Frost, P.C., Ebert, D., & Smith, V.H. Ecology. (2008).

"Responses of a bacterial pathogen to phosphorus limitation of its aquatic invertebrate host'.

Stoichiometric conditions of the food, whether living or not, are known to have strong effects on the organism doing the consuming. Nutrient quality has the potential to drive patterns in enemy fitness as well as to reciprocally affect the tolerance of the host or prey. Three main response variables were analyzed during the source of this experiment, whereby invertebrate Daphnia magna hosts were fed on specific nutrient-levels of food and dosed with a set number of spores of the highly effective microparasite Pasteuria ramosa.  The theoretical queries at the base of this experiment are whether nutrient poor conditions will limit the pathogen as well as the host, or whether under nutrient poor conditions, the pathogen will become preferentially more efficient at utilizing the limited nutrients, thus having a higher virulence on its host.
The infection rate of the bacterial pathogen was assessed by manipulating the nutrient conditions of the food for Daphnia during the infection period, but thereafter maintaining constant nutrient conditions across all treatments, in order to assess only the ability of the pathogen to infect. A linear relationship between phosphorous content of host food and infection rate was observed, with a higher degree of infection for high phosphorus conditions. Based on previous work the authors believe this result if most likely due to reduced growth of the bascterial spores within the host under low phosphorus conditions rather than due to reduced feeding habits or contact rates.
In contrast to the methodology used to assess infection rate, spore production of the pathogen was measured by maintaining constant nutrient conditions of the food during the infection period, but thereafter altering the food content by treatment. In general more spores were found in hosts fed on phosphorus rich foods, though the relationship was non-linear. This pattern seems to be largely driven by the reduced size of the host fed on nutrient poor foods, however the density of spores within the host was non-constant across treatments. this may be interesting for future work as it could help determine if the pattern of reduced spore counts is in fact fully linked with reduced host size. An interaction may exist whereby larger hosts may still contain a proportionately larger number of pathogens in nutrient rich conditions. An experiment with a higher number of treatments, or hosts that are measured for spore containment more often during the potential growth period, could reduce the irregularities within the results and indicate a more concrete relationship between pathogen density and nutrient conditions in this study system.
The final portion of this study hoped to look at the question of nutrient effects on host reproduction. The difference in reproduction at all nutrient conditions was assessed for both infected and uninfected individuals. not surprisingly, infection reduced host production, period. However, this decrease was more dramatic in hosts fed on a low phosphorus diet, indicating that the virulence effects of the pathogen on its host was in fact higher under nutrient-stressed conditions.