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PubMed1994

Molecular cloning and sequence analysis of yps-3, a yeast-phase-specific gene in the dimorphic fungal pathogen Histoplasma capsulatum.

Genes specifically expressed in the parasitic yeast phase of Histoplasma capsulatum have been cloned to clarify the mechanisms underlying both pathogenesis and morphogenesis in this human dimorphic fungal pathogen. Previous studies have determined that the yeast-phase-specific gene, yps-3, is expressed differentially in two non-isogenic strains which differ in their thermotolerance and virulence. We have cloned the yps-3 homologues from the high virulence (G217B) and low virulence (Downs) strains, and obtained a partial cDNA clone representing the expressed gene from H. capsulatum G217B. The Downs clone harbours a 287 bp insertion sequence that disrupts a long ORF defined by the yps-3 G217B cDNA. Although the insertion sequence contains features reminiscent of mobile genetic elements, including 15 bp direct repeats of flanking sequence, it is not randomly distributed in the H. capsulatum genome. S1 nuclease analysis was utilized to map the 5' end of the expressed yps-3 gene in G217B to potential regulatory regions which are largely homologous in both strains. This finding may point to a deficiency in a temperature inducible regulatory protein in the low virulence, temperature-sensitive Downs strain. The nucleotide sequence of the yps-3 gene and the predicted amino acid sequence of its product represents the first report of phase-specific gene and protein sequences in this widely distributed fungal pathogen. Further analysis of the product encoded by the yps-3 gene may provide significant insight into the pathogenic repertoire of H. capsulatum.

Amino Acid Sequence↗
PubMed2002

Redundancy, phylogeny and differential expression of Histoplasma capsulatum catalases.

Histoplasma capsulatum produces an extracellular catalase termed M antigen, which is similar to catalase B of Aspergillus and Emericella species. Evidence is presented here for two additional catalase isozymes in H. capsulatum. Catalase A is highly similar to a large-subunit catalase in Aspergillus and Emericella species, while catalase P is a small-subunit catalase protein with greatest similarity to known peroxisomal catalases of animals and Saccharomycotina yeasts. Complete cDNAs for the CATA and CATP genes (encoding catalases A and P, respectively) were isolated. The transcriptional expression of the H. capsulatum CATA, CATB (M antigen) and CATP genes was assessed by Northern blot hybridizations on total RNA. Results at the transcript levels for these genes are shown for three conditions: cell morphology (mycelial versus yeast phase cells), oxidative stress (in response to a challenge with H(2)O(2)) and carbon source (glucose vs glycerol). Collectively, these results demonstrated regulation of CATA by both cell morphology and oxidative stress, but not by carbon source, and regulation of CATB and CATP by carbon source but not cell morphology or oxidative stress. A phylogenetic analysis of presently available catalase sequences and intron residences was done. The results support a model for evolution of eukaryotic monofunctional catalase genes from prokaryotic genes.

Amino Acid Sequence↗
PubMed1991

Killing of Histoplasma capsulatum by gamma-interferon-activated human monocyte-derived macrophages: evidence for a superoxide anion-dependent mechanism.

The interaction of human macrophages with the yeast form of the thermally dimorphic fungal pathogen, Histoplasma capsulatum, was studied. Macrophages derived from monocytes by culture in vitro for 3 days ingested H. capsulatum, but were neither fungicidal or fungistatic. In contrast, when monocytes were exposed to human recombinant gamma-interferon (gamma-IFN) during their differentiation into macrophages, those macrophages were able to reduce the number of ingested or adherent cfu of H. capsulatum by 44-75% in 2 h. Activation of macrophages for fungicidal activity by gamma-IFN was dose dependent and 500-1000 units ml were optimal. Antibody to gamma-IFN abrogated the gamma-IFN activation process. Killing of H. capsulatum by activated macrophages in 2-h assays could be inhibited by superoxide dismutase but not by sodium azide.

Cell Adhesion↗
PubMed1995

Killing of Histoplasma capsulatum by macrophage colony stimulating factor-treated human monocyte-derived macrophages: role for reactive oxygen intermediates.

The interaction of human macrophages with the yeast-form of Histoplasma capsulatum was studied. The use of culture and a short-term assay period instead of microscopy gave direct evidence of the fungicidal activity of human macrophages. The present study reports the novel finding of fungicidal activity of macrophages derived from monocytes in the presence of macrophage colony-stimulating-factor (MCSF). The induction of fungicidal activity by this cytokine was dose dependent. MCSF at 10,000 U/ml was optimal with 73(SD3)% killing. Inhibition of macrophage killing by superoxide dismutase (SOD), but not catalase (CAT) or N-monomethyl-L-arginine (NMMA), established the role of the superoxide anion in the killing mechanism. The fungistatic activity of MCSF-derived human macrophages in a 24-h assay was also dose dependent and was not inhibited by SOD, CAT or NMMA. MCSF at 10,000 U/ml produced optimal macrophage fungistatic activity, 34.6(SD4)%.

Arginine↗
PubMed1986

Active substance of Histoplasma capsulatum that inhibits blastogenic response of lymphocytes.

A substance inhibiting blast transformation of murine spleen lymphocytes stimulated with various mitogens, such as LPS, PHA, and PWM, was obtained from yeast-form cells of Histoplasma capsulatum. This active substance was partially purified from the cell-free extract by DEAE-Sepharose CL-6B column chromatography. As a result of this partial purification, the inhibitory activity was 1.26 micrograms/ml in terms of ID50. Materials from H. capsulatum also inhibited blast transformation of murine spleen lymphocytes stimulated with the antigen PPD as well as mitogens LPS, PHA, and PWM. However, the con A-induced proliferative response was only slightly affected. A similar result was observed for the MLR. These inhibitory activities were abolished by heating at 70 C for 30 min. These results suggest that the heat-labile active substance produced by H. capsulatum might directly affect the lymphocytes, leading to inhibition of their blast transformation.

Animals↗
PubMed1995

Antifungal mechanisms of activated murine bronchoalveolar or peritoneal macrophages for Histoplasma capsulatum.

The first line of defence against natural infection by Histoplasma capsulatum (Hc) consists of bronchoalveolar macrophages (BAM) and an early inflammatory response in the lungs. Little is known about the interaction of BAM and Hc, consequently we studied murine BAM in vitro to assess their role in the pulmonary defence in histoplasmosis. A short-term 3-h assay was used to measure fungicidal activity of control BAM and interferon-gamma (IFN-gamma) plus lipopolysaccharide (LPS)-activated BAM. Fungistatic activity of BAM was determined with a 24-h assay. A method devised for measuring colony-forming units (CFU) of non-ingested non-adherent and adherent ingested yeast cells of Hc in BAM cocultures was used. Activated BAM killed Hc (reduced inoculum CFU by 25 +/- 12%; n = 4). The fungicidal activity of BAM was abrogated by 0.2 mM NG-monomethyl-L-arginine (NMMA) or catalase but not by superoxide dismutase. In fungistatic assays activated BAM inhibited multiplication of Hc by 61 +/- 4% (n = 3) compared with cocultures with control BAM. However, Hc multiplied 100% more in control BAM cocultures than in medium alone. Data indicated that this was due to advantages that Hc has in the intracellular environment. Only NMMA inhibited fungistatic activity of activated BAM. In experiments with peritoneal macrophages (PM), results similar to those with BAM were obtained. In conclusion, activated BAM and PM kill yeast cells of Hc by a mechanism dependent on hydrogen peroxide and products of the nitric oxide synthase (NOS) pathway, whereas fungistasis depends only on products of the NOS pathway.

Animals↗
PubMed1987

Heat shock 70 gene is differentially expressed in Histoplasma capsulatum strains with different levels of thermotolerance and pathogenicity.

The response to heat shock has been examined in two strains of the dimorphic pathogenic fungus Histoplasma capsulatum, which differ considerably in thermotolerance and pathogenicity. The gene for the 70 kD heat shock protein (hsp70) was isolated using a Drosophila hsp70 gene to screen a cosmid library of the DNA from the temperature-sensitive Downs strain (low level of thermotolerance for mice). Using the cloned gene as a probe, we have measured the transcription of the endogenous hsp70 gene at 25 degrees C and in response to temperature shift to 34 degrees, 37 degrees and 40 degrees C, temperatures that trigger the mycelial to yeast phase transition in this fungus. The gene is constitutively transcribed at low levels, both in the yeast and the mycelial stages. Synthesis of hsp70 mRNA was transiently increased 1 to 3 h after the temperature shifts. By Northern analysis, peak levels of transcription were shown to occur at 34 degrees C in the Downs strain and at 37 degrees C in the more pathogenic G222B strain. Our results are consistent with reports in which it has been shown that heat shock gene expression is part of temperature adaptation and probably developmental processes. The low levels of transcription of the hsp70 gene in the Downs strain at 37 degrees C correlate with its greater temperature sensitivity and low level of virulence.

Animals↗
PubMed1989

Mycelium-yeast transition in Histoplasma capsulatum. Early ultrastructural changes.

The ultrastructural changes which occur during the first 24 h of mycelium to yeast transition have been studied in the dimorphic fungus Histoplasma capsulatum. A temperature shift controls mycelial to yeast transition. During the first 24 h respiratory rate, ATP and cytochrome concentration fall to very low levels. Ultrastructural observations showed that the plasma membrane became undulated and the cell wall lost its characteristic fibrous outer layer. At 8 h the ordered lamellar structure of the mitochondria was no longer apparent. 24 h after the temperature shift 70% of the cells were lysed. The remaining cells contained many cytoplasmic membrane structures; mitochondria were rarely observed. These changes are considered to be the morphological expression of the physiological events characteristic of stage one in mycelial to yeast transition.

Histoplasma↗
PubMedDate not supplied

The second case of peritonitis due to Histoplasma capsulatum during continuous ambulatory peritoneal dialysis in Brazil.

This paper reports a case of infection due to Histoplasma capsulatum apparently restricted to the peritoneum in a woman submitted to continuous ambulatory peritoneal dialysis (CAPD). Diagnosis was established by direct examination and culture of dialysis effluent. Although the state of Rio Grande do Sul, the southernmost in Brazil, is not considered a region of high endemicity for histoplasmosis, this is the second case of infection occurring in a patient during CAPD.

Brazil↗
PubMed1998

Ribosomal genes of Histoplasma capsulatum var. duboisii and var. farciminosum.

A total of 1704 basepairs of the 18S rDNA of Histoplasma capsulatum var. duboisii (HCD, strain CBS175.57) and H. capsulatum var. farciminosum (HCF, strain CBS478.64) were sequenced (EMBL accession no. Z75306 and no. Z75307). The 18S rDNA of HCD was 100% identical to a published sequence of H. capsulatum var. capsulatum (HCC). The 18S rDNA of HCF showed one transversional point mutation at the nucleotide position 114 (ref. Saccharomyces cerevisiae). Hybridization confirmed that, in the 18S rDNA of two out of five strains of HCF, guanine was substituted for cytosine at the nucleotide position 114. Furthermore, identical group 1C1 introns (403 bp) were found to be inserted after position 1165 in four out of five strains of HCF, including the two strains with point mutations in the 18S rDNA, and a slightly different group 1C1 intron (408 bp) was detected in one strain of HCC without this point mutation. Intraspecific sequence variability in the highly conserved 18S rDNA because of occurrence of introns and mutations as a possible source of error in molecular diagnostics is discussed. In addition, internal transcribed spacer regions between the 18S rDNA and the 5.8S rDNA (ITS1) of three strains of HCF, and one strain each of HCC and HCD showed significant sequence variability between varieties and strains of H. capsulatum.

Base Sequence↗
PubMedDate not supplied

The effect of temperature on the ultrastructure of Histoplasma capsulatum during the mycelium-yeast transition.

The ultrastructural morphology of the early phases of mycelium-yeast transition in Histoplasma capsulatum after a temperature shift from 25 degrees C to only 34 degrees C is described. Under this condition of lower temperature oxidative phosphorylation is not completely uncoupled and maximum production of heat shock proteins (hsp) occurs. 24 h after temperature shift more than 90% of the cells still appear vital. Alterations in the organization of the mitochondrial cristae are the only ultrastructural changes observed in these cells. In contrast, 70% of the cells degenerate 24 h after a temperature shift from 25 degrees C to 37 degrees C and in the remaining cells mitochondria are rarely observed. These observations are discussed in relation to the production of hsp, the uncoupling of oxidative phosphorylation and the virulence of different strains of H. capsulatum.

Heat-Shock Proteins↗
PubMed1965

HISTOPLASMA CAPSULATUM FROM THE LIVER OF A BAT IN COLOMBIA.

Of 135 bats (eight species), one of the species Glossophaga sorcina sorcina, a nectar-feeding bat from Girardot, Colombia, harbored Histoplasma capsulatum. The microorganism was cultured from the liver. This is the second report of recovery of this fungus from bat tissue.

Animals↗
PubMed1970

Release of protoplasts in the yeast phase of Histoplasma capsulatum without added enzyme.

Cells of the yeast phase of the dimorphic systemic fungus pathogen Histoplasma capsulatum readily released large numbers of intact protoplasts without degradation of their cell walls by snail or microbial enzymes, previously regarded as a requirement for all yeast and mycelial fungal forms. Over 90 percent of "B" type yeast cells in the early logarithmic phase of growth released living protoplasts when incubated at 37 degrees C with 2 molar magnesium sulfate, whereas "A" type yeast cells required prior exposure for 24 hours to 2-deoxy-D-glucose before incubation in the 2 molar magnesium sulfate.

Hexoses↗
PubMed1972

Sexual stage of Histoplasma capsulatum.

Twelve primary subcultures of Histoplasma capsulatum, paired in all possible combinations on agar containing yeast extract and Alphacel, produced fertile cleistothecia, resembling those of Ajellomyces dermatitidis (Blastomyces dermatitidis).

Histoplasma↗
PubMed2000

Microbiology. Turning up the heat on Histoplasma capsulatum.

Many fungal pathogens are opportunistic, that is, they infect individuals who have a compromised immune system. Histoplasma capsulatum is a common pathogenic fungus that lives happily inside the phagosomes of macrophages. As Klein explains in his Perspective, an important H. capsulatum virulence factor, CBP1, has been found, which mops up free calcium ions within the phagosome, enabling the yeast to live under calcium-poor conditions (Sebhgati et al.). Chelating calcium ions may also have the added benefit that when the phagosome fuses with the lysosome, destructive lysosomal enzymes that require calcium ions for activity remain inactive.

Animals↗