Xerophilic

Paecilomyces variotii

Paecilomyces variotii is a heat-tolerant, xerophilic mold found in damp buildings, HVAC systems, soil, and on a wide variety of organic materials.

Water-damage indicatorXerophilic · Aw ≥ 0.79

Moisture niche · where this species can grow

XerophilicAw < 0.80
MesophilicAw 0.80–0.89
HydrophilicAw ≥ 0.90
Min Aw 0.79
← Drier conditions toleratedRequires liquid water →
Minimum Aw
0.79
EPA reference (GM)
2 SE/mg
Mycotoxin profile
2+ documented
Ecological role
Primary colonizer

About Paecilomyces variotii

Paecilomyces variotii is a heat-tolerant, xerophilic mold found in damp buildings, HVAC systems, soil, and on a wide variety of organic materials. It has gained attention in clinical settings as an emerging opportunistic pathogen, particularly for immunocompromised individuals. Unlike many molds, P. variotii can survive temperatures up to 60°C.

Ecology and water requirements

Paecilomyces variotii is classified as a primary colonizer with xerophilic adaptations: capable of germinating and growing at water activity as low as Aw 0.79[2], well below what most molds tolerate. Primary colonizers establish first in damp or even mildly humid environments, often before any visible moisture problem is apparent. Elevated Paecilomyces variotii on an ERMI test is more often associated with long-term high humidity than with a sudden water event[3]. Common contexts include poorly ventilated areas, conditioned-vs-unconditioned boundary zones (attics, crawl spaces, unfinished basements), and dusty environments where ambient relative humidity is sufficient to support growth on settled organic material.

Mycotoxin biology

Paecilomyces variotii produces a range of secondary metabolites with biological activity. The compounds documented in the literature for this species are listed in the chips below. Mycotoxin production is not uniform across all strains and is influenced by substrate, temperature, and water activity[4]. The same isolate may produce substantially different metabolite profiles on drywall paper versus wood versus settled dust[5]. DNA-based detection via the ERMI panel identifies species presence but does not directly measure mycotoxin presence; detection of a mycotoxin-producing species in household dust does not establish exposure to that mycotoxin at any specific concentration.

Detection in dust versus visual inspection

DNA-based detection of Paecilomyces variotii in settled household dust (the basis of the ERMI panel[1]) integrates spore material from current and recent growth in the home, capturing exposure history over weeks to months. A positive detection in dust does not necessarily indicate currently-active growth at the time of sampling; conversely, an active growth site can produce relatively low dust spore counts if the spores are not being aerosolized (sealed wall cavities, behind vapor barriers, or under flooring). Interpretation requires considering the dust signal alongside building inspection, occupant symptom history, and the broader pattern of species detected on the panel.

Where it’s typically found

Paecilomyces variotii is documented on the following substrates and locations:

  • HVAC systems and filters
  • damp building materials
  • soil
  • areas with standing or recurrent water

Mycotoxins

Compounds documented as produced by Paecilomyces variotii (presence and quantity vary by chemotype, strain, and substrate):

Viriditoxin· some strainsNot a primary mycotoxin concern indoors

Mycotoxin production is not uniform across all strains and is influenced by substrate, temperature, and water activity. Detection of a mycotoxin-producing species in household dust does not directly establish exposure to that mycotoxin at any specific concentration.

On your ERMI report

Paecilomyces variotii is one of the 26 EPA water-damage indicator species used to compute the SLG1 component of the ERMI score (sometimes labeled "Group 1" in EPA documentation). Whether the level detected in any specific home is concerning depends on the broader pattern: which other species are elevated, the water-activity profile of the elevated species, the home's climate context, and (where relevant) the occupant's sensitivity history. Our interpretation report puts Paecilomyces variotii in that broader pattern.

Related species

Aspergillus nigerAw ≥ 0.77 · XerophilicAspergillus ochraceusAw ≥ 0.77 · XerophilicAspergillus penicillioidesAw ≥ 0.73 · XerophilicAspergillus restrictusAw ≥ 0.75 · Xerophilic

References

  1. Vesper SJ, McKinstry C, Haugland RA, et al. Development of an Environmental Relative Moldiness Index for U.S. homes. J Occup Environ Med. 2007;49(8):829–833.
  2. Pitt JI, Hocking AD. Fungi and Food Spoilage. 3rd ed. New York: Springer; 2009.
  3. World Health Organization. WHO Guidelines for Indoor Air Quality: Dampness and Mould. Copenhagen: WHO Regional Office for Europe; 2009.
  4. Nielsen KF. Mycotoxin production by indoor molds. Fungal Genet Biol. 2003;39(2):103–117.
  5. Miller JD, McMullin DR. Fungal secondary metabolites as harmful indoor air contaminants: 10 years on. Appl Microbiol Biotechnol. 2014;98(24):9953–9966.