Evaluating response mechanisms of soil microbiomes and metabolomes to Bt toxin additions.

The accumulation and persistence of Bt toxins in soils from Bt plants and Bt biopesticides may result in environmental hazards such as adverse impacts on soil microorganisms. However, the dynamic relationships among exogenous Bt toxins, soil characteristics, and soil microorganisms are not well understood. Cry1Ab is one of the most commonly used Bt toxins and was added to soils in this study to evaluate subsequent changes in soil physiochemical properties, microbial taxa, microbial functional genes, and metabolites profiles via 16S rRNA gene pyrosequencing, high-throughput qPCR, metagenomic shotgun sequencing, and untargeted metabolomics. Higher additions of Bt toxins led to higher concentrations of soil organic matter (SOM), ammonium (NH+4-N), and nitrite (NO2--N) compared against controls without addition after 100 days of soil incubation. High-throughput qPCR analysis and shotgun metagenomic sequencing analysis revealed that the 500 ng/g Bt toxin addition significantly affected profiles of soil microbial functional genes involved in soil carbon (C), nitrogen (N), and phosphorus (P) cycling after 100 days of incubation. Furthermore, combined metagenomic and metabolomic analyses indicated that the 500 ng/g Bt toxin addition significantly altered low molecular weight metabolite profiles of soils. Importantly, some of these altered metabolites are involved in soil nutrient cycling, and robust associations were identified among differentially abundant metabolites and microorganisms due to Bt toxin addition treatments. Taken together, these results suggest that higher levels of Bt toxin addition can alter soil nutrients, probably by affecting the activities of Bt toxin-degrading microorganisms. These dynamics would then activate other microorganisms involved in nutrient cycling, finally leading to broad changes in metabolite profiles. Notably, the addition of Bt toxins did not cause the accumulation of potential microbial pathogens in soils, nor did it adversely affect the diversity and stability of microbial communities. This study provides new insights into the putative mechanistic associations among Bt toxins, soil characteristics, and microorganisms, providing new understanding into the ecological impacts of Bt toxins on soil ecosystems.

Combined metagenomic and metabolomic analyses reveal that Bt rice planting alters soil C-N metabolism.

The environmental impacts of genetically modified (GM) plants remain a controversial global issue. To address these issues, comprehensive environmental risk assessments of GM plants is critical for the sustainable development and application of transgenic technology. In this paper, significant differences were not observed between microbial metagenomic and metabolomic profiles in surface waters of the Bt rice (T1C-1, the transgenic line) and non-Bt cultivars (Minghui 63 (the isogenic line) and Zhonghua 11 (the conventional japonica cultivar)). In contrast, differences in these profiles were apparent in the rhizospheres. T1C-1 planting increased soil microbiome diversity and network stability, but did not significantly alter the abundances of potential probiotic or phytopathogenic microorganisms compared with Minghui 63 and Zhonghua 11, which revealed no adverse effects of T1C-1 on soil microbial communities. T1C-1 planting could significantly alter soil C and N, probably via the regulation of the abundances of enzymes related to soil C and N cycling. In addition, integrated multi-omic analysis of root exudate metabolomes and soil microbiomes showed that the abundances of various metabolites released as root exudates were significantly correlated with subsets of microbial populations including the Acidobacteria, Actinobacteria, Chloroflexi, and Gemmatimonadetes that were differentially abundant in T1C-1 and Mnghui 63 soils. Finally, the potential for T1C-1-associated root metabolites to exert growth effects on T1C-1-associated species was experimentally validated by analysis of bacterial cultures, revealing that Bt rice planting could selectively modulate specific root microbiota. Overall, this study indicate that Bt rice can directly modulate rhizosphere microbiome assemblages by altering the metabolic compositions of root exudates that then alters soil metabolite profiles and physiochemical properties. This study unveils the mechanistic associations of Bt plant-microorganism-environment, which provides comprehensive insights into the potential ecological impacts of GM plants.

A Rapid and Visual Method for Nucleic Acid Detection of Escherichia coli O157:H7 Based on CRISPR/Cas12a-PMNT.

Rapid, accurate and visual point-of-care testing (POCT) methods for pathogenic bacteria detection are essential for avoiding foodborne diseases caused by pathogens or their toxins. In this study, we proposed a rapid and visual detection method that we named "Cas12aVIP". By combining recombinase polymerase amplification (RPA), a CRISPR/Cas12a system and a cationic-conjugated polythiophene derivative (poly[3-(3'-N,N,N-triethylamino-1'-propyloxy)-4-methyl-2,5-thiophene hydrochloride] (PMNT) mixed with single-stranded DNA (ssDNA)), the solution turned red in the absence of the target DNA based on conformational modifications of the conjugated backbone of PMNT, whereas it displayed yellow, thus realizing the colorimetric detection of DNA. The Cas12aVIP method yielded high specificity and no interference from other nontargeted bacteria. The detection was accomplished in 40 min and the signal could be observed by the naked eye under natural light, presenting great potential for a variety of rapid nucleic acid detection applications without requiring technical expertise or ancillary equipment.

Detection and Quantification of Adulterated Beef and Mutton Products by Multiplex Droplet Digital PCR.

In order to seek high profit, businesses mix beef and mutton with cheap meat, such as duck, pork, and chicken. Five pairs of primers were designed for quintuple droplet digital PCR (qddPCR) of specific genomic regions from five selected species and specificity and amplification efficiency were determined. The mixed DNA template with an equal copy number was used for detecting the accuracy and limit of multiplex PCR. The results showed that the primers and probes of the five selected species had good specificity with the minimum number of detection copies: 0.15 copies/µL beef (Bos taurus), 0.28 copies/µL duck (Anas platyrhynchos), 0.37 copies/µL pork (Sus scrofa), 0.39 copies/µL chicken (Gallus gallus), and 0.41 copies/µL mutton (Ovis aries), respectively. The five sets of primers and probes could quickly judge whether the specified meat components existed in the food commodities.

Environmental Behaviors of Bacillus thuringiensis (Bt) Insecticidal Proteins and Their Effects on Microbial Ecology.

Bt proteins are crystal proteins produced by Bacillus thuringiensis (Bt) in the early stage of spore formation that exhibit highly specific insecticidal activities. The application of Bt proteins primarily includes Bt transgenic plants and Bt biopesticides. Transgenic crops with insect resistance (via Bt)/herbicide tolerance comprise the largest global area of agricultural planting. After artificial modification, Bt insecticidal proteins expressed from Bt can be released into soils through root exudates, pollen, and plant residues. In addition, the construction of Bt recombinant engineered strains through genetic engineering has become a major focus of Bt biopesticides, and the expressed Bt proteins will also remain in soil environments. Bt proteins expressed and released by Bt transgenic plants and Bt recombinant strains are structurally and functionally quite different from Bt prototoxins naturally expressed by B. thuringiensis in soils. The former can thus be regarded as an environmentally exogenous substance with insecticidal toxicity that may have potential ecological risks. Consequently, biosafety evaluations must be conducted before field tests and production of Bt plants or recombinant strains. This review summarizes the adsorption, retention, and degradation behavior of Bt insecticidal proteins in soils, in addition to their impacts on soil physical and chemical properties along with soil microbial diversity. The review provides a scientific framework for evaluating the environmental biosafety of Bt transgenic plants, Bt transgenic microorganisms, and their expression products. In addition, prospective research targets, research methods, and evaluation methods are highlighted based on current research of Bt proteins.

Stochastic processes drive bacterial and fungal community assembly in sustainable intensive agricultural soils of Shanghai, China.

Sustainable intensive cropping systems have been implemented for three decades in suburban agricultural districts of Shanghai, China. These human-managed soils have been developed from paleosol or alluvial soils across different regions. However, little is known about the geographical distribution patterns of microbes and microbial community assembly in the sustainable intensive soils after decades of anthropogenic disturbances. Here, we investigated the impact of local geochemical properties and geographic distance on stochastic/deterministic microbial community assembly processes using high-throughput sequencing and phylogenetic null modeling analysis. Our results showed that soil pH was the most important environmental factor determining bacterial and fungal community structure. Importantly, only soil organic matter was positively correlated with fungal α-diversity, suggesting the efficient use of carbon substrates in sustainable agricultural systems, compensating for the lack of chemical fertilization and reduced tillage in these systems. Both bacterial and fungal communities had robust distance-decay patterns, but the rate of turnover of bacterial taxa was faster than that of fungi. Variation in bacterial and fungal communities was mostly attributed to the simultaneous effects of environmental variables and spatial factors. We also mapped the spatial distributions of the dominant bacterial and fungal taxa across the sustainable agricultural fields, making it possible to forecast the responses of agricultural ecosystems to anthropogenic disturbance. Based on the patterns of the ß-nearest taxon index, this study demonstrated that stochastic processes shaped substantial bacterial and fungal community variation in sustainable intensive agricultural soils of the Shanghai suburbs. This variation may be attributed to the increasing microbial dispersal caused by hydrological connectivity in the agricultural fields or the release from environmental stress and weakened environmental filtering across the suitable pH range preferable for most soil microbes. These results unveil assembly mechanisms of soil microbial community after several decades of sustainable intensive management, and contribute to understand the role of microbes in ecosystems in establishing a functional equilibrium which may enable sustainability to be preserved.

Production and characterization of the 13 C/15 N single-labeled insecticidal protein Cry1Ab/Ac using recombinant Escherichia coli.

Synthetic Cry1Ab/Ac proteins expressed by genetically modified (GM) crops have a high potential to control insect pests without utilizing large amounts of chemical insecticides. Before these crops are used in agriculture, the environmental fate and interactions in the soil must be understood. Stable isotope-labeled Cry1Ab/Ac protein is a highly useful tool for collecting such data. We developed a protocol to produce 13 C/15 N single-labeled Cry proteins. The artificially synthesized gene Cry1Ab/Ac of Bt rice Huahui No. 1, which has been certified by the Chinese government to be safe for human consumption, was subcloned into pUC57, and the expression vector pET-28a-CryAb/Ac was constructed and transformed into Escherichia coli BL21 (DE3) competent cells. Next, 0.2 mM isopropyl thiogalactoside (IPTG) was added to these cells and cultured at 37°C for 4 h to induce the synthesis and formation of inclusion bodies in M9 growth media containing either [U-13 C] glucose (5% 13 C-enriched) or [15 N] ammonium chloride (5% 15 N-enriched). Then, Cry inclusion bodies were dissolved in urea and purified by affinity chromatography under denaturing conditions, renatured by dialysis, and further detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. The purities of 13 C/15 N-labeled Cry proteins reached 99% with amounts of 12.6 mg/L and 8.8 mg/L, respectively. The δ 13 C and ä 15 N values of 13 C-labeled Cry protein and 15 N-labeled Cry protein were 3,269‰ and 2,854‰, respectively. A bioassay test revealed that the labeled Cry1Ab/Ac proteins had strong insecticidal activity. The stable isotope-labeled insecticidal Cry proteins produced for the first time in this study will provide an experimental basis for future metabolic studies on Cry proteins in soil and the characteristics of nitrogen (N) and carbon (C) transformations. Our findings may also be employed as a reference for elucidating the environmental behavior and ecological effects of BT plants and expressed products.

The response of dominant and rare taxa for fungal diversity within different root environments to the cultivation of Bt and conventional cotton varieties.

BACKGROUND: Bacillus thuringiensis (Bt) crops have been cultivated at a large scale over the past several decades, which have raised concern about unintended effects on natural environments. Microbial communities typically contain numerous rare taxa that make up the majority of community populations. However, the response of dominant and rare taxa for fungal diversity to the different root environments of Bt plants remains unclear. RESULTS: We quantified fungal population sizes and community composition via quantitative PCR of ITS genes and 18S rRNA gene sequencing of, respectively, that were associated with Bt and conventional cotton variety rhizosphere soils from different plant growth stages. qPCR analyses indicated that fungal abundances reached their peak at the seedling stage and that the taproots and lateral root rhizospheres of the Bt cotton SGK321 were significantly different. However, no significant differences in population sizes were detected between the same root zones from Bt and the conventional cotton varieties. The overall patterns of fungal genera abundances followed that of the dominant genera, whereas overall patterns of fungal genera richness followed those of the rare genera. These results suggest that the dominant and rare taxa play different roles in the maintenance of rhizosphere microhabitat ecosystems. Cluster analyses indicated a separation of fungal communities based on the lateral roots or taproots from the three cotton varieties at the seedling stage, suggesting that root microhabitats had marked effects on fungal community composition. Redundancy analyses indicated that pH was more correlated to soil fungal community composition than Bt protein content. CONCLUSIONS: In conclusion, these results indicate that dominant and rare fungal taxa differentially contribute to community dynamics in different root microhabitats of both Bt and conventional cotton varieties. Moreover, these results showed that the rhizosphere fungal community of Bt cotton did not respond significantly to the presence of Bt protein when compared to the two conventional cotton varieties.

Cultivation of Drought-Tolerant and Insect-Resistant Rice Affects Soil Bacterial, but Not Fungal, Abundances and Community Structures.

The impacts of rice varieties with stacked drought tolerance and insect resistance on soil microbiomes are poorly understood. Hence, the objective of this study was to investigate the effects resulting from the cultivation of the drought-tolerant and insect-resistant rice cultivar, Hanhui3T, on soil physical-chemical properties, and bacterial and fungal community composition. Soil samples of Hanhui3T and conventional rice varieties (Hanhui3 and Zhonghua11) were collected in triplicate at the booting stage, and bacterial and fungal population sizes and community structures were assessed using qPCR and Illumina MiSeq sequencing, respectively. The Bt protein concentration of Hanhui3T was significantly higher than that of Hanhui3 and Zhonghua11, while the pH of Hanhui3T was significantly lower. Bacterial population sizes and community composition were significantly different between Hanhui3T and Hanhui3 (or Zhonghua11), while no similar effects were observed for fungal communities. These differences suggest that the effect of Hanhui3T cultivation on bacterial community composition is stronger than the effect on fungal communities. Moreover, bacterial abundance was positively correlated to soil pH, while bacterial community structure variations were mainly driven by soil pH and Bt protein concentration differences. In conclusion, the abundances and structure of bacterial communities were altered in rhizosphere with Hanhui3T cultivation that changed soil pH and Bt protein concentrations, while fungal communities displayed no such responsiveness.

Impact of transgenic Cry1Ac + CpTI cotton on diversity and dynamics of rhizosphere bacterial community of different root environments.

The objective of this study was to characterize the diversity and dynamics of rhizosphere bacterial community, especially the response of dominant and rare bacterial taxa to the cultivation of Bt cotton for different root environments at different growth stages. qPCR analyses indicated that bacterial abundances of the taproots and lateral root rhizospheres of the Bt cotton SGK321 were significantly different at seedling and bolling stages. But no significant differences were detected between the same root zones from Bt and the conventional cotton varieties. Total bacterial genera had similar pattern with dominant genera in abundance, and with rare genera in richness to the changes of bacterial community, respectively. Although the rhizosphere bacterial diversity of the three cotton varieties changed in taproot and lateral root, no significant differences were detected in the same root environments between Bt and conventional cotton. Moreover, Soil pH was more correlated with variations in the bacterial community composition than Bt proteins. In conclusion, these results revealed no indication that rhizosphere bacterial community of Bt cotton had different response to increased Bt protein regarding the same root environment. In particular, dominant and rare bacterial taxa showed the variation in diversity and community composition in different root microhabitats.

Development and inter-laboratory transfer of a decaplex polymerase chain reaction assay combined with capillary electrophoresis for the simultaneous detection of ten food allergens.

Food allergies cause health risks to susceptible consumers and regulations on labeling of food allergen contents have been implemented in many countries and regions. To achieve timely and accurate food allergen labeling, the development of fast and effective allergen detection methods is very important. Herein, a decaplex polymerase chain reaction (PCR) assay combined with capillary electrophoresis was developed to detect simultaneously 10 common food allergens from hazelnut, pistachio, oat, sesame, peanut, cashew, barley, wheat, soybean and pecan. The absolute limit of detection (LODa) of this system is between 2 and 20 copies of haploid genome, and the relative LOD (LODr) is as low as 0.005% (w/w) in simulated food mixtures. The developed assay was subsequently applied to 20 commercial food products and verified the allergen ingredients stated on the labels. Furthermore, results using this decaplex PCR assay was successfully replicated in three other laboratories, demonstrating the repeatability and applicability of this assay in routine analysis of the 10 food allergens.

Collaborative trial for the validation of event-specific PCR detection methods of genetically modified papaya Huanong No.1.

For transferring the event-specific PCR methods of genetically modified papaya Huanong No.1 to other laboratories, we validated the previous developed PCR assays of Huanong No.1 according to the international standard organization (ISO) guidelines. A total of 11 laboratories participated and returned their test results in this trial. In qualitative PCR assay, the high specificity and limit of detection as low as 0.1% was confirmed. For the quantitative PCR assay, the limit of quantification was as low as 25 copies. The quantitative biases among ten blind samples were within the range between 0.21% and 10.04%. Furthermore, the measurement uncertainty of the quantitative PCR results was calculated within the range between 0.28% and 2.92% for these ten samples. All results demonstrated that the Huanong No.1 qualitative and quantitative PCR assays were creditable and applicable for identification and quantification of GM papaya Huanong No.1 in further routine lab analysis.

Identification and quantification of genetically modified Moonshade carnation lines using conventional and TaqMan real-time polymerase chain reaction methods.

Genetically modified carnation (Dianthus caryophyllus L.) Moonshade was approved for planting and commercialization in several countries from 2004. Developing methods for analyzing Moonshade is necessary for implementing genetically modified organism labeling regulations. In this study, the 5'-transgene integration sequence was isolated using thermal asymmetric interlaced (TAIL)-PCR. Based upon the 5'-transgene integration sequence, conventional and TaqMan real-time PCR assays were established. The relative limit of detection for the conventional PCR assay was 0.05 % for Moonshade using 100 ng total carnation genomic DNA, corresponding to approximately 79 copies of the carnation haploid genome, and the limits of detection and quantification of the TaqMan real-time PCR assay were estimated to be 51 and 254 copies of haploid carnation genomic DNA, respectively. These results are useful for identifying and quantifying Moonshade and its derivatives.

Validation of a carnation-specific gene, ANS, used as an endogenous reference gene in qualitative and real-time quantitative PCR for carnations.

The validation of the anthocyanin synthase (ANS) gene as a carnation endogenous reference gene applicable both in classical and real-time PCR methods is a prerequisite for the development of PCR assays for genetically modified (GM) carnation detection. This is important due to the fact that GM carnation lines, developed by Florigene Pty Ltd, have been approved for commercialization. In this study, both methods were tested on 14 different carnation cultivars, and identical amplification products were obtained with all of them. No amplification products were observed with samples from 14 other plant species, which demonstrated that the system was specific to carnation. The results of Southern blot analysis confirmed that the ANS gene had a low copy number in the 10 tested carnation varieties. In qualitative and real-time PCR assays, the LOD values of 0.05 and 0.005 ng carnation DNA, respectively, were validated. Moreover, the real-time PCR system was validated with high PCR efficiency and linearity. Thus, the ANS gene had species specificity, low heterogeneity, and low copy number among the tested cultivars. These results provide evidence that the gene can be used as an endogenous reference gene of carnation, as well as in qualitative and quantitative PCR systems.

The paleoAP3-type gene CpAP3, an ancestral B-class gene from the basal angiosperm Chimonanthus praecox, can affect stamen and petal development in higher eudicots.

Wintersweet (Chimonanthus praecox), a basal angiosperm endemic to China, has high ornamental value for developing beautiful flowers with strong fragrance. The molecular mechanism regulating flower development in wintersweet remains largely elusive. In this project, we seek to determine the molecular features and expression patterns of the C. praecox paleoAP3-type gene CpAP3 and examine its potential role in regulating floral development via ectopic expression in Arabidopsis thaliana and Petunia hybrida. The expression of CpAP3 is tissue-specific, with the highest level in the tepals, moderate level in carpels, and weak levels in stamen and vegetative stem tissues. Its dynamic expression during flowering is associated with flower-bud formation. Ectopic expression of CpAP3 partially rescued stamen development in ap3 mutant Arabidopsis. Although no phenotypic effect has been observed in wild-type Arabidopsis, CpAP3 overexpression in petunia brought rich morphological changes and homeotic conversions to flowers, mainly involving disruption of petal and stamen development. Expressed in a broader range than those canonical B-function regulators, the ancestral B-class gene CpAP3 can affect petal and stamen development in higher eudicots. This gene also holds some bioengineering potential in creating novel floral germplasms.

AtCopeg1, the unique gene originated from AtCopia95 retrotransposon family, is sensitive to external hormones and abiotic stresses.

Retrotransposons, the important component of eukaryotic genome, are seeds of evolution and play great role in creating new genes. The compact Arabidopsis genome harbors over 200 Copia-like retrotransposons, but mostly silent. Here we isolated an expressed gene AtCopeg1 (Copia evolved gene 1), which shows higher than 90% identity to AtCopia95_I, the consensus sequence encoding AtCopia95 polyprotein. AtCopeg1 is the unique gene evolved from AtCopia95 family. It is an intron-containing gene with two alternative 3' ends. The transcript accumulation of AtCopeg1 is tissue-specific, also significantly affected by external hormones and abiotic stresses. The presence of regulatory elements in its promoter region (originating from AtCopia95_I and AtCopia95 long terminal repeat), is adequate for conferring its essential expression feature. Thus, AtCopeg1 is a versatile functional gene involved in many developmental and adaptive processes probably including the signaling crosstalk of hormone and nutrient stress. Our work highlighted the role of transposable elements in creating new functional genes, and will incite the enthusiasm for isolation and functional characterization of plant genes evolved from those previously considered as selfish and junk DNA.

Event-specific quantitative detection of nine genetically modified maizes using one novel standard reference molecule.

With the development of genetically modified organism (GMO) detection techniques, the Polymerase Chain Reaction (PCR) technique has been the mainstay for GMO detection, and real-time PCR is the most effective and important method for GMO quantification. An event-specific detection strategy based on the unique and specific integration junction sequences between the host plant genome DNA and the integrated gene is being developed for its high specificity. This study establishes the event-specific detection methods for TC1507 and CBH351 maizes. In addition, the event-specific TaqMan real-time PCR detection methods for another seven GM maize events (Bt11, Bt176, GA21, MON810, MON863, NK603, and T25) were systematically optimized and developed. In these PCR assays, the fluorescent quencher, TAMRA, was dyed on the T-base of the probe at the internal position to improve the intensity of the fluorescent signal. To overcome the difficulties in obtaining the certified reference materials of these GM maizes, one novel standard reference molecule containing all nine specific integration junction sequences of these GM maizes and the maize endogenous reference gene, zSSIIb, was constructed and used for quantitative analysis. The limits of detection of these methods were 20 copies for these different GM maizes, the limits of quantitation were about 20 copies, and the dynamic ranges for quantification were from 0.05 to 100% in 100 ng of DNA template. Furthermore, nine groups of the mixed maize samples of these nine GM maize events were quantitatively analyzed to evaluate the accuracy and precision. The accuracy expressed as bias varied from 0.67 to 28.00% for the nine tested groups of GM maize samples, and the precision expressed as relative standard deviations was from 0.83 to 26.20%. All of these indicated that the established event-specific real-time PCR detection systems and the reference molecule in this study are suitable for the identification and quantification of these GM maizes.

Event-specific qualitative and quantitative polymerase chain reaction analysis for genetically modified canola T45.

Polymerase chain reaction (PCR) methods have been the main technical support for the detection of genetically modified organisms (GMOs). To date, GMO-specific PCR detection strategies have been developed basically at four different levels, such as screening-, gene-, construct-, and event-specific detection methods. Event-specific PCR detection method is the primary trend in GMO detection because of its high specificity based on the flanking sequence of exogenous integrant. GM canola, event T45, with tolerance to glufosinate ammonium is one of the commercial genetically modified (GM) canola events approved in China. In this study, the 5'-integration junction sequence between host plant DNA and the integrated gene construct of T45 canola was cloned and revealed by means of TAIL-PCR. Specific PCR primers and TaqMan probes were designed based upon the revealed sequence, and qualitative and quantitative TaqMan real-time PCR detection assays employing these primers and probe were developed. In qualitative PCR, the limit of detection (LOD) was 0.1% for T45 canola in 100 ng of genomic DNA. The quantitative PCR assay showed limits of detection and quantification (LOD and LOQ) of 5 and 50 haploid genome copies, respectively. In addition, three mixed canola samples with known GM contents were detected employing the developed real-time PCR assay, and expected results were obtained. These results indicated that the developed event-specific PCR methods can be used for identification and quantification of T45 canola and its derivates.

Protective immune response of bacterially-derived recombinant FaeG in piglets.

FaeG is the key factor in the infection process of K88ad enterotoxigenic Escherichia coli(ETEC) fimbrial adhesin. In an attempt to determine the possibility of expressing recombinant FaeG with immunogenicity for a new safe and high-production vaccine in E. coli, we constructed the recombinant strain, BL21 (DE3+K88), which harbors an expression vector with a DNA fragment of faeG, without a signal peptide. Results of 15% SDS-polyacrylamide slab gel analysis showed that FaeG can be stably over-expressed in BL21 (DE3+K88) as inclusion bodies without FaeE. Immunoglobulin G (IgG) and M (IgM) responses in pregnant pigs, with boost injections of the purified recombinant FaeG, were detected 4 weeks later in the sera and colostrum. An in vitro villius-adhesion assay verified that the elicited antibodies in the sera of vaccinated pigs were capable of preventing the adhesion of K88ad ETEC to porcine intestinal receptors. The protective effect on the mortality rates of suckling piglets born to vaccinated mothers was also observed one week after oral challenge with the virulent ETEC strain, C83907 (K88ad, CT+, ST+). The results of this study proved that the adhesin of proteinaceous bacterial fimbriae or pili could be overexpressed in engineered E. coli strains, with protective immune responses to the pathogen.

Oral immunization of mice with plant-derived fimbrial adhesin FaeG induces systemic and mucosal K88ad enterotoxigenic Escherichia coli-specific immune responses.

The importance of adhesins in pathogenicity has resulted in them being useful targets in the defense against bacterial infections. To produce edible vaccines against piglet diarrhea caused by enterotoxigenic Escherichia coli (ETEC), plants were genetically engineered to produce recombinant fimbrial adhesin FaeG. To evaluate the efficacy of the edible vaccine FaeG in mice, the soluble protein extracts were examined by about 15 microg recombinant FaeG for each oral immunization dose per mouse. After four doses of vaccination, both IgG and IgA antibodies specific to K88ad fimbriae were elicited in serum, and specific IgA antibodies were also evoked in feces of the immunized mice. Moreover, visible K88ad ETEC agglutination by the specific serum from the immunized mice was observed, implying the antibody was highly specific and effective. Results from an in vitro villous-adhesion assay further confirmed that serum antibodies of the immunized mice could inhibit K88ad ETEC from adhering to pig intestinal receptors, further demonstrating the oral immune efficacy of the plant-derived FaeG. This study provides a promising, noninvasive method for vaccinating swine by feeding supplements of transgenic plant. Moreover, the low cost and ease of delivery of this edible ETEC vaccine will facilitate its application in economically disadvantaged regions.