Microbial Population Density Research Articles

A three‐year field experiment of faba bean var. minor effects on soil health and production of pepper grown under conventional farming system

AbstractSoil management using natural‐based approaches is becoming essential to minimize the use of synthetic agrochemicals and to ensure sustainability and resiliency of agriculture production. In this study, faba bean (Vicia faba L.) var. minor was used during three consecutive cropping years as green manure to restore soil fertility and biology and to improve the growth, yield and fruit quality parameters of pepper cv. ‘Baklouti’. Following green manuring with faba bean, significant enhancements in the total nitrogen (N), the available phosphorus (P) and potassium (K) contents, the soil organic carbon (SOC) and the soil organic matter (SOM) levels were recorded. The alkaline phosphatase activity was also increased by 30.04% after faba bean var. minor incorporation into the soil in the third year. The β‐glucosidase and urease activities were increased by 26.8%–34.03% and 47.01%–71.7% in faba bean‐amended soil during the three‐year trials. Green manuring also enriched soil with total cultivable bacteria, Pseudomonas fluorescens, actinobacteria, total fungi and Aspergillus spp. as compared to control soil. Pepper growth and yield parameters were improved by 16.5–33.7% and 27.5% following green manure amendment, respectively. Vitamin C content, total soluble solids (TSS) and titrable acidity of green and red pepper fruits were 39.1%–50.7% and 7.2%–13.4% higher in green manured soil than in control. The calcium, potassium and phosphorus contents were significantly 4.7%–9.6%, 16.4%–18.1% and 41.2%–42.9% higher in red fruits of pepper plants grown on green manured soil. The plant growth and yield parameters together with the fruit biochemical and mineral characteristics were positively linked to NPK soil levels, SOC, SOM and soil microbial population's density and activity. This study clearly demonstrated the efficiency of green manuring using faba bean var. minor residues as potential alternative to agrochemicals for the enhancement of soil health status and the improvement of pepper growth, yield and fruit nutritional quality.

Optimization of anaerobic soil disinfestation against Verticillium wilt in strawberry cultivation using local agrowastes as amendments.

The study explores anaerobic soil disinfection as an alternative to soil fumigants for controlling Verticillium wilt in strawberry crops. For this purpose, two agrowastes close to the strawberry-growing areas of Huelva province were tested as potential amendments for the control of Verticillium wilt: rice bran and residual strawberry extrudate. Furthermore, two application rates were evaluated: 13.50 and 20.00 t/ha for the rice bran and 16.89 and 25.02 t/ha for residual strawberry extrudate. Amended and anaerobically disinfested soils were compared with a non-amended soil under anaerobic conditions, a soil treated with the chemical fungicide metam sodium and an untreated soil. One week before the start of disinfection treatment, these soils were artificially inoculated with 250 microsclerotia/g dry soil of Verticillium dahliae. After disinfestation treatments, pathogens were quantified, and strawberry plants were cropped in a growth chamber to further evaluate Verticillium wilt severity, which was measured with a symptom scale in the same potting soils. Measurements of the anaerobic condition, pH and microbial population densities were performed, and the results showed significant differences between the different amendments. In addition, the treatment with rice bran at 20 t/ha recorded the lowest population density of V. dahliae. Likewise, it was possible to achieve a reduction in foliar disease severity in all amended treatments in similar percentage to those obtained by chemical treatment. These results suggest potential application of this technique for the control of Verticillium wilt in the strawberry-growing area of Huelva, reducing the use of chemical fumigants.

Biodegradation of polypropylene plastics in vitro and natural condition by Streptomyces sp. isolated from plastic-contaminated sites

Most plastic degradation studies are conducted under controlled laboratory conditions. The current study investigated the ability to degrade Polypropylene (PP) plastic by Streptomyces ardesiacus strain NBI0111 under both laboratory and natural conditions. This strain exhibited the ability to degrade PP when cultured in BH medium and using PP plastics as carbon sources. After a 90-day incubation period, the weight loss of PP plastics reached 17.52 % (p < 0.05). The surface of the PP plastic showed significant changes compared to the control group. Chemical changes in the plastic were also detected on the 60th and 90th days, as confirmed by FTIR and GC-MS analyses. This strain was applied to degrade PP plastic in soils under natural conditions. Strain NBI0111 also resulted in a notable weight loss. The biodegradation test group exhibited a significant 12.5 % decrease compared to only a 3.88 % decrease in the control group (p < 0.05). Furthermore, a strong positive correlation between the weight loss of PP plastic cups and the density of microbial populations was observed. The capabilities demonstrated by Streptomyces ardesiacus strain NBI0111 in this study hold great promise for on-site plastic remediation, offering a sustainable solution to the problem of plastic pollution in the future.

Deciphering linkages between DON and the microbial community for nitrogen removal using two green sorption media in a surface water filtration system

The presence of dissolved organic nitrogen (DON) in stormwater treatment processes is a continuous challenge because of the intertwined nature of its decomposition, bioavailability, and biodegradability and its unclear molecular characteristics. In this paper, 21 T Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in combination with quantitative polymerase chain reaction was applied to elucidate the molecular change of DON and microbial population dynamics in a field-scale water filtration system filled with two specialty adsorbents for comparison in South Florida where the dry and wet seasons are distinctive annually. The adsorbents included CPS (clay-perlite and sand sorption media) and ZIPGEM (zero-valent iron and perlite-based green environmental media). Our study revealed that seasonal effects can significantly influence the dynamic characteristics and biodegradability of DON. The microbial population density in the filter beds indicated that three microbial species in the nitrogen cycle were particularly thrived for denitrification, dissimilatory nitrate reduction to ammonium, and anaerobic ammonium oxidation via competition and commensalism relationships during the wet season. Also, there was a decrease in the compositional complexity and molecular weight of the DON groups (CnHmOpN1, CnHmOpN2, CnHmOpN3, and CnHmOpN4), revealed by the 21 T FT-ICR MS bioassay, driven by a microbial population quantified by polymerase chain reaction from the dry to the wet season. These findings indirectly corroborate the assumption that the metabolism of microorganisms is much more vigorous in the wet season. The results affirm that the sustainable materials (CPS and ZIPGEM) can sustain nitrogen removal intermittently by providing a suitable living environment in which the metabolism of microbial species can be cultivated and enhanced to facilitate physico-chemical nitrogen removal across the two types of green sorption media.

Characterizing the Influence of a Heterotrophic Bicosoecid Flagellate Pseudobodo sp. on the Dinoflagellate Gambierdiscus balechii.

Microbial interactions including competition, mutualism, commensalism, parasitism, and predation, which can be triggered by nutrient acquisition and chemical communication, are universal phenomena in the marine ecosystem. The interactions may influence the microbial population density, metabolism, and even their environmental functions. Herein, we investigated the interaction between a heterotrophic bicosoecid flagellate, Pseudobodo sp. (Bicoecea), and a dinoflagellate, Gambierdiscus balechii (Dinophyceae), which is a well-known ciguatera food poisoning (CFP) culprit. The presence of Pseudobodo sp. inhibited the algal proliferation and decreased the cardiotoxicity of zebrafish in the algal extract exposure experiment. Moreover, a significant difference in microbiome abundance was observed in algal cultures with and without Pseudobodo sp. Chemical analysis targeting toxins was performed by using liquid chromatography-tandem mass spectrometry (LC-MS/MS) combined with molecular networking (MN), showing a significant alteration in the cellular production of gambierone analogs and some super-carbon chain compounds. Taken together, our results demonstrated the impact of heterotrophic flagellate on the photosynthetic dinoflagellates, revealing the complex dynamics of algal toxin production and the ecological relationships related to dinoflagellates in the marine environment.

Interkingdom Detection of Bacterial Quorum-Sensing Molecules by Mammalian Taste Receptors.

Bitter and sweet taste G protein-coupled receptors (known as T2Rs and T1Rs, respectively) were originally identified in type II taste cells on the tongue, where they signal perception of bitter and sweet tastes, respectively. Over the past ~15 years, taste receptors have been identified in cells all over the body, demonstrating a more general chemosensory role beyond taste. Bitter and sweet taste receptors regulate gut epithelial function, pancreatic β cell secretion, thyroid hormone secretion, adipocyte function, and many other processes. Emerging data from a variety of tissues suggest that taste receptors are also used by mammalian cells to "eavesdrop" on bacterial communications. These receptors are activated by several quorum-sensing molecules, including acyl-homoserine lactones and quinolones from Gram-negative bacteria such as Pseudomonas aeruginosa, competence stimulating peptides from Streptococcus mutans, and D-amino acids from Staphylococcus aureus. Taste receptors are an arm of immune surveillance similar to Toll-like receptors and other pattern recognition receptors. Because they are activated by quorum-sensing molecules, taste receptors report information about microbial population density based on the chemical composition of the extracellular environment. This review summarizes current knowledge of bacterial activation of taste receptors and identifies important questions remaining in this field.

Core species and interactions prominent in fish-associated microbiome dynamics

BackgroundIn aquatic ecosystems, the health and performance of fish depend greatly on the dynamics of microbial community structure in the background environment. Nonetheless, finding microbes with profound impacts on fish’s performance out of thousands of candidate species remains a major challenge.MethodsWe examined whether time-series analyses of microbial population dynamics could illuminate core components and structure of fish-associated microbiomes in the background (environmental) water. By targeting eel-aquaculture-tank microbiomes as model systems, we reconstructed the population dynamics of the 9605 bacterial and 303 archaeal species/strains across 128 days.ResultsDue to the remarkable increase/decrease of constituent microbial population densities, the taxonomic compositions of the microbiome changed drastically through time. We then found that some specific microbial taxa showed a positive relationship with eels’ activity levels even after excluding confounding effects of environmental parameters (pH and dissolved oxygen level) on population dynamics. In particular, a vitamin-B12-producing bacteria, Cetobacterium somerae, consistently showed strong positive associations with eels’ activity levels across the replicate time series of the five aquaculture tanks analyzed. Network theoretical and metabolic modeling analyses further suggested that the highlighted bacterium and some other closely-associated bacteria formed “core microbiomes” with potentially positive impacts on eels.ConclusionsOverall, these results suggest that the integration of microbiology, ecological theory, and network science allows us to explore core species and interactions embedded within complex dynamics of fish-associated microbiomes. 2gKjfWoBRNSUwrepeh_GG8Video

Population Response of Rhizosphere Microbiota of Garden Pea Genotypes to Inoculation with Arbuscular Mycorrhizal Fungi.

This study of a legume's rhizosphere in tripartite symbiosis focused on the relationships between the symbionts and less on the overall rhizosphere microbiome. We used an experimental model with different garden pea genotypes inoculated with AM fungi (Rhizophagus irregularis and with a mix of AM species) to study their influence on the population levels of main trophic groups of soil microorganisms as well as their structure and functional relationships in the rhizosphere microbial community. The experiments were carried out at two phenological cycles of the plants. Analyzes were performed according to classical methods: microbial population density defined as CUF/g a.d.s. and root colonization rate with AMF (%). We found a proven dominant effect of AMF on the densities of micromycetes and actinomycetes in the direction of reduction, suggesting antagonism, and on ammonifying, phosphate-solubilizing and free-living diazotrophic Azotobacter bacteria in the direction of stimulation, an indicator of mutualistic relationships. We determined that the genotype was decisive for the formation of populations of bacteria immobilizing mineral NH4+-N and bacteria Rhizobium. We reported significant two-way relationships between trophic groups related associated with soil nitrogen and phosphorus ions availability. The preserved proportions between trophic groups in the microbial communities were indicative of structural and functional stability.

Augmentation of Plant Growth Attributes, Soil Physico-Chemical Properties and Microbial Population in Custard Apple cv. Balanagar in Response to Azospirillum brasilense and Vermicompost Application in Humid Zone of South Eastern Rajasthan, India

ABSTRACT Field experiments were conducted for two successive seasons July 2018 to November 2018 and July 2019 to November 2019 at the Fruit Instructional Farm, Department of Fruit Science, College of Horticulture and Forestry, Jhalawar district under Rajasthan state of India. The experiment consisted of different treatments of Azospirillum brasilense (AZS) and Vermicompost (V.C.). It was laid out in a Randomized Block Design with three replications. The 16 different treatment combinations of AZS and Vermicompost were applied to soil canopy of custard apple cv. Balanagar plants during first week of July 2018 and July 2019 in canopy rhizosphere of black vertisols in custard apple plants. Among different treatment combinations, T10 treatment consisting of AZS @ 50 g + V.C. @10 kg/plant was found relatively better over all other treatments with respect to most of the plant growth characteristics, including soil health properties and microbial population density in soil availability in canopy of custard apple cv. Balanagar plants. The pooled results of two years revealed comparative better plant growth parameters viz. rootstock girth (74.20 mm), scion girth (61.52 mm), plant height attribute (3.46 m), number of nodes per shoot (13.00), number of nodes per branch (86.17), number of shoots per branch (26.00), number of shoots per plant (151.00) have shown augmenting response in improvement of plant growth parameters under T10 treatment (AZS @ 50 g + V.C. @ 10 kg /plant) in custard apple cv. Balanagar plants. However, key soil parameters concerning bulk density (1.32 g/cm3), soil pH (7.39), and electrical conductivity (0.46 dS m−1) reduced significantly under T10 treatment over other treatments. The soil physico-chemical properties especially change in porosity (55.04%), organic carbon (0.55%), available nitrogen content (350.55 kg/ha), available phosphorous content (46.51 kg ha−1) and available potassium content (322.34 kg ha−1), bacterial population (26.67 cfu g−1), fungi population (15.00 cfu g−1) and actinomycetes population (10.00 cfu g−1) have shown tremendous response in improvement of soil parameters under T10 treatment (AZS @ 50 g + V.C. @ 10 kg /plant) with respect to overall soil health.

Neutralization of acidic soil using Myxococcus xanthus: Important parameters and their implications

ABSTRACT Soil acidification through acid rain/deposition has been a serious problem that adversely affects the soil environment. In this study, Myxococcus xanthus, myxobacteria, was assessed towards neutralization of artificial acidic soil. Differences in initial pH and peat moss content in soil with incubated M. xanthus were being compared using a one-variable-at-a-time approach. It showed that the M. xanthus could neutralize the acidified soil using their specific metabolism, producing ammonium ions and hydroxide simultaneously. Increasing peat moss content could direct the neutralization performance of M. xanthus towards inhibition whereas reducing the peat moss content could improve the neutralization performance. Among experimental parameters such as initial pH, peat moss content in soil, and microorganism concentration, the interaction of soil amount either with peat moss content or microbial population density was meaningfully correlated to the neutralization of acidic soil.

Long-term nitrogen addition in maize monocultures reduces in vitro inhibition of actinomycete standards by soil-borne actinomycetes.

Management of soil microbial communities for enhanced crop disease suppression is an attractive approach to biocontrol, but the effects of agricultural practices on the disease-suppressive potential of the soil microbial community remain unknown. We investigated the effects of long-term nitrogen addition (103kg ha-1 nitrogen as urea vs. no fertilizer) and crop residue incorporation vs. removal on in vitro antibiotic inhibitory capacities of actinomycetes from 57-year maize (Zea mays L.) monocultures in southeastern Minnesota. We hypothesized that both nitrogen and crop residue addition would increase inhibitor frequencies by increasing microbial population densities and thus increasing the importance of competitive interactions among microbes to their fitness. We found that although soil carbon and nitrogen and microbial densities (actinomycete and total colony-forming units) tended to be greater with nitrogen fertilizer, the frequency of in vitro inhibitory phenotypes among culturable actinomycetes in fertilized plots was approximately half that in non-fertilized plots. Residue incorporation had little to no effect on soil chemistry, microbial density and inhibitor frequency. These results suggest that density-mediated processes alone cannot explain the effects of amendments on inhibitor frequencies. Fitness costs and benefits of inhibitory phenotypes may vary over time and may depend on the type of resource amendment.

Effects of Disease Resistant Genetically Modified Rice on Soil Microbial Community Structure According to Growth Stage

BACKGROUND: This study investigated the effects of rice genetically modified to be resistant against rice blast and rice bacterial blight on the soil microbial community. A comparative analysis of the effects of rice genetically modified rice choline kinase (OsCK1) gene for disease resistance (GM rice) and the Nakdong parental cultivar (non-GM rice) on the soil microbial community at each stage was conducted using rhizosphere soil of the OsCK1 and Nakdong rice. METHODS AND RESULTS: The soil chemistry at each growth stage and the bacterial and fungal population densities were analyzed. Soil DNA was extracted from the samples, and the microbial community structures of the two soils were analyzed by pyrosequencing. No significant differences were observed in the soil chemistry and microbial population density between the two soils. The taxonomic analysis showed that Chloroflexi, Proteobacteria, Firmicutes, Actinobacteria, and Acidobacteria were present in all soils as the major phyla. Although the source tracking analysis per phylogenetic rank revealed that there were differences in the bacteria between the GM and non-GM soil as well as among the cultivation stages, the GM and non-GM soil were grouped according to the growth stages in the UPGMA dendrogram analysis. CONCLUSION: The difference in bacterial distributions between Nakdong and OsCK1 rice soils at each phylogenetic level detected in microbial community analysis by pyrosequencing may be due to the genetic modification done on GM rice or due to heterogeneity of the soil environment. In order to clarify this, it is necessary to analyze changes in root exudates along with the expression of transgene. A more detailed study involving additional multilateral soil analyses is required.

Effects of Phloroglucinol on In Vitro Methanogenesis, Rumen Fermentation, and Microbial Population Density

This study investigated the effect of phloroglucinol (1,3,5-trihydroxybenzene) supplementation alone on methane production, rumen fermentation profiles, and microbial population structure of mixed in vitro cultures. Treatments included a control group containing a substrate with no supplement, and substrates supplemented with 2, 4, 6, 8, or 10 mmol/L of phloroglucinol. The results revealed that phloroglucinol was able to decrease methane production in a dose-dependent manner. The highest decrease was observed with 8 and 10 mmol/L supplementations. The relative quantity of methanogen was not affected by phloroglucinol, whereas genus Coprococcus was increased with increasing concentrations of phloroglucinol (p<0.05). Total gas production, dry matter digestibility (DMD), and NH3-N were significantly lowered by phloroglucinol (p<0.001). Total short-chain fatty acid (SCFA) concentration was not affected by phloroglucinol. Acetate proportion increased with the addition of phloroglucinol at the expense of propionate (p<0.001). This might indicate the redirection of [H] from methane to acetate, and might be related to methane inhibition.. Our study concluded that supplementation of phloroglucinol alone could decrease methane production by inhibiting nutrient digestibility in the rumen and by possible redirection of rumen fermentation to acetate production. Genus Coprococcus could be an important actor for phloroglucinol metabolism in the rumen.

The influence of moisture content on the production of odor from food waste using path analysis.

Path analysis has been largely used in marketing research but has recently been applied in an environmental management context. This study evaluated the potential of path analysis in identifying the influence of moisture content on odor from decomposing food waste. Food waste with varying moisture content was monitored for odor concentration, microbial population density, oxygen uptake rate, volatile fatty acids, ammonia, and hydrogen sulfide. These various parameters were later analyzed using SmartPLS 3.0 software to produce the path analysis model using simultaneous equation modeling. Results indicate that odor concentration of food waste was not directly affected by moisture content (not significant, t-statistical 1.46 < 1.96), rather; moisture content influenced the microbial population density and biodegradability of the food residue which influenced the formation of hydrogen sulfide (significant, t-statistical 3.79 > 1.96) and subsequently odor. In order to manage food waste-related odors, it is recommended that the waste be kept at a moisture content lower than 40%. This is especially critical if prolonged storage is unavoidable.

Optimization of Mixed Cultivation of the Moderate Thermophilic Bioleaching Microorganisms for High Cell Density Using Statistical Methodology

The low functional microbial population density in the industrial bioleaching process has been a limiting factor for the high leaching efficiency, making the microbial cultivation and continuous inoculation an alternative for sustaining the microbial activity. In the present experiment, the defined mixed cultivation of Leptospirillum ferriphilum YSK, Sulfobacillus acidophilus TPY, Acidithiobacillus caldus S2, and Ferroplasma thermophilum L1 was evaluated and optimized by Statistical Methodology. Going through the Plackett–Burman experimental design, pH value, temperature, and c(MgSO4·7H2O) were considered as the most significant factors in the defined range. Then, the relationships were analyzed using the steepest ascent design, the central composite design, and finally the response surface methodology. It was suggested that the optimum parameters were pH 1.38, MgSO4·7H2O 0.552 g/L, temperature 44 °C, FeSO4·7H2O 40 g/L, sulfur 8 g/L, yeast 0.02% w/v, (NH4)2SO4 3g/L, K2HPO4 0.5g/L, KCl 0.1g/L, Ca(NO3)2 0.01 g/L, in which allowed total cell density of the microbial community to reach 7.63 × 108 cells/mL in the cultivation period. The lab experiments were routinely undertaken with the expectation that the L. ferriphilum YSK, S. acidophilus TPY, A. caldus S2, F. thermophilum L1 could rapid grown from initial cell density of 0.25 × 107 cells/mL to 2.82 × 108 cells/mL, 1.68 × 108 cells/mL, 2.76 × 108 cells/mL, 2.51 × 107 cells/mL, respectively in 58 h. It demonstrates a possibility to co-culture these microbes in a single reactor, providing an efficient way to regenerate of inoculation for biomining process.

Development, characterization and shelf-life testing of a novel pulse-based snack bar

With the globalization of food trade, we are observing tremendous changes in eating patterns of youngsters. Snack bars represent convenient, appropriately portioned, Ready-To-Eat food items, which not only supply nutrients to the body but also provide a feeling of satiety. The aim of this study was to formulate a novel high-protein, low Glycemic Index and low-fat snack bar that can be eaten on-the-move. Twelve different pulse-based bar formulations were developed and 85.1% of sensory panelists indicated that they particularly liked the taste of formulation M1. Since M1 contained peanuts, a nut-free and date-free equivalent (mM1) was developed to cater for individuals with allergies to these ingredients. A dehydrated mix (DM) based on the mM1 composition, was also developed. The microbiological and sensorial shelf lives of the products were then determined during storage at either ambient (ca. 23 ℃) or refrigerated temperatures (ca. 4 ℃) by determining counts of aerobic bacteria and yeast and mold. Mean aerobic bacteria and yeast and mold counts of M1 fell in the range of 8.4–9.4 and 4.5–5.4 log cfu/g and 7.5–8.6 and 3.8–4.9 log cfu/g during storage at room and refrigerated temperatures respectively. Aerobic bacteria and yeast and mold counts were consistently higher under ambient storage. Since a microbial population density >7 Log CFU/g usually marks the onset of microbiological spoilage, the bars were estimated to have a microbiological shelf-life of <2 days. Overall this study points to the development of a tasty and nutritious pulse-based Ready-To-Eat snack as well as a dehydrated mix that can be readily reconstituted at home or at work.

Effects of Phloroglucinol and the Forage:concentrate Ratio on Methanogenesis, In vitro Rumen Fermentation, and Microbial Population Density

Effects of Phloroglucinol and the Forage:concentrate Ratio on Methanogenesis, In vitro Rumen Fermentation, and Microbial Population Density

Effects of Difference Processing Methods on Microbiological Properties an African Oil Bean Product

The prepared seed slices of African oil bean (pentaclthra macrophylla Benth) were subjected to different fermentations periods and dried using different drying method to produce “Ugba”. Slices were milled to obtain flour. The flour from different ‘Ugba’ samples were analysed for microbial load. There were no significant difference p> 0.05) in the sizes of ugba. The micro organisms identified by characterization in the “ugba” samples after drying were Bacillus, Lactobacillus, staphylococcus, micrococcus Enterbacterium. Only the Bacillus were found to ferment the African oil bean seeds to “ugba”. They were also the predominant micro organisms present. After experiment of total microbial population density of the species of Bacillus found to be responsible for the fermentation of African oil bean seeds to “ugba” were identified as Bacillus Coagulans, Bacillus macerans, Bacillus megaterium, Bacillus pumilis, and Bacillus subtilis.

Insights into The Human Gut Microbiome - A Review

Various microbial communities and their genes collectively known as microbiome exist throughout the human body. The microbiome endows us with physiologic capacities that we have not had to evolve on our own and thus is both a manifestation of who we are genetically and metabolically, and a reflection of our state of well-being. Our distal gut is the known ecosystem with highest density of microbial population and the most comprehensively surveyed to date. The gut microbiome is a complex ecosystem that affects the development, immunological responses and nutritional status of the host. This review briefly discusses the significance of the gut microbiome in human health and wellness.

Yeast Surface Display of Escherichia coli Enterotoxin and Its Effects of Intestinal Microflora and Mucosal Immunity.

Enterotoxigenic Escherichia coli (ETEC) is a significant cause of infectious diarrhea in animals. In this study, yeast surface display technology was employed to investigate the effects of ETEC enterotoxin fusion protein on the intestinal flora and mucosal immunity of rats. ETEC estA, estB, and eltAB (heat-labile and heat-stable toxins) were expressed on the surface of yeast. Rats were divided into normal saline, yeast and display yeast groups. Fecal and jejunal content samples were collected on the 7th, 14th, and 21st days. Rats were then fed ETEC for 3days before again collecting these samples. Levels of SIgA, IL-2, IL-4, IFN-γ, and microbial population density and diversity were documented by ELISA, T-RFLP and real-time PCR. The results demonstrated that estA, estB, and eltAB fusion proteins were expressed on the surface of yeast. Following ETEC challenge, levels of SIgA, IL-2, IL-4, IFN-γ, and, the numbers and variety of intestinal microbes were significantly increased in rats receiving display yeast and yeast. These factors were significantly decreased in rats given normal saline and yeast. Our results indicate that display yeast and yeast can increase the number and diversity of intestinal microbes in rats and improve intestinal immune function. After ETEC challenge, the display yeast can better maintain the balance of intestinal bacteria and mucosal immunity.