Figure 1

Figure 1. Sampling locations for study of Histoplasma capsulatumin Antarctica. A) Location of the Antarctic Peninsula in the Antarctica continent; B) King George Island; C) Potter Peninsula and the Antarctic...

We collected environmental samples in the Potter Peninsula, an Antarctic Special Protected Area located in King George Island, during the summer of 2020 (Figure 1). In total, we collected 9 samples of penguin excreta, 3 samples of fur seal feces, and 8 samples of superficial soil using sterile material and kept them at 2°C–8°C until analysis.

We extracted DNA from the environmental samples and monitored crossover contamination by including 1 sterile water sample at every set (Appendix). We performed nested PCR twice for all samples, using methods specific for the detection and identification of H. capsulatum DNA according to Bialek et al. (9). To check for the presence of PCR inhibitors and to avoid false-negative results, we used H. capsulatum reference strain G217B as positive control. Sequence analysis detected H. capsulatum in 2 of 8 soil samples and in 3 of 9 samples from penguin excreta (Appendix Figure).

We submitted the 5 sequences we detected to GenBank (accession nos. MZ713369–73) and compared them with other H. capsulatum sequences. This comparison generated an identity of >98.56% (100% cover) with the deposited sequences of the 100-kDa-like protein gene from H. capsulatum and 85% similarity with the sequence of a transcription factor of Blastomyces dermatitidis SLH14081 and B. gilchristii SLH14081 (GenBank accession nos. XM_045419905 and XM_002628281.2).

Figure 2

Figure 2. Phylogenetic tree based on the 100-kDa–like protein partial gene sequences of Histoplasma capsulatumfrom Antarctica. The evolutionary history was inferred by using the maximum-likelihood method in in MEGA X...

Alignment with GenBank sequences from strains representing the different genetic lineages (Table) demonstrated a difference of up to 14 bp with the 3 haplotypes from Antarctica. The phylogenetic tree formed different groups corresponding to different geographic lineages. Two excreta samples and 1 soil sample grouped with representative strains of the Latin American lineage LAmB1, and 1 soil and 1 excreta sample grouped with a representative strain of LAmA2 lineage. No sample from Antarctica grouped with representative strains of the North America or Panama lineages (Figure 2), indicating a closer association of the newly discovered Histoplasma from Antarctica to the South America lineages.

Moderate temperatures (18°C–28°C), constant humidity (>60%), and a low light environment are thought to characterize suitable ecologic conditions for H. capsulatum growth (10). Despite the average temperature in Antarctica being below that recognized as ideal for the growth of the fungus, the molecular identification of H. capsulatum in 5 of 20 samples collected in Antarctica suggests this species complex could survive at lower temperatures.

Although molecular detection of the fungus does not guarantee its viability, this area of Antarctica is part of an Antarctic Special Protected Area and experiences strong influence of avifauna during the summer period, as well as being host to bird colonies, sea mammal breeding areas, and diverse plant species. Consequently, the soil has high levels of potassium, nitrogen, calcium, and total organic carbon (11), which are good conditions for fungal growth. Ideally, H. capsulatum should be isolated for complete phenotypic and genotypic study, but it is a slow-growth fungus, and its growth is overtaken by fast-growing fungi. Animal inoculation is often used to recover H. capsulatum, but it demands a Biosafety Level 3 facility, which was not available to us.

The molecular detection of H. capsulatum in penguin excreta and ornithogenic soil samples leads us to consider the possibility that the fungus could have been imported from outside the continent by migratory birds. Birds are the only terrestrial vertebrates that share with humans the peculiarity of traveling in a few hours across national and intercontinental borders (12). During migration, birds have the potential to disperse microorganisms that can be dangerous to humans and a threat to animals (13). The fact that high densities of cosmopolitan fungi were found in winter seasonal snow suggests those fungi might be present in air arriving at the Antarctica Peninsula (14). Another possibility could be human intervention in the region. Alien microbes, fungi, plants, and animals have arrived over approximately the previous 2 centuries, coinciding with human activity in Antarctica (6).

The differentiation of the 7 phylogenetic species in the complex could not be performed with the genetic marker used in this study. However, we detected different haplotypes that grouped with some of those geographically distinct phylogenetic species, suggesting dispersion of the fungus on multiple occasions and, perhaps, indicating adaptation on its way to becoming endemic to the Antarctic Peninsula. The detection of H. capsulatum genetically close to representative strains of the Latin American lineages (LAmA2/LAmB1) in Antarctica represents not only the geological history of the continent with South America but the complex dynamics of soil formation and presence of fauna and flora that enable adequate conditions for its maintenance.

This study evaluated a small geographic area of the peninsula, but it has already demonstrated that H. capsulatum occurs more broadly than previously suspected (15). Considering the capacity of the species to cause life-threatening epidemics and the intensifying human presence on the continent, identifying and monitoring fungi in various Antarctic habitats and animals becomes a fundamental strategy for surveilling emerging systemic mycoses and the flow of these agents between regions, animals, and humans.