T4SP: A Novel Tool and Database for Type IV Secretion Systems in Bacterial Genomes

Secretion systems, macromolecules to pass which can mediate the across cellular membranes, are essential for virulent and genetic material exchange among bacterial species[1]. Type IV secretion system （T4SS） is one of the secretion systems and it usually consists of 12 genes： VirB1, VirB2 ...VirB11, and VirD4[2]. The structure and molecular mechanisms of these genes have been well analyzed in Gram-negative strains[3] and Gram-positive strains were once believed to be lack of T4SS. However, some recent studies revealed that one or more virB/D genes also exist in some kinds of Gram-positive bacteria and play similar role, and form a T4SS-like system[3]. The VirBl-like, VirB4, VirB6, and VirD4 genes were identified in the chromosome of Gram-positive bacterium Streptococcus suis in our previous studies and their role as important mobile elements for horizontal transfer to recipients in an 89 K pathogenicity island （PAl） was demonstrated[45]. However, their structure and molecular mechanisms in other strains, especially in Gram-positive strains, are remained unclear.

Molecular Cloning,Bioinformatics Analysis and Expression Analysis of Type III Secretion System(T3SS)Injectisome Gene vscX from Vibrio alginolyticus

In order to enrich the research about type III secretion system （T3SS） injectisome of Vibrio alginolyticus, vscX gene was cloned from E algianlyticus strain HY9901 for bioinformatics analysis and expression analysis. Specific primers were designed according to the full-length geanme sequence of V. alginolyticus in GenBank. vscX gene （C, enBank accession number： FR780679） contained a 378 bp open reading frame （ORF）, encoding a putative protein of 125 amino acids. The theoretical molecular weight was 14.209 2 kD and theoretical pI was 5.75. By using Signal 4.1 Server and TMHMM Server 2.0, it was predicted that VscX protein had no transmembrane domain or signal peptide. The results of prediction using SoftBerry-Psite software showed that VscX protein contained three casein ki- nase lI phosphorylation sites, one N-myristoylation site and three C-terminal targeting signal sites. Subcellular localization revealed that VscX might be located in cytoplasm with the possibility of 56.5%. According to SMART prediction, VscX had one Pfam （ 1 - 125 aa） domain. Phylogenetic analysis revealed that VscX from V. alginolyticus and VscX from E parahemolyticus were clustered into the same group. Network interaction analysis showed that vscX was adjacent to vseY, vopB and sycN. By real-time fluorescent quantitative PCR technique and 2-△△△ method, the differences in expression levels of VscX mRNA in V. alginolyticus strain HY9901, T3SS deletion strain AvscO and complementary strain C-vscO at different growth stages were analyzed. The results showed that the expression levels of VscX mRNA in V. algianlyticus strain HY9901 and C-vscO were significantly up-regulated at stable growth stage （ P 〈0.01 ） ; the expression levels of VscX mRNA in deletion strain △vscO were significantly up-regulated at late growth stage （ P 〈0.01 ）. This study provided the basis for revealing the transport mechanism of T3SS injectisome of E alginolyticus.

SecReT6 update:a comprehensive resource of bacterial TypeⅥSecretion Systems

TypeⅥSecretion System(T6SS)plays significant roles in microbial activities via injecting effectors into adjacent cells or environments.T6SS increasingly gained attention due to its important influence on pathogenesis,microbial competition,etc.T6SS-associated research is explosively expanding on numerous grounds that call for an efficient resource.The SecReT6 version3 provides comprehensive information on T6SS and the interactions between T6SS and T6SS-related proteins such as T6SS regulators and T6SS effectors.To assist T6SS researches like microbial competition and regulatory mechanisms,SecReT6 v3developed online tools for detection and analysis of T6SS and T6SS-related proteins and estimation of T6SS-dependent killing risk.We have identified a novel T6SS regulator and T6SS-dependent killing capacity in Acinetobacter baumannii clinical isolates with the aid of SecReT6 v3.17,212 T6SSs and plentiful T6SS-related proteins in 26,573 bacterial complete genomes were also detected,analyzed and incorporated into the database.The database is freely available at https://bioinfo-mml.sjtu.edu.cn/SecReT6/.

A Fur-regulated type Ⅵ secretion system contributes to oxidative stress resistance and virulence in Yersinia pseudotuberculosis

The type Ⅵ secretion system(T6SS)is a widespread protein secretion apparatus deployed by many Gram-negative bacterial species to interact with competitor bacteria,host organisms,and the environment.Yersinia pseudotuber-culosis T6SS4 was recently reported to be involved in manganese acquisition;however,the underlying regulatory mechanism still remains unclear.In this study,we discovered that T6SS4 is regulated by ferric uptake regulator(Fur)in response to manganese ions(Mn^(2+)),and this negative regulation of Fur was proceeded by specifically recogniz-ing the promoter region of T6SS4 in Y.pseudotuberculosis.Furthermore,T6SS4 is induced by low Mn^(2+)and oxidative stress conditions via Fur,acting as a Mn^(2+)-responsive transcriptional regulator to maintain intracellular manganese homeostasis,which plays important role in the transport of Mn^(2+)for survival under oxidative stress.Our results pro-vide evidence that T6SS4 can enhance the oxidative stress resistance and virulence for Y.pseudotuberculosis.This study provides new insights into the regulation of T6SS4 via the Mn^(2+)-dependent transcriptional regulator Fur,and expands our knowledge of the regulatory mechanisms and functions of T6SS from Y.pseudotuberculosis.

Mannogalactoglucan from mushrooms protects pancreatic islets via restoring UPR and promotes insulin secretion in TIDM mice

Type 1 diabetes mellitus(T1DM) lacks insulin secretion due to autoimmune deficiency of pancreaticβ-cells.Protecting pancreatic islets and enhancing insulin secretion has been therapeutic approaches.Mannogalactoglucan is the main type of polysaccharide from natural mushroom,which has potential medicinal prospects.Nevertheless,the antidiabetic property of mannogalactoglucan in T1DM has not been fully elucidated.In this study,we obtained the neutral fraction of alkali-soluble Armillaria mellea polysaccharide(AAMP-N) with the structure of mannogalactoglucan from the fruiting body of A.mellea and investigated the potential therapeutic value of AAMP-N in T1DM.We demonstrated that AAMP-N lowered blood glucose and improved diabetes symptoms in T1DM mice.AAMP-N activated unfolded protein response(UPR) signaling pathway to maintain ER protein folding homeostasis and promote insulin secretion in vivo.Besides that,AAMP-N promoted insulin synthesis via upregulating the expression of transcription factors,increased Ca^(2+) signals to stimulate intracellular insulin secretory vesicle transport via activating calcium/calmodulin-dependent kinase Ⅱ(CamkⅡ) and cAMP/PKA signals,and enhanced insulin secretory vesicle fusion with the plasma membrane via vesicle-associated membrane protein 2(VAMP2).Collectively,these studies demonstrated that the therapeutic potential of AAMP-N on pancreatic islets function,indicating that mannogalactoglucan could be natural nutraceutical used for the treatment of T1DM.

The Effect of Umami Stimulation on Salivary Secretion Rate and Duration

Purpose: Umami reportedly promotes salivation. We aimed to investigate the effects of taste stimuli on slow and fast salivary secretion in humans using umami, sweet, and sour stimuli. Methods: Eight healthy women participated between 14:00 and 15:00, taking the circadian rhythm of salivary secretion into account. The types and concentrations of the taste solutions were glutamic acid (1.7 × 10−3 M), inosinic acid (9.8 × 10−3 M), and guanylic acid (9.8 × 10−3 M) for umami stimulation, citric acid (6.5 × 10−3 M) for acidity stimulation, and sucrose (1.6 × 10−2 M) for sweetness stimulation. First, the unstimulated salivary flow rate was measured. Then, 3 ml of a flavor solution was dropped under the tongue using a syringe. The saliva was expelled into an aluminum cup every minute and weighed. The first minute’s value minus 3 ml flavor solution was the stimulated salivary secretion rate produced by each flavor. The time-to-return to the initial unstimulated salivary flow rate was the duration of the stimulated saliva secretion rate. Results: The mean unstimulated salivary flow rate across participants was 0.64 ± 0.25 ml/min (range: 0.23 - 1.03 ml/min). The highest amount of saliva was induced by citric acid. There were significant differences between citric acid and the other flavor solutions (p < 0.05 for glutamic acid, inosinic acid, and sucrose;p < 0.01 for guanylic acid). There were no significant differences in duration of salivation between the flavor solutions. When the participants were divided into slow (0.45 ± 0.16 ml/min) and fast groups (0.83 ± 0.15 ml/min) based on their median resting salivary secretion rate, there were no significant differences between the two groups in the amount of saliva secreted at 1 minute after stimulation and the duration of the salivary secretion rate. Conclusion: Umami stimulation was effective in slowing salivary secretion and sustaining salivary secretion after stimulation.

Type Ⅳ secretion system in Helicobacter pylori:a new insight into pathogenicity

Objective To review the research progress on Type Ⅳ secretion system （T4SS） in HelicobacterpylorL Data sources The data used in this review were identified by searching of PUBMED （1995-2007） online resources using the key terms ＇Type Ⅳ secretion system＇ and ＇Helicobacter pylon. Study selection Mainly original articles and critical reviews written by major pioneer investigators of this field were selected. Results The research progress on T4SS in Helicobacter pylori was summarized. The structure and function was discussed. Conclusions T4SS is not only involved in toxin secretion and injection of virulence factors into eukaryotic host target cells, but also involved in horizontal DNA transfer to other bacteria and eukaryotic cells, through DNA uptake from or release into the extracellular milieu. It provides a new insight into the pathogenicity of Helicobacter pylori and a novel target for antimicrobials development. However, many challenges remain for us in understanding the biological role of T4SS in Helicobacter pylori.

Beyond dueling: roles of the type VI secretion system in microbiome modulation, pathogenesis and stress resistance

Bacteria inhabit diverse and dynamic environments,where nutrients may be limited and toxic chemicals can be prevalent.To adapt to these stressful conditions,bacteria have evolved specialized protein secretion systems,such as the type VI secretion system(T6SS)to facilitate their survival.As a molecular syringe,the T6SS expels various effectors into neighboring bacterial cells,eukaryotic cells,or the extracellular environment.These effectors improve the competitive fitness and environmental adaption of bacterial cells.Although primarily recognized as antibacterial weapons,recent studies have demonstrated that T6SSs have functions beyond interspecies competition.Here,we summarize recent research on the role of T6SSs in microbiome modulation,pathogenesis,and stress resistance.

The putative propeptide of MycP1 in mycobacterial type VII secretion system does not inhibit protease activity but improves protein stability

Mycosin-1 protease(MycP1)is a serine protease anchored to the inner membrane of Mycobacterium tuberculosis,and is essential in virulence factor secretion through the ESX-1 type VII secretion system(T7SS).Bacterial physiology studies demonstrated that MycP1 plays a dual role in the regulation of ESX-1 secretion and virulence,primarily through cleavage of its secretion substrate EspB.MycP1 contains a putative N-terminal inhibitory propeptide and a catalytic triad of Asp-His-Ser,classic hallmarks of a sub-tilase family serine protease.The MycP1 propeptide was previously reported to be initially inactive and activated after prolonged incubation.In this study,we have deter-mined crystal structures of MycP1 with(MycP124-422)and without(MycP1^(63-422))the propeptide,and conducted EspB cleavage assays using the two proteins.Very high struc-tural similarity was observed in the two crystal structures.Interestingly,protease assays demonstrated positive EspB cleavage for both proteins,indicating that the putative propeptide does not inhibit protease activity.Molecu-lar dynamic simulations showed higher rigidity in regions guarding the entrance to the catalytic site in MycP124-422 than in MycP1^(63-422),suggesting that the putative propeptide might contribute to the conformational stability of the active site cleft and surrounding regions.

Protein secretion systems in bacterial pathogens

Many bacterial pathogens utilize specialized secretion systems to deliver virulence factors into the extracellular milieu. These exported effectors act to manipulate various processes of targeted cells in order to create a suitable niche for bacterial growth. Currently, seven different types of secretion system have been described, of which Type I - VI are mainly present in Gram-negative bacteria and the newly discovered Type VII system seems exclusive to Gram-positive species. This review summaries our current understanding on the architecture and transport mechanisms of each secretion apparatus. We also discuss recent studies revealing the roles that these secretion systems and their substrates play in microbial pathogenesis.

Structural insights into substrate recognition by the type Ⅶ secretion system

Type VII secretion systems(T7SSs)are found in many disease related bacteria including Mycobacterium tuberculosis(Mtb).ESX-1[early secreted antigen 6 kilodaltons(ESAT-6)system 1]is one of the five subtypes(ESX-1?5)of T7SSs in Mfb,where it delivers virulence factors into host macrophages during infection.However,little is known about the molecular details as to how this occurs.Here,we provide high-resolution crystal structures of the C-terminal ATPase3 domains of EccC subunits from four different Mtb T7SS subtypes.These structures adopt a classic RecA-like a/p fold with a conserved Mg-ATP binding site.The structure of EccCbl in complex with the C-terminal peptide of EsxB identifies the location of substrate recognition site and shows how the specific signaling module XxxxMxF"for Mtb ESX-1 binds to this site resulting in a translation of the bulge loop.A comparison of all the ATPase3 structures shows there are significant differences in the shape and composition of the signal recognition pockets across the family,suggesting that distinct signaling sequences of substrates are required to be specifically recognized by different T7SSs.A hexameric model of the EccC-ATPase3 is proposed and shows the recognition pocket is located near the central substrate translocation channel.The diameter of the channel is?25-A,with a size that would allow helix-bundle shaped substrate proteins to bind and pass through.Thus,our work provides new molecular insights into substrate recognition for Mtb T7SS subtypes and also a possible transportation mechanism for substrate and/or virulence factor secretion.

Delivery of an Rhs-family nuclease effector reveals direct penetration of the gram-positive cell envelope by a type VI secretion system in Acidovorax citrulli

The type VI secretion system(T6SS)is a double-tubular nanomachine widely found in gram-negative bacteria.Its spear-like Hcp tube is capable of penetrating a neighboring cell for cytosol-to-cytosol protein delivery.However,gram-positive bacteria have been considered impenetrable to such T6SS action.Here we report that the T6SS of a plant pathogen,Acidovorax citrulli(AC),could deliver an Rhsfamily nuclease effector RhsB to kill not only gram-negative but also gram-positive bacteria.Using bioinformatic,biochemical,and genetic assays,we systematically identified T6SS-secreted effectors and determined that RhsB is a crucial antibacterial effector.RhsB contains an N-terminal PAAR domain,a middle Rhs domain,and an unknown C-terminal domain.RhsB is subject to self-cleavage at both its N-and C-terminal domains and its secretion requires the upstream-encoded chaperone EagT2 and VgrG3.The toxic Cterminus of RhsB exhibits DNase activities and such toxicity is neutralized by either of the two downstream immunity proteins,RimB1 and RimB2.Deletion of rhsB significantly impairs the ability of killing Bacillus subtilis while ectopic expression of immunity proteins RimB1 or RimB2 confers protection.We demonstrate that the AC T6SS not only can effectively outcompete Escherichia coli and B.subtilis in planta but also is highly potent in killing other bacterial and fungal species.Collectively,these findings highlight the greatly expanded capabilities of T6SS in modulating microbiome compositions in complex environments.

Dimensionless Study on Secretion Clearance of a Pressure Controlled Mechanical Ventilation System with Double Lungs

A pressure controlled mechanical ventilator with an automatic secretion clearance function can improve secretion clearance safely and efficiently.Studies on secretion clearance by pressure controlled systems show that these are suited for clinical applications.However,these studies are based on a single lung electric model and neglect the coupling between the two lungs.The research methods applied are too complex for the analysis of a multi-parameter system.In order to understand the functioning of the human respiratory system,this paper develops a dimensionless mathematical model of doublelung mechanical ventilation system with a secretion clearance function.An experiment is designed to verify the mathematical model through comparison of dimensionless experimental data and dimensionless simulation data.Finally,the coupling between the two lungs is studied,and an orthogonal experiment designed to identify the impact of each parameter on the system.

Neurotransmitters regulateβcells insulin secretion:A neglected factor

βcells are the main cells responsible for the hypoglycemic function of pancreatic islets,and the insulin secreted by these cells is the only hormone that lowers blood glucose levels in the human body.βcells are regulated by various factors,among which neurotransmitters make an important contribution.This paper discusses the effects of neurotransmitters secreted by various sympathetic and parasympathetic nerves onβcells and summarizes the mechanisms by which various neurotransmitters regulate insulin secretion.Many neurotransmitters do not have a single source and are not only released from nerve terminals but also synthesized byβcells themselves,allowing them to synergistically regulate insulin secretion.Almost all of these neurotransmitters depend on the presence of glucose to function,and their actions are mostly related to the Ca^(2+)and cAMP concentrations.Although neurotransmitters have been extensively studied,many of their mechanisms remain unclear and require further exploration by researchers.

Short-Term Effects of Liraglutide versus Vildagliptin on Insulin Secretion and Sensitivity in Type 2 Diabetes: A Single Blinded Randomized Controlled Trial (LIRAVIS Study)

Background: We aimed to evaluate the short-term metabolic effects of a GLP-1a, (liraglutide) versus a DPP-4i, (vildagliptin) in a group of sub-Saharan type 2 diabetes patients. Methods: We conducted a randomized controlled single blinded clinical trial in 14 uncontrolled type 2 diabetes patients (HbA1c ≥ 53 mmol/mol) with mean duration of diabetes of 8 [1 - 12] years and median age of 57 [49 - 61] years. Baseline treatment consisted of metformin in monotherapy or metformin plus sulfonylureas. Participants were randomly allocated to 2 groups of add-on 1.2 mg/day subcutaneous liraglutide in group 1 or 100 mg/day of oral vildagliptin in group 2 for 2 weeks. In all participants, insulin secretion in response to mixed meal tolerance test, insulin sensitivity by 80 mU/m2/min hyperinsulinemic-euglycemic clamp, body composition, and lipid profile were measured before and after intervention. Results: At the end of intervention, insulin sensitivity remained unchanged both with liraglutide from 6.6 [4.2 - 7.9] to 6.9 [4.3 - 10.8] mg/kg/min;p = 0.61 and vildagliptin from 7.1 [5.3 - 9.0] to 6.5 [5.6 - 9.4] mg/kg/min (p = 0.86). The area under the C-peptide curve varied from 5.5 [1.0 - 10.9] to 14.9 [10.8 - 17.2] nmol/L/120min, p = 0.09 in group 1 and from 1.1 [0.5 - 14.1] to 13.0 [9.6 - 16.9] nmol/L/120min (p = 0.17) in group 2. LDL Cholesterol levels decreased significantly with liraglutide from 0.85 g/L [0.51 - 1.02] to 0.54 g/L [0.50 - 0.73] (p = 0.04) but not with Vildagliptin. Body weight tended to decrease in group 1 (−0.6 kg) versus modest increase in group 2 (+1.1 kg). Conclusion: Short-term metabolic effects of Liraglutide and Vildagliptin add-on therapy are comparable in sub-Saharan type 2 diabetes patients with a more favorable trend for Liraglutide on body weight, lipid profile, and insulin secretion.

Effects of Beverage Ingredients on Salivary Fluid Secretion with an <i>ex Vivo</i>Submandibular Gland Perfusion System: Tannic Acid as a Key Component for the Inhibition of Saliva Secretion

Tannic acid (TA) and TA containing beverage have been proved to inhibit Ca2+-activated Cl- channel located apical membrane of the secretory cells. However, their effect on salivary fluid secretion is not well investigated. We used mouse ex Vivo submandibular gland perfusion technique to identify the general effect of TA and related beverage samples on muscarinic agonist carbachol induced fluid secretion. Green tea inhibited fluid secretion by 64% from the control, where oolong tea was by 53%, and red wine by 43% which was linked with their TA concentration. On the other hand, though TA was contained at 4.7 μM in white wine sample and 33 μM in coffee extract, no adverse effect was observed. In addition, coffee induced salivation in the absence of carbachol. TA had a negative effect on fluid secretion with a concentration dependent manner. The effects of TA on carbachol induced calcium increase showed identical as fluid secretion, which was initially no effect, and then gradually decreased over the time. These results demonstrate that TA directly inhibits the salivary fluid secretion and it affects not only Ca2+-activated Cl- channel but also intracellular Ca2+ increasing mechanisms.

Vascular endothelial growth factor B improves impaired glucose tolerance through insulin-mediated inhibition of glucagon secretion

BACKGROUND Impaired glucose tolerance(IGT)is a homeostatic state between euglycemia and hyperglycemia and is considered an early high-risk state of diabetes.When IGT occurs,insulin sensitivity decreases,causing a reduction in insulin secretion and an increase in glucagon secretion.Recently,vascular endothelial growth factor B(VEGFB)has been demonstrated to play a positive role in improving glucose metabolism and insulin sensitivity.Therefore,we constructed a mouse model of IGT through high-fat diet feeding and speculated that VEGFB can regulate hyperglycemia in IGT by influencing insulin-mediated glucagon secretion,thus contributing to the prevention and cure of prediabetes.AIM To explore the potential molecular mechanism and regulatory effects of VEGFB on insulin-mediated glucagon in mice with IGT.METHODS We conducted in vivo experiments through systematic VEGFB knockout and pancreatic-specific VEGFB overexpression.Insulin and glucagon secretions were detected via enzyme-linked immunosorbent assay,and the protein expression of phosphoinositide 3-kinase(PI3K)/protein kinase B(AKT)was determined using western blot.Further,mRNA expression of forkhead box protein O1,phosphoenolpyruvate carboxykinase,and glucose-6 phosphatase was detected via quantitative polymerase chain reaction,and the correlation between the expression of proteins was analyzed via bioinformatics.RESULTS In mice with IGT and VEGFB knockout,glucagon secretion increased,and the protein expression of PI3K/AKT decreased dramatically.Further,in mice with VEGFB overexpression,glucagon levels declined,with the activation of the PI3K/AKT signaling pathway.CONCLUSION VEGFB/vascular endothelial growth factor receptor 1 can promote insulin-mediated glucagon secretion by activating the PI3K/AKT signaling pathway to regulate glucose metabolism disorders in mice with IGT.

Efficacy of tolvaptan in an infant with syndrome of inappropriate antidiuretic hormone secretion associated with holoprosencephaly:A case report

BACKGROUND Holoprosencephaly(HPE)is a congenital malformation with various degrees of incomplete separation of the cerebral hemispheres due to differentiation disorders of the forebrain.Although HPE with diabetes insipidus due to associated pituitary dysfunction has been reported,HPE with the syndrome of inappropriate antidiuretic hormone secretion(SIADH)is very rare.Tolvaptan,a vasopressin V2 receptor antagonist,is effective in adults with SIADH.However,there is no report of its efficacy in infants with SIADH.The purpose of this report is to demonstrate that tolvaptan is effective for SIADH in infants and that administration of tolvaptan eliminates the need for restriction of water intake and sodium administration.CASE SUMMARY A 2414-g female infant was born at 38 wk by normal vaginal delivery.Facial anomalies and head magnetic resonance imaging indicated semilobar HPE.After birth,she had hyponatremia due to SIADH and was treated using water and sodium restriction.However,she developed an exaggerated response to the fluid restrictions,resulting in large fluctuations in serum sodium levels.Subsequent administration of tolvaptan improved the fluctuations in serum sodium levels without the need for adjustment of water or sodium administration.Serum sodium was maintained within the normal range after discontinuation of tolvaptan at 80 d of life.There were no side effects,such as hypernatremia or liver dysfunction,during the administration of tolvaptan.CONCLUSION This is the first report on the safety and efficacy of tolvaptan in an infant with SIADH associated with HPE.

Molecular investigation of exoU and exoY virulence genes in Pseudomonas aeruginosa collected from hospitalized patients in North of Iran:A descriptive-analytical study

Objective:To investigate the frequency of exoU and exoY genes in patients with Pseudomonas aeruginosa infection.Methods:In this study,100 clinical isolates of Pseudomonas aeruginosa were collected from patients hospitalized in educational-therapeutic hospitals and were identified using standard microbiological tests.Then,the antibiotic resistance pattern of the isolates was determined by the disk agar diffusion method.The bacterial DNAs were extracted by the alkaline lysis method.Finally,the presence of exoU and exoY genes was evaluated by the PCR test.Results:In this study,47%,72%,29%,39%,40%,and 44%of the isolates were non-susceptible to piperacillin,aztreonam,ceftazidime,imipenem,tobramycin,and ciprofloxacin,respectively.In addition,95%and 93%of the clinical isolates carried the exoU and exoY genes.Blood and fecal isolates had both virulence genes,while only one wound isolate had neither genes.Meanwhile,all urinary isolates contained the exoY gene and only one isolate lacked the exoU gene.Also,88 isolates simultaneously had both exoU and exoY genes.Conclusions:High prevalence of exoU and exoY genes in this region indicates a significant role of typeⅢsecretion system in pathogenesis of Pseudomonas aeruginosa.The typeⅢsecretion system may be a suitable target to reduce the pathogenicity of this bacterium.

Comparative Study of the Biological Activities of the Skin Secretions from Six Common Chinese Amphibians

Water soluble skin secretions of six common Chinese amphibians were studied for their biological and enzymatic activities.The skin secretions of Tylototriton verrucosus,Bombina maxima ,and Bufo andrewsi were found toxic to mice with the intraperitoneal LD 50 of 11 5?mg/kg,18 8?mg/kg,and 264?mg/kg,respectively.No acute lethal toxicities were observed for the skin secretions of Rana nigromaculata,Rana guentheri and Rana limnocharis in a dose up to 500?mg/kg.The lethal toxicities of the skin secretions of T verrucosus and B maxima to mice are in the same grade as those of Viperidae snake venoms.The toxic components in T verrucosus and B maxima skin secretions are the proteins with molecular weights ranging from 3 to 60?kDa.All the skin secretions had both proteolytic activity and trypsin inhibitory activity.The skin secretions from T verrucosus , B maxima and B andrewsi also displayed wide spectrum antimicrobial activity.On the other hand,the skin secretions from B andrewsi and B maxima showed cytotoxicity on human cancer cells.All the six samples had not significant effects on mammalian blood coagulation system.Phospholipase A 2 activity was only found in the skin secretions of T verrucosus .None of these skin secretions showed acetylcholine esterase activity.