Pseudomonas aeruginosa diaminopimelate decarboxylase: evolutionary relationship with other amino acid decarboxylases

The lysA gene encodes meso-diaminopimelate (DAP) decarboxylase (E.C.4.1.1.20), the last enzyme of the lysine biosynthetic pathway in bacteria. We have determined the nucleotide sequence of the lysA gene from Pseudomonas aeruginosa. Comparison of the deduced amino acid sequence of the lysA gene product revealed extensive similarity with the sequences of the functionally equivalent enzymes from Escherichia coli and Corynebacterium glutamicum. Even though both P. aeruginosa and E. coli are Gram-negative bacteria, sequence comparisons indicate a greater similarity between enzymes of P. aeruginosa and the Gram- positive bacterium C. glutamicum than between those of P. aeruginosa and E. coli enzymes. Comparison of DAP decarboxylase with protein sequences present in data bases revealed that bacterial DAP decarboxylases are homologous to mouse (Mus musculus) ornithine decarboxylase (E.C.4.1.1.17), the key enzyme in polyamine biosynthesis in mammals. On the other hand, no similarity was detected between DAP decarboxylases and other bacterial amino acid decarboxylases.      

Differential binding of lectins IL-2 and CSL to candida albicans and cancer cells

The demonstration that interleukin 2 (IL-2) is a lectin specific for oligomannosides allows to understand a new function for this cytokine: as a bifunctional molecule when bound to its receptor ss, IL-2 associates the latter which the CD3/TCR complex, interacting with oligosaccharides of CD3 through its carbohydrate-recognition domain (Zanetta et al. , 1996, Biochem. J., 318, 49-53). This induces the tyrosine phosphorylation of the IL-2R beta by ++p56(lck) , the first step of the IL-2-dependent signaling. Since this specific association is disrupted in vitro by oligomannosides with five and six mannose residues, we made the hypothesis that pathogenic cells or microorganisms could bind IL-2, consequently disturbing the IL-2- dependent response. This study shows that the pathogenic yeast Candida albicans (in contrast with nonpathogenic yeasts) binds high amounts of IL-2 as did cancer cells. In contrast with cancer cells, yeasts do not bind the Man6GlcNAc2-specific lectin CSL, an endogenous "amplifier of activation signals" (Zanetta et al. , 1995, Biochem. J., 311, 629-636).      

Comparison of the host ranges and antigenicity of Cryptosporidium parvum and Cryptosporidium wrairi from guinea pigs.

Oocysts of a Cryptosporidium isolate from guinea pigs were not infectious for adult mice, but were infectious for two of three newborn calves and for suckling mice. However, oocysts isolated from calves or mice infected with guinea pig Cryptosporidium were not infectious for guinea pigs. Four isolates of C. parvum from calves were incapable of infecting weanling guinea pigs. Microscopic examination of tissue from the colon and cecum of suckling guinea pigs inoculated with C. parvum revealed sparse infection of some pups. These host range studies and previously described differences in 125I-labeled oocyst surface protein profiles between Cryptosporidium sp. from guinea pigs and C. parvum suggest they are distinct species. We propose the name Cryptosporidium wrairi be retained. Studies with monoclonal antibodies indicate that C. wrairi and C. parvum are antigenically related.     

Recognizing the forest for the trees: testing temporal patterns of cladogenesis using a null model of stochastic diversification

Computer simulations are developed and employed to examine the expected temporal distributions of nodes under a null model of stochastic lineage bifurcation and extinction. These Markovian models of phylogenetic process were constructed so as to permit direct comparisons against empirical phylogenetic trees generated from molecular or other information available solely from extant species. For replicate simulated phylads with n extant species, cumulative distribution functions (cdf's) of branching times were calculated, and compared (using the Kolmogorov-Smirnov test statistic D) to those from three published empirical trees. Molecular phylogenies for columbine plants and avian cranes showed statistically significant departures from the null expectations, in directions indicating recent and ancient species' radiations, respectively, whereas a molecular phylogeny for the Drosophila virilis species group showed no apparent historical clustering of branching events. Effects of outgroup choice and phylogenetic frame of reference were investigated for the columbines and found to have a predictable influence on the types of conclusions to be drawn from such analyses. To enable other investigators to statistically test for nonrandomness in temporal cladogenetic pattern in empirical trees generated from data on extant species, we present tables of mean cdf's and associated probabilities under the null model for expected branching times in phylads of varying size. The approaches developed in this report complement and extend those of other recent methods for employing null models to assess the statistical significance of pattern in evolutionary trees.      

Dehydroepiandrosterone-induced reduction of Cryptosporidium parvum infections in aged Syrian golden hamsters.

Cryptosporidiosis, a parasitic disorder caused by Cryptosporidium parvum, is frequently a fulminating and life-threatening disease in immunocompromised hosts. The immune status of the host plays a critical role in determining the length and severity of the disease. Dehydroepiandrosterone (DHEA) is an immunomodulator that has been demonstrated to upregulate immune parameters. Ten aged (20-24 mo) Syrian golden hamsters were treated with DHEA for 7 days prior to intragastric inoculation with 1 x 10(6) C. parvum oocysts. An additional 10 aged hamsters were infected similarly but retained as untreated controls. The untreated hamsters presented with generalized infections as determined by oocyst shedding in the feces and parasite colonization of the small intestine. Hamsters treated with DHEA exhibited a significant reduction in cryptosporidial infection when compared to untreated hamsters. These results suggest that DHEA may be an effective prophylactic agent for cryptosporidiosis in immunocompromised patients.     

CRS–MIS in Candida glabrata: sphingolipids modulate echinocandin–Fks interaction

Infections with the azole‐refractory yeast Candida glabrata are now commonly treated with the echinocandins caspofungin (CSF) or micafungin (MCF). True resistance (> 32‐fold decreased susceptibility) to these lipopeptide inhibitors of cell wall synthesis is rare and strictly associated with mutations in integral membrane proteins Fks1 or Fks2. In contrast, mutants exhibiting 4‐ to 32‐fold CSF reduced susceptibility (CRS) were readily selected in vitro, and surprisingly demonstrated 4‐ to 32‐fold MCF increased susceptibility (MIS). Sequencing and gene deletion demonstrated that CRS–MIS is Fks‐independent. To explore alternative mechanisms, we initially employed Saccharomyces cerevisiae, and observed that CRS was conferred by multiple mutations (fen1Δ, sur4Δ, cka2Δ and tsc10‐ts) disrupting sphingolipid biosynthesis. Following this lead, C. glabrata fen1Δ and cka2Δ deletants were constructed, and shown to exhibit CRS–MIS. Sphingolipid analysis of CRS–MIS laboratory mutants and clinical isolates demonstrated elevated dihydrosphingosine (DHS) and phytosphingosine (PHS) levels, and consistent with this sequencing revealed fen1, sur4, ifa38 and sur2 mutations. Moreover, exogenous DHS or PHS conferred a CRS–MIS phenotype on wild‐type C. glabrata. Exogenous PHS failed, however, to suppress CRS–MIS in a sur2 mutant blocked in conversion of DHS to PHS, implying that accumulation of these intermediates confers CRS–MIS. We conclude that membrane sphingolipids modulate echinocandin–Fks interaction.