Identification of the conserved coding sequences of three chitin synthase genes in Fonsecaea pedrosoi

Chromoblastomycosis

Chromoblastomycosis (CBM), also known as chromomycosis, is one of the most prevalent implantation fungal infections, being the most common of the gamut of mycoses caused by melanized or brown-pigmented fungi. CBM is mainly a tropical or subtropical disease that may affect individuals with certain risk factors around the world. The following characteristics are associated with this disease: (i) traumatic inoculation by implantation from an environmental source, leading to an initial cutaneous lesion at the inoculation site; (ii) chronic and progressive cutaneous and subcutaneous tissular involvement associated with fibrotic and granulomatous reactions associated with microabscesses and often with tissue proliferation; (iii) a nonprotective T helper type 2 (Th2) immune response with ineffective humoral involvement; and (iv) the presence of muriform (sclerotic) cells embedded in the affected tissue. CBM lesions are clinically polymorphic and are commonly misdiagnosed as various other infectious and noninfectious diseases. In its more severe clinical forms, CBM may cause an incapacity for labor due to fibrotic sequelae and also due to a series of clinical complications, and if not recognized at an early stage, this disease can be refractory to antifungal therapy.

Rapid detection of pathogenic fungi using loop-mediated isothermal amplification, exemplified by Fonsecaea agents of chromoblastomycosis

Loop-mediated isothermal amplification (LAMP) was developed for rapid detection of pathogenic or allergenic fungal in the environment. Primers applied were derived from the rDNA Internal Transcribed Spacer and the 5.8S rRNA gene. The assay enabled amplification of target fungi at the level of genus or closely related species using pure cultures after 1h reaction at 65 degrees C in a water bath. No cross-reactivity to related species was observed. The DNA detection limit was 0.2fg. The method also proved to work well with fungi on non-sterile adhesive tape. Amplification products were detected by visual inspection using SYBR Green I as well as by electrophoresis on agarose gels. As a model organism we selected Fonsecaea, a fungal genus containing etiologic agents of chromoblastomycosis, a widely distributed tropical and subtropical skin disease in otherwise healthy patients and supposed to be acquired by environmental inoculation. It is suggested that LAMP can also be used for rapid clinical diagnosis, for environmental detection, and for retrospective studies in archived clinical samples.

Rapid identification of Fonsecaea by duplex polymerase chain reaction in isolates from patients with chromoblastomycosis

Fonsecaea pedrosoi is the most common etiologic agent of chromoblastomycosis. F. pedrosoi and other dematiaceous fungi are usually identified by morphologic studies. We have developed a duplex polymerase chain reaction (PCR) targeting the ribosomal DNA for rapid and more specific identification of the genus Fonsecaea. DNA samples from 103 isolates of Fonsecaea species and other dematiaceous fungi were amplified by PCR using universal and specific primers targeting ITS1-5.8S-ITS2 region of the ribosomal DNA. Universal primers were used for detection of non-Fonsecaea DNA. Fonsecaea-specific PCR product was found in 70 (68.0%) isolates including 4 strains that did not develop conidiogenesis. Thirty non-Fonsecaea and 3 Fonsecaea compacta isolates were negative by duplex PCR. These results were confirmed by DNA sequencing analysis indicating the high specificity of the duplex PCR assay. In conclusion, the duplex PCR is a rapid and specific assay for identification of Fonsecaea isolates mainly for the strains that are difficult to identify by morphologic methods.

Internal transcribed spacer rRNA gene-based phylogenetic reconstruction using algorithms with local and global sequence alignment for black yeasts and their relatives

Sequences of rRNA gene internal transcribed spacer (ITS) of a standard set of black yeast-like fungal pathogens were compared using two methods: local and global alignments. The latter is based on DNA-walk divergence analysis. This method has become recently available as an algorithm (DNAWD program) which converts sequences into three-dimensional walks. The walks are compared with, or fit to, each other generating global alignments. The DNA-walk geometry defines a proper metric used to create a distance matrix appropriated for phylogenetic reconstruction. In this work, the analyses were carried out for species currently classified in Capronia, Cladophialophora, Exophiala, Fonsecaea, Phialophora, and Ramichloridium. Main groups were verified by small-subunit rRNA gene data. DNAWD applied to ITS2 alone enabled species recognition as well as phylogenetic reconstruction reflecting clades discriminated in small-subunit rRNA gene phylogeny, which was not possible with any other algorithm using local alignment for the same data set. It is concluded that DNAWD provides rapid insight into broader relationships between groups using genes that otherwise would be hardly usable for this purpose.

Biochemistry of chitin synthase

This article compiles the papers dealing with the biochemistry of chitin synthase (CS) published during the last decade, provides up-to-date information on the state of knowledge and understanding of chitin synthesis in vitro, and points out some firmly entrenched ideas and tenets of CS biochemistry that have become of age without hardly ever having been critically re-evaluated. The subject is dealt with under the headings "Components of the CS reaction" (educt, cation requirement and intermediates; product), "Regulation of CS" (cooperativity and allostery; non-allosteric activation or priming of CS; latency), "Concerted action of CS and enzymes of chitinolysis", "Inhibition of CS", "Multiplicity of CSs", and "Structure of CS" (the putative UDPGlcNAc-binding domain of CS; identification of CS polypeptides; glycoconjugation). The prospects are outlined of obtaining a refined three-dimensional (3D) model of the catalytic site of CS for biotechnological applications.

WdChs4p, a homolog of chitin synthase 3 in Saccharomyces cerevisiae, alone cannot support growth of Wangiella (Exophiala) dermatitidis at the temperature of infection

By using improved transformation methods for Wangiella dermatitidis, and a cloned fragment of its chitin synthase 4 structural gene (WdCHS4) as a marking sequence, the full-length gene was rescued from the genome of this human pathogenic fungus. The encoded chitin synthase product (WdChs4p) showed high homology with Chs3p of Saccharomyces cerevisiae and other class IV chitin synthases, and Northern blotting showed that WdCHS4 was expressed at constitutive levels under all conditions tested. Reduced chitin content, abnormal yeast clumpiness and budding kinetics, and increased melanin secretion resulted from the disruption of WdCHS4 suggesting that WdChs4p influences cell wall structure, cellular reproduction, and melanin deposition, respectively. However, no significant loss of virulence was detected when the wdchs4Delta strain was tested in an acute mouse model. Using a wdchs1Delta wdchs2Delta wdchs3Delta triple mutant of W. dermatitidis, which grew poorly but adequately at 25 degrees C, we assayed WdChs4p activity in the absence of activities contributed by its three other WdChs proteins. Maximal activity required trypsin activation, suggesting a zymogenic nature. The activity also had a pH optimum of 7.5, was most stimulated by Mg(2+), and was more inhibited by polyoxin D than by nikkomycin Z. Although the WdChs4p activity had a broad temperature optimum between 30 to 45 degrees C in vitro, this activity alone did not support the growth of the wdchs1Delta wdchs2Delta wdchs3Delta triple mutant at 37 degrees C, a temperature commensurate with infection.

CHS2, a chitin synthase gene from the oomycete Saprolegnia monoica

PCR was used to amplify fragments corresponding to the chitin synthase (CHS) genes from the Oomycetes Saprolegnia monoica, Phytophthora capsici and Achlya ambisexualis, utilizing as primers, oligonucleotides designed from the conserved region of CHS genes of chitinous fungi. Chitin synthase homologues were found in the three cellulosic fungi. The chitin synthase 2 gene (CHS2) from S. monoica was cloned, sequenced and characterized. The amino acid sequence deduced from the CHS2 genomic DNA revealed several domains, corresponding to the catalytic domains and polypeptide signatures, of high identity with CHS genes from chitinous fungi. Existence of a CHS gene family in S. monoica was supported by the identification of two CHS sequences among the PCR products, the localization of CHS homologues on two chromosomes, and the detection of two transcripts in mycelia and protoplasts. Polyclonal anti-chitin synthase antibodies raised against the N-terminal and the neutral fragments of the CHS2 products revealed, respectively, two and four proteins in membrane fractions and a truncated active form in entrapped product. The overall comparison of the structure and organization of CHS genes indicates that in spite of their divergent evolution, Oomycetes and chitinous fungi have evolved with conserved chitin synthase systems.