Evaluation of Lentilactobacillus parafarraginis A6-2 strain for aluminum removal and anti-inflammatory effects: implications for alleviating Al toxicity

AIM

To assess the effectiveness of Lentilactobacillus parafarraginis A6-2 cell lysate for the removal of aluminum (Al), which induces neurotoxicity, and its protective effect at cellular level.

METHODS AND RESULTS

The cell lysate of the selected L. parafarraginis A6-2 strain demonstrated superior Al removal compared to live or dead cells. The Al removal efficiency of L. parafarraginis A6-2 cell lysate increased with decreasing pH and increasing temperature, primarily through adsorption onto peptidoglycan. Neurotoxicity mitigation potential of L. parafarraginis A6-2 was evaluated using C6 glioma cells. C6 cells exposed with increasing concentration of Al led to elevated toxicity and inflammation, which were gradually alleviated upon treatment with L. parafarraginis A6-2. Moreover, Al-induced oxidative stress in C6 cells showed a concentration-dependent reduction upon treatment with L. parafarraginis A6-2.

CONCLUSIONS

This study demonstrated that L. parafarraginis A6-2 strain, particularly in its lysate form, exhibited enhanced capability for Al removal. Furthermore, it effectively mitigated Al-induced toxicity, inflammation, and oxidative stress.

Lactococcus lactis Mutants Obtained From Laboratory Evolution Showed Elevated Vitamin K2 Content and Enhanced Resistance to Oxidative Stress

Vitamin K2 is an important vitamin for human health. Vitamin K2 enrichment in the human diet is possible by using vitamin K2-producing bacteria such as Lactococcus lactis in food fermentations. Based on previous observations that aerated cultivation conditions improved vitamin K2 content in L. lactis, we performed laboratory evolution on L. lactis MG1363 by cultivating this strain in a shake flask in a sequential propagation regime with transfers to a fresh medium every 72h. After 100 generations of propagation, we selected three evolved strains that showed improved stationary phase survival in oxygenated conditions. In comparison to the original strain MG1363, the evolved strains showed 50-110% increased vitamin K2 content and exhibited high resistance against hydrogen peroxide-induced oxidative stress. Genome sequencing of the evolved strains revealed common mutations in the genes ldh and gapB. Proteomics analysis revealed overproduction of glyceraldehyde 3-phosphate dehydrogenase (GapA), universal stress protein A2 (UspA2), and formamidopyrimidine-DNA glycosylase (MutM) under aerated conditions in evolved strains, proteins with putative functions in redox reactions, universal stress response, and DNA damage repair, all of which could contribute to the enhanced oxidative stress resistance. The mechanisms underlying elevated vitamin K2 content in the evolved strains remain to be elucidated. Two out of the three evolved strains performed similar to the original strain MG1363 in terms of growth and acidification of culture media. In conclusion, this study demonstrated a natural selection approach without genetic manipulations to obtain vitamin K2 overproducers that are highly relevant for food applications and contributed to the understanding of oxidative stress resistance in L. lactis.

Bioengineering of LAB vector expressing Haemolysin co-regulated protein (Hcp): a strategic approach to control gut colonization of Campylobacter jejuni in a murine model

Background

Campylobacter jejuni (C. jejuni) is accountable for more than 400 million cases of gastroenteritis each year and is listed as a high-priority gut pathogen by the World Health Organization (WHO). Although the acute infection of C. jejuni (campylobacteriosis) is commonly treated with macrolides and fluoroquinolones, the emergence of antibiotic resistance among C. jejuni warrants the need for an alternative approach to control campylobacteriosis in humans. To this end, vaccines remain a safe, effective, and widely accepted strategy for controlling emerging and re-emerging infectious diseases. In search of a suitable vaccine against campylobacteriosis, recently, we demonstrated the potential of recombinant Haemolysin co-regulated protein (Hcp) of C. jejuni Type VI secretion system (T6SS) in imparting significant immune-protection against cecal colonization of C. jejuni; however, in the avian model. Since clinical features of human campylobacteriosis are more complicated than the avians, we explored the potential of Hcp as a T6SS targeted vaccine in a murine model as a more reliable and reproducible experimental host to study vaccine-induced immune-protection against C. jejuni. Because C. jejuni primarily utilizes the mucosal route for host pathogenesis, we analyzed the immunogenicity of a mucosally deliverable bioengineered Lactic acid bacteria (LAB), Lactococcus lactis (L. lactis), expressing Hcp. Considering the role of Hcp in both structural (membrane-bound) and functional (effector protein) exhibition of C. jejuni T6SS, a head-to-head comparison of two different forms of recombinant LAB vectors (cell wall anchored and secreted form of Hcp) were tested and assessed for the immune phenotypes of each modality in BALB/c mice.

Results

We show that regardless of the Hcp protein localization, mucosal delivery of bioengineered LAB vector expressing Hcp induced high-level production of antigen-specific neutralizing antibody (sIgA) in the gut with the potential to reduce the cecal load of C. jejuni in mice.

Conclusion

Together with the non-commensal nature of L. lactis, short gut transit time in humans, and the ability to express the heterologous protein in the gut, the present study highlights the benefits of bioengineered LAB vectors based mucosal vaccine modality against C. jejuni without the risk of immunotolerance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13099-021-00444-2.

Safety Aspects of Genetically Modified Lactic Acid Bacteria

Lactic acid bacteria (LAB) have a long history of use in the food industry. Some species are part of the normal human microbiota and have beneficial properties for human health. Their long-standing use and considerable biotechnological potential have led to the development of various systems for their engineering. Together with novel approaches such as CRISPR-Cas, the established systems for engineering now allow significant improvements to LAB strains. Nevertheless, genetically modified LAB (GM-LAB) still encounter disapproval and are under extensive regulatory requirements. This review presents data on the prospects for LAB to obtain 'generally recognized as safe' (GRAS) status. Genetic modification of LAB is discussed, together with problems that can arise from their engineering, including their dissemination into the environment and the spread of antibiotic resistance markers. Possible solutions that would allow the use of GM-LAB are described, such as biocontainment, alternative selection markers, and use of homologous DNA. The use of GM-LAB as cell factories in closed systems that prevent their environmental release is the least problematic aspect, and this is also discussed.

Genome editing of lactic acid bacteria: opportunities for food, feed, pharma and biotech

This mini-review provides a perspective of traditional, emerging and future applications of lactic acid bacteria (LAB) and how genome editing tools can be used to overcome current challenges in all these applications. It also describes available tools and how these can be further developed, and takes current legislation into account. Genome editing tools are necessary for the construction of strains for new applications and products, but can also play a crucial role in traditional ones, such as food and probiotics, as a research tool for gaining mechanistic insights and discovering new properties. Traditionally, recombinant DNA techniques for LAB have strongly focused on being food-grade, but they lack speed and the number of genetically tractable strains is still rather limited. Further tool development will enable rapid construction of multiple mutants or mutant libraries on a genomic level in a wide variety of LAB strains. We also propose an iterative Design–Build–Test–Learn workflow cycle for LAB cell factory development based on systems biology, with ‘cell factory’ expanding beyond its traditional meaning of production strains and making use of genome editing tools to advance LAB understanding, applications and strain development.

Co-expression of Nisin Z and Leucocin C as a Basis for Effective Protection Against Listeria monocytogenes in Pasteurized Milk

Nisin, an important bacteriocin from Lactococcus lactis subsp., is primarily active against various Gram-positive bacteria. Leucocin C, produced by Leuconostoc carnosum 4010, is a class IIa bacteriocin used to inhibit the growth of Listeria monocytogenes. Because two bacteriocins have different modes of action, the combined use of them could be a potential strategy for effective inhibition of foodborne pathogens. In this study, L. lactis N8-r-lecCI (N8 harboring lecCI gene) coexpressing nisin–leucocin C was constructed based on the food-grade carrier L. lactis N8. Production of both bacteriocins was stably maintained. Antimicrobial measurements showed that the recombinant strain is effectively against Listeria monocytogenes and Staphylococcus aureus and moderately against Salmonella enterica serovar Enteritidis and Escherichia coli because of its stronger antibacterial activity than the parental strain, this result first demonstrated that the co-expression of nisin and leucocin C results in highly efficient antimicrobial activity. The checkerboard assay showed that the antibacterial activity of L. lactis N8-r-lecCI supernatant was enhanced in the presence of low concentration of EDTA. Analysis of the scanning electron microscope image showed the biggest cellular morphology change in L. monocytogenes treated with a mixture of EDTA and L. lactis N8-r-lecCI supernatant. The practical effect was verified in pasteurized milk through time-kill assay. The L. lactis N8-r-lecCI strain expressing both nisin and leucocin C has a promising application prospect in pasteurized milk processing and preservation because of its strong antibacterial activity.

Lactic Acid Bacteria from Andean Grain Amaranth: A Source of Vitamins and Functional Value Enzymes

Amaranth is a rediscovered pseudocereal with high nutritional properties. Lactic acid fermentation can increase the functional and nutritional value of foods. The aims of this study were to isolate and evaluate the functionality of lactic acid bacteria (LAB) from amaranth. LAB strains (<i>n</i> = 29) isolated from amaranth sourdough and grains included <i>Lactobacillus</i> (<i>L.</i>) <i>plantarum</i> (<i>n</i> = 8), <i>L. rhamnosus</i> (<i>n</i> = 6), <i>Enterococcus</i> (<i>E.</i>) <i>mundtii</i> (<i>n</i> = 4), <i>E. hermanniensis</i> (<i>n</i> = 3), <i>E. durans</i> (<i>n</i> = 1), <i>Enterococcus</i> sp. (<i>n</i> = 1), <i>Leuconostoc</i> (<i>Lc.</i>) <i>mesenteroides</i> (<i>n</i> = 3), and <i>Lc. mesenteroides </i>subsp<i>. mesenteroides </i>(<i>n</i> = 3). Only 21% of the strains showed the ability to synthesize capsular exopolysaccharides or display ropiness and only 8 strains showed amylolytic activity. <i>L. plantarum </i>CRL 2106 and <i>E. durans </i>CRL 2122 showed the highest phytase activity, which is of importance for mineral bioavailability. <i>L. plantarum </i>CRL 2106 and CRL 2107 and <i>Lc. mesenteroides </i>subsp.<i> mesenteroides</i> CRL 2131 synthesized the highest concentrations of B₂ and B₉ vitamin (140-250 ng/mL). This study demonstrates the potential of LAB to improve the nutritional and functional values of pseudocereal-derived foods.

Lactic acid bacteria as a cell factory for riboflavin production

Consumers are increasingly becoming aware of their health and nutritional requirements, and in this context, vitamins produced in situ by microbes may suit their needs and expectations. B groups vitamins are essential components of cellular metabolism and among them riboflavin is one of the vital vitamins required by bacteria, plants, animals and humans. Here, we focus on the importance of microbial production of riboflavin over chemical synthesis. In addition, genetic abilities for riboflavin biosynthesis by lactic acid bacteria are discussed. Genetically modified strains by employing genetic engineering and chemical analogues have been developed to enhance riboflavin production. The present review attempts to collect the currently available information on riboflavin production by microbes in general, while placing greater emphasis on food grade lactic acid bacteria and human gut commensals. For designing riboflavin‐enriched functional foods, proper selection and exploitation of riboflavin‐producing lactic acid bacteria is essential. Moreover, eliminating the in situ vitamin fortification step will decrease the cost of food production.

Production of aroma compounds in lactic fermentations

This review describes recent scientific research on the production of aroma compounds by lactic acid bacteria (LAB) in fermented food products. We discuss the various precursor molecules for the formation of aroma compounds in connection with the metabolic pathways involved. The roles of nonmetabolic properties such as cell lysis are also described in relation to aroma formation. Finally, we provide an overview of the literature on methods to steer and control aroma formation by LAB in mixed culture fermentations. We demonstrate that the technological progress made recently in high-throughput analysis methods has been driving the development of new approaches to understand, control, and steer aroma formation in (dairy) fermentation processes. This currently entails proposing new rules for designing stable, high-performance mixed cultures constituting a selection of strains, which in concert and on the basis of their individual predicted gene contents deliver the required functionalities.

Selection of mutants tolerant of oxidative stress from respiratory cultures of Lactobacillus plantarum C17

AIMS

Lactobacillus plantarum is a lactic acid bacterium involved in the production of many fermented foods. Recently, several studies have demonstrated that aerobic or respiratory metabolism in this species leads to improved technological and stress response properties.

METHODS AND RESULTS

We investigated respiratory growth, metabolite production and stress resistance of Lact. plantarum C17 during batch, fed-batch and chemostat cultivations under respiratory conditions. Sixty mutants were selected for their ability to tolerate oxidative stress using H2 O2 and menadione as selective agents and further screened for their capability to growth under anaerobic, respiratory and oxidative stress conditions. Dilution rate clearly affected the physiological state of cells and, generally, slow-growing cultures had improved survival to stresses, catalase production and oxygen uptake. Most mutants were more competitive in terms of biomass production and ROS degradation compared with wild-type strain (wt) C17 and two of these (C17-m19 and C17-m58) were selected for further experiments.

CONCLUSIONS

This work confirms that, in Lact. plantarum, respiration and low growth rates confer physiological and metabolic advantages compared with anaerobic cultivation.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our strategy of natural selection successfully provides a rapid and inexpensive screening for a large number of strains and represents a food-grade approach of practical relevance in the production of starter and probiotic cultures.

Isolation of Pediococcus acidilactici Kp10 with ability to secrete bacteriocin-like inhibitory substance from milk products for applications in food industry

Background

Lactic acid bacteria (LAB) can be isolated from traditional milk products. LAB that secrete substances that inhibit pathogenic bacteria and are resistant to acid, bile, and pepsin but not vancomycin may have potential in food applications.

Results

LAB isolated from a range of traditional fermented products were screened for the production of bacteriocin-like inhibitory substances. A total of 222 LAB strains were isolated from fermented milk products in the form of fresh curds, dried curds, and ghara (a traditional flavor enhancer prepared from whey), and fermented cocoa bean. Eleven LAB isolates that produced antimicrobial substances were identified as Lactococcus lactis, Lactobacillus plantarum, and Pediococcus acidilactici strains by biochemical methods and 16S rDNA gene sequencing. Of these, the cell-free supernatant of Kp10 (P. acidilactici) most strongly inhibited Listeria monocytogenes. Further analysis identified the antimicrobial substance produced by Kp10 as proteinaceous in nature and active over a wide pH range. Kp10 (P. acidilactici) was found to be catalase-negative, able to produce β-galactosidase, resistant to bile salts (0.3%) and acidic conditions (pH 3), and susceptible to most antibiotics.

Conclusion

Traditionally prepared fermented milk products are good sources of LAB with characteristics suitable for industrial applications. The isolate Kp10 (P. acidilactici) shows potential for the production of probiotic and functional foods.

Bioengineering: a bacteriocin perspective

While the bacteriocin Nisin has been employed by the food industry for 60 y, it remains the only bacteriocin to be extensively employed as a food preservative. This is despite the fact that the activity of Nisin against several food spoilage and pathogenic bacteria is poor and the availability of many other bacteriocins with significant potential in this regard. An alternative route to address the deficiencies of Nisin is the application of bioengineered derivatives of the peptide which, despite differing only subtly, possess enhanced capabilities of commercial value. The career path which has taken me from learning for the first time what bacteriocins are to understanding the potential of bacteriocin bioengineering has been a hugely enjoyable experience and promises to get even more interesting in the years to come.

Food-grade gene expression in lactic acid bacteria

In the 1990s, significant efforts were invested in the research and development of food-grade expression systems in lactic acid bacteria (LAB). At this time, Lactococcus lactis in particular was demonstrated to be an ideal cell factory for the food-grade production of recombinant proteins. Steady progress has since been made in research on LAB, including Lactococcus, Lactobacillus and Streptococcus, in the areas of recombinant enzyme production, industrial food fermentation, and gene and metabolic pathway regulation. Over the past decade, this work has also led to new approaches on chromosomal integration vectors and host/vector systems. These newly constructed food-grade gene expression systems were designed with specific attention to self-cloning strategies, food-grade selection markers, plasmid replication and chromosomal gene replacements. In this review, we discuss some well-characterized chromosomal integration and food-grade host/vector systems used in LAB, with a special focus on sustainability, stability and overall safety, and give some attractive examples of protein expression that are based on these systems.

Highest Observed Intake: definition, regulatory uses and provisional values

For nutrients and related substances, the Tolerable Upper Intake Level (UL) has become the internationally accepted risk assessment method. The major limitation of the UL method as applied by authoritative groups thus far is that no UL has been set for nutrients without established adverse effects. In contrast to the limitations inherent in the UL method, an alternative approach is available; it identifies a risk assessment value termed the Highest Observed Intake (HOI). In the absence of a UL, the HOI is the highest intake with adequate data to show, with acceptable confidence, the absence of adverse effects up to that intake. With this concept defined and accepted in a report by the authoritative international organizations FAO and WHO, a complete risk assessment for the nutrients and related substances would have to identify UL values for those with known adverse effects and HOI values for those without known adverse effects. The need for the HOI concept and value is illustrated by the unjustified policy and regulatory actions taken in relation to vitamin B12. Regulatory utility is explained and tentative HOI values are identified for several vitamins and non-essential nutrients. Endorsement of the concept and development of HOI values by authoritative bodies is likely to be required for broad acceptance and use.

Importance of IL-10 modulation by probiotic microorganisms in gastrointestinal inflammatory diseases

Lactic acid bacteria (LAB) represent a heterogeneous group of microorganisms that are naturally present in many foods and possess a wide range of therapeutic properties. The aim of this paper is to present an overview of the current expanding knowledge of one of the mechanisms by which LAB and other probiotic microorganisms participate in the prevention and treatment of gastrointestinal inflammatory disease through their immune-modulating properties. A special emphasis will be placed on the critical role of the anti-inflammatory cytokine IL-10, and a brief overview of the uses of genetically engineered LAB that produce this important immune response mediator will also be discussed. Thus, this paper will demonstrate the critical role that IL-10 plays in gastrointestinal inflammatory diseases and how probiotics could be used in their treatment.

Generation and characterization of thymidine/D-alanine auxotrophic recombinant Lactococcus lactis subsp. lactis IL1403 expressing BmpB

Genetic engineering of Lactococcus lactis to produce a heterologous protein may cause potential risks to the environment despite the industrial usefulness of engineered strains. To reduce the risks, we generated three auxotrophic recombinant L. lactis subsp. lactis IL1403 strains expressing a heterologous protein, BmpB, using thyA- and alr-targeting integration vectors: ITD (thyA(-)alr(+) bmpB(+)), IAD (thyA(+)alr(-)bmpB(+)), and ITDAD (thyA(-)alr(-) bmpB(+)). After construction of integration vectors, each vector was introduced into IL1403 genome. Integration of BmpB expression cassette, deletion of thyA, and inactivation of alr were verified by using PCR reaction. All heterologous DNA fragments except bmpB were eliminated from those recombinants during double crossover events. By using five selective agar plates, we also showed thymidine auxotrophy of ITD and ITDAD and D-alanine auxotrophy of IAD and ITDAD. In M17G and skim milk (SYG) media, the growth of the three recombinants was limited. In MRS media, the growth of IAD and ITDAD was limited, but ITD showed a normal growth pattern as compared with the wild-type strain (WT). All the recombinants showed maximal BmpB expression at an early stationary phase when they were cultivated in M17G supplemented with thymidine and D-alanine. These results suggest that auxotrophic recombinant L. lactis expressing a heterologous protein could be generated to reduce the ecological risks of a recombinant L. lactis.

Bacterial vitamin B2, B11 and B12 overproduction: An overview

Consumers are becoming increasingly health conscious and therefore more discerning in their food choices. The production of fermented food products with elevated levels of B-vitamins increase both their commercial and nutritional value, and eliminate the need for subsequent fortification with these essential vitamins. Such novel products could reduce the incidence of inadequate vitamin intake which is common in many parts of the world, not only in developing countries, but also in many industrialised countries. Moreover, the concept of in situ fortification by bacterial fermentation opens the way for development of food products targeted at specific groups in society such as the elderly and adolescents. This review looks at how vitamin overproduction strategies have been developed, some of which have successfully been tested in animal models. Such innovative strategies could be relatively easily adapted by the food industry to develop novel vitamin-enhanced functional foods with enhanced consumer appeal.