Clostridial hydrolytic enzymes degrading extracellular components

Development and application of a method for counterselectable in-frame deletion in Clostridium perfringens

Many pathogenic clostridial species produce toxins and enzymes. To facilitate genome-wide identification of virulence factors and biotechnological application of their useful products, we have developed a markerless in-frame deletion method for Clostridium perfringens which allows efficient counterselection and multiple-gene disruption. The system comprises a galKT gene disruptant and a suicide galK plasmid into which two fragments of a target gene for in-frame deletion are cloned. The system was shown to be accurate and simple by using it to disrupt the alpha-toxin gene of the organism. It was also used to construct of two different virulence-attenuated strains, ΗΝ1303 and HN1314: the former is a disruptant of the virRS operon, which regulates the expression of virulence factors, and the latter is a disruptant of the six genes encoding the α, θ, and κ toxins; a clostripain-like protease; a 190-kDa secretory protein; and a putative cell wall lytic endopeptidase. Comparison of the two disruptants in terms of growth ability and the background levels of secreted proteins showed that HN1314 is more useful than ΗΝ1303 as a host for the large-scale production of recombinant proteins.

Clostridial toxins

Clostridia produce the highest number of toxins of any type of bacteria and are involved in severe diseases in humans and other animals. Most of the clostridial toxins are pore-forming toxins responsible for gangrenes and gastrointestinal diseases. Among them, perfringolysin has been extensively studied and it is the paradigm of the cholesterol-dependent cytolysins, whereas Clostridium perfringens epsilon-toxin and Clostridium septicum alpha-toxin, which are related to aerolysin, are the prototypes of clostridial toxins that form small pores. Other toxins active on the cell surface possess an enzymatic activity, such as phospholipase C and collagenase, and are involved in the degradation of specific cell-membrane or extracellular-matrix components. Three groups of clostridial toxins have the ability to enter cells: large clostridial glucosylating toxins, binary toxins and neurotoxins. The binary and large clostridial glucosylating toxins alter the actin cytoskeleton by enzymatically modifying the actin monomers and the regulatory proteins from the Rho family, respectively. Clostridial neurotoxins proteolyse key components of neuroexocytosis. Botulinum neurotoxins inhibit neurotransmission at neuromuscular junctions, whereas tetanus toxin targets the inhibitory interneurons of the CNS. The high potency of clostridial toxins results from their specific targets, which have an essential cellular function, and from the type of modification that they induce. In addition, clostridial toxins are useful pharmacological and biological tools.

Islet isolation for clinical transplantation

Islet transplantation is emerging as a viable treatment option for selected patients with type 1 diabetes. Following the initial report in 2000 from Edmonton of insulin independence in seven out of seven consecutive recipients, there has been a huge expansion in clinical islet transplantation. The challenge we now face is the apparent decline in graft function over time. Isolating high-quality human islets which survive and function for a longer period will no doubt contribute to further improvement in long-term clinical outcome. This chapter reviews the selection of appropriate donors for islet isolation and transplantation, describes each step during islet isolation, and discusses the scope for further improvements.

Identification of a two-component VirR/VirS regulon in Clostridium perfringens

Clostridium perfringens, a Gram-positive anaerobic pathogen, is a causative agent of human gas gangrene that leads to severe rapid tissue destruction and can cause death within hours unless treated immediately. Production of several toxins is known to be controlled by the two-component VirR/VirS system involving a regulatory RNA (VR-RNA) in C. perfringens. To elucidate the precise regulatory network governed by VirR/VirS and VR-RNA, a series of microarray screening using VirR/VirS and VR-RNA-deficient mutants was performed. Finally, by qRT-PCR analysis, 147 genes (30 single genes and 21 putative operons) were confirmed to be under the control of the VirR/VirS-VR-RNA regulatory cascade. Several virulence-related genes for alpha-toxin, kappa-toxin, hyaluronidases, sialidase, and capsular polysaccharide synthesis were found. Furthermore, some genes for catalytic enzymes, various genes for transporters, and many genes for energy metabolism were also found to be controlled by the cascade. Our data indicate that the VirR/VirS-VR-RNA system is a global gene regulator that might control multiple cellular functions to survive and multiply in the host, which would turn out to be a lethal flesh-eating infection.

Effect of anticoagulants on the plasma hyaluronidase activities

Mammalian hyaluronidases (HAases) are an endo-beta-N-acetyl-hexosaminidases that degrade hyaluronan (HA) and have been implicated in diverse pathophysiological functions. Several pathological conditions, such as diabetes, monoclonal gammapathy, and bladder and prostate tumors, report the distorted plasma HAase activity. However, the plasma HAase (hHyal-1) activity has been presumed to change with the circulating HA level and serves as an early marker for several diseases. It has been generally practised to use the anticoagulants such as tri-sodium citrate/di-sodium EDTA/heparin for the preparation of plasma for both biochemical and clinical analyses. In the present investigation, the effect of anticoagulants on plasma HAaseactivity was evaluated and compared with the serum HAase activity that is devoid of anticoagulants as no study provides information in this regard. The results suggested that the plasma HAase activity in the presence of the recommended concentration of EDTA was highly comparable/similar to that of the serum HAase activity. In contrast, citrated or heparinized plasma recorded a significantly reduced level of activity than that of the serum HAase activity. In conclusion, our results suggested that the EDTA-treated plasma samples are a better choice compared with heparin and citrated samples to assess the HAase activity.

A universal strategy for high-yield production of soluble and functional clostridial collagenases in E. coli

Clostridial collagenases are foe and friend: on the one hand, these enzymes enable host infiltration and colonization by pathogenic clostridia, and on the other hand, they are valuable biotechnological tools due to their capacity to degrade various types of collagen and gelatine. However, the demand for high-grade preparations exceeds supply due to their pathogenic origin and the intricate purification of homogeneous isoforms. We present the establishment of an Escherichia coli expression system for a variety of constructs of collagenase G (ColG) and H (ColH) from Clostridium histolyticum and collagenase T (ColT) from Clostridium tetani, mimicking the isoforms in vivo. Based on a setup of five different expression strains and two expression vectors, 12 different constructs were expressed, and a flexible purification platform was established, consisting of various orthogonal chromatography steps adaptable to the individual needs of the respective variant. This fast, cost-effective, and easy-to-establish platform enabled us to obtain at least 10 mg of highly pure mono-isoformic protein per liter of culture, ideally suited for numerous sophisticated downstream applications. This production and purification platform paves the way for systematic screenings of recombinant collagenases to enlighten the biochemical function and to identify key residues and motifs in collagenolysis.

Diversifying and stabilizing selection of sialidase and N-acetylneuraminate catabolism in Mycoplasma synoviae

Sialidase activity varies widely among strains and tends to correlate with strain virulence in the avian pathogen Mycoplasma synoviae. To characterize the forms of selection acting on enzymes required for sialic acid scavenging and catabolism, the ratios of nonsynonymous (K(a)) to synonymous (K(s)) mutation frequency were calculated for codons in the sialidase gene of 16 strains of M. synoviae and for its nearly identical homolog in four strains of Mycoplasma gallisepticum. The K(a)/K(s) (omega) values for the linked genes required for nutritive N-acetylneuraminate catabolism (nanA, nagC, nanE, nagA, and nagB) from nine strains of M. synoviae were also determined. To provide context, omega was determined for all corresponding genes of 26 strains of Clostridium perfringens and Streptococcus pneumoniae. Bayesian models of sequence evolution showed that only the sialidase of M. synoviae was under significant (P < 0.001) diversifying selection, while the M. synoviae genes for N-acetylneuraminate catabolism and all genes examined from M. gallisepticum, C. perfringens, and S. pneumoniae were under neutral to stabilizing selection. Diversifying selection acting on the sialidase of M. synoviae, but not on the sialidase of M. gallisepticum or the sialidases or other enzymes essential for sialic acid scavenging in other Firmicutes, is evidence that variation in specific activity of the enzyme is perpetuated by a nonnutritive function in M. synoviae that is influenced by the genomic context of the organism.

Biochemical characterization of the catalytic domains of three different clostridial collagenases

Clostridial collagenases are used for a broad spectrum of biotechnological applications and represent prime target candidates for both therapy and diagnosis of clostridial infections. In this study, we biochemically characterized the catalytic domains of three clostridial collagenases, collagenase G (ColG) and H (ColH) from Clostridium histolyticum, and collagenase T (ColT) from C. tetani. All protein samples showed activity against a synthetic peptidic substrate (furylacryloyl-Leu-Gly-Pro-Ala, FALGPA) with ColH showing the highest overall activity and highest substrate affinity. Whereas the K m values of all three enzymes were within the same order of magnitude, the turnover rate k cat of ColG decreased 50- to 150-fold when compared to ColT and ColH. It is noteworthy that the protein N-terminus significantly impacts their substrate affinity and substrate turnover as well as their inhibition profile with 1,10-phenanthroline. These findings were complemented with the discovery of a strictly conserved double-glycine motif, positioned 28 amino acids upstream of the HEXXH zinc binding site, which is critical for enzymatic activity. These observations have consequences with respect to the topology of the N-terminus relative to the active site as well as possible activation mechanisms.

Development and characterization of a collagen degradation assay to assess purified collagenase used in islet isolation

OBJECTIVES

A collagen degradation activity (CDA) assay was developed to improve the biochemical characterization of purified collagenase used for islet isolation.

MATERIALS AND METHODS

Purified class I collagenase (CI) or class II collagenase (CII) from Clostridium histolyticum cultures were used in all experiments. The CDA assay was performed by incubating 50 microg/mL of FITC fibrils with CI or CII for 60 minutes at 35 degrees C. The correlation of the molecular species of the enzyme to CDA was determined by fractionating CI:CII mixtures over an anion exchange column. Individual fractions were analyzed for A280, CDA activity, and by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) to correlate chromatographic analysis of these enzyme mixtures to the molecular species of collagenase effective in collagen degradation.

RESULTS

CI has approximately 6 to 17 x higher specific activity than CII in this assay. Assays of different individual fractions recovered after anion exchange chromatography showed that the CDA of collagenase was dependent on the molecular species of the enzyme. Only intact CII and CI with molecular weights >or=100 kDa could degrade collagen fibrils.

CONCLUSIONS

This assay provides a more reliable assessment of the functional activity of collagenase enzymes than peptide substrates currently used today. Fractionation of purified collagenase mixtures by anion exchange chromatography followed by analysis of individual fractions by SDS-PAGE and CDA assays will provide a powerful tool to analyze the molecular species of CI and CII required for islet isolation.

Genetic variation in sialidase and linkage to N-acetylneuraminate catabolism in Mycoplasma synoviae

We explored the genetic basis for intraspecific variation in mycoplasmal sialidase activity that correlates with virulence, and its potentially advantageous linkage to nutrient catabolism. Polymorphism in N-acetylneuraminate scavenging and degradation genes (sialidase, N-acetylneuraminate lyase, N-acetylmannosamine kinase, N-acetylmannosamine-6-phosphate epimerase, N-acetylglucosamine-6-phosphate deacetylase, and glucosamine-6-phosphate deaminase) was evident among eight strains of the avian pathogen Mycoplasma synoviae. Most differences were single nucleotide polymorphisms, ranging from 0.34+/-0.04 substitutions per 100 bp for N-acetylmannosamine kinase to 0.65+/-0.03 for the single-copy sialidase gene nanI. Missense mutations were twice as common as silent mutations in nanI; 26% resulted in amino acids dissimilar to consensus; and there was a 12-base deletion near the nanI promoter in strain WVU1853(T), supporting a complex genetic basis for differences in sialidase activity. Two strains had identical frameshifts in the N-acetylneuraminate lyase gene nanA, resulting in nonsense mutations, and both had downstream deletions in nanA. Such genetic lesions uncouple extracellular liberation of sialic acid from generation of fructose-6-phosphate and pyruvate via intracellular N-acetylneuraminate degradation. Retention of nanI by such strains, but not others in the M. synoviae phylogenetic cluster, is evidence that sialidase has an important non-nutritional role in the ecology of M. synoviae and certain other mycoplasmas.

Sialidase activity in Mycoplasma synoviae

Eleven strains of the avian pathogen Mycoplasma synoviae were evaluated for the presence of sialidase activity with the use of the fluorogenic substrate 2'-(4-methylumbelliferyl)-alpha-D-N-acetylneuraminic acid and the sialidase inhibitor 2-deoxy-2,3- didehydro-N-acetylneuraminic acid. The kinetics of in vitro growth in modified Frey medium were also assessed for each strain. Five strains had been isolated from clinically symptomatic chickens, and strains WVU 1853T and K3344 have been demonstrated to be capable of reproducing disease in specific-pathogen-free chickens. All strains exhibited sialidase activity, although the amount varied 65-fold among strains (P < 0.0001) from 1.3 x 10(-7) to 2.0 x 10(-9) activity units per colony-forming unit. Strains originally isolated from clinically symptomatic birds had more (P < 0.05) sialidase activity than strains from asymptomatic birds. Strain WVU1853T exhibited the most sialidase activity (P < 0.0001) and grew to the highest culture density (P < 0.0001) among strains, but across strains, the rank correlation of growth rate with sialidase activity was not significant. Negligible activity was detected in conditioned culture supernatant fluid. This is the first report of sialidase activity in pathogenic strains of M. synoviae, which suggests a potential enzymatic basis for virulence of the organism.

The magic glue hyaluronan and its eraser hyaluronidase: a biological overview

Hyaluronan (HA) is a multifunctional high molecular weight polysaccharide found throughout the animal kingdom, especially in the extracellular matrix (ECM) of soft connective tissues. HA is thought to participate in many biological processes, and its level is markedly elevated during embryogenesis, cell migration, wound healing, malignant transformation, and tissue turnover. The enzymes that degrade HA, hyaluronidases (HAases) are expressed both in prokaryotes and eukaryotes. These enzymes are known to be involved in physiological and pathological processes ranging from fertilization to aging. Hyaluronidase-mediated degradation of HA increases the permeability of connective tissues and decreases the viscosity of body fluids and is also involved in bacterial pathogenesis, the spread of toxins and venoms, acrosomal reaction/ovum fertilization, and cancer progression. Furthermore, these enzymes may promote direct contact between pathogens and the host cell surfaces. Depolymerization of HA also adversely affects the role of ECM and impairs its activity as a reservoir of growth factors, cytokines and various enzymes involved in signal transduction. Inhibition of HA degradation therefore may be crucial in reducing disease progression and spread of venom/toxins and bacterial pathogens. Hyaluronidase inhibitors are potent, ubiquitous regulating agents that are involved in maintaining the balance between the anabolism and catabolism of HA. Hyaluronidase inhibitors could also serve as contraceptives and anti-tumor agents and possibly have antibacterial and anti-venom/toxin activities. Additionally, these molecules can be used as pharmacological tools to study the physiological and pathophysiological role of HA and hyaluronidases.

Factors influencing the collagenase digestion phase of human islet isolation

Substantial advances in human islet isolation technology have occurred during the past decade. However, it is still difficult to recover the entire quantity of islets contained in a pancreas. A major obstacle to successful human islet isolation has been the variability of the collagenase digestion phase of islet isolation. Future advances in enzyme technology will make it possible to optimally liberate islets with enzyme blends "tailor-made" for each individual donor pancreas. Such innovative strategies will be advantageous in improving islet isolation efficiency, recovery, viability, and ultimately posttransplant function.

The venom of the Lonomia caterpillar: an overview

Contact with the Lonomia caterpillar causes numerous accidents, especially in Venezuela and the southern region of Brazil, where it is considered a public health problem. The Lonomia obliqua venom causes disseminated intravascular coagulation and a consumptive coagulopathy, which can lead to a hemorrhagic syndrome. The venom of Lonomia achelous also causes hemorrhage, but through increased fibrinolysis. In vivo and in vitro studies have shown that the venom of the Lonomia caterpillar contains several toxins with procoagulant, anticoagulant and antithrombotic activities. These toxins also affect the endothelium. The recent construction of cDNA libraries of the transcripts from L. obliqua bristles enables the use of biotechnological approaches to study the venom. This paper presents an overview of the biochemical and biological properties of Lonomia caterpillar venom, discussing aspects of human accidents, experimental envenomation, toxins and targets and future perspectives.

Mycoplasma alligatoris infection promotes CD95 (FasR) expression and apoptosis of primary cardiac fibroblasts

Mycoplasma alligatoris causes acute lethal primary infection of susceptible hosts. A genome survey implicated sialidase and hyaluronidase, potential promoters of CD95-mediated eukaryotic cell death, as virulence factors of M. alligatoris. We used immunofluorescence imaging and flow cytometry to examine the effects of M. alligatoris infection in vitro on CD95 expression and apoptosis by alligator cardiac fibroblasts, a major cell type of a target organ of M. alligatoris infection in vivo. A uniform distribution of CD95 in primary cultured cardiac, skeletal muscle, and embryonic fibroblasts was demonstrated by using polyclonal antibodies against the N or C terminus of mouse or human CD95. Anti-CD95 antibodies reacted on Western blots of fibroblast lysates with a band with the predicted apparent molecular weight of CD95, but soluble CD95 was not detected in plasma from control or M. alligatoris-infected alligators. The proportion of CD95-gated cardiac fibroblasts increased threefold (P<0.01) 48 h after inoculation with M. alligatoris. Infection induced morphological changes in cardiac fibroblasts, including translocation of CD95 characteristic of apoptosis and an eightfold increase (P<0.16) in 5-bromo-2'-deoxyuridine (BrdU) incorporation measured in a terminal deoxynucleotide transferase dUTP nick end-labeling apoptosis assay. The proportion of BrdU-gated controls activated with agonistic immunoglobulin M against human CD95 also increased threefold (P<0.03 for muscle). Heat-inactivated M. alligatoris and sterile M. alligatoris-conditioned culture supernatant had no effect. This is the first report of a CD95 homolog in the class Reptilia and establishes a new model that can be used to test the direct bacterial interaction with upstream components of the CD95 signal transduction pathway.

Snake venom hyaluronidase: a therapeutic target

The diffusion of toxins from the site of a bite into the circulation is essential for successful envenomation. Degradation of hyaluronic acid in the extracellular matrix (ECM) by venom hyaluronidase is a key factor in this diffusion. Hyaluronidase not only increases the potency of other toxins but also damages the local tissue. In spite of its important role, little attention has been paid to this enzyme. Hyaluronidase exists in various isoforms and generates a wide range of hyaluronic acid degradation products. This suggests that beyond its role as a spreading factor venom hyaluronidase deserves to be explored as a possible therapeutic target for inhibiting the systemic distribution of venom and also for minimizing local tissue destruction at the site of the bite.

Regulation of Apoptosis by Gram-Positive Bacteria: Mechanistic Diversity and Consequences for Immunity

Apoptosis, or programmed cell death (PCD), is an important physiological mechanism, through which the human immune system regulates homeostasis and responds to diverse forms of cellular damage. PCD may also be involved in immune counteraction to microbial infection. Over the past decade, the amount of research on bacteria-induced PCD has grown tremendously, and the implications of this mechanism on immunity are being elucidated. Some pathogenic bacteria actively trigger the suicide response in critical lineages of leukocytes that orchestrate both the innate and adaptive immune responses; other bacteria proactively prevent PCD to benefit their own survival and persistence. Currently, the microbial virulence factors, which represent the keys to unlocking the suicide response in host cells, are a primary focus of this field. In this review, we discuss these bacterial "apoptosis regulatory molecules" and the apoptotic events they either trigger or prevent, the host target cells of this regulatory activity, and the possible ramifications for immunity to infection. Gram-positive pathogens including Staphylococcus, Streptococcus, Bacillus, Listeria, and Clostridia species are discussed as important agents of human infection that modulate PCD pathways in eukaryotic cells.

Inhibition of Naja naja venom hyaluronidase: Role in the management of poisonous bite

Hyaluronidase is present virtually in all snake venoms and has been known as a "spreading factor." The enzyme damages the extracellular matrix at the site of the bite, leading to severe morbidity. In this study, the benefits of inhibiting the hyaluronidase activity of Indian cobra (Naja naja) venom have been investigated. Anti-NNH1 and aristolochic acid both inhibited the in vitro activity of the purified hyaluronidase, (NNH1) and the hyaluronidase activity of whole venom in a dose-dependent manner. Both anti-NNH1 and aristolochic acid abolished the degradation of hyaluronan in human skin tissue sections by NNH1 and by whole venom. Aristolochic acid quenched the fluorescent emission of NNH1. A non-competitive mechanism of NNH1 inhibition was observed with aristolochic acid. NNH1 potentiates the toxicity of Daboia russellii VRV-PL-VIII myotoxin and hemorrhagic complex-I. However, the potentiation of toxicity was inhibited dose-dependently by anti-NNH1 and aristolochic acid. Further, mice injected with whole venom which had been preincubated with anti-NNH1/aristolochic acid, showed more than a two-fold increase in survival time, compared to mice injected with venom alone. A more moderate increase in survival time was observed when mice were injected with anti-NNH1/aristolochic acid 10 min after whole venom injection. This study illustrates the significance of venom hyaluronidase in the pathophysiology of snake venom poisoning and the therapeutic value of its inhibition.

Improved enzymatic isolation of fibroblasts for the creation of autologous skin substitutes

The number of medical applications using autologous fibroblasts is increasing rapidly. We investigated thoroughly the procedure to isolate cells from skin using the enzymatic tissue dissociation procedure. Tissue digestion efficiency, cell viability, and yield were investigated in relation to size of tissue fragments, digestion volume to tissue ratio, digestion time, and importance of other protease activities present in Clostridium histolyticum collagenase (CHC) (neutral protease, clostripain, and trypsin). The results showed that digestion was optimal with small tissue fragments (2-3 mm3) and with volumes tissue ratios > or =2 ml/g tissue. For incubations < or =10 h, the digestion efficiency and cell isolation yields were significantly improved by increasing the collagenase, neutral protease, or clostripain activity, whereas trypsin activity had no effects. However, a too high proteolytic activity of one of the proteases present in CHC digestion solution or long exposure times interfered with cell viability and cell culture yields. The optimal range of CHC proteases activities per milliliter digestion solutions was determined for digestions < or =10 h (collagenase 2700-3900 Mandl U/ml, neutral protease 5100-10,000 caseinase U/ml, and clostripain 35-48 BAEE U/ml) and for longer digestions (>14 h) (collagenase 1350- 3000 U/ml, neutral protease 2550-7700 U/ml, and clostripain 18-36 U/ml). Using these conditions, a maximum fibroblast expansion was achieved when isolated cells were seeded at 1 x 10(4) cells/cm2. These results did not only allow selection of optimal CHC batches able to digest dermal tissue with an high cell viability but also significantly increased the fibroblast yields, enabling us to produce autologous dermal tissue in a clinically acceptable time frame of 3 wk.

Genomic analysis of the protein secretion systems in Clostridium acetobutylicum ATCC 824

Consistent information about protein secretion in Gram-positive bacteria is essentially restricted to the model organism Bacillus subtilis. Among genome-sequenced clostridia, Clostridium acetobutylicum has been the most extensively studied from a physiological point of view and is the organism for which the largest variety of molecular biology tools have been developed. Following in silico analyses, both secreted proteins and protein secretion systems were identified. The Tat (Twin arginine translocation; TC #2.A.64) pathway and ABC (ATP binding cassette) protein exporters (TC #3.A.1.) could not be identified, but the Sec (secretion) pathway (TC #3.A.5) appears to be used prevalently. Similarly, a flagella export apparatus (FEA; TC #3.A.6.), holins (TC #1.E.), and an ESAT-6/WXG100 (early secreted antigen target of 6 kDa/proteins with a WXG motif of approximately 100 residues) secretion system were identified. Here, we report for the first time the identification of a fimbrilin protein exporter (FPE; TC #3.A.14) and a Tad (tight adherence) export apparatus in C. acetobutylicum. This investigation highlights the potential use of this saprophytic bacterium in biotechnological and biomedical applications as well as a model organism for studying protein secretion in pathogenic Gram-positive bacteria.

Inhibition of Naja naja Venom Hyaluronidase by Plant-Derived Bioactive Components and Polysaccharides

The inhibitory effect of several bioactive compounds on the activity of hyaluronidase enzyme purified from Naja naja venom was investigated in vitro. Compounds were found to inhibit the hyaluronidase activity dose dependently. Among glycosaminoglycans, heparin, heparan sulfate, and dermatan sulfate showed maximum inhibition compared to chondroitin sulfates. Different molecular forms of chitosan inhibit the enzyme, and inhibition appears to depend on the chain length. In addition, plant-derived bioactive compounds also inhibited the activity of hyaluronidase dose dependently. Among those tested, aristolochic acid, indomethacin, quercetin, curcumin, tannic acid, and flavone exhibited inhibition, with aristolochic acid and quercetin completely inhibiting the enzyme activity. It is concluded that the inhibitors of hyaluronidase could be used as potent first aid agents in snakebite therapy. Furthermore, these inhibitors not only reduce the local tissue damage but also retard the easy diffusion of systemic toxins and hence increase survival time.

The genome sequence of Rickettsia felis identifies the first putative conjugative plasmid in an obligate intracellular parasite

We sequenced the genome of Rickettsia felis, a flea-associated obligate intracellular α-proteobacterium causing spotted fever in humans. Besides a circular chromosome of 1,485,148 bp, R. felis exhibits the first putative conjugative plasmid identified among obligate intracellular bacteria. This plasmid is found in a short (39,263 bp) and a long (62,829 bp) form. R.felis contrasts with previously sequenced Rickettsia in terms of many other features, including a number of transposases, several chromosomal toxin–antitoxin genes, many more spoT genes, and a very large number of ankyrin- and tetratricopeptide-motif-containing genes. Host-invasion-related genes for patatin and RickA were found. Several phenotypes predicted from genome analysis were experimentally tested: conjugative pili and mating were observed, as well as β-lactamase activity, actin-polymerization-driven mobility, and hemolytic properties. Our study demonstrates that complete genome sequencing is the fastest approach to reveal phenotypic characters of recently cultured obligate intracellular bacteria.

Rickettsia felis is an obligate intracellular bacterium that lives in fleas and causes spotted fever in humans. Its genome sequence provides the first evidence that such bacteria can undergo conjugation.

Isolation and characterization of hyaluronidase a "spreading factor" from Indian cobra (Naja naja) venom

Hyaluronidase, ubiquitous enzyme in snake venoms, known originally as "spreading factor", has not been well studied. The present study describes the purification and characterization of hyaluronidase from Indian cobra (Naja naja) venom and provides systematic evaluation of the spreading property of the enzyme. Hyaluronidase (NNH1) has been purified through gel permeation and ion exchange chromatography. The molecular mass was found to be 70.406 kDa by MALDI-TOF mass spectrometry and with the (p)i pI of 9.2. The amino acid sequence of the N-terminus was found to be NEQSTHGAYV. The enzyme shows absolute specificity for hyaluronan and belongs to the group of neutral active enzymes. Tetrasaccharides are the final product of hyaluronan digestion. The enzyme cleaves beta 1,4-glycosidic linkage and belongs to a group of endo-beta-N-acetyl hexosaminidases. Hyaluronidase indirectly potentiates the myotoxicity of VRV-PL-VIII, a phospholipolytic myotoxin, and also the hemorrhagic potency of a hemorrhagic complex-I. Localization of hyaluronan in human skin section and selective degradation by venom hyaluronidase (NNH1) corroborate the plausible in vivo degradation of hyaluronan in the extracellular matrix (ECM) resulting in easy dissemination of VRV-PL-VIII myotoxin and hemorrhagic complex-I.

The mechanism of bacterial indigo reduction

The reduction of water-insoluble indigo by the recently isolated moderate thermophile, Clostridium isatidis, has been studied with the aim of developing a sustainable technology for industrial indigo reduction. The ability to reduce indigo was not shared with C. aurantibutyricum, C. celatum and C. papyrosolvens, but C. papyrosolvens could reduce indigo carmine (5,5'-indigosulfonic acid), a soluble indigo derivative. The supernatant from cultures of C. isatidis, but not from cultures of the other bacteria tested, decreased indigo particle size to one-tenth diameter. Addition of madder powder, anthraquinone-2,6-disulfonic acid, and humic acid all stimulated indigo reduction by C. isatidis. Redox potentials of cultures of C. isatidis were about 100 mV more negative than those of C. aurantibutyricum, C. celatum and C. papyrosolvens, and reached -600 mV versus the SCE in the presence of indigo, but potentials were not consistently affected by the addition of the quinone compounds, which probably act by modifying the surface of the bacteria or indigo particles. It is concluded that C. isatidis can reduce indigo because (1) it produces an extracellular factor that decreases indigo particle size, and (2) it generates a sufficiently reducing potential.

Spreading factors of Mycoplasma alligatoris, a flesh-eating mycoplasma

Mycoplasma alligatoris causes lethal invasive disease of alligators and caimans. A homolog of the nagH gene, encoding a hyaluronidase secreted by Clostridium perfringens, and a C. perfringens hyaluronidase nagI or nagK pseudogene were discovered in the M. alligatoris genome. The nagH gene was detected by PCR in the closest relative of M. alligatoris, Mycoplasma crocodyli, but not in 40 other species representing the Mycoplasma hominis, Mycoplasma pneumoniae, and Spiroplasma phylogenetic clusters. The hyaluronidase activity in the cellular fraction of M. alligatoris and M. crocodyli SP4 broth cultures was equivalent to 10(-16) U of Streptomyces hyalurolyticus hyaluronidase CFU(-1). Negligible activity was present in the cell-free supernatant fraction. No chondroitinase activity was detected. There is also a novel homolog of the nanI gene, which encodes a sialidase secreted by C. perfringens, in the M. alligatoris genome. The signature YRIP and SXDXGXTW motifs and catalytic residues of the clostridial sialidase are conserved in the mycoplasmal gene, but the leader sequence necessary for its secretion by C. perfringens is absent. The gene was not detected by PCR in any other mycoplasma. Potent cell-associated sialidase activity was present in M. alligatoris colonies on agar but not in the cell-free supernatants of broth cultures or in M. crocodyli. The presence of hyaluronidase and sialidase in M. alligatoris is consistent with the rapid invasiveness and necrotizing effects of this organism, and the lack of sialidase in M. crocodyli is consistent with its comparatively attenuated virulence. This genetic and biochemical evidence suggests that the spreading factors hyaluronidase and sialidase, a combination unprecedented in mycoplasmas, are the basis of the virulence of M. alligatoris.