Temperature-water and competitive interactions in vitro of two toxic black molds, Fusarium oxysporum and Rhizopus stolonifer isolated from a shower setting

Abstract: We report differences in secondary resource capture and upper lethal temperature as survival attributes for Fusarium oxysporum (FOSC) and Rhizopus stolonifer, two medically important fungi that were co-isolated from a table shower caddy. Isolates of these two shower-associated fungi have been deposited at the University of Alberta Microfungus Collection and Herbarium, Centre for Global Microfungal Biodiversity (UAMH, Toronto, CAN) as R. stolonifer UAMH 11965 and F. oxysporum (FOSC) UAMH 11966; this paper provides growth characteristics for these two strains that can be used for further studies on black molds in bathrooms given the relevance to public health. Both R. stolonifer UAMH 11965 and F. oxysporum (FOSC) UAMH 11966 require contact with a wet surface substrate with water activity ≥ 0.95 a_w for growth and sporulation. In contrast to F. oxysporum, R. stolonifer has a 4-6x, faster radial growth rate, superior colonizing ability, and capacity for overgrowth (exploitative competition). This F. oxysporum (FOSC) strain, however, is thermotolerant, as demonstrated by broader thermal growth range and higher optimum temperature, which puts fewer limitations on its growth compared to R. stolonifer. This is a point of public awareness for mold-sensitive and immunocompromised people that wet, wood substrates in a shower can permit colonization and competitive interactions that can concentrate R. stolonifer and F. oxysporum spores.

Key words: 
• Bathroom /
• fungal ecology /
• public health /
• radial growth /
• resource capture