Vehicles, replicators, and intercellular movement of genetic information: evolutionary dissection of a bacterial cell

Abstract

Prokaryotic biosphere is vastly diverse in many respects. Any given bacterial cell may harbor in different combinations viruses, plasmids, transposons, and other genetic elements along with their chromosome(s). These agents interact in complex environments in various ways causing multitude of phenotypic effects on their hosting cells. In this discussion I perform a dissection for a bacterial cell in order to simplify the diversity into components that may help approach the ocean of details in evolving microbial worlds. The cell itself is separated from all the genetic replicators that use the cell vehicle for preservation and propagation. I introduce a classification that groups different replicators according to their horizontal movement potential between cells and according to their effects on the fitness of their present host cells. The classification is used to discuss and improve the means by which we approach general evolutionary tendencies in microbial communities. Moreover, the classification is utilized as a tool to help formulating evolutionary hypotheses and to discuss emerging bacterial pathogens as well as to promote understanding on the average phenotypes of different replicators in general. It is also discussed that any given biosphere comprising prokaryotic cell vehicles and genetic replicators may naturally evolve to have horizontally moving replicators of various types.

Figure 1

The basic terminology used throughout the paper and their biological counterparts.

Figure 2

Replicators with horizontal movement potential can become common in various cell-vehicle lineages and therefore free of the survival of any particular lineage.

Figure 3

A cell vehicle, which contains its essential genetic information in multiple independent replicators, may be prone to lose some replicators during cell division and thus produce incompetent cells.

Figure 4

When plasmid- and chromosome-borne antibiotic resistances are compared, the plasmid-borne resistance can become more abundant after exposure to antibiotics.

Figure 5

Positioning of the different classes of the classification into a two-dimensional plot where on one axis there is the horizontal movement potential of the class and on the other there is the effect of the replicator on its present cell vehicle.