A Morphological Investigation of the Co-existence of Host-Dependent Bdellovibrio bacteriovorus and its Host-Independent Variants by Atomic Force Microscopy

Abstract

The persistence in the environment of Bdellovibrio bacteriovorus , a Gram-negative bacterium that hunts and invades other Gram-negative bacteria in its host-dependent lifestyle, is the underlying scientific theme of this investigation. This experiment tracks these Host-dependent (HD) bdellovibrios, that have recently preyed on E. coli and are trapped at an interface with a high concentration of nutrients and no prey cells. When the HD bdellovibrios have been exposed to the nutrient environment, after several days, there is a yellow growth where the HD bdellovibrios were placed, called a plaque, that is larger in volume than the original sample. Host-independent (HI) bdellovibrios are found to be thriving among HD bdellovibrios in the new plaque. The co-existence of the two phenotypes may serve as a model for bacterial persistence in the environment, in the interest that the natural environment of this organism has abrupt shifts in conditions, such as nutrients, temperature, and other microbial populations. To explore this co-existence and to ultimately investigate the survival techniques this organism uses in the environment, like the cell morphology observed in the yellow plaque, I utilized atomic force microscopy to measure cell morphology as a function of time at molecular level. Two models for persistence in the lifestyle phenotype are hypothesized. One relies on stochastic phenotypic switching while the other is based on spontaneous point mutations. Moreover, chemical signaling by bdellovibrios may be operative in a more complex mechanism for persistence. These persistence models along with preliminary atomic force microscopy images will be presented and interpreted.