The Endosymbiotie Bacterium Holospora obtusa Enhances Heat‐Shock Gene Expression of the Host Paramecium caudatum

Abstract

The bacterium Holospora obtusa is a macronuclear-specific symbiont of the ciliate Paramecium caudatum. H. obtusa-bearing paramecia could survive even after the cells were quickly heated from 25 degrees C to 35 degrees C. To determine whether infection with H. obtusa confers heat shock resistance on its host, we isolated genes homologous to the heat shock protein genes hsp60 and hsp70 from P. caudatum. The deduced amino acid sequences of both cDNAs were highly homologous to hsp family sequences from other eukaryotes. Competitive PCR showed that H. obtusa-free paramecia expressed only trace amounts of hsp60 and hsp70 mRNA at 25 degrees C, but that expression of hsp70 was enhanced immediately after the cells were transferred to 35 degrees C. H. obtusa-bearing paramecia expressed high levels of hsp7O mRNA even at 25 degrees C and the level was further enhanced when the cells were incubated at 35 degrees C. In contrast, the expression pattern of hsp60 mRNA was the same in H. obtusa-bearing as in H. obtusa-free paramecia. These results indicate that infection with its endosymbiont can confer a heat-shock resistant nature on its host cells.

Costs and benefits of symbiont infection in aphids: variation among symbionts and across temperatures

“…Evidence for improved heat tolerance has been previously documented for A. pisum infected with S. symbiotica, which increased host fecundity under constant rearing at 25 8C (Chen et al 2000) and under heat shock conditions similar to those utilized in our experiments (Montllor et al 2002). A parallel finding was obtained from research on a Paramecium and its intracellular bacterial endosymbiont, which improved host viability after exposure to high temperatures (Hori & Fujishima 2003). In this instance, symbionts induced increased expression of a host heat shock gene, providing a potential explanation for their role in heat tolerance.…”

Temporal variation in temperature determines disease spread and maintenance inParameciummicrocosm populations

“…As in other organisms [40], tolerance of Paramecium to heat stress is partly mediated by the upregulation of heat-shock proteins, and infection with Holospora can further boost this response, thereby conferring heat stress protection [28]. 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.…”

“…Inclusion of these temperatures in analyses including constant treatments only does not change the results (not shown). Incidence of host extinction was measured as the proportion of times the host population, arcsine square-root transformed, was found to be extinct across the four main sampling days (6,13,20,27) of the experiment. Analyses investigating host extinction excluded populations in constant environments as extinctions were only observed in constant environments of 358C.…”

“…This was achieved by taking the residuals over the entire dataset from a generalized linear model with a binomial error structure, with extinction as the response variable and number of Paramecium from which extinction was estimated (number on slide) as the explanatory variable. Mean residual extinction was calculated across the four main sampling days (6,13,20,27) of the experiment. We then took the mean of the residuals across sampling days 6, 13, 20 and 27 as a measure of extinction.…”

“…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].…”