Phage Biology

Phage infection is dependent not only on the species of host and phage, but also on the metabolic state of the host. Environmental conditions (e.g. temperature, pH, carbon source) determine the host’s metabolic state and thus the availability of the materials, energy, and enzymes necessary for phage replication. Most of the studies of T-even phage infection have been carried out during logarithmic growth of Escherichia coli in rich, well-aerated media. Outside of the lab, however, E. coli is found primarily in the anaerobic environment of the mammalian gut; these experiments are designed to better understand growth under those conditions. The data from these experiments will then serve as a baseline for studies of anaerobic phage infections.

In the rumen of primary consumers such as cattle, E. coli obtains energy from substrates primarily through fermentation. In the colon, most five and six-carbon sugars have already been absorbed or fermented so anaerobic respiration predominates. The early phase of the research utilizes defined media to allow control of the metabolic pathways of the host. In the fermentation medium, glucose serves as both carbon source and electron acceptor. In the studies of anaerobic respiration, glycerol is used as the carbon source because it cannot be fermented and forces the bacteria to follow a respiratory pathway, using nitrate (NO3-) as an alternative electron acceptor. We will discuss the fundamental properties of each pathway. We are also growing E. coli aerobically in the anaerobic respiration medium to determine which changes in growth rate are due to the media and which are attributable to the anaerobic conditions.

We are using three strains of E. coli:

1) E. coli B. We chose this strain because it has been the host for so many studies of T4 and other T-even phages and so provides a common reference point between aerobic and anaerobic studies. It also adds to the genetic spread of the E. coli we are examining, as B is only distantly related to most other strains of E. coli.

2) K12 MG1655. We wanted a K12 strain because most of the E. coli metabolic studies have been done in K12 strains, including extensive proteomic work and other studies under a variety of growth conditions. Of the K12 strains, we chose MG1655 because it has been fully sequenced and also because preliminary trials indicated that this strain grows more readily in anaerobic conditions than the other K12 strains tested, including W3110 and K803. This may be because MG1655 possesses a functional nitrate reductase gene that is thought to be lacking in many other K12 strains.

3) ECOR4. Our lab has done extensive work with various E. coli Collection of Reference (ECOR) strains as representatives of the wild-type. This collection broadly represents the enzyme genotypic diversity of E. coli species, and we chose ECOR4 because it is infected by a broad range of T-even type phage, although it is not infected by T4 under aerobic conditions.

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Last Updated: May 29, 2008

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