Tolerance of acid-adapted and non-adapted Escherichia coli O157:H7 cells to reduced pH as affected by type of acidulant

A study was carried out to determine if three strains of Escherichia coli O157:H7 grown (18 h) in Tryptic Soy Broth (TSB) and TSB supplemented with 1.25% glucose (TSBG), i.e. unadapted and acid-adapted cells, respectively, exhibited changes in tolerance to reduced pH when plated on Tryptic Soy Agar (TSA) acidified (pH 3.9, 4.2, 4.5, 4.8, 5.1 and 5.4) with acetic, citric or malic acids. All test strains grew well on TSA acidified with acetic acid at pH > or = 5.4 or malic acid at pH > or = 4.5; two strains grew on TSA acidified with citric acid at pH > or = 4.5, while the third strain grew at pH > or = 4.8. Acid-adapted and control (unadapted) cells differed little in their ability to form visible colonies on TSA containing the same acid at the same pH. However, on plates not showing visible colonies, acid-adapted cells retained higher viability than unadapted cells when plated on acidified TSA. Growth of acid-adapted and control cells of E. coli O157:H7 inoculated into TSB containing acetic acid (pH 5.4 and 5.7) and citric or malic acids (pH 4.2 and 4.5) was also studied. There was essentially no difference in growth characteristics of the two types of cells in TSB acidified at the same pH with a given acid. Tolerance of acid-adapted and control cells on subsequent exposure to low pH is influenced by the type of acidulant. The order of sensitivity at a given pH is acetic > citric > malic acid. When performing acid challenge studies to determine survival and growth characteristics of E. coli O157:H7 in foods, consideration should be given to the type of acid to which cells have been exposed previously, the procedure used to achieve acidic environments and possible differences in response among strains. The use of strains less affected by pH than type of acidulant or vice versa could result in an underestimation of the potential for survival and growth of E. coli O157:H7 in acid foods.     

Cutting edge: CD94/NKG2 is expressed on Th1 but not Th2 cells and costimulates Th1 effector functions

Th1 and Th2 cells can be phenotypically distinguished by very few cell surface markers. To identify cell surface molecules that are specifically expressed on Th1 cells, we have generated a panel of mAbs that specifically bind the surfaces of murine Th1 but not Th2 cells. One of these Abs identified the NK cell receptor CD94 as a molecule also specifically expressed on the surface of Th1 cells. As in NK cells, CD94 is expressed on Th1 cells together with members of the NKG2 family of molecules, including NKG2A, C, and E. Cross-linking these receptors on differentiated Th1 cells in vitro costimulates proliferation and cytokine production with a potency similar to that obtained by cross-linking CD28. We propose that CD94/NKG2 heterodimers may costimulate effector functions of differentiated Th1 cells.     

Identification of peptides that antagonize formyl peptide receptor-like 1-mediated signaling

Formyl peptide receptor-like 1 (FPRL1) is an important classical chemoattractant receptor that is expressed in phagocytic cells in the peripheral blood and brain. Recently, various novel agonists have been identified from several origins, such as host-derived molecules. Activation of FPRL1 is closely related to inflammatory responses in the host defense mechanism and neurodegenerative disorders. In the present study we identified several novel peptides by screening hexapeptide libraries that inhibit the binding of one of FPRL1's agonists (Trp-Lys-Tyr-Met-Val-D-Met-CONH(2) (WKYMVm)) to its specific receptor, FPRL1, in RBL-2H3 cells. Among the novel peptides, Trp-Arg-Trp-Trp-Trp-Trp-CONH(2) (WRWWWW (WRW(4))) showed the most potent activity in terms of inhibiting WKYMVm binding to FPRL1. We also found that WRW(4) inhibited the activation of FPRL1 by WKYMVm, resulting in the complete inhibition of the intracellular calcium increase, extracellular signal-regulated kinase activation, and chemotactic migration of cells toward WKYMVm. For the receptor specificity of WRW(4) to the FPR family, we observed that WRW(4) specifically inhibit the increase in intracellular calcium by the FPRL1 agonists MMK-1, amyloid beta42 (Abeta42) peptide, and F peptide, but not by the FPR agonist, fMLF. To investigate the effect of WRW(4) on endogenous FPRL1 ligand-induced cellular responses, we examined its effect on Abeta42 peptide in human neutrophils. Abeta42 peptide-induced superoxide generation and chemotactic migration of neutrophils were inhibited by WRW(4), which also completely inhibited the internalization of Abeta42 peptide in human macrophages. WRW(4) is the first specific FPRL1 antagonist and is expected to be useful in the study of FPRL1 signaling and in the development of drugs against FPRL1-related diseases.     

Optimization of fed-batch fermentation for xylitol production by Candida tropicalis

Xylitol, a functional sweetener, was produced from xylose by biological conversion using Candida tropicalis ATCC 13803. Based on a two-substrate fermentation using glucose for cell growth and xylose for xylitol production, fed-batch fermentations were undertaken to increase the final xylitol concentration. The effects of xylose and xylitol on xylitol production rate were studied to determine the optimum concentrations for fed-batch fermentation. Xylose concentration in the medium (100 g l⁻¹) and less than 200 g l⁻¹ total xylose plus xylitol concentration were determined as optimum for maximum xylitol production rate and xylitol yield. Increasing the concentrations of xylose and xylitol decreased the rate and yield of xylitol production and the specific cell growth rate, probably because of an increase in osmotic stress that would interfere with xylose transport, xylitol flux to secretion to cell metabolism. The feeding rate of xylose solution during the fed-batch mode of operation was determined by using the mass balance equations and kinetic parameters involved in the equations in order to increase final xylitol concentration without affecting xylitol and productivity. The optimized fed-batch fermentation resulted in 187 g l⁻¹ xylitol concentration, 0.75 g xylitol g xylose⁻¹ xylitol yield and 3.9 g xylitol l⁻¹ h⁻¹ volumetric productivity. Journal of Industrial Microbiology & Biotechnology (2002) 29, 16–19 doi:10.1038/sj.jim.7000257 Received 15 October 2001/ Accepted in revised form 30 March 2002     

Microbial treatment of high-strength perchlorate wastewater

To treat wastewater containing high concentrations of perchlorate, a perchlorate reducing-bacterial consortium was obtained by enrichment culture grown on high-strength perchlorate (1200 mg L⁻¹) feed medium, and was characterized in a sequence batch reactor (SBR) over a long-time operation. The consortium removed perchlorate in the SBR with high reduction rates (35-90 mg L⁻¹ h⁻¹) and stable removal efficiency over 200-day operations. The maximum specific perchlorate reduction rate (q_max), half saturation constant (K_s), and optimal pH range were 0.67 mg-perchlorate mg-dry cell weight⁻¹ h⁻¹, 193.8 mg-perchlorate L⁻¹, and pH 7-9, respectively. The perchlorate reduction yield was 0.48 mol-perchlorate mol-acetate⁻¹. A clone library prepared using the amplicons of cld gene encoding chlorate dismutase showed that the dominant (per)chlorate reducing bacteria in the consortium were Dechlorosoma sp. (53%), Ideonella sp. (28%), and Dechloromonas sp. (19%).     

Tanshinones as selective and slow-binding inhibitors for SARS-CoV cysteine proteases

In the search for anti-SARS-CoV, tanshinones derived from Salvia miltiorrhiza were found to be specific and selective inhibitors for the SARS-CoV 3CL^pro and PL^pro, viral cysteine proteases. A literature search for studies involving the seven isolated tanshinone hits showed that at present, none have been identified as coronaviral protease inhibitors. We have identified that all of the isolated tanshinones are good inhibitors of both cysteine proteases. However, their activity was slightly affected by subtle changes in structure and targeting enzymes. All isolated compounds (1–7) act as time dependent inhibitors of PL^pro, but no improved inhibition was observed following preincubation with the 3CL^pro. In a detail kinetic mechanism study, all of the tanshinones except rosmariquinone (7) were identified as noncompetitive enzyme isomerization inhibitors. However, rosmariquinone (7) showed a different kinetic mechanism through mixed-type simple reversible slow-binding inhibition. Furthermore, tanshinone I (5) exhibited the most potent nanomolar level inhibitory activity toward deubiquitinating (IC₅₀ = 0.7 μM). Additionally, the inhibition is selective because these compounds do not exert significant inhibitory effects against other proteases including chymotrysin, papain, and HIV protease. These findings provide potential inhibitors for SARS-CoV viral infection and replication.     

A cry for help from leaf to root: Aboveground insect feeding leads to the recruitment of rhizosphere microbes for plant self-protection against subsequent diverse attacks

Plants have evolved general and specific defense mechanisms to protect themselves from diverse enemies, including herbivores and pathogens. To maintain fitness in the presence of enemies, plant defense mechanisms are aimed at inducing systemic resistance: in response to the attack of pathogens or herbivores, plants initiate extensive changes in gene expression to activate “systemic acquired resistance” against pathogens and “indirect defense” against herbivores. Recent work revealed that leaf infestation by whiteflies, stimulated systemic defenses against both an airborne pathogen and a soil-borne pathogen, which was confirmed by the detection of the systemic expression of pathogenesis-related genes in response to salicylic acid and jasmonic acid-signaling pathway activation. Further investigation revealed that plants use self protection mechanisms against subsequent herbivore attacks by recruiting beneficial microorganisms called plant growth-promoting rhizobacteria/fungi, which are capable of reducing whitefly populations. Our results provide new evidence that plant-mediated aboveground to belowground communication and vice versa are more common than expected.Key words: aboveground, induced systemic resistance, pepper, plant growth-promoting rhizobacteria, underground, whiteflyAs sessile organisms, plants are unable to actively avoid the attack of predators. To overcome this, plants have evolved a multilayer immune system against herbivores and pathogens.¹ Plants, unlike animals, lack adaptive immunity. Instead, plants are dependent on a heritable, innate immunity based on the recognition by receptors of the presence of microbial triggers (cues) including effector proteins and microbe-associated molecular patterns.¹ The perception of microbial cues leads to the induction of a broad spectrum of plant defenses called systemic acquired resistance (SAR).² Until recently, SAR was thought to be limited to the induction of plant defenses against foliar microbial pathogens. However, recent results suggested that plants can activate signal exchanges between aboveground (AG) and belowground (BG) responses.³ Three phenomena indicate that plants can make use of cues that are systemically indicative of future enemy attack: (1) induced resistance against AG pathogens by BG microbes and vice versa, (2) indirect defenses against AG insects by AG herbivore infestation and (3) BG pathogen infection leading to root exudate-mediated recruitment of BG bacteria. First, many strains of rhizosphere microbes referred to as plant growth-promoting rhizobacteria/fungi (PGPR/PGPF) have beneficial effects by positively affecting plant growth and resistance against foliar plant pathogens—a process known as induced systemic resistance (ISR).⁴ Inducible defense responses triggered by the foliar pathogen Pseudomonas syringae pv. tomato DC3000 included the induction of root secretions such as L-malic acid that effectively recruited a PGPR strain, Bacillus subtilis FB17, in Arabidopsis roots.⁵ Second, herbivore attacks on plants trigger the induction of distinct resistance responses referred to as “indirect defenses.”⁶ In addition to the “direct defense” reaction mediated by the de novo production of toxic secondary compounds against enemies, plants also defend themselves by releasing volatile organic compounds (VOCs) or extrafloral nectar (EFN) to attract natural enemies (carnivores) of the herbivores AG.⁷ Third, as plant root exudates function as BG signaling molecules that affect the composition of rhizosphere microbial populations,⁸ certain rhizobacteria express antifungal-associated genes such as the 2,4-diacetylphloroglucinol biosynthesis gene phlA. The expression of these genes is in turn influenced by root exudates, which are modulated by soilborne fungal infections.⁹In prior studies, only one-way signal transduction was considered, such as AG to BG, AG to AG or BG to BG (Fig. 1).^10–13 The above three examples provide evidence of induced resistance against the same or a similar group of organisms, such as resistance against insects by insects, or against microbes by microbes. However, there are few studies addressing insect-microbe combinations during the elicitation of induced resistance. More specifically, indirect defenses by symbiotic root interactions AG were found, such as the volatile blends released by plants with arbuscular mycorrhizal fungi, which were more attractive to aphid parasitoids than the blends from plants without mycorrhiza.¹⁴ The BG to AG defense responses of plants are not limited to arbuscular mycorrhizal fungi against herbivores. In addition to mycorrhiza-altered insect feeding preferences, a combination of Pseudomonas spp. strains affected the development of leaffolder pest and actively enhanced resistance against leaffolder attack by triggering the synthesis of systemic defense enzymes such as chitinase and proteinase inhibitors in rice plants.¹⁵ Bacillus sp. PGPR strain treatment of tomato triggered ISR to Tomato mottle virus under natural conditions by reducing the population of the silverleaf whitefly vector.¹⁶Open in a separate windowFigure 1Putative model of plant-mediated aboveground to belowground communication and vice versa during the induction of systemic resistance via tritrophic (insect-plant-rhizobacteria) interactions. (A) A plant under normal condition. (B) Whitefly infestation elicits plant systemic defenses against leaf and root pathogens. Chemical cues from root exudates secreted from AG whitefly infestation trigger the recruitment of beneficial microbes including saprophytic fungi, Gram-positive bacteria and actinomycetes. (C) The induction of systemic resistance by colonization by beneficial microbes confers plant self-protection against subsequent herbivore attacks.Recently, we found another type of induced resistance response: bidirectional signal exchanges between AG and BG (Fig. 1).¹⁷ Our study demonstrated that the phloem feeding whiteflies can induce systemic resistance against both a leaf bacterial pathogen and a soil-borne bacterial pathogen. A similar study using the whitefly as an AG feeding insect to test the induction of plant defenses only observed its effects against conspecific insect herbivore competitors AG.¹⁸ However, in our study, foliar attack by the whitefly not only elicited AG resistance against a leaf pathogenic bacterium, Xanthomonas axonopodis pv. vesicatoria, but also enhanced resistance against the soil-borne pathogenic bacterium, Ralstonia solanacearum. The induction of systemic resistance was confirmed by significant upregulation of the SA and JA defense signaling pathway marker genes, Capsicum annuum pathogenesis-related protein (CaPR)1, CaPR4, CaPR10 and Ca protease inhibitor (CaPIN) in both leaves (AG) and roots (BG) after whitefly feeding. Interestingly, AG white-fly feeding significantly increased the population density of beneficial BG microflora including Gram-positive bacteria, actinomycetes and saprophytic fungi that may induce systemic resistance (Fig 1).⁴ Among BG microbial groups, several Grampositive Bacillus sp. strains significantly elicited plant systemic defenses against the whitefly population in the tomato field.¹⁶ Our studies provide a new understanding of tritrophic (insect-plant-PGPR) interactions and their role in the induction of defense mechanisms. In the near future, it will be important to define plant defense signaling molecules from AG to BG and to dissect the signaling transduction pathways using “omics” technology to reveal the mechanisms by which plants protect themselves against enemy attacks.     

Transgenic rice with low sucrose-phosphate synthase activities retain more soluble protein and chlorophyll during flag leaf senescence

We investigated whether changes in sucrose-phosphate synthase (EC 2.4.1.14, SPS) activity could alter N remobilization during leaf senescence. Transgenic rice (Oryza sativa L. cv. Nipponbare) with low SPS activities and wild-type rice plants were grown with basal N (1.0 mM NH₄NO₃) until the late vegetative stage. Subsequently, half of the plants were transferred to a low N (0.1 mM NH₄NO₃) condition to accelerate leaf senescence, and the others were continuously grown with basal N. With low N supply, the amounts of chlorophyll and soluble protein in flag leaf blades decreased after anthesis in both the low SPS plants and wild-type plants, although the decrease was less in the low SPS plants. Panicle weights were significantly lower in the low SPS plant than in the wild-type plant. These results suggest that the remobilization of N from flag leaves was diminished by suppressing the development of reproductive sinks in the low SPS plant.     

Noninvasive electrocardiographic imaging for cardiac electrophysiology and arrhythmia

Over 7 million people worldwide die annually from erratic heart rhythms (cardiac arrhythmias), and many more are disabled. Yet there is no imaging modality to identify patients at risk, provide accurate diagnosis and guide therapy. Standard diagnostic techniques such as the electrocardiogram (ECG) provide only low-resolution projections of cardiac electrical activity on the body surface. Here we demonstrate the successful application in humans of a new imaging modality called electrocardiographic imaging (ECGI), which noninvasively images cardiac electrical activity in the heart. In ECGI, a multielectrode vest records 224 body-surface electrocardiograms; electrical potentials, electrograms and isochrones are then reconstructed on the heart's surface using geometrical information from computed tomography (CT) and a mathematical algorithm. We provide examples of ECGI application during atrial and ventricular activation and ventricular repolarization in (i) normal heart (ii) heart with a conduction disorder (right bundle branch block) (iii) focal activation initiated by right or left ventricular pacing, and (iv) atrial flutter.     

Optical and dielectric response of two-dimensional WX2 (X = Cl,O, S,Se, Te) monolayers: A comprehensive study based on density functional theory

Here, we study the dielectric and optical properties of two-dimensional (2D) WX₂ monolayers, where X is Cl, O, S, Se, and Te. First principle electronic band structure calculations reveal that all materials are direct band gap semiconductors except WO₂ and WCl₂, which are found to be indirect band gap semiconducting 2D materials. The dielectric response of these materials is also systematically investigated. The obtained results suggest that these materials are suitable as dielectric materials to suppress unwanted signal noise. The optical properties of these 2D materials, such as absorption, reflection and extinction coefficients, refractive index, and optical conductivity, are also calculated from the dielectric function. It is found that these materials exhibit excellent optical response. The present electronic, dielectric, and optical findings indicate that WX₂ monolayers have an opportunity in electronic, optical, and optoelectronic device applications.