Molecular and Biological Differences Among <i>Ochroconis</i> Strains Collected from Indoor and Outdoor Environments

Abstract

The molecular, morphological, and physiological characters of 55 Ochroconis strains collected from indoor and outdoor environments were studied. In Japan, Ochroconis species are often found in indoor detergent-rich environments, such as bathrooms and washing machines, and the predominant species have been identified as O. humicola, similar to that in other Asian and European countries. Although Ochroconis species have rarely been found in outdoor environments such as mountains, forests, and agricultural fields, in the present study, Ochroconis strains were specifically isolated from the soils of urban city parks. Phylogenetic analysis conducted using the 28S ribosomal RNA 28S rDNA gene sequence showed that almost all of the Ochroconis strains found in indoor environments i.e., water supply were O. humicola. Although city parks were often surrounded by residences, more than half of the Ochroconis strains collected from the soils of city parks examined in this study were different Ochroconis species. The ability to use detergents as nutrients was found in a new genetic group probably a new species isolated from the soils of city parks as well as in O. humicola and O. constricta. Ochroconis humicola is assumed to adapt mostly to indoor environments and to penetrate from the outdoors, e.g., soils of urban areas. To elucidate the factors promoting indoor fungal predominance, the ability of using surfactants as nutrients was compared among these three species. Additionally, growth under alkaline and drought conditions, and heat tolerance were examined. Indoor predominance of O. humicola compared to that of the other two species was attributed to the ability of using a non-ionic surfactant as nutrient and to growth under alkaline conditions.

<i>Ochroconis</i> Species Isolated from Limestone Areas as the Origin of Indoor <i>Ochroconis</i>

“…Group P can use detergents as nutrients and grows under alkaline conditions. However, O. humicola was not found in the city parks of the Honshu and Kyushu Islands (Hamada and Abe, 2018) .…”

“…To isolate Ochroconis strains, we collected soil samples from limestone areas, including inside limestone caves. At each sampling site, about 30 g of superficial soil from the surface layer was collected at 6-12 spots, as previously described for sample collection from city parks (Hamada and Abe, 2018) .…”

“…The pH of the soil samples (10 g) in which the fungi were detected was measured following a standard method (Hamada and Abe, 2018) .…”

“…The 42 precultured outdoor strains were examined for their physiological characteristics, as described previously (Hamada and Abe, 2018) . A 0.5 mL of the conidial suspension from each strain was plated uniformly on two culture plates containing media with different compositions (see below) .…”

“…We tried to collect Ochroconis strains from rural outdoor environments, such as mountains, forests, and agricultural fields. However, it was difficult to collect not only O. humicola, but also some other species of Ochroconis (Hamada and Abe, 2018) . Some strains of Ochroconis were found in the superficial soils of urban city parks, on which the fine dust of cement slightly accumulates, making it more alkaline than superficial soils in forests and fields.…”