ABSTRACT
The pH of the defined medium is Spherule cultures incubated at 40°C and purged with 20% COz/80% air daily for 7 days show a fall in pH to -5.2. The ability of both the saprobic and parasitic phases of C. immitis to produce ammonia has long been known [39] but not investigated. Ammonia and ammonium ions appear to be released from parasitic cells by secretion of the contents of cytoplasmic transport vesicles [II]. Using a fluorescent pH indicator (seminapthofluorescein; SNAFL), discrete cytoplasmic vesicles with alkaline contents have been observed. These vesicles appear to be more abundant in endospores and young spherules than in mature, segmented spherules. Bump [39] pointed out that greater amounts of ammonia are produced by C. immitis as the pH of the growth medium is reduced. We tested this observation by determination of relative amounts of ammonia/ammonium released into tissue culture media (RPMI 1640) by spherules and endospores isolated separately from the defined glucose-salts medium, and then transferred to RPMI and incubated for 12 hr at 37°C (5% COz). At pH 4.0, little growth of either inoculum occurred, but at pH 5.0 the endospores had clearly released more ammonia into the culture medium than the mature spherules. Ammonia production by both endospores and spherules decreased sharply above pH 6.0. An intriguing possibility is that this enhanced production of ammonia by endospores in an acidic environment may be related to their ability to survive in the presence of host phagocytes [14]. Both macrophages and PMNs are inefficient in killing C. immitis endospores. H. capsulatum yeast survival within the phagolysosome of host macrophages is at least partly due to their ability to modulate the pH within these organelles, which in tum may interfere with the activity of many lysosomal enzymes [40). Whether alkalinization of the phagolysosome is also a factor associated with in vivo survival of C. immitis endospores is unknown.
