Arcanobacterium haemolyticum phospholipase D is genetically and functionally similar to Corynebacterium pseudotuberculosis phospholipase D

Protein salvage and repurposing in evolution: Phospholipase D toxins are stabilized by a remodeled scrap of a membrane association domain

The glycerophosphodiester phosphodiesterase (GDPD)-like SMaseD/PLD domain family, which includes phospholipase D (PLD) toxins in recluse spiders and actinobacteria, evolved anciently in bacteria from the GDPD. The PLD enzymes retained the core (β/α)8 barrel fold of GDPD, while gaining a signature C-terminal expansion motif and losing a small insertion domain. Using sequence alignments and phylogenetic analysis, we infer that the C-terminal motif derives from a segment of an ancient bacterial PLAT domain. Formally, part of a protein containing a PLAT domain repeat underwent fusion to the C terminus of a GDPD barrel, leading to attachment of a segment of a PLAT domain, followed by a second complete PLAT domain. The complete domain was retained only in some basal homologs, but the PLAT segment was conserved and repurposed as the expansion motif. The PLAT segment corresponds to strands β7-β8 of a β-sandwich, while the expansion motif as represented in spider PLD toxins has been remodeled as an α-helix, a β-strand, and an ordered loop. The GDPD-PLAT fusion led to two acquisitions in founding the GDPD-like SMaseD/PLD family: (1) a PLAT domain that presumably supported early lipase activity by mediating membrane association, and (2) an expansion motif that putatively stabilized the catalytic domain, possibly compensating for, or permitting, loss of the insertion domain. Of wider significance, messy domain shuffling events can leave behind scraps of domains that can be salvaged, remodeled, and repurposed.

Promiscuous phospholipid biosynthesis enzymes in the plant pathogen Pseudomonas syringae

Bacterial membranes are primarily composed of phosphatidylethanolamine (PE), phosphatidylglycerol (PG) and cardiolipin (CL). In the canonical PE biosynthesis pathway, phosphatidylserine (PS) is decarboxylated by the Psd enzyme. CL formation typically depends on CL synthases (Cls) using two PG molecules as substrates. Only few bacteria produce phosphatidylcholine (PC), the hallmark of eukaryotic membranes. Most of these bacteria use phospholipid N-methyltransferases to successively methylate PE to PC and/or a PC synthase (Pcs) to catalyze the condensation of choline and CDP-diacylglycerol (CDP-DAG) to PC. In this study, we show that membranes of Pseudomonas species able to interact with eukaryotes contain PE, PG, CL and PC. More specifically, we report on PC formation and a poorly characterized CL biosynthetic pathway in the plant pathogen P. syringae pv. tomato. It encodes a Pcs enzyme responsible for choline-dependent PC biosynthesis. CL formation is catalyzed by a promiscuous phospholipase D (PLD)-type enzyme (PSPTO_0095) that we characterized in vivo and in vitro. Like typical bacterial CL biosynthesis enzymes, it uses PE and PG for CL production. This enzyme is also able to convert PE and glycerol to PG, which is then combined with another PE molecule to synthesize CL. In addition, the enzyme is capable of converting ethanolamine or methylated derivatives into the corresponding phospholipids such as PE both in P. syringae and in E. coli. It can also hydrolyze CDP-DAG to yield phosphatidic acid (PA). Our study adds an example of a promiscuous Cls enzyme able to synthesize a suite of products according to the available substrates.

An alkali-tolerant phospholipase D from Sphingobacterium thalpophilum 2015: Gene cloning, overproduction and characterization

The phospholipase pl-S.t gene of Sphingobacterium thalpophilum 2015 was cloned and the gene sequence was submitted to NCBI with Accession Number KX674735.1. The phylogenetic analysis showed that this PL-S.t was clustered to phospholipase D (PLD). As far as we know, the PL-S.t with a molecular mass of 22.5 kDa is the lowest of the currently purified bacterial PLDs, which belongs to a non-HKD PLD enzyme. This PL-S.t was resistant to a wide range of alkali pHs (7.5-9.0) after 1 h incubation, retaining more than 90% of its maximum activity. The PL-S.t activity can be enhanced by Ni²⁺, Co²⁺ and Mn²⁺. This PL-S.t has only one cysteine residue and fewer negatively-charged amino acids (AAs). The hydrogen bonds network was found around the cystein108, which may be beneficial to the stability and activity of PL-S.t in Ni²⁺ solution. This study has laid the foundation for further research on the molecular mechanism of the catalytic characteristics of low molecular weight alkalic PLD from S. thalpophilum 2015.

Sphingomyelinase D Activity in Sicarius tropicus Venom: Toxic Potential and Clues to the Evolution of SMases D in the Sicariidae Family

The spider family Sicariidae includes three genera, Hexophthalma, Sicarius and Loxosceles. The three genera share a common characteristic in their venoms: the presence of Sphingomyelinases D (SMase D). SMases D are considered the toxins that cause the main pathological effects of the Loxosceles venom, that is, those responsible for the development of loxoscelism. Some studies have shown that Sicarius spiders have less or undetectable SMase D activity in their venoms, when compared to Hexophthalma. In contrast, our group has shown that Sicarius ornatus, a Brazilian species, has active SMase D and toxic potential to envenomation. However, few species of Sicarius have been characterized for their toxic potential. In order to contribute to a better understanding about the toxicity of Sicarius venoms, the aim of this study was to characterize the toxic properties of male and female venoms from Sicarius tropicus and compare them with that from Loxosceles laeta, one of the most toxic Loxosceles venoms. We show here that S. tropicus venom presents active SMases D. However, regarding hemolysis development, it seems that these toxins in this species present different molecular mechanisms of action than that described for Loxosceles venoms, whereas it is similar to those present in bacteria containing SMase D. Besides, our results also suggest that, in addition to the interspecific differences, intraspecific variations in the venoms' composition may play a role in the toxic potential of venoms from Sicarius species.

Arcanobacterium haemolyticum Utilizes Both Phospholipase D and Arcanolysin To Mediate Its Uptake into Nonphagocytic Cells

Arcanobacterium haemolyticum is an emerging human pathogen that causes pharyngitis and wound infections. A few studies have suggested that A. haemolyticum is able to induce its uptake into nonphagocytic epithelial cells, but the bacterial factors associated with host cell invasion and the host cell processes involved have yet to be studied. We investigated how two A. haemolyticum virulence factors, arcanolysin (ALN) and phospholipase D (PLD), affect the ability of the bacteria to adhere to and subsequently invade Detroit 562 pharyngeal epithelial cells. The sphingomyelinase activity of phospholipase D was necessary to increase bacterial adherence, while the absence of a functional arcanolysin had no effect on A. haemolyticum adherence but did lead to a decrease in A. haemolyticum invasion into Detroit 562 cells. Because of the known roles of cholesterol-dependent cytolysins in disrupting calcium gradients and inducing F-actin-mediated bacterial internalization, we sought to determine whether ALN and PLD played a similar role in the ability of A. haemolyticum to invade nonphagocytic cells. Elimination of extracellular calcium and inhibition of the Arp2/3 complex or F-actin polymerization also caused a decrease in the ability of A. haemolyticum to invade Detroit 562 cells. Overall, our findings suggest that A. haemolyticum utilizes phospholipase D primarily for adherence and utilizes arcanolysin primarily for invasion into Detroit 562 cells in a process dependent on extracellular calcium and F-actin polymerization. Our work marks the first insight into how the individual activities of arcanolysin and phospholipase D affect A. haemolyticum host-pathogen interactions using the biologically relevant Detroit 562 cell line.

Evolutionary dynamics of origin and loss in the deep history of phospholipase D toxin genes

Background

Venom-expressed sphingomyelinase D/phospholipase D (SMase D/PLD) enzymes evolved from the ubiquitous glycerophosphoryl diester phosphodiesterases (GDPD). Expression of GDPD-like SMaseD/PLD toxins in both arachnids and bacteria has inspired consideration of the relative contributions of lateral gene transfer and convergent recruitment in the evolutionary history of this lineage. Previous work recognized two distinct lineages, a SicTox-like (ST-like) clade including the arachnid toxins, and an Actinobacterial-toxin like (AT-like) clade including the bacterial toxins and numerous fungal homologs.

Results

Here we expand taxon sampling by homology detection to discover new GDPD-like SMase D/PLD homologs. The ST-like clade now includes homologs in a wider variety of arthropods along with a sister group in Cnidaria; the AT-like clade now includes additional fungal phyla and proteobacterial homologs; and we report a third clade expressed in diverse aquatic metazoan taxa, a few single-celled eukaryotes, and a few aquatic proteobacteria. GDPD-like SMaseD/PLDs have an ancient presence in chelicerates within the ST-like family and ctenophores within the Aquatic family. A rooted phylogenetic tree shows that the three clades derived from a basal paraphyletic group of proteobacterial GDPD-like SMase D/PLDs, some of which are on mobile genetic elements. GDPD-like SMase D/PLDs share a signature C-terminal motif and a shortened βα1 loop, features that distinguish them from GDPDs. The three major clades also have active site loop signatures that distinguish them from GDPDs and from each other. Analysis of molecular phylogenies with respect to organismal relationships reveals a dynamic evolutionary history including both lateral gene transfer and gene duplication/loss.

Conclusions

The GDPD-like SMaseD/PLD enzymes derive from a single ancient ancestor, likely proteobacterial, and radiated into diverse organismal lineages at least in part through lateral gene transfer.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1302-2) contains supplementary material, which is available to authorized users.

Bacterial and Arachnid Sphingomyelinases D: Comparison of Biophysical and Pathological Activities

Sphingomyelinases D have only been identified in arachnid venoms, Corynebacteria, Arcanobacterium, Photobacterium and in the fungi Aspergillus and Coccidioides. The arachnid and bacterial enzymes share very low sequence identity and do not contain the HKD sequence motif characteristic of the phospholipase D superfamily, however, molecular modeling and circular dichroism of SMases D from Loxosceles intermedia and Corynebacterium pseudotuberculosis indicate similar folds. The phospholipase, hemolytic and necrotic activities and mice vessel permeabilities were compared and both enzymes possess the ability to hydrolyze phospholipids and also promote similar pathological reactions in the host suggesting the existence of a common underlying mechanism in tissue disruption. J. Cell. Biochem. 118:2053-2063, 2017. © 2016 Wiley Periodicals, Inc.

Corynebacterium ulcerans, an emerging human pathogen

While formerly known infections of Corynebacterium ulcerans are rare and mainly associated with contact to infected cattle, C. ulcerans has become an emerging pathogen today. In Western Europe, cases of respiratory diphtheria caused by C. ulcerans have been reported more often than infections by Corynebacterium diphtheria, while systemic infections are also increasingly reported. Little is known about factors that contribute to host colonization and virulence of this zoonotic pathogen. Research in this field has received new impetus by the publication of several C. ulcerans genome sequences in the past years. This review gives a comprehensive overview of the basic knowledge of C. ulcerans, as well as the recent advances made in the analysis of putative virulence factors.

Spider, bacterial and fungal phospholipase D toxins make cyclic phosphate products

Phospholipase D (PLD) toxins from sicariid spiders, which cause disease in mammals, were recently found to convert their primary substrates, sphingomyelin and lysophosphatidylcholine, to cyclic phospholipids. Here we show that two PLD toxins from pathogenic actinobacteria and ascomycete fungi, which share distant homology with the spider toxins, also generate cyclic phospholipids. This shared function supports divergent evolution of the PLD toxins from a common ancestor and suggests the importance of cyclic phospholipids in pathogenicity.

Legionella phospholipases implicated in virulence

Phospholipases are diverse enzymes produced in eukaryotic hosts and their bacterial pathogens. Several pathogen phospholipases have been identified as major virulence factors acting mainly in two different modes: on the one hand, they have the capability to destroy host membranes and on the other hand they are able to manipulate host signaling pathways. Reaction products of bacterial phospholipases may act as secondary messengers within the host and therefore influence inflammatory cascades and cellular processes, such as proliferation, migration, cytoskeletal changes as well as membrane traffic. The lung pathogen and intracellularly replicating bacterium Legionella pneumophila expresses a variety of phospholipases potentially involved in disease-promoting processes. So far, genes encoding 15 phospholipases A, three phospholipases C, and one phospholipase D have been identified. These cell-associated or secreted phospholipases may contribute to intracellular establishment, to egress of the pathogen from the host cell, and to the observed lung pathology. Due to the importance of phospholipase activities for host cell processes, it is conceivable that the pathogen enzymes may mimic or substitute host cell phospholipases to drive processes for the pathogen's benefit. The following chapter summarizes the current knowledge on the L. pneumophila phospholipases, especially their substrate specificity, localization, mode of secretion, and impact on host cells.

Arcanolysin is a cholesterol-dependent cytolysin of the human pathogen Arcanobacterium haemolyticum

Background

Arcanobacterium haemolyticum is an emerging human pathogen that causes pharyngitis, wound infections, and a variety of occasional invasive diseases. Since its initial discovery in 1946, this Gram positive organism has been known to have hemolytic activity, yet no hemolysin has been previously reported. A. haemolyticum also displays variable hemolytic activity on laboratory blood agar that is dependent upon which species the blood is derived.

Results

Here we describe a cholesterol-dependent cytolysin (CDC) secreted by A. haemolyticum, designated arcanolysin (aln), which is present in all strains (n = 52) tested by DNA dot hybridization. Among the known CDCs, ALN is most closely related to pyolysin (PLO) from Trueperella (formerly Arcanobacterium) pyogenes. The aln probe, however, did not hybridize to DNA from T. pyogenes. The aln open reading frame has a lower mol %G+C (46.7%) than the rest of the A. haemolyticum genome (53.1%) and is flanked by two tRNA genes, consistent with probable acquisition by horizontal transfer. The ALN protein (~ 64 kDa) contains a predicted signal sequence, a putative PEST sequence, and a variant undecapeptide within domain 4, which is typically important for function of the toxins. The gene encoding ALN was cloned and expressed in Escherichia coli as a functional recombinant toxin. Recombinant ALN had hemolytic activity on erythrocytes and cytolytic activity on cultured cells from human, rabbit, pig and horse origins but was poorly active on ovine, bovine, murine, and canine cells. ALN was less sensitive to inhibition by free cholesterol than perfringolysin O, consistent with the presence of the variant undecapeptide.

Conclusions

ALN is a newly identified CDC with hemolytic activity and unique properties in the CDC family and may be a virulence determinant for A. haemolyticum.

Phospholipase D promotes Arcanobacterium haemolyticum adhesion via lipid raft remodeling and host cell death following bacterial invasion

BACKGROUND

Arcanobacterium haemolyticum is an emerging bacterial pathogen, causing pharyngitis and more invasive infections. This organism expresses an unusual phospholipase D (PLD), which we propose promotes bacterial pathogenesis through its action on host cell membranes. The pld gene is found on a genomic region of reduced %G + C, suggesting recent horizontal acquisition.

RESULTS

Recombinant PLD rearranged HeLa cell lipid rafts in a dose-dependent manner and this was inhibited by cholesterol sequestration. PLD also promoted host cell adhesion, as a pld mutant had a 60.3% reduction in its ability to adhere to HeLa cells as compared to the wild type. Conversely, the pld mutant appeared to invade HeLa cells approximately two-fold more efficiently as the wild type. This finding was attributable to a significant loss of host cell viability following secretion of PLD from intracellular bacteria. As determined by viability assay, only 15.6% and 82.3% of HeLa cells remained viable following invasion by the wild type or pld mutant, respectively, as compared to untreated HeLa cells. Transmission electron microscopy of HeLa cells inoculated with A. haemolyticum strains revealed that the pld mutant was contained within intracellular vacuoles, as compared to the wild type, which escaped the vacuole. Wild type-infected HeLa cells also displayed the hallmarks of necrosis. Similarly inoculated HeLa cells displayed no signs of apoptosis, as measured by induction of caspase 3/7, 8 or 9 activities.

CONCLUSIONS

These data indicate that PLD enhances bacterial adhesion and promotes host cell necrosis following invasion, and therefore, may be important in the disease pathogenesis of A. haemolyticum infections.

Necrotising fasciitis in a bull due to infection with Arcanobacterium haemolyticum

CASE HISTORY

A 2-year-old Hereford bull was lame for one week before becoming recumbent.

CLINICAL AND PATHOLOGICAL FINDINGS

The scrotum and ventral perineal region were cold and blackened caudally. The semimembranosus and semitendinosus muscles were firm on palpation. The bull was subject to euthanasia, and necropsy revealed that the skin and S/C tissues of the caudal half of the scrotum were grey and necrotic. The caudal and distal aspects of the semimembranosus and semitendinosus muscles were grey and necrotic to a depth of approximately 15 cm, and these changes appeared to track along fascial planes. The tissue had an offensive smell, and large amounts of flocculent, watery, brown fluid and some gas were present. Histology of affected muscle and S/C tissues revealed coagulative necrosis, with oedema and large numbers of bacteria that were predominantly Gram-positive rods. Adjacent blood vessels contained thrombi while the epidermis overlying the affected areas appeared diffusely necrotic, suggesting infarction. Culture of the fluid yielded a pure growth of Arcanobacterium spp., which was identified as Arcanobacterium haemolyticum, using an API Coryne biochemical test strip.

DIAGNOSIS

Necrotising fasciitis and myositis due to Arcanobacterium haemolyticum.

CLINICAL RELEVANCE

Arcanobacterium haemolyticum has not previously been reported as a cause of necrotising fasciitis in any species. Necrotising fasciitis is probably an under-reported condition in cattle due to its clinical similarity to clostridial disease.

Synergistic and antagonistic hemolytic activities of bacteria of genus Arcanobacterium and CAMP-like hemolysis of Arcanobacterium phocae and Arcanobacterium haemolyticum with Psychrobacter phenylpyruvicus

A total of 57 bacteria representing eight species of genus Arcanobacterium (A.) were investigated for hemolytic properties on blood agar containing sheep and rabbit blood and for CAMP-like reactions. An enhanced hemolysis on blood agar containing rabbit blood compared to sheep blood could be observed for A. haemolyticum, less pronounced for A. hippocoleae and A. pluranimalium. A synergistic hemolytic reaction with staphylococcal beta-hemolysin appeared to be constantly visible for A. hippocoleae, A. pluranimalium and A. pyogenes, with Streptococcus agalactiae for A. phocae and A. haemolyticum, with Rhodococcus equi for A. phocae, A. haemolyticum, A. pluranimalium and A. pyogenes and with A. haemolyticum for A. hippocoleae, A. pluranimalium and A. pyogenes, respectively. A reverse CAMP-reaction in the zone of staphylococcal beta-hemolysin could be observed for A.phocae and A.haemolyticum. In addition, a novel CAMP-like reaction could be noted between Psychrobacter phenylpyruvicus, identified by 16S rDNA sequencing, and A. phocae and A. haemolyticum. These synergistic or antagonistic hemolytic properties could possibly be used as additional criteria for identification of bacteria of genus Arcanobacterium.

Phenotypic and genotypic characterization of Arcanobacterium haemolyticum isolates from infections of horses

The present study was designed to characterize phenotypically and genotypically seven Arcanobacterium haemolyticum strains obtained from infections of six horses. All seven strains showed the cultural and biochemical properties typical of A. haemolyticum and were susceptible to most of the antibiotics tested. The species identification could be confirmed by amplification and sequencing of the 16S rRNA gene and the 16S-23S rRNA intergenic spacer region and by PCR amplification of species-specific parts of the gene encoding phospholipase D in A. haemolyticum. Use of the latter could possibly improve future identification of this generally human pathogenic bacterial species which, according to the present results, seems to occur also in infections of horses.

Sphingomyelinase D from venoms of Loxosceles spiders: evolutionary insights from cDNA sequences and gene structure

Loxosceles spider venoms cause dermonecrosis in mammalian tissues. The toxin sphingomyelinase D (SMaseD) is a sufficient causative agent in lesion formation and is only known in these spiders and a few pathogenic bacteria. Similarities between spider and bacterial SMaseD in molecular weights, pIs and N-terminal amino acid sequence suggest an evolutionary relationship between these molecules. We report three cDNA sequences from venom-expressed mRNAs, analyses of amino acid sequences, and partial characterization of gene structure of SMaseD homologs from Loxosceles arizonica with the goal of better understanding the evolution of this toxin. Sequence analyses indicate SMaseD is a single domain protein and a divergent member of the ubitiquous, broadly conserved glycerophosphoryl diester phosphodiesterase family (GDPD). Bacterial SMaseDs are not identifiable as homologs of spider SMaseD or GDPD family members. Amino acid sequence similarities do not afford clear distinction between independent origin of toxic SMaseD activity in spiders and bacteria and origin in one lineage by ancient horizontal transfer from the other. The SMaseD genes span at least 6500bp and contain at least 5 introns. Together, these data indicate L. arizonica SMaseD has been evolving within a eukaryotic genome for a long time ruling out origin by recent transfer from bacteria.

Mechanism of induction of complement susceptibility of erythrocytes by spider and bacterial sphingomyelinases

We have recently shown that the sphingomyelinase toxins P1 and P2 from the venom of the spider Loxosceles intermedia induce complement (C)-dependent lysis of autologous erythrocytes by induction of the cleavage of cell surface glycophorins through activation of an endogenous metalloproteinase facilitating the activation of the alternative pathway of C. Phospholipase D (PLD) from Corynebacterium pseudotuberculosis shows some degree of homology with the spider sphingomyelinases and can induce similar clinical symptoms to those observed after spider envenomation. The aim of this study was to investigate if the bacterial PLD-induced haemolysis of human erythrocytes was C dependent and if cleavage of glycophorins occurred. We show here that haemolysis of both PLD- and P1-treated human erythrocytes was C dependent, but while PLD-mediated haemolysis was dependent on activation of the classical pathway of C, P1 induced lysis via both the classical and alternative pathways. P1, but not PLD, induced cleavage of glycophorins and no change in expression of complement regulators was induced by either of the toxins. In both cases, annexin V binding sites were exposed, suggesting that the membrane asymmetry had been disturbed causing exposure of phosphatidylserine to the cell surface. Our results suggest that C susceptibility induced by L. intermedia and C. pseudotuberculosis PLD is a result of exposure of phosphatidylserine, and the higher potency of P1 toxin can be explained by its additional effect of cleavage of glycophorins.

Phospholipase D-neutralization in serodiagnosis of Arcanobacterium haemolyticum and Corynebacterium pseudotuberculosis infections

Phospholipase D (PLD) neutralization was used to examine sera of humans (n = 40) with a spontaneous infection by Arcanobacterium haemolyticum, sheep and goats (n = 76 and 79 respectively) with a spontaneous infection by Corynebacterium pseudotuberculosis, mice (n = 26) experimentally immunized with PLD from A. haemolyticum (PLD-A) and mice (n = 28) experimentally immunized with PLD from C. pseudotuberculosis (PLD-C). PLD-A and PLD-C were also used as neutralizing antigens. A positive result of neutralization was due to an inhibition of the haemolytic synergism with the equi factor from Rhodococcus equi. The titres of sera neutralizing the homologous PLD were always significantly higher than those neutralizing the heterologous PLD. The proportion of sera that were able to neutralize the homologous PLD in sheep, goats and mice immunized with PLD-A significantly exceeded the proportion of sera that neutralized the heterologous PLD. The antigenic properties of PLD-A and PLD-C were similar but not identical.

Sphingomyelinases in the venom of the spider Loxosceles intermedia are responsible for both dermonecrosis and complement-dependent hemolysis

The bite of spiders of the genus Loxosceles can induce a variety of biological effects, including dermonecrosis and complement (C) dependent haemolysis. The aim of this study was to characterise the toxins in the venom responsible for the different biological effects. We have previously shown that a 35 kDa protein, named F35, purified from Loxosceles intermedia venom, incorporates into the membranes of human erythrocytes and renders them susceptible to the alternative pathway of autologous C. Here we have further purified the F35 protein which was resolved by reversed phase chromatography into three tightly contiguous peaks termed P1, P2, and P3. P1 and P2 were shown to be homogeneous by SDS-PAGE and N-terminal aminoacid analysis, while P3 consisted of two highly homologous proteins. N-terminal sequencing of all four proteins showed a high degree of homology, which was confirmed by cross-reactivity of antisera raised against the individual purified proteins. Functional characterisation of P1 and P2 indicated the presence of sphingomyelinase activity and either protein in isolation was capable of inducing all the in vivo effects seen with whole spider venom, including C-dependent haemolysis and dermonecrosis. In all assays, P2 was more active than P1, while P3 was completely inactive. These data show that different biological effects of L. intermedia venom can be assigned to the sphingomyelinase activity of two highly homologous proteins, P1 and P2. Identification of these proteins as inducers of the principal pathological effects induced by whole venom will aid studies of the mechanism of action of the venom and the development of a effective therapy.

Bacterial phospholipases and their role in virulence

Virulence of many bacterial pathogens is based, at least in part, on the action of phospholipases. The consequences may be immediate and direct, as in the action of Clostridium perfringens alpha toxin on red cells or platelets, or subtle, as with phosphatidylinositol-specific phospholipases of Listeria monocytogenes and other bacteria.

Clinical microbiology of coryneform bacteria

Coryneform bacteria are aerobically growing, asporogenous, non-partially-acid-fast, gram-positive rods of irregular morphology. Within the last few years, there has been a massive increase in the number of publications related to all aspects of their clinical microbiology. Clinical microbiologists are often confronted with making identifications within this heterogeneous group as well as with considerations of the clinical significance of such isolates. This review provides comprehensive information on the identification of coryneform bacteria and outlines recent changes in taxonomy. The following genera are covered: Corynebacterium, Turicella, Arthrobacter, Brevibacterium, Dermabacter. Propionibacterium, Rothia, Exiguobacterium, Oerskovia, Cellulomonas, Sanguibacter, Microbacterium, Aureobacterium, "Corynebacterium aquaticum," Arcanobacterium, and Actinomyces. Case reports claiming disease associations of coryneform bacteria are critically reviewed. Minimal microbiological requirements for publications on disease associations of coryneform bacteria are proposed.

Rhodococcus equi and Arcanobacterium haemolyticum: two "coryneform" bacteria increasingly recognized as agents of human infection

Rhodococcus equi and Arcanobacterium haemolyticum, formerly classified in the genus Corynebacterium, are members of the loosely defined taxon "coryneform" bacteria. Although they are the etiologic agents of distinct human infections, both organisms are frequently overlooked, which results in missed or delayed diagnoses. R. equi, long known as an important pathogen of immature horses, has become in the past three decades an opportunistic pathogen of severely immunosuppressed humans. Most cases are secondary to HIV infection. When specifically sought in throat swab cultures, A. haemolyticum is found responsible for 0.5% to 2.5% of bacterial pharyngitis, especially among adolescents. These two microorganisms represent a spectrum of disease in humans: from a mild, common illness to a rare life-threatening infection. Each organism elaborates lipid hydrolyzing enzymes (cholesterol oxidase by R. equi and sphingomyelinase D by A. haemolyticum) that are toxic to animals and humans and damaging to mammalian cell membranes. The participation of the cytotoxins in pathogenicity is discussed. Greater awareness of the properties of these two bacteria may promote faster, more accurate diagnoses and better clinical management.

Enzymology of mammalian phospholipases D: in vitro studies

The existence of multiple forms of phopholipase D was clearly established in a large number of biochemical studies that described and characterized the enzymological properties of the different PLD activities. This review summarizes the in vitro evidence showing differential subcellular localization and chromatographic properties of putative PLD isozymes, their phospholipid and alcohol substrate specificities, their modulation by various divalent cations, small G proteins and protein kinase c isozymes, and the role of phosphatidylinositol 4,5-bisphosphate as a cofactor of phospholipase D.

Toxic phospholipases D of Corynebacterium pseudotuberculosis, C. ulcerans and Arcanobacterium haemolyticum: cloning and sequence homology

The genes encoding toxic phospholipases D (PLD) from Corynebacterium pseudotuberculosis (Cp)biovar equi and C. ulcerans (Cu) have been cloned and sequenced. The deduced proteins are 307 amino acids (aa) in length and include a putative signal sequences of 26-aa. A molecular mass of 31.2 and 31.0 kDa and pI values of 8.84 and 6.73 are predicted for the secreted (mature) proteins from Cp and Cu, respectively. Comparison of the deduced primary structure of the two proteins to those of the PLD produced by Cp biovar ovis and Arcanobacterium haemolyticum (Ah) revealed that the four enzymes share 64-97% identity. The aa sequences of this group of proteins were unique when compared to the sequences of other phospholipases in GenBank and were found to share only small regions of homology with other proteins, including two conserved domains of glyceraldehyde-3-phosphate dehydrogenase (G3PD). The similarity of PLD from Cp biovar equi, Cu and Ah to the PLD of Cp biovar ovis suggests that these enzymes may act as virulence determinants.