Development of a chromosome-plasmid balanced lethal system for Lactobacillus acidophilus with thyA gene as selective marker

Advances in Escherichia coli Nissle 1917 as a customizable drug delivery system for disease treatment and diagnosis strategies

With the in-depth and comprehensive study of bacteria and their related ecosystems in the human body, bacterial-based drug delivery system has become an emerging biomimetic platform that can retain the innate biological functions. Benefiting from its good biocompatibility and ideal targeting ability as a biological carrier, Escherichia coli Nissle 1917 (ECN) has been focused on the treatment strategies of inflammatory bowel disease and tumor. The advantage of a bacterial carrier is that it can express exogenous protein while also acting as a natural capsule by releasing drug slowly as a result of its own colonization impact. In order to survive in harsh environments such as the digestive tract and tumor microenvironment, ECN can be modified or genetically engineered to enhance its function and host adaptability. The adoption of ECN carries or expresses drugs which are essential for accurate diagnosis and treatment. This review briefly describes the properties of ECN, the relationship between ECN and inflammation and tumor, and the strategy of using surface modification and genetic engineering to modify ECN as a delivery carrier for disease treatment.

Escherichiacoli Nissle 1917 as a Novel Microrobot for Tumor-Targeted Imaging and Therapy

Highly efficient drug delivery systems with excellent tumor selectivity and minimal toxicity to normal tissues remain challenging for tumor treatment. Although great effort has been made to prolong the blood circulation and improve the delivery efficiency to tumor sites, nanomedicines are rarely approved for clinical application. Bacteria have the inherent properties of homing to solid tumors, presenting themselves as promising drug delivery systems. Escherichia coli Nissle 1917 (EcN) is a commonly used probiotic in clinical practice. Its facultative anaerobic property drives it to selectively colonize in the hypoxic area of the tumor for survival and reproduction. EcN can be engineered as a bacteria-based microrobot for molecular imaging, drug delivery, and gene delivery. This review summarizes the progress in EcN-mediated tumor imaging and therapy and discusses the prospects and challenges for its clinical application. EcN provides a new idea as a delivery vehicle and will be a powerful weapon against cancer.

Second-generation Probiotics Producing IL-22 Increase Survival of Mice After Total Body Irradiation

BACKGROUND/AIM

Intestinal damage induced by total body irradiation (TBI) reduces leucine-rich repeat-containing G-protein-coupled receptor 5 (Lgr5)-expressing stem cells, goblet, and Paneth cells, breaching the epithelial lining, and facilitating bacterial translocation, sepsis, and death.

MATERIALS AND METHODS

Survival was measured after TBI in animals that received wild-type or recombinant bacteria producing interleukin-22 (IL-22). Changes in survival due to microbially delivered IL-22 were measured. Lactobacillus reuteri producing IL-22, or Escherichia coli-IL-22 were compared to determine which delivery system is better.

RESULTS

C57BL/6 mice receiving IL-22 probiotics at 24 h after 9.25 Gy TBI, demonstrated green fluorescent protein-positive bacteria in the intestine, doubled the number of Lgr5+ intestinal stem cells, and increased 30-day survival. Bacteria were localized to the jejunum, ileum, and colon.

CONCLUSION

Second-generation probiotics appear to be valuable for mitigation of TBI, and radiation protection during therapeutic total abdominal irradiation.

Exploiting Prophage-Mediated Lysis for Biotherapeutic Release by Lactobacillus reuteri

Lactobacillus reuteri has the potential to be developed as a microbial therapeutic delivery platform because of an established safety profile, health-promoting properties, and available genome editing tools. Here, we show that L. reuteri VPL1014 exhibits a low mutation rate compared to other Gram-positive bacteria, which we expect will contribute to the stability of genetically modified strains. VPL1014 encodes two biologically active prophages, which are induced during gastrointestinal transit. We hypothesized that intracellularly accumulated recombinant protein can be released following bacteriophage-mediated lysis. To test this, we engineered VPL1014 to accumulate leptin, our model protein, inside the cell. In vitro prophage induction of recombinant VPL1014 released leptin into the extracellular milieu, which corresponded to bacteriophage production. We also employed a plasmid system that does not require antibiotic in the growth medium for plasmid maintenance. Collectively, these data provide new avenues to exploit native prophages to deliver therapeutic molecules.IMPORTANCE Lactic acid bacteria (LAB) have been explored as potential biotherapeutic vehicles for the past 20 years. To secrete a therapeutic in the extracellular milieu, one typically relies on the bacterial secretion pathway, i.e., the Sec pathway. Overexpression of a secreted protein can overload the secretory pathway and impact the organism's fitness, and optimization of the signal peptide is also required to maximize the efficiency of the release of mature protein. Here, we describe a previously unexplored approach to release therapeutics from the probiotic Lactobacillus reuteri We demonstrate that an intracellularly accumulated recombinant protein is released following prophage activation. Since we recently demonstrated that prophages are activated during gastrointestinal transit, we propose that this method will provide a straightforward and efficient approach to deliver therapeutics in vivo.

Biological Containment of Genetically Modified Bacillus subtilis

Genetic manipulation of bacterial spores of the genus Bacillus has shown potential for vaccination and for delivery of drugs or enzymes. Remarkably, proteins displayed on the spore surface retain activity and generally are not degraded. The heat stability of spores, coupled with their desiccation resistance, makes them suitable for delivery to humans or to animals by the oral route. Despite these attributes, one regulatory obstacle has remained regarding the fate of recombinant spores shed into the environment as viable spores. We have addressed the biological containment of GMO spores by utilizing the concept of a thymineless death, a phenomenon first reported 6 decades ago. Using Bacillus subtilis, we have inserted chimeric genes in the two thymidylate synthase genes, thyA and thyB, using a two-step process. Insertion is made first at thyA and then at thyB whereby resistance to trimethoprim enables selection of recombinants. Importantly, this method requires introduction of no new antibiotic resistance genes. Recombinant spores have a strict dependence on thymine (or thymidine), and in its absence cells lyse and die. Insertions are stable with no evidence for suppression or reversion. Using this system, we have successfully created a number of spore vaccines as well as spores displaying active enzymes.IMPORTANCE Genetic manipulation of bacterial spores offers a number of exciting possibilities for public and animal health, including their use as heat-stable vehicles for delivering vaccines or enzymes. Despite this, one remaining problem is the fate of recombinant spores released into the environment where they could survive in a dormant form indefinitely. We describe a solution whereby, following genetic manipulation, the bacterium is rendered dependent on thymine. As a consequence, spores if released would produce bacteria unable to survive, and they would exhibit a thymineless death due to rapid cessation of metabolism. The method we describe has been validated using a number of exemplars and solves a critical problem for containing spores of GMOs in the environment.

Development of a gene delivery system in Streptococcus gordonii using thymidylate synthase as a selection marker

Streptococcus gordonii, a commensal bacterium of the human oral cavity, is a potential live vaccine vector. In this study, we have developed a system that delivers a vaccine antigen gene onto the chromosome of S. gordonii. The system consisted of a recipient strain, that is a thymidine auxotroph constructed by deletion of a portion of thyA gene, and a linear gene delivery construct, composed of the functional thyA gene, the vaccine antigen gene, and a DNA fragment immediately downstream of thyA. The construct is assembled by a ligation and polymerase chain reaction strategy. Upon introduction into the thyA mutant, the vaccine antigen gene integrated into the chromosome via a double crossing-over event. Using the above strategy, a test vaccine antigen gene coding for a fusion protein composed of the Bordetella pertussis filamentous hemagglutinin type I domain and the single chain antibody against complement receptor 1 was successfully delivered to S. gordonii. The resulting S. gordonii expressed the fusion protein and the delivered gene was stable in the bacterium in vitro and in a mouse colonization experiment. Mice colonized by the fusion protein-expressing S. gordonii developed antibodies that recognized the native filamentous hemagglutinin protein suggesting that an immune response was elicited.

Bioengineered probiotics, a strategic approach to control enteric infections

Enteric infections account for high morbidity and mortality and are considered to be the fifth leading cause of death at all ages worldwide. Seventy percent of all enteric infections are foodborne. Thus significant efforts have been directed toward the detection, control and prevention of foodborne diseases. Many antimicrobials including antibiotics have been used for their control and prevention. However, probiotics offer a potential alternative intervention strategy owing to their general health beneficial properties and inhibitory effects against foodborne pathogens. Often, antimicrobial probiotic action is non-specific and non-discriminatory or may be ineffective. In such cases, bioengineered probiotics expressing foreign gene products to achieve specific function is highly desirable. In this review we summarize the strategic development of recombinant bioengineered probiotics to control enteric infections, and to examine how scientific advancements in the human microbiome and their immunomodulatory effects help develop such novel and safe bioengineered probiotics.

Increase of stress resistance in Lactococcus lactis via a novel food-grade vector expressing a shsp gene from Streptococcus thermophilus

The effects of the expression of a small heat shock protein (shsp) gene from Streptococcus thermophilus on stress resistance in Lactococcus lactis under different environmental stresses were investigated in this study. pMG36e-shsp, an expression vector, was first constructed by inserting a shsp open reading frame (ORF) cloned from S. thermophilus strain St-QC into pMG36e. Then, a food-grade expression vector, pMG-shsp, was generated by deleting the erythromycin resistance gene from pMG36e-shsp. The transformation rate of pMG-shsp was comparable to that of pMG36e-shsp when each of these two vectors was introduced into L. lactis. These results demonstrated that the shsp ORF could successfully used as a food-grade selection marker in both pMG-shsp and pMG36e-shsp. Furthermore, the growth characteristics were almost the same between L. lactis ML23 transformants harboring pMG36e or pMG-shsp. The survival rate of L. lactis ML23 expressing the shsp ORF were increased to 0.032%, 0.006%, 0.0027%, 0.03%, and 0.16% under the following environmental stresses: heat, acid, ethanol, bile salt and H2O2, respectively. These results indicated that the expression of the shsp gene in the food-grade vector pMG-shsp conferred resistance to environmental stresses without affecting the growth characteristics of L. lactis ML23.

The nisin-controlled gene expression system: Construction, application and improvements

Lactic acid bacteria are widely used in industrial fermentation. The potential use of these bacteria as homologous and heterologous protein expression hosts has been investigated extensively. The NIsin-Controlled gene Expression system (the NICE system) is an efficient and promising gene expression system based on the autoregulation mechanism of nisin biosynthesis in the Lactococcus lactis. In the NICE system, the membrane-located histidine kinase NisK senses the inducing signal nisin and autophosphorylates, then transfers phosphorous group to intracellular response regulator protein NisR which activates nisA promoter to express the downstream gene(s). The NICE system allows regulated overproduction of a variety of interest proteins by several Gram-positive bacteria, especially L. lactis. The essential elements for system construction, its application for expression of some biotechnologically important proteins and further improvements of this system are discussed.

ThyA as a selection marker in construction of food-grade host-vector and integration systems for Streptococcus thermophilus

We constructed food-grade host-vector and integration systems for Streptococcus thermophilus by using a thymidylate synthase gene (thyA) as the selection marker. Two thyA genes, thyA(St) and thyA(Lb), were cloned from S. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, respectively. Thymidine-requiring mutants of S. thermophilus were obtained after successive cultures in the presence of trimethoprim, and one of them, TM1-1, was used as the host. Food-grade vectors were constructed by using either thyA(St) or thyA(Lb) as the selection marker. Transformants of TM1-1 created by using these vectors were selected for thymidine autotrophy as efficiently as for erythromycin resistance. By using the host-vector system developed in this way, a foreign amylase gene (amyA) was expressed in TM1-1 and was also integrated into the chromosome by use of a temperature-sensitive integration vector constructed with thyA(Lb) as the selection marker via a double-crossover event. The results obtained show that thyA is an efficient and safe selection marker for S. thermophilus that is suitable for food applications.

Genetically engineered probiotics

Probiotic micro-organisms have been used for many years. Originating as food supplements, they are now most often administered orally and offer an attractive alternative for treating of intestinal disorders. A better understanding of the mechanisms by which these micro-organisms act has now opened up possibilities for designing new probiotic strains. Through genetic engineering, it is possible not only to strengthen the effects of existing strains, but also to create completely new probiotics. These need not necessarily be composed only of bacterial products but can also include elements of regulatory systems or enzymes derived from a foreign-human-source. If designed carefully and with absolute attention to biological safety in its broadest sense, the development of genetically modified probiotics has the potential to revolutionize alimentary health.

Application of the shsp gene, encoding a small heat shock protein, as a food-grade selection marker for lactic acid bacteria

Plasmid pSt04 of Streptococcus thermophilus contains a gene encoding a protein with homology to small heat shock proteins (A. Geis, H. A. M. El Demerdash, and K. J. Heller, Plasmid 50:53-69, 2003). Strains cured from the shsp plasmids showed significantly reduced heat and acid resistance and a lower maximal growth temperature. Transformation of the cloned shsp gene into S. thermophilus St11 lacking a plasmid encoding shsp resulted in increased resistance to incubation at 60 degrees C or pH 3.5 and in the ability to grow at 52 degrees C. A food-grade cloning system for S. thermophilus, based on the plasmid-encoded shsp gene as a selection marker, was developed. This approach allowed selection after transfer of native and recombinant shsp plasmids into different S. thermophilus and Lactococcus lactis strains. Using a recombinant plasmid carrying an erythromycin resistance (Em(r)) gene in addition to shsp, we demonstrated that both markers are equally efficient in selecting for plasmid-bearing cells. The average transformation rates in S. thermophilus (when we were selecting for heat resistance) were determined to be 2.4 x 10(4) and 1.0 x 10(4) CFU/0.5 micro g of DNA, with standard deviations of 0.54 x 10(4) and 0.32 x 10(4), for shsp and Em(r) selection, respectively. When we selected for pH resistance, the average transformation rates were determined to be 2.25 x 10(4) and 3.8 x 10(3) CFU/0.5 micro g of DNA, with standard deviations of 0.63 x 10(4) and 3.48 x 10(3), for shsp and Em(r) selection, respectively. The applicability of shsp as a selection marker was further demonstrated by constructing S. thermophilus plasmid pHRM1 carrying the shsp gene as a selection marker and the restriction-modification genes of another S. thermophilus plasmid as a functional trait.

New integration vector using a cellulase gene as a screening marker for Lactobacillus

The new integration vector for Lactobacillus, pJC4, was developed using the extracellular endoglucanase A gene (celA) of Clostridium thermocellum as a screening marker. pJC4 was transformed into four Lactobacillus species, Lb. johnsonii, Lb. gasseri, Lb. bulgaricus, and Lb. plantarum. In each species, the pJC4 integrants were easily and accurately detected by the appearance of a clear halo on a cellulase screening plate without any false transformants. Polymerase chain reaction and Southern hybridization indicated that all transformants with clear halos contained pJC4 in their chromosomal DNAs. The celA gene could be a useful screening marker for other lactic acid bacteria.

Biological containment of genetically modified Lactococcus lactis for intestinal delivery of human interleukin 10

Genetically modified Lactococcus lactis secreting interleukin 10 provides a therapeutic approach for inflammatory bowel disease. However, the release of such genetically modified organisms through clinical use raises safety concerns. In an effort to address this problem, we replaced the thymidylate synthase gene thyA of L. lactis with a synthetic human IL10 gene. This thyA- hIL10+ L. lactis strain produced human IL-10 (hIL-10), and when deprived of thymidine or thymine, its viability dropped by several orders of magnitude, essentially preventing its accumulation in the environment. The biological containment system and the bacterium's capacity to secrete hIL-10 were validated in vivo in pigs. Our approach is a promising one for transgene containment because, in the unlikely event that the engineered L. lactis strain acquired an intact thyA gene from a donor such as L. lactis subsp. cremoris, the transgene would be eliminated from the genome.

A food-grade approach for functional analysis and modification of native plasmids in Lactococcus lactis

While plasmids from lactic acid bacteria possess many traits that are of industrial value, their exploitation is often frustrated by an inability to conduct food-grade engineering of native plasmids or to readily screen for their transfer. Here we describe a system that uses a RepA(+) temperature-sensitive helper plasmid and a RepA(-) cloning vector to overcome these problems while maintaining the food-grade status of the native plasmid. This strategy was used to precisely delete ltnA1 alone, or in conjunction with ltnA2 (encoding the structural proteins of the lantibiotic lacticin 3147), from the native 60.2-kb plasmid pMRC01 and to select for the transfer of pMRC01 between Lactococcus lactis strains.