces (n = 9), and used comparative genomics to explore the genetic information of L. crispatus from the feces and vagina. No significant difference was found in the three sources of genomic features such as genome size, GC content, and number of protein coding sequences (CDS). However, in a phylogenetic tree constructed based on core genes, vagina-derived L. crispatus and feces-derived strains were each clustered separately. Therefore, the niche exerted an important impact on the evolution of L. crispatus. According to gene annotation, the L. crispatus derived from the vagina possessed a high abundance of genes related to acid tolerance, redox reactions, pullulanase, and carbohydrate-binding modules (CBMs). These genes helped L. crispatus to better adapt to the acidic environment of the vagina and obtain more nutrients, maintaining its dominance in the vagina in competition with other strains. In feces-derived bacteria, more genes encoding CRISPR/Cas system, glycoside hydrolases (GHs) family, and tetracycline/lincomycin resistance genes were found to adapt to the complex intestinal environment. This study highlights the evolutionary relationship of L. crispatus strains isolated from the vagina and feces, and the adaptation of L. crispatus to the host environment.

Assembly of hundreds of novel bacterial genomes from the chicken caecum

Background

Chickens are a highly important source of protein for a large proportion of the human population. The caecal microbiota plays a crucial role in chicken nutrition through the production of short-chain fatty acids, nitrogen recycling, and amino acid production. In this study, we sequence DNA from caecal content samples taken from 24 chickens belonging to either a fast or a slower growing breed consuming either a vegetable-only diet or a diet containing fish meal.

Results

We utilise 1.6 T of Illumina data to construct 469 draft metagenome-assembled bacterial genomes, including 460 novel strains, 283 novel species, and 42 novel genera. We compare our genomes to data from 9 European Union countries and show that these genomes are abundant within European chicken flocks. We also compare the abundance of our genomes, and the carbohydrate active enzymes they produce, between our chicken groups and demonstrate that there are both breed- and diet-specific microbiomes, as well as an overlapping core microbiome.

Conclusions

This data will form the basis for future studies examining the composition and function of the chicken caecal microbiota.

Genome editing using the endogenous type I CRISPR-Cas system in Lactobacillus crispatus

CRISPR-Cas systems are now widely used for genome editing and transcriptional regulation in diverse organisms. The compact and portable nature of class 2 single effector nucleases, such as Cas9 or Cas12, has facilitated directed genome modifications in plants, animals, and microbes. However, most CRISPR-Cas systems belong to the more prevalent class 1 category, which hinges on multiprotein effector complexes. In the present study, we detail how the native type I-E CRISPR-Cas system, with a 5'-AAA-3' protospacer adjacent motif (PAM) and a 61-nucleotide guide CRISPR RNA (crRNA) can be repurposed for efficient chromosomal targeting and genome editing in Lactobacillus crispatus, an important commensal and beneficial microbe in the vaginal and intestinal tracts. Specifically, we generated diverse mutations encompassing a 643-base pair (bp) deletion (100% efficiency), a stop codon insertion (36%), and a single nucleotide substitution (19%) in the exopolysaccharide priming-glycosyl transferase (p-gtf). Additional genetic targets included a 308-bp deletion (20%) in the prophage DNA packaging Nu1 and a 730-bp insertion of the green fluorescent protein gene downstream of enolase (23%). This approach enables flexible alteration of the formerly genetically recalcitrant species L. crispatus, with potential for probiotic enhancement, biotherapeutic engineering, and mucosal vaccine delivery. These results also provide a framework for repurposing endogenous CRISPR-Cas systems for flexible genome targeting and editing, while expanding the toolbox to include one of the most abundant and diverse systems found in nature.

A functional type II-A CRISPR-Cas system from Listeria enables efficient genome editing of large non-integrating bacteriophage

CRISPR-Cas systems provide bacteria with adaptive immunity against invading DNA elements including bacteriophages and plasmids. While CRISPR technology has revolutionized eukaryotic genome engineering, its application to prokaryotes and their viruses remains less well established. Here we report the first functional CRISPR-Cas system from the genus Listeria and demonstrate its native role in phage defense. LivCRISPR-1 is a type II-A system from the genome of L. ivanovii subspecies londoniensis that uses a small, 1078 amino acid Cas9 variant and a unique NNACAC protospacer adjacent motif. We transferred LivCRISPR-1 cas9 and trans-activating crRNA into Listeria monocytogenes. Along with crRNA encoding plasmids, this programmable interference system enables efficient cleavage of bacterial DNA and incoming phage genomes. We used LivCRISPR-1 to develop an effective engineering platform for large, non-integrating Listeria phages based on allelic replacement and CRISPR-Cas-mediated counterselection. The broad host-range Listeria phage A511 was engineered to encode and express lysostaphin, a cell wall hydrolase that specifically targets Staphylococcus peptidoglycan. In bacterial co-culture, the armed phages not only killed Listeria hosts but also lysed Staphylococcus cells by enzymatic collateral damage. Simultaneous killing of unrelated bacteria by a single phage demonstrates the potential of CRISPR-Cas-assisted phage engineering, beyond single pathogen control.

Purification of Antilisterial Peptide (Subtilosin A) from Novel Bacillus tequilensis FR9 and Demonstrate Their Pathogen Invasion Protection Ability Using Human Carcinoma Cell Line

This study focuses on isolation, screening, and characterization of novel probiotics from gastrointestinal tract of free-range chicken (Gallus gallus domesticus). Fifty seven colonies were isolated and three isolates (FR4, FR9, and FR12) were selected and identified as Lactobacillus gasseri FR4, Bacillus tequilensis FR9, and L. animalis FR12 by 16S rRNA sequencing. Three strains were able to survive in stimulated acidic and bile conditions and inhibit the growth of pathogens. Especially, FR9 exhibited maximum inhibition against Listeria monocytogenes and none of them exhibited hemolytic activity. Native-PAGE revealed the presence of low molecular weight (3.4-5.0 KDa) antimicrobial peptide. The peptide was further purified by Sephadex G-50 column and RP-HPLC using C18 column. N-terminal amino acid sequencing of antimicrobial peptide showed 100% consensus to antilisterial peptide Subtilosin A and SboA gene was amplified from FR9 genome. FR9 showed maximum aggregation activity, exopolysaccharide production (85.46 mg/L) and cholesterol assimilation (63.12 ± 0.05 μg/mL). Strong adhesion property (12.6%) and pathogen invasion protection ability was revealed by B. tequilensis FR9 towards HCT-116 human colon carcinoma cell line. This is the first study to demonstrate antilisterial Subtilosin A production of B. tequilensis. Our results indicate that B. tequilensis FR9 strain furnish the essential characteristics of a potential probiotics and might be incorporated into human and animal food supplements.

Draft Genome Sequence of Lactobacillus crispatus C25 Isolated from Chicken Cecum

Lactic acid bacteria are important members of the gut microbiota of humans and animals. Here, we present the genome sequence of Lactobacillus crispatus strain C25, originally isolated from the cecum of 4-week-old chicken fed a standard diet. This isolate represents a potential probiotic strain for poultry.

Isolation, characterization and evaluation of probiotic lactic acid bacteria for potential use in animal production

In livestock production, lactic acid bacteria (LAB) are the most common microorganisms used as probiotics. For such use, these bacteria must be correctly identified and characterized to ensure their safety and efficiency. In the present study, LAB were isolated from broiler excreta, where a fermentation process was used. Nine among sixteen isolates were identified by biochemical and molecular (sequencing of the 16S rRNA gene) methods as Lactobacillus crispatus (n=1), Lactobacillus pentosus (n=1), Weissella cibaria (n=1), Pediococcus pentosaceus (n=2) and Enterococcus hirae (n=4). Subsequently, these bacteria were characterized for their growth capabilities, lactic acid production, acidic pH and bile salts tolerance, cell surface hydrophobicity, antimicrobial susceptibility and antagonistic activity. Lactobacillus pentosus strain LB-31, which showed the best characteristics, was selected for further analysis. This strain was administered to broilers and showed the ability of modulating the immune response and producing beneficial effects on morpho-physiological, productive and health indicators of the animals.

The Absence of a Mature Cell Wall Sacculus in Stable Listeria monocytogenes L-Form Cells Is Independent of Peptidoglycan Synthesis

L-forms are cell wall-deficient variants of otherwise walled bacteria that maintain the ability to survive and proliferate in absence of the surrounding peptidoglycan sacculus. While transient or unstable L-forms can revert to the walled state and may still rely on residual peptidoglycan synthesis for multiplication, stable L-forms cannot revert to the walled form and are believed to propagate in the complete absence of peptidoglycan. L-forms are increasingly studied as a fundamental biological model system for cell wall synthesis. Here, we show that a stable L-form of the intracellular pathogen Listeria monocytogenes features a surprisingly intact peptidoglycan synthesis pathway including glycosyl transfer, in spite of the accumulation of multiple mutations during prolonged passage in the cell wall-deficient state. Microscopic and biochemical analysis revealed the presence of peptidoglycan precursors and functional glycosyl transferases, resulting in the formation of peptidoglycan polymers but without the synthesis of a mature cell wall sacculus. In conclusion, we found that stable, non-reverting L-forms, which do not require active PG synthesis for proliferation, may still continue to produce aberrant peptidoglycan.

Reporter systems for in vivo tracking of lactic acid bacteria in animal model studies

Bioluminescence (BLI) and fluorescence imaging (FI) allow for non-invasive detection of viable microorganisms from within living tissue and are thus ideally suited for in vivo probiotic studies. Highly sensitive optical imaging techniques detect signals from the excitation of fluorescent proteins, or luciferase-catalyzed oxidation reactions. The excellent relation between microbial numbers and photon emission allow for quantification of tagged bacteria in vivo with extreme accuracy. More information is gained over a shorter period compared to traditional pre-clinical animal studies. The review summarizes the latest advances in in vivo bioluminescence and fluorescence imaging and points out the advantages and limitations of different techniques. The practical application of BLI and FI in the tracking of lactic acid bacteria in animal models is addressed.

Evaluation of phytate-degrading Lactobacillus culture administration to broiler chickens

Probiotics have been demonstrated to promote growth, stimulate immune responses, and improve food safety of poultry. While widely used, their effectiveness is mixed, and the mechanisms through which they contribute to poultry production are not well understood. Microbial phytases are increasingly supplemented in feed to improve digestibility and reduce antinutritive effects of phytate. The microbial origin of these exogenous enzymes suggests a potentially important mechanism of probiotic functionality. We investigated phytate degradation as a novel probiotic mechanism using recombinant Lactobacillus cultures expressing Bacillus subtilis phytase. B. subtilis phyA was codon optimized for expression in Lactobacillus and cloned into the expression vector pTRK882. The resulting plasmid, pTD003, was transformed into Lactobacillus acidophilus, Lactobacillus gallinarum, and Lactobacillus gasseri. SDS-PAGE revealed a protein in the culture supernatants of Lactobacillus pTD003 transformants with a molecular weight similar to that of the B. subtilis phytase. Expression of B. subtilis phytase increased phytate degradation of L. acidophilus, L. gasseri, and L. gallinarum approximately 4-, 10-, and 18-fold over the background activity of empty-vector transformants, respectively. Phytase-expressing L. gallinarum and L. gasseri were administered to broiler chicks fed a phosphorus-deficient diet. Phytase-expressing L. gasseri improved weight gain of broiler chickens to a level comparable to that for chickens fed a control diet adequate in phosphorus, demonstrating proof of principle that administration of phytate-degrading probiotic cultures can improve performance of livestock animals. This will inform future studies investigating whether probiotic cultures are able to provide both the performance benefits of feed enzymes and the animal health and food safety benefits traditionally associated with probiotics.

Genetic characterisation and heterologous expression of leucocin C, a class IIa bacteriocin from Leuconostoc carnosum 4010

Leuconostoc carnosum 4010 is a protective culture for meat products. It kills the foodborne pathogen Listeria monocytogenes by producing two class IIa (pediocin-like) bacteriocins, leucocin A and leucocin C. The genes for leucocin A production have previously been characterised from Leuconostoc gelidum UAL 187, whereas no genetic studies about leucocin C has been published. Here, we characterised the genes for the production of leucocins A and C in L. carnosum 4010. In this strain, leucocin A and leucocin C operons were localised in different plasmids. Unlike in L. gelidum, leucocin A operon in L. carnosum 4010 only contained the structural and the immunity genes lcaAB without transporter genes lcaECD. On the contrary, leucocin C cluster included two intact operons. Novel genes lecCI encode the leucocin C precursor and the 97-aa immunity protein LecI, respectively. LecI shares 48 % homology with the immunity proteins of sakacin P and listeriocin. Another leucocin C operon lecXTS, encoding an ABC transporter and an accessory protein, was 97 % identical with the leucocin A transporter operon lcaECD of L. gelidum. For heterologous expression of leucocin C in Lactococcus lactis, the mature part of the lecC gene was fused with the signal sequence of usp45 in the secretion vector pLEB690. L. lactis secreted leucocin C efficiently, as shown by large halos on lawns of L. monocytogenes and Leuconostoc mesenteroides indicators. The function of LecI was then demonstrated by expressing the gene lecI in L. monocytogenes. LecI-producing Listeria was less sensitive to leucocin C than the vector strain, thus corroborating the immunity function of LecI.

Transformation of, and heterologous protein expression in, Lactobacillus agilis and Lactobacillus vaginalis isolates from the chicken gastrointestinal tract

Lactobacilli are naturally found in the gastrointestinal tract of chickens, and there is interest in utilizing autochthonous strains for the delivery of therapeutic proteins. Previously we identified three chicken-derived Lactobacillus strains, Lactobacillus agilis La3, Lactobacillus vaginalis Lv5, and Lactobacillus crispatus Lc9, which persist in the gastrointestinal tract of chickens fed either a commercial or high-protein diet. In the current study, we investigated the ability to electrotransform these strains, determined plasmid vector stability, and compared reporter gene expression directed by several different promoters. The La3 and Lv5 strains were reproducibly transformed with efficiencies of 10(8) and 10(6) transformants per microgram of plasmid DNA, respectively. The third strain tested, L. crispatus Lc9, was recalcitrant to all transformation protocols examined. The plasmid vectors pTRK563 and pTRKH2 were maintained over 100 generations in La3 and Lv5, respectively. The ability of La3 and Lv5 to express the heterologous reporter gene gfp was analyzed using heterologous and homologous promoters. Transformants of both La3 and Lv5 containing the La3 ldhL promoter were the most fluorescent. To our knowledge, this is the first report of successful transformation and heterologous protein expression in L. agilis and L. vaginalis. The ability of these strains to express heterologous proteins in vitro indicates their potential utility as in vivo delivery vectors for therapeutic peptides to the chicken gastrointestinal tract.

Use of green fluorescent protein to monitorLactobacillusin the gastro-intestinal tract of chicken

Lactobacilli, like other gut commensal bacteria, are well known for their use in industrial food fermentations and for their probiotic properties. However, little is known about the interaction of these microorganisms with the gastro-intestinal epithelia when administered in vivo. To specifically monitor the passage of lactobacilli after oral administration, the gfp gene was cloned downstream from the constitutive l-lactate dehydrogenase promoter (pldhL) in the experiment. The recombinant expression vector pLEM415::gfp was electroporated into different lactobacilli isolated from chicken. Green fluorescent protein (GFP) was expressed successfully in Lactobacillus delbrueckii ssp. lactis D17 (D17-GFP) and Lactobacillus fructosus C2 (C2-GFP). Moreover, oral administration of D17-GFP in chickens allowed us to trace it in the gastro-intestinal tract. Six hours after ingestion, D17-GFP was detectable in all luminal contents (stomach, jejunum, ileum and caecum). At 42 h post-administration the microorganism was present throughout the intestine with maximum concentrations about 10(5.5) in all intestinal sections. No fluorescent lactobacilli were detected in the spleen or liver of chickens at any time. Using fluorescence microscopy, it became apparent that the D17-GFP were mainly embedded in the mucus, localized close to the epithelial surface of the intestine and scattered in the intestine lamina propria.

C terminus of NisI provides specificity to nisin

Nisin-producing Lactococcus lactis protects its own cell membrane against the bacteriocin with the ABC transporter NisFEG, and the immunity lipoprotein NisI. In this study, in order to localize a site for specific nisin interaction in NisI, a C-terminal deletion series of NisI was constructed, and the C-terminally truncated NisI proteins were expressed in L. lactis. The shortest deletion (5 aa) decreased the nisin immunity capacity considerably in the nisin-negative strain MG1614, resulting in approximately 78% loss of immunity function compared with native NisI. A deletion of 21 aa decreased the immunity level even more, but longer deletions, up to 74 aa, provided the same level of nisin immunity as the 21 aa deletion, i.e. approximately 14% of the immunity provided by native NisI. Similar to native NisI, all the C-terminally truncated NisI proteins provided higher immunity to nisin in the NisFEG-expressing strain NZ9840 than in MG1614, i.e. approximately 40-50% of the immunity capacity of native NisI. Then, it was determined whether the NisI C-terminal 21 aa fragment could protect cells against nisin. To target the 21 aa fragment to its natural location, 21 C-terminal amino acids from the subtilin-specific immunity lipoprotein SpaI were replaced by 21 C-terminal amino acids from NisI. The expression of the SpaI'-'NisI fusion in L. lactis strains significantly increased their nisin immunity. This is the first time the immunity function of a lantibiotic immunity protein has been transferred to another protein. However, unlike native NisI, and the C-terminally truncated NisI fragments, the increase in nisin immunity conferred by the SpaI'-'NisI fusion was the same in both the NisFEG strain NZ9840 and MG1614. In conclusion, the SpaI'-'NisI fusion could not enhance nisin immunity by interacting with NisFEG, whereas the C-terminally truncated NisI fragments and native NisI were able to enhance nisin immunity, probably by co-operation with NisFEG. The results made it evident that the C terminus of NisI is involved in specific interaction with nisin, and that it confers specificity for the NisI immunity lipoprotein.

Modified electroporation protocol for Lactobacilli isolated from the chicken crop facilitates transformation and the use of a genetic tool

Isolates of Lactobacillus spp. from a collection of potentially probiotic strains isolated from the crops of broiler chickens were found to be non-electrotransformable using published techniques. One strain of Lactobacillus salivarius was shown to develop electrocompetence when an overnight culture was incubated in fresh medium. The effect was enhanced if glycine was incorporated into the fresh growth medium. When these modifications were applied to a number of other crop isolates of Lactobacillus spp., electrocompetence could be detected in approximately half the strains tested. Two temperature sensitive plasmid vectors that had been used for the genetic modification of other lactic acid bacteria were introduced into a crop strain of Lb. salivarius. Both showed temperature sensitivity at 42 degrees C and above but were relatively stable at 37 degrees C. The genetic tool harbouring an IS element allowed the delivery of the plasmid to multiple independent sites in the host chromosome. Harnessing such genetic tools will facilitate the future genetic analysis of the host bacterium.