Sporulation is a strategy used by many organisms, including bacteria, fungi, protozoa, algae, and ferns to survive conditions that are too harsh to sustain vegetative growth. Survival is generally facilitated by developing specialized cells (spores) with physical properties that confer resistance to environmental assault. Many organisms also produce spores on specialized structures that are adapted for efficient dispersal via wind or water currents. Through these adaptations, sporulation is an effective mechanism to either persist until local conditions improve or disperse to new environments conducive for growth.
For pathogenic microbes, favorable growth conditions are often found in a mammalian host, resulting in serious consequences for human health. For example, spores of protozoan parasites, such as the oocytes of Cryptosporidium sp., can be found in untreated or fecal waste-contaminated water and have been estimated to cause >50% of water-borne parasitic disease worldwide, including major outbreaks in the United States. Spores of bacterial pathogens, such as those produced by Bacillus anthracis, are extremely resistant to physical and chemical insult, making B. anthracis a potentially devastating biological weapon. In fungi, spores are thought to be the infectious particles of many fungal pathogens. This has been shown rigorously for a number of plant fungal pathogens, such as the wheat rusts, Puccinia sp., which disperse globally on an annual basis and cause damage to food crops totaling 3 billion dollars per year.
Among human fungal pathogens, spores are presumed infectious particles for many organisms. The infection-causing potential of spores from human fungal pathogens is exemplified by Coccidioides immitis, as few as 10 spores can establish disease and cause fatal disease. Because these highly infectious spores are adapted for wind dispersal, C. immitis spores, similar to spores from B. anthracis, have been postulated to be serious threats as biological weapons. Despite the demonstrated capacity of spores from human fungal pathogens to infect mammalian hosts, the specific roles that spores play in establishing disease are less clear.
Dueling in the lung: how Cryptococcus spores race the host for survival. Curr Opin Microbiol. Jun 4 2010
Many human fungal pathogens infect people when they are inhaled as spores. Despite the serious impact of fungal spores on human health, little is known about their basic properties or how they interact with the host. This is particularly true for Cryptococcus neoformans, a human fungal pathogen that causes more than 600,000 deaths annually. Spores of C. neoformans have not been well characterized previously because of technical challenges in isolating them; however, recent advances in spore isolation have lead to the first direct analyses of spores. Novel insights into the spore-host interaction, specifically how spores interact with alveolar macrophages, have provided a new model of cryptococcosis that could have broad implications for human fungal pathogenesis.