Phage ecology

Bacteriophages (phages), potentially the most numerous 'organisms' on Earth, are the viruses of bacteria (more generally, of prokaryotes). Phage ecology is the study of the interaction of bacteriophages with their environments. Bacteriophages (phages), potentially the most numerous 'organisms' on Earth, are the viruses of bacteria (more generally, of prokaryotes). Phage ecology is the study of the interaction of bacteriophages with their environments. Phages are obligate intracellular parasites meaning that they are able to reproduce only while infecting bacteria. Phages therefore are found only within environments that contain bacteria. Most environments contain bacteria, including our own bodies (called normal flora). Often these bacteria are found in large numbers. As a consequence, phages are found almost everywhere. As a rule of thumb, many phage biologists expect that phage population densities will exceed bacterial densities by a ratio of 10-to-1 or more (VBR or virus-to-bacterium ratio; see for a summary of actual data). As there exist estimates of bacterial numbers on Earth of approximately 1030, there consequently is an expectation that 1031 or more individual virus (mostly phage) particles exist , making phages the most numerous category of 'organisms' on our planet. Bacteria (along with archaea) appear to be highly diverse and there possibly are millions of species. Phage-ecological interactions therefore are quantitatively vast: huge numbers of interactions. Phage-ecological interactions are also qualitatively diverse: There are huge numbers of environment types, bacterial-host types, and also individual phage types The study of phage ecology reflects established scientific disciplines in ecological studies in scope, the most obvious being general ecology. Accordingly, phage ecology is treated under the following heads— 'organismal' ecology, population ecology, community ecology, and ecosystem ecology. Phage ecology also may be considered (though mostly less well formally explored) from perspectives of phage behavioral ecology, evolutionary ecology, functional ecology, landscape ecology, mathematical ecology, molecular ecology, physiological ecology (or ecophysiology), and spatial ecology. Phage ecology additionally draws (extensively) from microbiology, particularly in terms of environmental microbiology, but also from an enormous catalog (90 years) of study of phage and phage-bacterial interactions in terms of their physiology and, especially, their molecular biology. Phage 'organismal' ecology is primarily the study of the evolutionary ecological impact of phage growth parameters: Another way of envisioning phage 'organismal' ecology is that it is the study of phage adaptations that contribute to phage survival and transmission to new hosts or environments. Phage 'organismal' ecology is the most closely aligned of phage ecology disciplines with the classical molecular and molecular genetic analyses of bacteriophage. From the perspective of ecological subdisciplines, we can also consider phage behavioral ecology, functional ecology, and physiological ecology under the heading of phage 'organismal' ecology. However, as noted, these subdisciplines are not as well developed as more general considerations of phage 'organismal' ecology. Phage growth parameters often evolve over the course of phage experimental adaptation studies. In the mid 1910s, when phage were first discovered, the concept of phage was very much a whole-culture phenomenon (like much of microbiology), where various types of bacterial cultures (on solid media, in broth) were visibly cleared by phage action. Though from the start there was some sense, especially by Fėlix d'Hėrelle, that phage consisted of individual 'organisms', in fact it wasn't until the late 1930s through the 1940s that phages were studied, with rigor, as individuals, e.g., by electron microscopy and single-step growth experiments. Note, though, that for practical reasons much of 'organismal' phage study is of their properties in bulk culture (many phage) rather than the properties of individual phage virions or individual infections.