Parasite-mediated protection against osmotic stress for Paramecium caudatum infected by Holospora undulata  is host genotype specific

Abstract

Under certain conditions, otherwise parasitic organisms may become beneficial to their host. Parasite-mediated heat and osmotic stress resistance have been demonstrated for Paramecium caudatum, infected by several species of parasitic bacteria of the genus Holospora. Here, using the micronucleus-specific bacterium Holospora undulata, we investigate how infection mediates the response of two genotypes (clones 'K8' and 'VEN') of P. caudatum to heat (35 1C) and osmotic (0.24% NaCl) stress. In contrast to previous findings, we find no evidence for heat stress protection in infected individuals. We do, however, show an effect of symbiont-mediated osmotic stress resistance for the K8 clone, with infected individuals having higher survival than their uninfected counterparts up to 24 h after the onset of salt exposure. Despite this, both infected and uninfected individuals of the VEN clone showed higher survival rates than clone K8 individuals under osmotic stress. Thus, it would seem that parasite-mediated stress protection is restricted to certain combinations of host genotypes and types of stress and does not represent a general phenomenon in this system.

Temporal variation in temperature determines disease spread and maintenance inParameciummicrocosm populations

“…We found no evidence for this, as infected populations were smaller and had higher extinction than uninfected populations, even in variable environments with low mean temperatures. This corroborates a recent study where we do not find evidence for parasite-mediated heat shock protection for the two clones used in this study [29]. Our results highlight the negative impact of even occasional, brief exposure to heat stress.…”

“…Horizontal transmission occurs when infectious forms are released into the environment during host division or upon host death. Holospora undulata reduces host division rate and carrying capacity of P. caudatum and increases host mortality [29,34,35].…”

“…(b) Host and parasite origins Two Paramecium clones were used in this experiment-clones K8 and VEN (see [29] for details). Prior to the experiment, we seeded mass cultures of each clone from single individuals.…”

“…Paramecium species [24] and this bacterial parasite are both sensitive to heat stress [25]. There is evidence that infected Paramecium can sometimes benefit from a transient protection against heat and osmotic stress owing to a general stress response induced by infection ( [26][27][28] but see [29]). Parasite viability declines rapidly at higher temperature thus hindering transmission [25].…”

Stochastic environmental fluctuations drive epidemiology in experimental host–parasite metapopulations

“…Paramecium clone VEN [32] was used in this experiment. Three months prior to the experiment, we seeded a mass culture of this clone from a single individual.…”