Detection of Histoplasma capsulatum in Organic Fertilizers by Hc100 Nested Polymerase Chain Reaction and Its Correlation with the Physicochemical and Microbiological Characteristics of the Samples.

Histoplasma capsulatum is the causative agent of histoplasmosis and this fungus inhabits soils rich in phosphorus and nitrogen that are enriched with bird and bat manure. The replacement of organic matter in agroecosystems is necessary in the tropics, and the use of organic fertilizers has increased. Cases and outbreaks due to the presence of the fungus in these components have been reported. The Instituto Colombiano Agropecuario resolution 150 of 2003 contains the parameters set by the Colombian Technical Standard (NTC 5167) on the physicochemical and microbiological features of fertilizers, but it does not regulate the search for H. capsulatum. The aim of this study was to demonstrate H. capsulatum presence in organic fertilizers by nested polymerase chain reaction (PCR). A total of 239 samples were collected: 201 (84.1%) corresponded to organic fertilizers, 30 (12.5%) to bird excrement, and 8 (3.4%) to cave soils. The Hc100 nested PCR had a detection limit of 0.1 pg/µL and a specificity of 100%. A total of 25 (10.5%) samples were positive and validated by sequencing. Seven of the positive samples represented locations where H. capsulatum was previously detected, suggesting the persistence of the fungus. No significant correlations were detected between the physicochemical and microbiological parameters with the presence of H. capsulatum by nested PCR, indicating the fungus existence in organic fertilizers that complied with the NTC 5167. The Hc100 nested PCR targeting H. capsulatum standardized in this work will improve the evaluation of organic fertilizers and ensure the prevention of outbreaks and cases due to manufacturing, marketing, and use of fertilizers contaminated with H. capsulatum.

Background selection at the chitin synthase II (chs2) locus in Paracoccidioides brasiliensis species complex.

In fungi, chitin synthases have been classified into five classes according to differences in regions of high sequence conservation. The current investigation was initiated to examine the causes for the polymorphism patterns found in a class II chitin synthase gene (chs2) of Paracoccidioides brasiliensis, in an attempt to determine the evolutionary forces affecting the chitin synthesis metabolic pathway. Neutrality tests were applied to the chs2 sequences exhibited by P. brasiliensis species complex. According to these tests and based on non-synonymous differences, P. brasiliensis data rejected the null hypothesis for a pure drift mutational process owing to a large excess of unique polymorphisms. In contrast, the synonymous and intron site differences did not reject the null hypothesis. This pattern appears consistent with weak selection against most amino acid changes, in which the effect of background selection was not detectable at synonymous nor at intron sites.