In vitro studies on the mechanisms of endospore release by Rhinosporidium seeberi

Studies of Rhinosporidium seeberi have demonstrated that this organism has a complex life cycle in infected tissues. Its in vivo life cycle is initiat ed with the release of endospores into a host's tissues from its spherical sporangia. However, little is known about the mechanisms of sporangium form ation and endospore release since this pathogen is intractable to culture. We have studied the in vitro mechanisms of endospore release from viable R. seeberi's sporangia. It was found that watery substances visibly stimulate s the mature sporangia of R. seeberi to the point of endospore discharge. T he internal rearrangement of the endospores within the mature sporangia, th e opening of an apical pore in R. seeberi's cell wall, and the active relea se of the endospores were the main features of this process. Only one pore per sporangium was observed. The finding of early stages of pore developmen t in juvenile and intermediate sporangia suggested that its formation is ge netically programed and that it is not a random process. The stimulation of R. seeberi's sporangia by water supports the epidemiological studies that had linked this pathogen with wet environments. It also explains, in part, its affinities for mucous membranes in infected hosts. The microscopic feat ures of endospore discharge suggest a connection with organisms classified in the Kingdom Protoctista. This study strongly supports a recent finding t hat placed R. seeberi with organisms in the protoctistan Mesomycetozoa clad e.