Rhizosphere microorganism effects on soluble amino acids,sugars and organic acids in the root zone ofAgropyron cristatum,A. smithii andBouteloua gracilis

Three axenic and rhizosphere microorganism-inoculated shortgrass steppe plant species were evaluated for possible differences in residual organic carbon and nitrogen present as sugars, organic acids and amino acids. IntroducedAgropyron cristatum was compared toA. smithii andBouteloua gracilis, which are dominant species in the native shortgrass steppe. These plants, grown for 90 days in root growth chambers, showed differences in residual organic carbon and nitrogen per gram of root, and rhizosphere microbe presence resulted in additional changes in these compounds. The root biomass ofB. gracilis was significantly increased with microbes present. TheAgropyron species had significantly lower amino acid levels with microbes present, while under the same conditions, theB. gracilis showed significant decreases in residual sugars. Based on the amino acids, sugars and organic acids, the C/N ratio of the sterileA. cristatum was higher than forB. gracilis. Rhizosphere microbe presence did not result in changes in these C/N ratios. These results suggest thatA. cristatum, with microbes present, will have lower levels of amino acids present, whileB. gracilis, with a lower C/N ratio, will have sugars used to a greater extent by the rhizosphere microbes. This resulted in the higher levels of residual soluble organic C and N in the rhizosphere ofB. gracilis, in comparison with the introducedA. cristatum. These differences may be critical in influencing the course of nutrient accumulation and plant competition in short-grass steppe communities, and in understanding basic aspects of plant-rhizosphere microorganism interactions.     

Factors affecting production of COS and CS2 in Leucaena and Mimosa species

Carbon disulfide (CS₂) and carbonyl sulfide (COS) are colorless, foul-smelling, volatile sulfur compounds with biocidal properties. Some plants produce CS₂ or COS or both. When used as an intercrop or forecrop, these plants may have agronomic potential in protecting other plants. Most of the factors which affect production of these plant-generated organic sulfides are unknown. We determined the effects of sulfate concentration, plant age, nitrogen fixation, drought stress, root injury (through cutting), and undisturbed growth on COS production in Leucaena retusa or Leucaena leucocephala and the effect of some of these factors on CS₂ production in Mimosa pudica. In addition, we determined if organic sulfides were produced in all Leucaena species. When L. retusa and M. pudica seedlings were grown in a plant nutrient medium with different sulfate concentrations (50 to 450 mg SL^-1), COS or CS₂ from crushed roots generally increased with increasing sulfate concentration. COS production was highest (74 ng mg^-1 dry root) for young L. retusa seedlings and declined to low amounts (<5 ng mg^-1 dry root) for older seedlings. Nitrogen fixation reduced the amounts of COS or CS₂ produced in L. leucocephala and M. pudica. Under conditions of undisturbed growth, root cutting, or drought stress, no COS production was detected in 4-to 8-weeks-old L. retusa plants. COS or CS₂ or both was obtained from crushed roots or shoots of all 13 known Leucaena species.     

A Review of the Functionality of Probiotics in the Larviculture Food Chain

During the past two decades, the use of probiotics as an alternative to the use of antibiotics has shown to be promising in aquaculture, particularly in fish and shellfish larviculture. This article reviews the studies on probiotics in larviculture, focusing on the current knowledge of their in vivo mechanisms of action. The article highlights that the in vivo mechanisms of action largely remain to be unravelled. Several methodologies are suggested for further in vivo research, including studies on gut microbiota composition, the use of gnotobiotic animals as test models, and the application of molecular techniques to study host–microbe and microbe–microbe interactions.     

Protective Effect of Japanese Green Tea Extract on Gnotobiotic Mice Infected with an Escherichia coli O157:H7 Strain

We examined the effect of Japanese green tea extract (JGTE) on enterohemorrhagic Escherichia coli (EHEC) O157:H7 infection in a gnotobiotic mouse model. Gnotobiotic mice inoculated with an EHEC strain developed neurologic and systemic symptoms, usually culminating in death. In contrast, none of mice receiving dietary JGTE showed clinical signs or death. This report describes the effect of JGTE, which includes the inhibition of bacterial growth in vivo. The Shiga-like toxin (SLT) level in the feces of the JGTE diet group was significantly lower than that of the control group.     

Absence of cecal secondary bile acids in gnotobiotic mice associated with two human intestinal bacteria with the ability to dehydroxylate bile acids in vitro.

Germ-free mice were orally inoculated with human intestinal 7alpha-dehydroxylating bacterial strains to evaluate their ability to transform bile acids in vivo. Three weeks after inoculation of the bacteria, cecal bile acids were examined. Among free-form bile acids, only beta-muricholic acid was detected in the cecal contents of gnotobiotic mice associated with Bacteroides distasonis strain K-5. No secondary bile acid was observed in the cecal contents of any of the gnotobiotic mice associated with 7alpha-dehydroxylating bacteria, Clostridium species strain TO-931 or Eubacterium species strain 36S.     

悉生培养微缩体系食细菌线虫提高土壤激素含量的机制

研究土壤食细菌线虫与细菌的相互作用及其生态功能是土壤生态学的核心内容之一。食细菌线虫取食细菌可以促进土壤中氮素的矿化,提高氮素养分的供给,改善土壤的营养条件,从而促进植物的生长发育。土壤食细菌线虫促进植物根系生长的"养分作用机制"已得到确认,而"激素作用机制"还存在争议。从供试土壤中筛选获得一株高效产IAA细菌和两种不同cp值的食细菌线虫,通过设置简化的悉生培养系统,对这两种土著食细菌线虫与土著产IAA细菌之间的相互作用,及其对土壤中IAA含量变化的影响进行研究。结果表明:两种食细菌线虫的取食均能促进细菌数量和活性的增强,食细菌线虫与产IAA细菌相互作用也能显著增加土壤中IAA的含量;这些促进作用受到接种食细菌线虫的种类以及培养时间的影响:在培养第10天和第20天时,接种cp值为1的中杆属食细菌线虫显著增加了产IAA细菌的数量;在培养第10天和第30天时,相比较接种cp值为2的头叶属食细菌线虫,接种中杆属食细菌线虫显著提高了土壤中IAA的含量。     

Generation of insulin-producing cells from gnotobiotic porcine skin-derived stem cells

A major problem in the treatment of type 1 diabetes mellitus is the limited availability of alternative sources of insulin-producing cells for islet transplantation. In this study, we investigated the effect of bone morphogenetic protein 4 (BMP-4) treatments of gnotobiotic porcine skin-derived stem cells (gSDSCs) on their reprogramming and subsequent differentiation into insulin-producing cells (IPCs). We isolated SDSCs from the ear skin of a gnotobiotic pig. During the proliferation period, the cells expressed stem-cell markers Oct-4, Sox-2, and CD90; nestin expression also increased significantly. The cells could differentiate into IPCs after treatments with activin-A, glucagon-like peptide-1 (GLP-1), and nicotinamide. After 15 days in the differentiation medium, controlled gSDSCs began expressing endocrine progenitor genes and proteins (Ngn3, Neuro-D, PDX-1, NKX2.2, NKX6.1, and insulin). The IPCs showed increased insulin synthesis after glucose stimulation. The results indicate that stem cells derived from the skin of gnotobiotic pigs can differentiate into IPCs under the appropriate conditions in vitro. Our three-stage induction protocol could be applied without genetic modification to source IPCs from stem cells in the skin of patients with diabetes for autologous transplantation.     

Comparative study of vanA gene transfer from Enterococcus faecium to Enterococcus faecalis and to Enterococcus faecium in the intestine of mice

Vancomycin-resistant enterococci represent a large reservoir in animals because of the use of avoparcin as a growth promoter in Europe. These strains of animal origin enter the food chain and can either colonize the human gut or transfer their resistance genes to the human microbiota. In this study, we compared the transfer of vancomycin resistance from resistant animal Enterococcus faecium to sensitive human Enterococcus faecalis and E. faecium. We analysed these transfers in dibiotic mice and human faecal flora-associated mice. VanA transfer from animal E. faecium to human E. faecalis occurred in dibiotic mice. The transconjugants appeared rapidly and persisted at levels between 3.0 and 4.0 log10 colony-forming units g(-1) of faeces. In human faecal flora-associated mice, vanA gene transfer was not detected towards E. faecalis but was possible between E. faecium strains. Our experiments revealed the possibility of vanA transfer from animal E. faecium to human E. faecalis in vitro and in vivo in the intestine of dibiotic mice. However, intraspecies transfer of vanA gene seems more common than interspecies transfer among enterococci.     

Characterization of the NleF effector protein from attaching and effacing bacterial pathogens

Enterohemorrhagic Escherichia coli (EHEC) is a water- and food-borne pathogen that causes hemorrhagic colitis. EHEC uses a type III secretion system (T3SS) to translocate effector proteins that subvert host cell function. T3SS-substrates encoded outside of the locus of enterocyte effacement are important to E. coli pathogenesis. We discovered an EHEC secreted protein, NleF, encoded by z6020 in O-island 71 of E. coli EDL933 that we hypothesized to be a T3SS substrate. Experiments are presented that probe the function of NleF and its role in virulence. Immunoblotting of secreted and translocated proteins suggest that NleF is secreted by the T3SS and is translocated into host cells in vitro where it localizes to the host cytoplasm. Infection of HeLa cells with E. coli possessing or lacking nleF and transient expression of NleF-GFP via transfection did not reveal a significant role for NleF in several assays of bacterial adherence, host cytoskeletal remodeling, or host protein secretion. However, competitive coinfection of mice with Citrobacter rodentium strains possessing or lacking nleF suggested a contribution of NleF to bacterial colonization. Challenge of gnotobiotic piglets also revealed a role for NleF in colonization of the piglet colon and rectoanal junction.     

Horizontal transfer of tet(M) and erm(B) resistance plasmids from food strains of Lactobacillus plantarum to Enterococcus faecalis JH2-2 in the gastrointestinal tract of gnotobiotic rats

Two wild-type strains of Lactobacillus plantarum previously isolated from fermented dry sausages were analysed for their ability to transfer antibiotic resistance plasmids in the gastrointestinal tract. For this purpose, we used gnotobiotic rats as an in vivo model. Rats were initially inoculated with the recipient Enterococcus faecalis JH2-2 at a concentration of 10(10) CFU mL(-1). After a week, either of the two donors L. plantarum DG 522 (harbouring a tet(M)-containing plasmid of c. 40 kb) or L. plantarum DG 507 [harbouring a tet(M)-containing plasmid of c. 10 kb and an erm(B)-containing plasmid of c. 8.5 kb] was introduced at concentrations in the range of 10(8)-10(10) CFU mL(-1). Two days after donor introduction, the first transconjugants (TCs) were detected in faecal samples. The detected numbers of tet(M)-TCs were comparable for the two donors. In both cases, this number increased to c. 5 x 10(2) CFU g(-1) faeces towards the end of the experiment. For erm(B)-TCs, the number was significantly higher and increased to c. 10(3) CFU g(-1) faeces. To our knowledge, this is the first study showing in vivo transfer of wild-type antibiotic resistance plasmids from L. plantarum to E. faecalis.