Pradeep Ram, A.S. & Sime-Ngando, T. Environmental Microbiology. (2010).

"Resources drive trade-off between viral lifestyles in the planton: evidence from freshwater microbial microcosms"

Reviewed: 11/18/11

The two possible lifestyles of viruses living in aquatic systems has often been considered as a trade-off. Each lifestyle presenting its benefits and costs under certain environmental conditions, and both lifestyles having persisted across evolutionary time because of this very antagonism in the trade-off. The investigators of this paper chose to look at nutrient conditions might be responsible for the conversion of a lytic cycle pathogen into its lysogenic state. They tested the hypothesis that the addition of organic and inorganic nutrients decreases the presence of the lysogenic lifestyle overall. The experiment was conducted in a laboratory setting on samples collected from a freshwater lake in France.
Mytomycin C is an antibiotic that crosslinks DNA and can initiate a repair pathway within cells. It was this chemical that was used to induce prophages to leave the lysogenic stage. This is a common experimental technique used to determine proportion lysogenic stage (based on difference from lytic). More evidence needs to be collected on its accuracy, but overall it seemed to be a better estimating method than the TEM-based counts used as the alternative by the researchers.
Viral abundance increased under conditions where its host was fed on high nutrient based foods. This result was particularly true for inorganic, as well as organic, carbon additions. This increase however, seemed more closely linked to the benefit that the nutrient additions provided to host growth rates and abundance. researchers also measured the burst size, or internal reproduction of the virus within their hosts. The magnitude of this response was again linked to increased carbon conditions.
A ratio of lytic to lysogenic frequencies showed that a higher proportion of lysogens were found in ambient nutrient conditions, as well as for samples that had been experimentally manipulated to contain reduced viral to host ratios. The authors propose that more lysogens can be found in virus-reduced samples because the direct competition between hosts increases, creating poorer host conditions for a potentially lytic-stage virus. This finding was also proposed to be a result of lower contact frequency between host and pathogen stimulating a waiting-type lifestyle (lysogeny), until higher contact rates could be achieved.
Analysis of the Pearson product-moment correlation coefficients shows a very clear antagonism between the frequency of lytic viruses and that of lysogenic ones. This supports the idea that these two lifestyles do in fact represent a distinct trade-off in life-history metrics. The other key result from this experiment, as prevously stated, showed that nutrient additions beyond the ambient increased the proportion of lytic-lifestyle viruses largely as a result of increased bacterial population numbers. However, the study did not demonstrate that decreasing the nutrient conditions within the samples could lead to higher counts of lysogeny. This could be achieved in the future by placing the host species into a broader range of nutrient conditions by chemically manipulating the waters found naturally in the freshwater lake used in this study.