The mycobiome of Australian tree hollows in relation to the Cryptococcus gattii and C. neoformans species complexes

Abstract

Cryptococcosis is a fungal infection caused by members of the Cryptococcus gattii and C. neoformans species complexes. The C. gattii species complex has a strong environmental association with eucalypt hollows (particularly Eucalyptus camaldulensis), which may present a source of infection. It remains unclear whether a specific mycobiome is required to support its environmental survival and growth. Conventional detection of environmental Cryptococcus spp. involves culture on differential media, such as Guizotia abyssinica seed agar. Next‐generation sequencing (NGS)‐based culture‐independent identification aids in contextualising these species in the environmental mycobiome. Samples from 23 Australian tree hollows were subjected to both culture‐ and amplicon‐based metagenomic analysis to characterize the mycobiome and assess relationships between Cryptococcus spp. and other fungal taxa. The most abundant genera detected were Coniochaeta, Aspergillus, and Penicillium, all being commonly isolated from decaying wood. There was no correlation between the presence of Cryptococcus spp. in a tree hollow and the presence of any other fungal genus. Some differences in the abundance of numerous taxa were noted in a differential heat tree comparing samples with or without Cryptococcus‐NGS reads. The study expanded the known environmental niche of the C. gattii and C. neoformans species complexes in Australia with detections from a further five tree species. Discrepancies between the detection of Cryptococcus spp. using culture or NGS suggest that neither is superior per se and that, rather, these methodologies are complementary. The inherent biases of amplicon‐based metagenomics require cautious interpretation of data through consideration of its biological relevance.

Fungicide effects on human fungal pathogens: Cross-resistance to medical drugs and beyond

“…neoformans do not usually occur in crops, flower beds, and commercial plant-based products. They are found in association with Eucalyptus and other trees, especially in trunk hollows [ 151 , 166 , 167 ]. Thus, it is unusual to link these species with fungicide exposure in the environment, as these chemicals are often employed to preserve and treat plant diseases of commercial relevance [ 26 , 28 , 33 ].…”

“…Moreover, Chowdhary and colleagues isolated azole-resistant A . fumigatus from trunk hollows in Tanzania [ 75 ], the same niche of pathogenic Cryptococcus [ 151 , 166 ]. On that account, Del Poeta and Casadevall hypothesized that fungicides could also be driving cryptococcus virulence and resistance evolution [ 168 ].…”

Cryptococcus in Wildlife and Free-Living Mammals

“…Most koala cases where the causative agent was definitively identified were attributable to the C. gattii species complex [ 77 ], with a single case caused by the C. neoformans species complex in a captive koala in Spain [ 75 ]. In most of Australia, especially along the east coast, cryptococcosis is usually caused by C. gattii VGI, although in south-western Western Australia (WA) infections can also involve C. gattii VGII, including cases where koalas have been infected in WA and developed disease following translocation elsewhere within Australia [ 78 ].…”

“…The authors’ speculation is that the typical goat breed, the Murciana, raised in the Murcia region (Alicante) but extensively exported across the Mediterranean area, including Sardinia, probably resulted in asymptomatic carrier goats (colonized by VGI) being responsible for the introduction of this molecular type of C. gattii to Sardinia. Such translocation events have been well demonstrated in koalas exported within Australia, or from Australia to Japan, and in people who have visited Vancouver Island from Europe [ 77 , 78 , 99 ].…”

Vaccines and Protective Immune Memory against Cryptococcosis

“…1,2) Cryptococcosis is a life-threatening infection caused by inhaling the encapsulated yeasts in Cryptococcus neoformans and C. gattii species complexes. 3,4) Cryptococcal cells often disseminate to the central nervous system, leading to meningoencephalitis. C. neoformans generally infects immunocompromised hosts such as AIDS patients, and approximately 220000 cases of cryptococcal meningitis occur among AIDS patients worldwide each year, leading to 180000 deaths annually.…”