High efficiency electrotransformation of Lactobacillus casei

A Critical Review on Akkermansia muciniphila: Functional Mechanisms, Technological Challenges, and Safety Issues

Due to its physiological benefits from in vitro and in vivo points of view, Akkermansia muciniphila, a common colonizer in the human gut mucous layer, has consistently been identified as an option for the next-generation probiotic. A. muciniphila is a significant bacterium that promotes host physiology. However, it also has a great deal of potential to become a probiotic due to its physiological advantages in a variety of therapeutic circumstances. Therefore, it can be established that the abundance of A. muciniphila in the gut environment, which is controlled by many genetic and dietary variables, is related to the biological behaviors of the intestinal microbiota and gut dysbiosis/eubiosis circumstances. Before A. muciniphila is widely utilized as a next-generation probiotic, regulatory obstacles, the necessity for significant clinical trials, and the sustainability of manufacturing must be eliminated. In this review, the outcomes of recent experimental and clinical reports are comprehensively reviewed, and common colonization patterns, main factors involved in the colonization of A. muciniphila in the gut milieu, their functional mechanisms in establishing homeostasis in the metabolic and energy pathways, the promising delivery role of microencapsulation, potential genetic engineering strategies, and eventually safety issues of A. muciniphila have been discussed.

Illuminating the oral microbiome and its host interactions: tools and approaches for molecular microbiology studies

Advancements in DNA sequencing technologies within the last decade have stimulated an unprecedented interest in the human microbiome, largely due the broad diversity of human diseases found to correlate with microbiome dysbiosis. As a direct consequence of these studies, a vast number of understudied and uncharacterized microbes have been identified as potential drivers of mucosal health and disease. The looming challenge in the field is to transition these observations into defined molecular mechanistic studies of symbiosis and dysbiosis. In order to meet this challenge, many of these newly identified microbes will need to be adapted for use in experimental models. Consequently, this review presents a comprehensive overview of the molecular microbiology tools and techniques that have played crucial roles in genetic studies of the bacteria found within the human oral microbiota. Here, we will use specific examples from the oral microbiome literature to illustrate the biology supporting these techniques, why they are needed in the field, and how such technologies have been implemented. It is hoped that this information can serve as a useful reference guide to help catalyze molecular microbiology studies of the many new understudied and uncharacterized species identified at different mucosal sites in the body.

A Novel Probiotic-Based Oral Vaccine against SARS-CoV-2 Omicron Variant B.1.1.529

COVID-19 pandemic, caused by the SARS-CoV-2 virus, is still affecting the entire world via the rapid emergence of new contagious variants. Vaccination remains the most effective prevention strategy for viral infection, yet not all countries have sufficient access to vaccines due to limitations in manufacturing and transportation. Thus, there is an urgent need to develop an easy-to-use, safe, and low-cost vaccination approach. Genetically modified microorganisms, especially probiotics, are now commonly recognized as attractive vehicles for delivering bioactive molecules via oral and mucosal routes. In this study, Lactobacillus casei has been selected as the oral vaccine candidate based on its' natural immunoadjuvant properties and the ability to resist acidic gastric environment, to express antigens of SARS-CoV-2 Omicron variant B.1.1.529 with B-cell and T-cell epitopes. This newly developed vaccine, OMGVac, was shown to elicit a robust IgG systemic immune response against the spike protein of Omicron variant B.1.1.529 in Golden Syrian hamsters. No adverse effects were found throughout this study, and the overall safety was evaluated in terms of physiological and histopathological examinations of different organs harvested. In addition, this study illustrated the use of the recombinant probiotic as a live delivery vector in the initiation of systemic immunity, which shed light on the future development of next-generation vaccines to combat emerging infectious diseases.

Gut microbiota-derived tryptamine and phenethylamine impair insulin sensitivity in metabolic syndrome and irritable bowel syndrome

The incidence of metabolic syndrome is significantly higher in patients with irritable bowel syndrome (IBS), but the mechanisms involved remain unclear. Gut microbiota is causatively linked with the development of both metabolic dysfunctions and gastrointestinal disorders, thus gut dysbiosis in IBS may contribute to the development of metabolic syndrome. Here, we show that human gut bacterium Ruminococcus gnavus-derived tryptamine and phenethylamine play a pathogenic role in gut dysbiosis-induced insulin resistance in type 2 diabetes (T2D) and IBS. We show levels of R. gnavus, tryptamine, and phenethylamine are positively associated with insulin resistance in T2D patients and IBS patients. Monoassociation of R. gnavus impairs insulin sensitivity and glucose control in germ-free mice. Mechanistically, treatment of R. gnavus-derived metabolites tryptamine and phenethylamine directly impair insulin signaling in major metabolic tissues of healthy mice and monkeys and this effect is mediated by the trace amine-associated receptor 1 (TAAR1)-extracellular signal-regulated kinase (ERK) signaling axis. Our findings suggest a causal role for tryptamine/phenethylamine-producers in the development of insulin resistance, provide molecular mechanisms for the increased prevalence of metabolic syndrome in IBS, and highlight the TAAR1 signaling axis as a potential therapeutic target for the management of metabolic syndrome induced by gut dysbiosis.

The plasmid-encoded lactose operon plays a vital role in the acid production rate of Lacticaseibacillus casei during milk beverage fermentation

Lacticaseibacillus casei is used extensively in the fermented milk-beverage industry as a starter culture. Acid production capacity during fermentation is the main criterion for evaluating starters although it is strain-dependent. In this study, the acid production rates of 114 L. casei strains were determined and then classified into high acid (HC), medium acid (MC), and low acid (LC) groups. Comparative genomics analysis found that the lac operon genes encoding the phosphoenolpyruvate-lactose phosphotransferase system (PTSLac) were located on plasmids in the HC strains; however, it is notable that the corresponding operons were located on the chromosome in LC strains. Real-time PCR analysis showed that the copy numbers of lac operon genes in HC strains were between 3.1 and 9.3. To investigate the relationship between copy number and acid production rate, the lac operon cluster of the HC group was constitutively expressed in LC strains. The resulting copy numbers of lac operon genes were between 15.8 and 18.1; phospho-β-galactosidase activity increased by 1.68-1.99-fold; and the acid production rates increased by 1.24-1.40-fold, which enhanced the utilization rate of lactose from 17.5 to 42.6% in the recombinant strains. The markedly increased expression of lac operon genes increased lactose catabolism and thereby increased the acid production rate of L. casei.

The plasmid-encoded lactose operon plays a vital role in the acid production rate of Lacticaseibacillus casei during milk beverage fermentation

Lacticaseibacillus casei is used extensively in the fermented milk-beverage industry as a starter culture. Acid production capacity during fermentation is the main criterion for evaluating starters although it is strain-dependent. In this study, the acid production rates of 114 L. casei strains were determined and then classified into high acid (HC), medium acid (MC), and low acid (LC) groups. Comparative genomics analysis found that the lac operon genes encoding the phosphoenolpyruvate-lactose phosphotransferase system (PTS^Lac) were located on plasmids in the HC strains; however, it is notable that the corresponding operons were located on the chromosome in LC strains. Real-time PCR analysis showed that the copy numbers of lac operon genes in HC strains were between 3.1 and 9.3. To investigate the relationship between copy number and acid production rate, the lac operon cluster of the HC group was constitutively expressed in LC strains. The resulting copy numbers of lac operon genes were between 15.8 and 18.1; phospho-β-galactosidase activity increased by 1.68–1.99-fold; and the acid production rates increased by 1.24–1.40-fold, which enhanced the utilization rate of lactose from 17.5 to 42.6% in the recombinant strains. The markedly increased expression of lac operon genes increased lactose catabolism and thereby increased the acid production rate of L. casei.

AroC, a Chorismate Synthase, is Required for the Formation of Edwardsiella tarda biofilms

Biofilms contribute to the resistance of Edwardsiella tarda to antibiotics and host immunity. AroC in the shikimate pathway produces chorismate to synthesize crucial intermediates such as indole. In this study, the differences between biofilms produced by aroC mutants (△aroC), wild-type (WT) strains, and △aroC complementary strains (C△aroC) were detected both in vitro with 96-well plates, tubes, or coverslips and in vivo using a mouse model of subcutaneous implants. When examining potential mechanisms, we found that the diameters of the movement rings in soft agar plates and the flagellar sizes and numbers determined by silver staining were all lower for △aroC than for WT and C△aroC. Moreover, qRT-PCR showed that the transcription levels of flagellar synthesis genes, fliA and fliC, were reduced in △aroC. AroC, FliC, or FliA may accompany the motility of △aroC strains. In addition, compared with the WT and C△aroC, the amounts of indole in △aroC were significantly decreased. Notably, the formation of biofilms by these strains could be promoted by exogenous indole. Therefore, the aroC gene could affect the biofilm formation of E. tarda concerning its impact on flagella and indole.

Akkermansia muciniphila: from its critical role in human health to strategies for promoting its abundance in human gut microbiome

Akkermansia muciniphila, a frequent colonizer in the gut mucous layer of individuals, has constantly been recognized as a promising candidate for the next generation of probiotics due to its biological advantages from in vitro and in vivo investigations. This manuscript comprehensively reviewed the features of A. muciniphila in terms of its function in host physiology and frequently utilized nutrition using the published peer-reviewed articles, which should present valuable and critical information to scientists, engineers, and even the general population. A. muciniphila is an important bacterium that shows host physiology. However, its physiological advantages in several clinical settings also have excellent potential to become a probiotic. Consequently, it can be stated that there is a coherent and direct relation between the biological activities of the gut microbiota, intestinal dysbiosis/eubiosis, and the population of A. muciniphila in the gut milieu, which is influenced by various genetical and nutritional factors. Current regulatory barriers, the need for large-scale clinical trials, and the feasibility of production must be removed before A muciniphila can be extensively used as a next-generation probiotic.

Probiotic Releasing Angiotensin (1-7) in a Drosophila Model of Alzheimer's Disease Produces Sex-Specific Effects on Cognitive Function

BACKGROUND

While extensive research on the brain has failed to identify effective therapies, using probiotics to target the gut microbiome has shown therapeutic potential in Alzheimer's disease (AD). Genetically modified probiotics (GMP) are a promising strategy to deliver key therapeutic peptides with high efficacy and tissue specificity. Angiotensin (Ang)-(1-7) levels inversely correlate to AD severity, but its administration is challenging. Our group has successfully established a GMP-based method of Ang-(1-7) delivery.

OBJECTIVE

Since Drosophila represents an excellent model to study the effect of probiotics on complex disorders in a high throughput manner, we tested whether oral supplementation with Lactobacillus paracasei releasing Ang-(1-7) (LP-A) delays memory loss in a Drosophila AD model.

METHODS

Flies overexpressing the human amyloid-β protein precursor and its β-site cleaving enzyme in neurons were randomized to receive four 24-h doses of Lactobacillus paracasei alone (LP), LP-A or sucrose over 14 days. Memory was assessed via an aversive phototaxic suppression assay.

RESULTS

Optimal dilution,1:2, was determined based on palatability. LP-A improved memory in trained AD males but worsened cognition in AD females. LP-supplementation experiments confirmed that Ang-(1-7) conferred additional cognitive benefits in males and was responsible for the deleterious cognitive effects in females. Sex-specific differences in the levels of angiotensin peptides and differential activation of the kynurenine pathway of tryptophan metabolism in response to supplementation may underlie this male-only therapeutic response.

CONCLUSION

In summary, LP-A ameliorated the memory deficits of a Drosophila AD model, but effects were sex-specific. Dosage optimization may be required to address this differential response.

High-efficiency transformation of Streptococcus thermophilus using electroporation

BACKGROUND

Streptococcus thermophilus, one of the most important lactic acid bacteria, is widely used in food fermentation, which is beneficial to improve food quality. However, the current genetic transformation systems are inefficient for S. thermophilus S-3, which hinders its further study.

RESULTS

We developed three electroporation transformation methods for S. thermophilus S-3, and optimized various parameters to enhance the transformation efficiency up to 1.3 × 10⁶  CFU/μg DNA, which was 32-fold higher than that of unoptimized. Additionally, transcriptional analysis showed that a series of competence genes in S. thermophilus S-3 were remarkedly up-regulated after optimization, indicating that improvement of transformation efficiency was attributed to the expression level of competence genes. Furthermore, to prove their potential, expression of competence genes (comEA, cbpD and comX) were employed to increase transformation efficiency. The maximum transformation efficiency was obtained by overexpression of comEA, which was 14-fold higher than that of control.

CONCLUSION

This is the first report of competence gene expression for enhancing transformability in S. thermophilus, which exerts a positive effect on the development of desirable characteristics strains. © 2021 Society of Chemical Industry.

Recent progress on n-butanol production by lactic acid bacteria

n-Butanol is an essential chemical intermediate produced through microbial fermentation. However, its toxicity to microbial cells has limited its production to a great extent. The anaerobe lactic acid bacteria (LAB) are the most resistant to n-butanol, so it should be the first choice for improving n-butanol production. The present article aims to review the following aspects of n-butanol production by LAB: (1) the tolerance of LAB to n-butanol, including its tolerance level and potential tolerance mechanisms; (2) genome editing tools in the n-butanol-resistant LAB; (3) methods of LAB modification for n-butanol production and the production levels after modification. This review will provide a theoretical basis for further research on n-butanol production by LAB.

Effects of carbon concentration, oxygen, and controlled pH on the engineering strain Lactiplantibacillus casei E1 in the production of bioethanol from sugarcane molasses

Sugarcane molasses are considered a potential source for bioethanol's commercial production because of its availability and low market price. It contains high concentrations of fermentable sugars that can be directly metabolized by microbial fermentation. Heterofermentative lactic acid bacteria, especially Lactiplantibacillus casei, have a high potential to be a biocatalyst in ethanol production that they are characterized by strong abilities of carbohydrate metabolism, ethanol synthesis, and high alcohol tolerance. This study aimed to evaluate the feasibility of producing ethanol by Lactiplantibacillus casei used the ethanologen engineering strain L. casei E1 as a starter culture and cane molasses as substrate medium. The effects of environmental factors on the metabolism of L. casei E1 were analyzed by high-performance liquid chromatography (HPLC) system, and the gene expression of key enzymes in carbon source metabolism was detected using quantitative real-time PCR (RT-qPCR). Results showed that the strain could grow well, ferment sugar quickly in cane molasses. By fermenting this bacterium anaerobically at 37 °C for 36 h incubation in 5 °BX molasses when the fermenter's pH was controlled at 6.0, ethanol yield reached 13.77 g/L, and carbohydrate utilization percentage was 78.60%. RT-qPCR results verified the strain preferentially ferment glucose and fructose of molasses to ethanol at the molecular level. In addition, the metabolism of sugars, especially fructose, would be inhibited by elevating acidity. Our findings support the theoretical basis for exploring Lactic acid bacteria as a starter culture for converting sugarcane molasses into ethanol.

Therapeutic Delivery of Ang(1-7) via Genetically Modified Probiotic: A Dosing Study

In recent years a number of beneficial health effects have been ascribed to the renin-angiotensin system (RAS) that extend beyond lowering blood pressure, primarily mediated via the angiotensin-converting enzyme-2 (ACE2)/angiotensin (1–7) or Ang(1–7)/MAS receptor axis. Moreover, once thought as merely a systemic effector, RAS components exist within tissues. The highest tissue concentrations of ACE2 mRNA are located in the gut making it an important target for altering RAS function. Indeed, genetically engineered recombinant probiotics are promising treatment strategies offering delivery of therapeutic proteins with precision. An Ang(1–7) secreting Lactobacillus paracasei (LP) or LP-A has been described for regulation of diabetes and hypertension; however, we are the first to the best of our knowledge to propose this paradigm as it relates to aging. In this Research Practice manuscript, we provide proof of concept for using this technology in a well-characterized rodent model of aging: the Fisher344 x Brown Norway Rat (F344BN). Our primary findings suggest that LP-A increases circulating levels of Ang(1–7) both acutely and chronically (after 8 or 28 treatment days) when administered 3× or 7×/week over 4 weeks. Our future preclinical studies will explore the impact of this treatment on gut and other age-sensitive distal tissues such as brain and muscle.

Engineered Akkermansia muciniphila: A promising agent against diseases (Review)

Achieving a harmonious gut microbial ecosystem has been hypothesized to be a successful method for alleviating metabolic disorders. The administration of probiotics, such as Lactobacillus and Bifidobacteria, is a known traditional and safe pathway to regulate human commensal microbes. With advancements in genetic sequencing and genetic editing tools, more bacteria are able to function as engineered probiotics with multiple therapeutic properties. As one of the next-generation probiotic candidates, Akkermansia muciniphila (A. muciniphila) has been discovered to enhance the gut barrier function and moderate inflammatory responses, exhibit improved effects with pasteurization and display beneficial probiotic effects in individuals with obesity, type 2 diabetes, atherosclerosis and autism-related gastrointestinal disturbances. In view of this knowledge, the present review aimed to summarize the effects of A. muciniphila in the treatment of metabolic disorders and to discuss several mature recombination systems for the genetic modification of A. muciniphila. From gaining an enhanced understanding of its genetic background, ingested A. muciniphila is expected to be used in various applications, including as a diagnostic tool, and in the site-specific delivery of therapeutic drugs.

Angiotensin-(1-7) Expressed From Lactobacillus Bacteria Protect Diabetic Retina in Mice

Purpose

A multitude of animal studies substantiates the beneficial effects of Ang-(1-7), a peptide hormone in the protective axis of the renin angiotensin system, in diabetes and its associated complications including diabetic retinopathy (DR). However, the clinical application of Ang-(1-7) is limited due to unfavorable pharmacological properties. As emerging evidence implicates gut dysbiosis in pathogenesis of diabetes and supports beneficial effects of probiotics, we sought to develop probiotics-based expression and delivery system to enhance Ang-(1-7) and evaluate the efficacy of engineered probiotics expressing Ang-(1-7) in attenuation of DR in animal models.

Methods

Ang-(1-7) was expressed in the Lactobacillus species as a secreted fusion protein with a trans-epithelial carrier to allow uptake into circulation. To evaluate the effects of Ang-(1-7) expressed from Lactobacillus paracasei (LP), adult diabetic eNOS-/- and Akita mice were orally gavaged with either 1 × 109 CFU of LP secreting Ang-(1-7) (LP-A), LP alone or vehicle, 3 times/week, for 8 and 12 weeks, respectively.

Results

Ang-(1-7) is efficiently expressed from different Lactobacillus species and secreted into circulation in mice fed with LP-A. Oral administration of LP-A significantly reduced diabetes-induced loss of retinal vascular capillaries. LP-A treatment also prevented loss of retinal ganglion cells, and significantly decreased retinal inflammatory cytokine expression in both diabetic eNOS-/- and Akita mice.

Conclusions

These results provide proof-of-concept for feasibility and efficacy of using engineered probiotic species as live vector for delivery of Ang-(1-7) with enhanced bioavailability.

Translational Relevance

Probiotics-based delivery of Ang-(1-7) may hold important therapeutic potential for the treatment of DR and other diabetic complications.

Target genes directly regulated by Eha are required for Edwardsiella tarda survival within macrophages

Eha is a virulence regulator in Edwardsiella tarda (E. tarda). The present study examined how Eha regulated its target genes to affect the bacterial survival within the cells. We constructed the reporter a pGEX-4T-ehaflag plasmid expressing Eha tagged at its C terminus with the flag epitope, and introduced the plasmid into an eha mutant ET13 strain, and obtained a Cehaflag strain. The expression and activity of an EhaFlag fusion protein restored the survival of the Cehaflag as the wild type in macrophages by Western blotting and intracellular survival experiments. We used a monoclonal anti-Flag antibody to precipitate EhaFlag-DNA complexes using chromatic immunoprecipitation (ChIP). We then designed primers based on the differentially-expressed genes identified from RNA-sequencing, and identified ten Eha-interacting genes by qPCR. We amplified the promoter regions of the ten genes and the eha gene from ET13 strain by PCR, constructed pBD-P_targetlacZ and pBD-P_ehalacZ plasmids. The eha gene directly and positively regulated these target genes, and be negatively auto-regulated by Eha in E. tarda, as determined by comparing their β-Galactosidase activities. These target genes were distributed in the categories involved in the bacterial growth, movement and resistance to H₂O₂ or acid. We further constructed a ETATCC_RS15225 mutant (△dcuA1), a ETATCC_ RS14855 mutant (△flgK) anda ETATCC_RS07650 mutant (ΔtnaA), and a partial complementary strains of △eha-tnaA and △eha-flgK and the complementary strains of CΔflgK and CΔtnaA. The ETATCC_RS15225 gene probably encoded a transporter protein DcuA1 at outer membrane with SDS-PAGE and RT-PCR. The ETATCC _RS14855 gene probably encoded FlgK protein and affected the bacterial motility. The ETATCC_RS07650 gene encoded Tryptophanase, which affected the bacterial survival within macrophages. With the assistance of these above strains, our results showed that the eha gene was able to regulate the ETATCC_RS15225 gene to express its outer membrane protein DcuA1, the ETATCC _RS14855 gene to control the flagellar motility and the ETATCC_RS07650 to affect the bacterial survival within macrophages. With the combination of other functions of above three genes, our results suggested that Eha directly regulates the target genes to affect E. tarda to survive within the cells.

Multiple pulse electroporation of lactic acid bacteria Lactococcus lactis and Lactobacillus casei

Genetic manipulation of lactic acid bacteria is often difficult due to the inability to transform them with high efficiency. Multi-pulse electroporation offers a simple approach to increase transformation efficiencies. Using cells grown with 1% glycine and pretreated with lithium acetate and dithiothreitol, multi-pulse electroporation (five pulses of 12.5 kV cm^-1) of Lactococcus lactis JB704 cells resulted in a transformation efficiency of up to 1.2 × 10⁶ colony forming units (CFU) μg^-1 pGK13, an 8-fold increase in the transformation efficiency compared to single pulse electroporation. Other cell growth and pretreatment conditions with JB704 resulted in lower transformation efficiencies but had 4-fold to 27-fold higher transformation efficiencies with the five pulse electroporations. With similarly grown and pretreated Lactobacillus casei 32G cells, multi-pulse electroporation (five pulses of 7.5 kV cm^-1) resulted in a mean transformation efficiency of 7.3 × 10³ CFU μg^-1 pTRKH2, a 4-fold increase in the transformation efficiency compared to single pulse electroporation.

Expression of Human ACE2 in Lactobacillus and Beneficial Effects in Diabetic Retinopathy in Mice

The angiotensin converting enzyme 2 (ACE2) catalyzes the degradation of Angiotensin II (Ang II) to generate Angiotensin-(1-7), which reduces inflammation and oxidative stress stimulated by Ang II. ACE2 has been shown to be protective in cardiovascular and metabolic diseases including diabetes and its complications. However, the challenge for its clinical application is large-scale production of high-quality ACE2 with sufficient target tissue bioavailability. We developed an expression and delivery system based on the use of probiotic species Lactobacillus paracasei (LP) to serve as a live vector for oral delivery of human ACE2. We show that codon-optimized ACE2 can be efficiently expressed in LP. Mice treated with the recombinant LP expressing the secreted ACE2 in fusion with the non-toxic subunit B of cholera toxin, which acts as a carrier to facilitate transmucosal transport, showed increased ACE2 activities in serum and tissues. ACE2-LP administration reduced the number of acellular capillaries, blocked retinal ganglion cell loss, and decreased retinal inflammatory cytokine expression in two mouse models of diabetic retinopathy. These results provide proof of concept for feasibility of using engineered probiotic species as live vector for delivery of human ACE2 with enhanced tissue bioavailability for treating diabetic retinopathy, as well as other diabetic complications.

Sensitivity to the two peptide bacteriocin plantaricin EF is dependent on CorC, a membrane-bound, magnesium/cobalt efflux protein

Lactic acid bacteria produce a variety of antimicrobial peptides known as bacteriocins. Most bacteriocins are understood to kill sensitive bacteria through receptor‐mediated disruptions. Here, we report on the identification of the Lactobacillus plantarum plantaricin EF (PlnEF) receptor. Spontaneous PlnEF‐resistant mutants of the PlnEF‐indicator strain L. plantarum NCIMB 700965 (LP965) were isolated and confirmed to maintain cellular ATP levels in the presence of PlnEF. Genome comparisons resulted in the identification of a single mutated gene annotated as the membrane‐bound, magnesium/cobalt efflux protein CorC. All isolates contained a valine (V) at position 334 instead of a glycine (G) in a cysteine‐β‐synthase domain at the C‐terminal region of CorC. In silico template‐based modeling of this domain indicated that the mutation resides in a loop between two β‐strands. The relationship between PlnEF, CorC, and metal homeostasis was supported by the finding that PlnEF‐resistance was lost when PlnEF was applied together with high concentrations of Mg²⁺, Co²⁺, Zn²⁺, or Cu²⁺. Lastly, PlnEF sensitivity was increased upon heterologous expression of LP965 corC but not the G334V CorC mutant in the PlnEF‐resistant strain Lactobacillus casei BL23. These results show that PlnEF kills sensitive bacteria by targeting CorC.

Lactobacillus casei expressing methylglyoxal synthase causes browning and heterocyclic amine formation in Parmesan cheese extract

Undesired browning of Parmesan cheese can occur during the latter period of ripening and cold storage despite the relative absence of reducing sugars and high temperatures typically associated with Maillard browning. Highly reactive α-dicarbonyls such as methylglyoxal (MG) are products and accelerants of Maillard browning chemistry and can result from the microbial metabolism of sugars and AA by lactic acid bacteria. We demonstrate the effects of microbially produced MG in a model Parmesan cheese extract using a strain of Lactobacillus casei 12A engineered for inducible overexpression of MG synthase (mgsA) from Thermoanaerobacterium thermosaccharolyticum HG-8. Maximum induction of plasmid-born mgsA led to 1.6 mM MG formation in Parmesan cheese extract and its distinct discoloration. The accumulation of heterocyclic amines including β-carboline derivatives arising from mgsA expression were determined by mass spectrometry. Potential MG-contributing reaction mechanisms for the formation of heterocyclic amines are proposed. These findings implicate nonstarter lactic acid bacteria may cause browning and influence nutritional aspects of Parmesan by enzymatic conversion of triosephosphates to MG. Moreover, these findings indicate that the microbial production of MG can lead to the formation of late-stage Maillard reaction products such as melanoidin and β-carbolines, effectively circumventing the thermal requirement of the early- and intermediate- stage Maillard reaction. Therefore, the identification and control of offending microbiota may prevent late-stage browning of Parmesan. The gene mgsA may serve as a genetic biomarker for cheeses with a propensity to undergo MG-mediated browning.

Prebiotics for Lactose Intolerance: Variability in Galacto-Oligosaccharide Utilization by Intestinal Lactobacillus rhamnosus

Lactose intolerance, characterized by a decrease in host lactase expression, affects approximately 75% of the world population. Galacto-oligosaccharides (GOS) are prebiotics that have been shown to alleviate symptoms of lactose intolerance and to modulate the intestinal microbiota, promoting the growth of beneficial microorganisms. We hypothesized that mechanisms of GOS utilization by intestinal bacteria are variable, impacting efficacy and response, with differences occurring at the strain level. This study aimed to determine the mechanisms by which human-derived Lactobacillus rhamnosus strains metabolize GOS. Genomic comparisons between strains revealed differences in carbohydrate utilization components, including transporters, enzymes for degradation, and transcriptional regulation, despite a high overall sequence identity (>95%) between strains. Physiological and transcriptomics analyses showed distinct differences in carbohydrate metabolism profiles and GOS utilization between strains. A putative operon responsible for GOS utilization was identified and characterized by genetic disruption of the 6-phospho-β-galactosidase, which had a critical role in GOS utilization. Our findings highlight the importance of strain-specific bacterial metabolism in the selection of probiotics and synbiotics to alleviate symptoms of gastrointestinal disorders including lactose intolerance.

Genome alterations associated with improved transformation efficiency in Lactobacillus reuteri

Background

Lactic acid bacteria (LAB) are one of the microorganisms of choice for the development of protein delivery systems for therapeutic purposes. Although there are numerous tools to facilitate genome engineering of lactobacilli; transformation efficiency still limits the ability to engineer their genomes. While genetically manipulating Lactobacillus reuteri ATCC PTA 6475 (LR 6475), we noticed that after an initial transformation, several LR 6475 strains significantly improved their ability to take up plasmid DNA via electroporation. Our goal was to understand the molecular basis for how these strains acquired the ability to increase transformation efficiency.

Results

Strains generated after transformation of plasmids pJP067 and pJP042 increased their ability to transform plasmid DNA about one million fold for pJP067, 100-fold for pSIP411 and tenfold for pNZ8048. Upon sequencing of the whole genome from these strains, we identified several genomic mutations and rearrangements, with all strains containing mutations in the transformation related gene A (trgA). To evaluate the role of trgA in transformation of DNA, we generated a trgA null that improved the transformation efficiency of LR 6475 to transform pSIP411 and pJP067 by at least 100-fold, demonstrating that trgA significantly impairs the ability of LR 6475 to take-up plasmid DNA. We also identified genomic rearrangements located in and around two prophages inserted in the LR 6475 genome that included deletions, insertions and an inversion of 336 Kb. A second group of rearrangements was observed in a Type I restriction modification system, in which the specificity subunits underwent several rearrangements in the target recognition domain. Despite the magnitude of these rearrangements in the prophage genomes and restriction modification systems, none of these genomic changes impacted transformation efficiency to the level induced by trgA.

Conclusions

Our findings demonstrate how genetic manipulation of LR 6475 with plasmid DNA leads to genomic changes that improve their ability to transform plasmid DNA; highlighting trgA as the primary driver of this phenotype. Additionally, this study also underlines the importance of characterizing genetic changes that take place after genome engineering of strains for therapeutic purposes.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-0986-8) contains supplementary material, which is available to authorized users.

Intra-species Genomic and Physiological Variability Impact Stress Resistance in Strains of Probiotic Potential

Large-scale microbiome studies have established that most of the diversity contained in the gastrointestinal tract is represented at the strain level; however, exhaustive genomic and physiological characterization of human isolates is still lacking. With increased use of probiotics as interventions for gastrointestinal disorders, genomic and functional characterization of novel microorganisms becomes essential. In this study, we explored the impact of strain-level genomic variability on bacterial physiology of two novel human Lactobacillus rhamnosus strains (AMC143 and AMC010) of probiotic potential in relation to stress resistance. The strains showed differences with known probiotic strains (L. rhamnosus GG, Lc705, and HN001) at the genomic level, including nucleotide polymorphisms, mutations in non-coding regulatory regions, and rearrangements of genomic architecture. Transcriptomics analysis revealed that gene expression profiles differed between strains when exposed to simulated gastrointestinal stresses, suggesting the presence of unique regulatory systems in each strain. In vitro physiological assays to test resistance to conditions mimicking the gut environment (acid, alkali, and bile stress) showed that growth of L. rhamnosus AMC143 was inhibited upon exposure to alkaline pH, while AMC010 and control strain LGG were unaffected. AMC143 also showed a significant survival advantage compared to the other strains upon bile exposure. Reverse transcription qPCR targeting the bile salt hydrolase gene (bsh) revealed that AMC143 expressed bsh poorly (a consequence of a deletion in the bsh promoter and truncation of bsh gene in AMC143), while AMC010 had significantly higher expression levels than AMC143 or LGG. Insertional inactivation of the bsh gene in AMC010 suggested that bsh could be detrimental to bacterial survival during bile stress. Together, these findings show that coupling of classical microbiology with functional genomics methods for the characterization of bacterial strains is critical for the development of novel probiotics, as variability between strains can dramatically alter bacterial physiology and functionality.

Oxalate-Degrading Enzyme Recombined Lactic Acid Bacteria Strains Reduce Hyperoxaluria

OBJECTIVE

To develop recombinant lactic acid bacteria (LAB) strains that express oxalate-degrading enzymes through biotechnology-based approach for the treatment of hyperoxaluria by oral administration.

MATERIAL AND METHODS

The coding gene of oxalate decarboxylase (ODC) and oxalate oxidase (OxO) was transformed into Lactococcus lactis MG1363. The oxalate degradation ability in vitro was evaluated in media with high concentration of oxalate. Hyperoxaluria rat models through high oxalate diet were given recombinant LAB through oral administration. Twenty-four-hour urinary oxalate was measured, and kidney stone formation was investigated.

RESULTS

LAB recombined with the coding gene of ODC could effectively decrease the amount of oxalate in the media and in the urine of rats. Moreover, the formation of calcium oxalate crystals in kidneys was also inhibited. The acid-induced promoter p170 significantly enhanced the reduction of hyperoxaluria. However, recombinant LAB expressing heterologous OxO showed less efficiency in oxalate degradation even in the presence of p170.

CONCLUSION

LAB expressing ODC is more efficient in degradation of oxalate in vitro and in vivo than that expressing OxO. This present study provided novel recombinant probiotic strains as a potential treatment tool against oxalosis.

Transient MutS-Based Hypermutation System for Adaptive Evolution of Lactobacillus casei to Low pH

This study explored transient inactivation of the gene encoding the DNA mismatch repair enzyme MutS as a tool for adaptive evolution of Lactobacillus casei MutS deletion derivatives of L. casei 12A and ATCC 334 were constructed and subjected to a 100-day adaptive evolution process to increase lactic acid resistance at low pH. Wild-type parental strains were also subjected to this treatment. At the end of the process, the ΔmutS lesion was repaired in representative L. casei 12A and ATCC 334 ΔmutS mutant isolates. Growth studies in broth at pH 4.0 (titrated with lactic acid) showed that all four adapted strains grew more rapidly, to higher cell densities, and produced significantly more lactic acid than untreated wild-type cells. However, the adapted ΔmutS derivative mutants showed the greatest increases in growth and lactic acid production. Further characterization of the L. casei 12A-adapted ΔmutS derivative revealed that it had a significantly smaller cell volume, a rougher cell surface, and significantly better survival at pH 2.5 than parental L. casei 12A. Genome sequence analysis confirmed that transient mutS inactivation decreased DNA replication fidelity in both L. casei strains, and it identified genetic changes that might contribute to the lactic acid-resistant phenotypes of adapted cells. Targeted inactivation of three genes that had acquired nonsense mutations in the adapted L. casei 12A ΔmutS mutant derivative showed that NADH dehydrogenase (ndh), phosphate transport ATP-binding protein PstB (pstB), and two-component signal transduction system (TCS) quorum-sensing histidine protein kinase (hpk) genes act in combination to increase lactic acid resistance in L. casei 12A.IMPORTANCE Adaptive evolution has been applied to microorganisms to increase industrially desirable phenotypes, including acid resistance. We developed a method to increase the adaptability of Lactobacillus casei 12A and ATCC 334 through transient inactivation of the DNA mismatch repair enzyme MutS. Here, we show this method was effective in increasing the resistance of L. casei to lactic acid at low pH. Additionally, we identified three genes that contribute to increased acid resistance in L. casei 12A. These results provide valuable insight on methods to enhance an organism's fitness to complex phenotypes through adaptive evolution and targeted gene inactivation.

The effect of temperature and bacterial growth phase on protein extraction by means of electroporation

Different chemical and physical methods are used for extraction of proteins from bacteria, which are used in variety of fields. But on a large scale, many methods have severe drawbacks. Recently, extraction by means of electroporation showed a great potential to quickly obtain proteins from bacteria. Since many parameters are affecting the yield of extracted proteins, our aim was to investigate the effect of temperature and bacterial growth phase on the yield of extracted proteins. At the same time bacterial viability was tested. Our results showed that the temperature has a great effect on protein extraction, the best temperature post treatment being 4°C. No effect on bacterial viability was observed for all temperatures tested. Also bacterial growth phase did not affect the yield of extracted proteins or bacterial viability. Nevertheless, further experiments may need to be performed to confirm this observation, since only one incubation temperature (4°C) and one incubation time before and after electroporation (0.5 and 1h) were tested for bacterial growth phase. Based on our results we conclude that temperature is a key element for bacterial membrane to stay in a permeabilized state, so more proteins flow out of bacteria into surrounding media.

Lactobacillus casei as a biocatalyst for biofuel production

Microbial fermentation of sugars from plant biomass to alcohols represents an alternative to petroleum-based fuels. The optimal biocatalyst for such fermentations needs to overcome hurdles such as high concentrations of alcohols and toxic compounds. Lactic acid bacteria, especially lactobacilli, have high innate alcohol tolerance and are remarkably adaptive to harsh environments. This study assessed the potential of five Lactobacillus casei strains as biocatalysts for alcohol production. L. casei 12A was selected based upon its innate alcohol tolerance, high transformation efficiency and ability to utilize plant-derived carbohydrates. A 12A derivative engineered to produce ethanol (L. casei E1) was compared to two other bacterial biocatalysts. Maximal growth rate, maximal optical density and ethanol production were determined under conditions similar to those present during alcohol production from lignocellulosic feedstocks. L. casei E1 exhibited higher innate alcohol tolerance, better growth in the presence of corn stover hydrolysate stressors, and resulted in higher ethanol yields.

Room temperature electrocompetent bacterial cells improve DNA transformation and recombineering efficiency

Bacterial competent cells are essential for cloning, construction of DNA libraries, and mutagenesis in every molecular biology laboratory. Among various transformation methods, electroporation is found to own the best transformation efficiency. Previous electroporation methods are based on washing and electroporating the bacterial cells in ice-cold condition that make them fragile and prone to death. Here we present simple temperature shift based methods that improve DNA transformation and recombineering efficiency in E. coli and several other gram-negative bacteria thereby economizing time and cost. Increased transformation efficiency of large DNA molecules is a significant advantage that might facilitate the cloning of large fragments from genomic DNA preparations and metagenomics samples.