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Cryptococcus small cells arise from ordinary yeast mothers

Small cells called titanides emerged from ordinary yeast mothers in Cryptococcus neoformans, a fungus that can affect people with weakened immune systems. The peer-reviewed study followed their formation with live imaging, observed renewed growth in fresh medium and demonstrated infection in mice. It clarifies the fungus’s cellular diversity, while leaving their natural frequency and role in human disease unresolved.

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A small oval bud attached to a larger yeast cell in a pale microscopy field, with other cells at different depths of focus.

Small cells were infectious in mice

Titanides, a small cell form of the fungus Cryptococcus neoformans, were infectious in a mouse experiment. This fungus can infect the lungs and be associated with meningitis, especially in people whose immune systems are weakened. A single peer-reviewed study examined the cells’ origin, growth and capacity to participate in infection.[1]

The survival comparison followed eight mice in each group after either titanides or ordinary yeast cells were administered through the nose. The titanide group had a median survival of about 18 days, compared with 17.5 days for ordinary yeast; the difference was not significant. Early spread to the brain and final fungal burdens in organs also showed no clear advantage for titanides.[1]

Live imaging identified the mother cells

The oval titanides measured 2–4 micrometres across and had thin walls, small capsules and a single birth scar. Live imaging in microfluidic chambers traced them to ordinary yeast mothers averaging 4.9 micrometres. They did not arise from the giant titan cells with which their name associates them. Titanides appeared in 74 of the 81 isolates sampled from patients and the environment.[1]

Fresh medium restarted growth

Newborn titanides initially stopped proliferating. After transfer to fresh medium, they swelled before returning to yeast-like division, accompanied by changes in the compact appearance of their nuclei. Their responses to some laboratory stressors differed from ordinary yeast. The culture and mouse experiments leave their natural frequency in humans and contribution to long-lasting latent infection unresolved.[1]

References

  1. News sourcePLOS BiologySmall cells of a pathogenic fungus were traced to ordinary yeast mothers↩1↩2↩3↩4
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