Heterologous expression of linoleic acid isomerase from Propionibacterium acnes and anti-proliferative activity of recombinant trans-10, cis-12 conjugated linoleic acid

Engineering the β-Oxidation Pathway in Yarrowia lipolytica for the Production of trans-10, cis-12-Conjugated Linoleic Acid

trans-10, cis-12-Conjugated linoleic acid (t10, c12-CLA) is an octadecadienoic acid with various biological benefits. Previously, linoleic acid isomerase from Propionibacterium acnes (PAI) was overexpressed in Yarrowia lipolytica (Y. lipolytica) to produce t10, c12-CLA. However, the t10, c12-CLA yield was restricted by the peroxisomal β-oxidation pathway. In this study, to minimize the degradation of t10, c12-CLA, four genetically modified strains of Y. lipolytica (Δpox2-oPAI, Δpox3-oPAI, Δpox2Δpox3-oPAI, and Δpex10-oPAI) were constructed and compared in terms of production stability and yield of t10, c12-CLA using safflower seed oil as substrates. The Δpex10-oPAI strain exhibited the best results, as revealed by the reduction of the t10, c12-CLA degradation rate from 58.5 to 18.6 mg/L/h. Additionally, the YLUpex10mP recombinant strain bearing six copies of oPAI combined with PEX10 deletion enhanced t10, c12-CLA production to 7.4 g/L and exhibited a CLA degradation rate of 19.7 mg/L/h, a 78% decrease from that of the control strain. Finally, in a bioreactor containing low-cost volatile fatty acids as partial carbon sources, the t10, c12-CLA content in the YLUpex10mP strain increased to 9.7 g/L, 1.3 times higher than in flasks. To our knowledge, this is the highest t10, c12-CLA yield through microbial synthesis reported to date.

Measuring Conjugated Linoleic Acid (CLA) Production by Bifidobacteria

The biological significance of conjugated fatty acids (CFAs) has been linked to positive health effects based on biomedical, in vitro, and clinical studies. Of note, conjugated linoleic acids (CLAs) are the most widely characterized fatty acids as geometric isomers cis-9,trans-11 and trans-10,cis-12 CLA occur naturally in ruminant fats, dairy products, and hydrogenated oils. Concerning CLAs, it is known that bacterial biohydrogenation, a process whereby ruminal bacteria or starter cultures of lactic acid bacteria have the ability to synthesize CLA by altering the chemical structure of essential fatty acids via enzymatic mechanisms, produces a multitude of isomers with desirable properties. Bifidobacterium species are classed as food grade microorganisms and some of these strains harness molecular determinants that are responsible for the bioconversion of free fatty acids to CLAs. However, molecular mechanisms have yet to be fully elucidated. Reports pertaining to CLAs have been attributed to suppressing tumor growth, delaying the onset of diabetes mellitus and reducing body fat in obese individuals. Given the increased attention for their bioactive properties, we describe in this chapter the qualitative and quantitative methods used to identify and quantify CLA isomers produced by bifidobacterial strains in supplemented broth media. These approaches enable rapid detection of potential CLA producing strains and accurate measurement of fatty acids in biological matrices.

LysR Family Regulator LttR Controls Production of Conjugated Linoleic Acid in Lactobacillus plantarum by Directly Activating the cla Operon

Conjugated linoleic acids (CLAs) have attracted more attention as functional lipids due to their potential physiological activities, including anticancer, anti-inflammatory, anti-cardiovascular disease, and antidiabetes activities. Microbiological synthesis of CLA has become a compelling method due to its high isomer selectivity and convenient separation and purification processes. In Lactobacillus plantarum, the generation of CLA from linoleic acids (LAs) requires the combination of CLA oleate hydratase (CLA-HY), CLA short-chain dehydrogenase (CLA-DH), and CLA acetoacetate decarboxylase (CLA-DC), which are separately encoded by cla-hy, cla-dh, and cla-dc. However, the regulatory mechanisms of CLA synthesis remain unknown. In this study, we found that a LysR family transcriptional regulator, LTTR, directly bound to the promoter region of the cla operon and activated the transcription of cla-dh and cla-dc. The binding motif was also predicted by bioinformatics analysis and verified by electrophoretic mobility shift assays (EMSAs) and DNase I footprinting assays. The lttR overexpression strain showed a 5-fold increase in CLA production. Moreover, we uncovered that the transcription of lttR is activated by LA. These results indicate that LttR senses LA and promotes CLA production by activating the transcription of cla-dh and cla-dc. This study reveals a new regulatory mechanism in CLA biotransformation and provides a new potential metabolic engineering strategy to increase the yield of CLA.IMPORTANCE Our work has identified a novel transcriptional regulator, LTTR, that regulates the production of CLA by activating the transcription of cla-dh and cla-dc, essential genes participating in CLA synthesis in Lactobacillus plantarum This study provides insight into the regulatory mechanism of CLA synthesis and broadens our understanding of the synthesis and regulatory mechanisms of the biosynthesis of CLA.

Novel Lactobacillus reuteri HI120 Affects Lipid Metabolism in C57BL/6 Obese Mice

Intestinal probiotics are a primary focus area of current medical research. Probiotics such as bifidobacteria and lactobacilli can positively impact obesity and other metabolic diseases by directly or indirectly affecting lipid metabolism. However, the precise mechanisms of these effects remain unclear. In our previous work, the novel strain Lactobacillus reuteri HI120 was isolated and identified. HI120 expresses high levels of linoleic isomerase, resulting in the production of large amounts of conjugated linoleic acid (CLA) when mixed with linoleic acid (LA). As HI120 can efficiently transform LA into CLA, the effect of HI120 on the lipid metabolism in C57BL/6 obese mice was studied and the underlying molecular mechanism was explored in vitro. The results revealed no significant change in the diet, body weight, and serum triglyceride levels in mice. However, serum cholesterol levels were significantly decreased. The underlying mechanism may involve a CLA-mediated reduction in the gene expression levels of NPC1L1, SREBP-2, and HMG-CR, resulting in reduced cholesterol synthesis and absorption. Thus, HI120 can be developed as a potential probiotic formulation. After oral administration, LA from certain food sources can be converted into CLA in the human intestine to contribute to the prevention and treatment of obesity and hyperlipidemia.

A single amino acid substitution in the FAD-binding domain causes the inactivation of Propionibacterium Acnes isomerase

We previously demonstrated the efficient production of trans 10, cis 12-conjugated linoleic acid (t10c12-CLA) in Lactococcus lactis by ectopically expressing a Propionibacterium acnes isomerase (pai) gene and also mentioned that a recombinant strain was unable to accumulate t10c12-CLA product, despite the normal transcription. Here, the molecular analysis indicated that this mutated strain harbors a pai gene with a single-nucleotide mutation converting GC⁵⁰A to GTA, leading to a corresponding change of Alanine residue into Valine. The expression of the reverse mutation resulted in the recovery for enzyme activity. Site-directed mutagenesis indicated that the codon usage of Val¹⁷ was not responsible for the enzyme inactivation in the Ala¹⁷Val mutation. Western blot analysis revealed that the recombinant PAI protein was not detectable in the His tag-marked Ala¹⁷Val mutant. It is, therefore, reasonable to assume that Ala¹⁷ residue is critical for PAI functionality.Abbreviations: pai: propionibacterium acnes isomerase; CLA: conjugated linoleic acid; t10c12-CLA: trans 10, cis 12-CLA; LA: linoleic acid (18:2n-6); FAD: flavin adenine dinucleotide.

Microbial Production of Conjugated Linoleic Acid and Conjugated Linolenic Acid Relies on a Multienzymatic System

Conjugated linoleic acids (CLAs) and conjugated linolenic acids (CLNAs) have gained significant attention due to their anticarcinogenic and lipid/energy metabolism-modulatory effects. However, their concentration in foodstuffs is insufficient for any therapeutic application to be implemented. From a biotechnological standpoint, microbial production of these conjugated fatty acids (CFAs) has been explored as an alternative, and strains of the genera Propionibacterium, Lactobacillus, and Bifidobacterium have shown promising producing capacities. Current screening research works are generally based on direct analytical determination of production capacity (e.g., trial and error), representing an important bottleneck in these studies. This review aims to summarize the available information regarding identified genes and proteins involved in CLA/CLNA production by these groups of bacteria and, consequently, the possible enzymatic reactions behind such metabolic processes. Linoleate isomerase (LAI) was the first enzyme to be described to be involved in the microbiological transformation of linoleic acids (LAs) and linolenic acids (LNAs) into CFA isomers. Thus, the availability of lai gene sequences has allowed the development of genetic screening tools. Nevertheless, several studies have reported that LAIs have significant homology with myosin-cross-reactive antigen (MCRA) proteins, which are involved in the synthesis of hydroxy fatty acids, as shown by hydratase activity. Furthermore, it has been suggested that CLA and/or CLNA production results from a stress response performed by the activation of more than one gene in a multiple-step reaction. Studies on CFA biochemical pathways are essential to understand and characterize the metabolic mechanism behind this process, unraveling all the gene products that may be involved. As some of these bacteria have shown modulation of lipid metabolism in vivo, further research to be focused on this topic may help us to understand the role of the gut microbiota in human health.

Conjugated linoleic acid enriched skim milk prepared with Lactobacillus fermentum DDHI27 endorsed antiobesity in mice

Aim: This study evaluated the antiobesity effect of skim milk prepared with conjugated linoleic acid producing probiotic Lactobacillus fermentum DDHI27 (PCLA). Materials & methods: C57BL/6 J mice were divided into five groups, and different obesity-associated parameters were studied. Results: PCLA supplementation alleviated body weight, epididymal and mesenteric fats and improves lipid profiles. Significant ameliorations in leptin, blood glucose, hepatic steatosis and reduction in adipocytes size were also observed. Additionally, feeding also led to positive alterations in the adipogenesis transcription factors and key lipogenesis genes. Improvement in the gut microbiota dysbiosis was also revealed. Conclusion: Results inferred that PCLA exerted an antiobesity effect in diet-induced obese mice and may be further developed in the functional foods for the management of obesity.

Symposium review: Understanding diet-microbe interactions to enhance productivity of dairy cows

Ruminants are dependent on the microbiota (bacteria, protozoa, archaea, and fungi) that inhabit the reticulo-rumen for digestion of feedstuffs. Nearly 70% of energy and 50% of protein requirements for dairy cows are met by microbial fermentation in the rumen, emphasizing the need to characterize the role of microbes in feed breakdown and nutrient utilization. Over the past 2 decades, next-generation sequencing technologies have allowed for rapid expansion of knowledge concerning microbial populations and alterations in response to forages, concentrates, supplements, and probiotics in the rumen. Advances in gene sequencing and emerging bioinformatic tools have allowed for increased throughput of data to aid in our understanding of the functional relevance of microbial genomes. In particular, metagenomics can identify specific genes involved in metabolic pathways, and metatranscriptomics can describe the transcriptional activity of microbial genes. These powerful approaches help untangle the complex interactions between microbes and dietary nutrients so that we can more fully understand the physiology of feed digestion in the rumen. Application of genomics-based approaches offers promise in unraveling microbial niches and respective gene repertoires to potentiate fiber and nonfiber carbohydrate digestion, microbial protein synthesis, and healthy biohydrogenation. New information on microbial genomics and interactions with dietary components will more clearly define pathways in the rumen to positively influence milk yield and components.

Conjugated linoleic acid: A potent fatty acid linked to animal and human health

Conjugated linoleic acid (CLA) is a mixture of isomers of linoleic acid (C18:2 n-6), which is mostly found in the ruminant meat and dairy products. The CLA is known to have many potential health benefits, and considered a potent powerful fatty acid, which is linked to animal and human health. The present work aims to discuss the source and production, mechanism of action, and effects of CLA on humans, poultry, and ruminants by reviewing the recent studies carried out on CLA. Despite most of the recent studies indicating beneficial effects of CLA on improving body weight control parameters, its effects on reducing risk factors of cardiovascular diseases (CVD), inflammation, blood glucose, and insulin are still controversial, and need to be further studied in different hosts.

Bacterial conjugated linoleic acid production and their applications

Conjugated linoleic acid (CLA) has been shown to exert various potential physiological properties including anti-carcinogenic, anti-obesity, anti-cardiovascular and anti-diabetic activities, and consequently has been considered as a promising food supplement. Bacterial biosynthesis of CLA is an attractive approach for commercial production due to its high isomer-selectivity and convenient purification process. Many bacterial species have been reported to convert free linoleic acid (LA) to CLA, hitherto only the precise CLA-producing mechanisms in Propionibacterium acnes and Lactobacillus plantarum have been illustrated completely, prompting the development of recombinant technology used in CLA production. The purpose of the article is to review the bacterial CLA producers as well as the recent progress on describing the mechanism of microbial CLA-production. Furthermore, the advances and potential in the heterologous expression of CLA genetic determinants will be presented.

Green Synthesis of Conjugated Linoleic Acids from Plant Oils Using a Novel Synergistic Catalytic System

A novel and efficient method has been developed for converting plant oil into a specific conjugated linoleic acid (CLA) using a synergistic biocatalytic system based on immobilized Propionibacterium acnes isomerase (PAI) and Rhizopus oryzae lipase (ROL). PAI exhibited the greatest catalytic activity when immobilized on D301R anion-exchange resin under optimal conditions (PAI dosage of 12 410 U of PAI/g of D301R, glutaraldehyde concentration of 0.4%, and reaction conditions of pH 7.0, 25 °C, and 60 min). Up to 109 g/L trans-10,cis-12-CLA was obtained after incubation of 200 g/L sunflower oil with PAI (1659 U/g of oil) and ROL (625 mU/g of oil) at pH 7.0 and 35 °C for 36 h; the corresponding conversion ratio of linoleic acid (LA) to CLA was 90.5%. This method exhibited the highest proportion of trans-10,cis-12-CLA yet reported and is a promising method for large-scale production.

Linoleic acid isomerase gene FgLAI12 affects sensitivity to salicylic acid, mycelial growth and virulence of Fusarium graminearum

Fusarium graminearum is the major causal agent of fusarium head blight in wheat, a serious disease worldwide. Linoleic acid isomerase (LAI) catalyses the transformation of linoleic acid (LA) to conjugated linoleic acid (CLA), which is beneficial for human health. We characterised a cis-12 LAI gene of F. graminearum (FGSG_02668; FgLAI12), which was downregulated by salicylic acid (SA), a plant defence hormone. Disruption of FgLAI12 in F. graminearum resulted in decreased accumulation of cis-9,trans-11 CLA, enhanced sensitivity to SA, and increased accumulation of LA and SA in wheat spikes during infection. In addition, mycelial growth, accumulation of deoxynivalenol, and pathogenicity in wheat spikes were reduced. Re-introduction of a functional FgLAI12 gene into ΔFgLAI12 recovered the wild-type phenotype. Fluorescent microscopic analysis showed that FgLAI12 protein was usually expressed in the septa zone of conidia and the vacuole of hyphae, but was expressed in the cell membrane of hyphae in response to exogenous LA, which may be an element of LA metabolism during infection by F. graminearum. The cis-12 LAI enzyme encoded by FgLAI12 is critical for fungal response to SA, mycelial growth and virulence in wheat. The gene FgLAI12 is potentially valuable for biotechnological synthesis of cis-9,trans-11 CLA.

A metabolic engineering strategy for producing conjugated linoleic acids using the oleaginous yeast Yarrowia lipolytica

Conjugated linoleic acids (CLAs) have been found to have beneficial effects on human health when used as dietary supplements. However, their availability is limited because pure, chemistry-based production is expensive, and biology-based fermentation methods can only create small quantities. In an effort to enhance microbial production of CLAs, four genetically modified strains of the oleaginous yeast Yarrowia lipolytica were generated. These mutants presented various genetic modifications, including the elimination of β-oxidation (pox1-6∆), the inability to store lipids as triglycerides (dga1∆ dga2∆ are1∆ lro1∆), and the overexpression of the Y. lipolytica ∆12-desaturase gene (YlFAD2) under the control of the constitutive pTEF promoter. All strains received two copies of the pTEF-oPAI or pPOX-oPAI expression cassettes; PAI encodes linoleic acid isomerase in Propionibacterium acnes. The strains were cultured in neosynthesis or bioconversion medium in flasks or a bioreactor. The strain combining the three modifications mentioned above showed the best results: when it was grown in neosynthesis medium in a flask, CLAs represented 6.5% of total fatty acids and in bioconversion medium in a bioreactor, and CLA content reached 302 mg/L. In a previous study, a CLA degradation rate of 117 mg/L/h was observed in bioconversion medium. Here, by eliminating β-oxidation, we achieved a much lower rate of 1.8 mg/L/h.

Bacterial production of conjugated linoleic and linolenic Acid in foods: a technological challenge

Conjugated linoleic acid (CLA) and conjugated linolenic acid (CLNA) isomers are present in foods derived from ruminants as a result of the respective linoleic acid (LA) and α-linolenic acid (LNA) metabolism by ruminal microorganisms and in animals' tissues. CLA and CLNA have isomer-specific, health-promoting properties, including anticarcinogenic, antiatherogenic, anti-inflammatory, and antidiabetic activity, as well as the ability to reduce body fat. Besides ruminal microorganisms, such as Butyrivibrio fibrisolvens, many food-grade bacteria, such as bifidobacteria, lactic acid bacteria (LAB), and propionibacteria, are able to convert LA and LNA to CLA and CLNA, respectively. Linoleate isomerase activity, responsible for this conversion, is strain-dependent and probably related to the ability of the producer strain to tolerate the toxic effects of LA and LNA. Since natural concentrations of CLA and CLNA in ruminal food products are relatively low to exert their health benefits, food-grade bacteria with linoleate isomerase activity could be used as starter or adjunct cultures to develop functional fermented dairy and meat products with increased levels of CLA and CLNA or included in fermented products as probiotic cultures. However, results obtained so far are below expectations due to technological bottlenecks. More research is needed to assess if bacterial production kinetics can be increased and can match food processing requirements.

Sources and Bioactive Properties of Conjugated Dietary Fatty Acids

The group of conjugated fatty acids known as conjugated linoleic acid (CLA) isomers have been extensively studied with regard to their bioactive potential in treating some of the most prominent human health malignancies. However, CLA isomers are not the only group of potentially bioactive conjugated fatty acids currently undergoing study. In this regard, isomers of conjugated α-linolenic acid, conjugated nonadecadienoic acid and conjugated eicosapentaenoic acid, to name but a few, have undergone experimental assessment. These studies have indicated many of these conjugated fatty acid isomers commonly possess anti-carcinogenic, anti-adipogenic, anti-inflammatory and immune modulating properties, a number of which will be discussed in this review. The mechanisms through which these bioactivities are mediated have not yet been fully elucidated. However, existing evidence indicates that these fatty acids may play a role in modulating the expression of several oncogenes, cell cycle regulators, and genes associated with energy metabolism. Despite such bioactive potential, interest in these conjugated fatty acids has remained low relative to the CLA isomers. This may be partly attributed to the relatively recent emergence of these fatty acids as bioactives, but also due to a lack of awareness regarding sources from which they can be produced. In this review, we will also highlight the common sources of these conjugated fatty acids, including plants, algae, microbes and chemosynthesis.

Yeast cell surface display of linoleic acid isomerase from Propionibacterium acnes and its application for the production of trans-10, cis-12 conjugated linoleic acid

Conjugated linoleic acid (CLA), a family of geometric and positional isomers of linoleic acid, has many health-promoting properties. Different isomers of CLA may have very different physiological effects. In the current work, we explore the possibility to produce single isomer of CLA by using biocatalysis based on displayed biocatalysts on the yeast cell surfaces. A reporter system used to assess gene expression and protein distribution was established by combining the egfp gene to the N-terminus of Propionibacterium acnes pai gene encoding the linoleic isomerase onto vector pYD1. After induction of the yeast strains containing pYD1::egfp::pai with galactose, strong green fluorescence was observed on the surface of cells, demonstrating that the fusion protein was successfully displayed. Using the engineered strains as whole-cell biocatalyst, trans-10, cis-12 CLA was detected in the reaction mixture. To improve the biocatalytic potential of this system, the first 20 amino codons of pai were modified, and the catalytic reaction conditions were optimized. Optimization of the codon usage resulted in 35% increase of CLA production, and the maximum yield of CLA was observed within 20 H in the optimal conditions: pH 7.0, 4 mg/mL linoleic acid, 37 °C. The system established in the present work can guide the development of biocatalytic strategies to produce trans-10, cis-12 CLA single isomer.

Genetic engineering of Yarrowia lipolytica for enhanced production of trans-10, cis-12 conjugated linoleic acid

Background

Conjugated linoleic acid (CLA) has been extensively studied for decades because of its health benefits including cancer prevention, anti-atherogenic and anti-obesity effects, and modulation of the immune system. We previously described the production of trans-10, cis-12 CLA in Yarrowia lipolytica by expressing the gene coding for linoleic acid isomerase from Propionibacterium acnes (pai). However the stable strain produced CLA at about 0.08% of dry cell weight (DCW), a level of production which was not high enough for practical applications. The goal of the present study was to enhance production of CLA by genetic engineering of Y. lipolytica strains.

Results

We have now co-expressed the delta 12-desaturase gene (FADS12, d12) from Mortierella alpina together with the codon-optimized linoleic acid isomerase (opai) gene in Y. lipolytica, expressed under the control of promoter hp16d modified by fusing 12 copies of UAS1B to the original promoter hp4d. A multi-copy integration plasmid was used to further enhance the expression of both genes. Using glucose as the sole carbon source, the genetically-modified Y. lipolytica produced trans-10, cis-12-CLA at a level of up to 10% of total fatty acids and 0.4% of DCW. Furthermore, when the recombinant yeast was grown with soybean oil, trans-10, cis-12-CLA now accumulated at a level of up to 44% of total fatty acids, which represented 30% of DCW after 38.5 h of cultivation. In addition, trans-10, cis-12-CLA was also detected in the growth medium up to 0.9 g/l.

Conclusions

We have successfully produced trans-10, cis-12-CLA with a titre of 4 g/l of culture (3.1 g/l in cells and 0.9 g/l in culture medium). Our results demonstrate the potential use of Y. lipolytica as a promising microbial cell factory for trans-10, cis-12-CLA production.

Actual concept of "probiotics": Is it more functional to science or business?

It is our contention that the concept of a probiotic as a living bacterium providing unspecified health benefits is inhibiting the development and establishment of an evidence base for the growing field of pharmacobiotics. We believe this is due in part to the current regulatory framework, lack of a clear definition of a probiotic, the ease with which currently defined probiotics can be positioned in the market place, and the enormous profits earned for minimum investment in research. To avoid this, we believe the following two actions are mandatory: international guidelines by a forum of stakeholders made available to scientists and clinicians, patient organizations, and governments; public research funds made available to the scientific community for performing independent rigorous studies both at the preclinical and clinical levels.

De novo synthesis of trans-10, cis-12 conjugated linoleic acid in oleaginous yeast Yarrowia lipolytica

Background

Conjugated linoleic acid (CLA) has many well-documented beneficial physiological effects. Due to the insufficient natural supply of CLA and low specificity of chemically produced CLA, an effective and isomer-specific production process is required for medicinal and nutritional purposes.

Results

The linoleic acid isomerase gene from Propionibacterium acnes was expressed in Yarrowia lipolytica Polh. Codon usage optimization of the PAI and multi-copy integration significantly improved the expression level of PAI in Y. lipolytica. The percentage of trans-10, cis-12 CLA was six times higher in yeast carrying the codon-optimized gene than in yeast carrying the native gene. In combination with multi-copy integration, the production yield was raised to approximately 30-fold. The amount of trans-10, cis-12 CLA reached 5.9% of total fatty acid yield in transformed Y. lipolytica.

Conclusions

This is the first report of production of trans-10, cis-12 CLA by the oleaginous yeast Y. lipolytica, using glucose as the sole carbon source through expression of linoleic acid isomerase from Propionibacterium acnes.

Recombinant lactobacilli expressing linoleic acid isomerase can modulate the fatty acid composition of host adipose tissue in mice

We have previously demonstrated that oral administration of a metabolically active Bifidobacterium breve strain, with ability to form cis-9, trans-11 conjugated linoleic acid (CLA), resulted in modulation of the fatty acid composition of the host, including significantly elevated concentrations of c9, t11 CLA and omega-3 (n-3) fatty acids in liver and adipose tissue. In this study, we investigated whether a recombinant lactobacillus expressing linoleic acid isomerase (responsible for production of t10, c12 CLA) from Propionibacterium acnes (PAI) could influence the fatty acid composition of different tissues in a mouse model. Linoleic-acid-supplemented diets (2 %, w/w) were fed in combination with either a recombinant t10, c12 CLA-producing Lactobacillus paracasei NFBC 338 (Lb338), or an isogenic (vector-containing) control strain, to BALB/c mice for 8 weeks. A third group of mice received linoleic acid alone (2 %, w/w). Tissue fatty acid composition was assessed by GLC at the end of the trial. Ingestion of the strain expressing linoleic acid isomerase was associated with a 4-fold increase (P<0.001) in t10, c12 CLA in adipose tissues of the mice when compared with mice that received the isogenic non-CLA-producing strain. The livers of the mice that received the recombinant CLA-producing Lb338 also contained a 2.5-fold (albeit not significantly) higher concentration of t10, c12 CLA, compared to the control group. These data demonstrate that a single gene (encoding linoleic acid isomerase) expressed in an intestinal microbe can influence the fatty acid composition of host fat.

Production of conjugated linoleic acid and conjugated linolenic acid isomers by Bifidobacterium species

Conjugated linoleic acid (CLA) and conjugated linolenic acid (CLNA) isomers have attracted great interest because of their potential health benefits. Formation of CLA and CLNA takes place in the rumen during biohydrogenation. Several studies have indicated that certain types of intestinal bacteria, including bifidobacteria, are able to convert linoleic acid (LA) to CLA. The role of intestinal bacteria in the formation of CLNA isomers is largely unknown. In the present study, a screening of 36 different Bifidobacterium strains for their ability to produce CLA and CLNA from free LA and alpha-linolenic acid (LNA), respectively, was performed. The strains were grown in MRS broth, to which LA or LNA (0.5 mg ml(-1)) were added after 7 h of bacterial growth. Cultures were further incubated at 37 degrees C for 72 h. Six strains (four Bifidobacterium breve strains, a Bifidobacterium bifidum strain and a Bifidobacterium pseudolongum strain) were able to produce different CLA and CLNA isomers. Conversion percentages varied from 19.5% to 53.5% for CLA production and from 55.6% to 78.4% for CLNA production among these strains. The CLA isomers produced were further identified with Ag(+)-HPLC. LA was mainly converted to t9t11-CLA and c9t11-CLA. The main CLNA isomers were identified with GC-MS as c9t11c15-CLNA and t9t11c15-CLNA.