Biotechnology Center
Biotechnology Center

Applied Microbiology

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Screening Photorhabdus luminescens for Antibacterial Properties Using a Modified Version of the Kirby-Bauer Method.

Floyd L. Inman, III*, Len Holmes

The aim of this work was to observe and determine the bacteriocidal properties of Photorhabdus luminescens. A modified version of the Kirby-Bauer method was used to screen this bacterium for bacteriocidal properties against a collection of 28 different bacteria. The collection of bacteria used contained bacterial species with different cellular morphologies and Gram stain reactions. The measurements of the zones of sensitivity were used to observe and determine these bacteriocidal properties. The Kirby-Bauer method was slightly modified to achieve the aim of this work. The modification consisted of using blank, sterile disks that had been inoculated with a liquid culture of mid-log phased P. luminescens. From these 28 different species of bacteria, 11 bacterial species was determined to be sensitive to P. luminescens.

Trehalose as a Carbohydrate Source for the Culture and Stability of the Phase I Variant of Photorhabdus luminescens.

Floyd L. Inman, III; Len Holmes*

Photorhabdus luminescens is a Gram-negative, bioluminescent, pigment producing enteric bacterium that is pathogenic to insects. This bacterium has the ability to undergo phase variation. The phase I variant exists as a mutualistic symbiont in the digestive tract of the nematode, Heterorhabditis bacteriophora, and plays a critical role in the life-cycle of this commercially-reared beneficial entomopathogenic nematode. Only phase I cells support development of the nematode. It is critical to understand the stability requirements of this bacterial variant. The bacterium receives its requirements (i.e. carbohydrates) from the hemolymph of the larval insect host. The sugar trehalose, an α-1,1 linked   non-reducing disaccharide of glucose, is important in the physiology of microbes, insects and nematodes. Trehalose has been shown to be the most abundant sugar found within hemolymph. Acting as a physical and chemical protectant, trehalose has been implicated with thermal stress, dehydration and osmotic protection. It is also a store of glucose for glycolysis. We propose that trehalose will best support, in vitro, the stability of the phenotypic traits of the phase I variant. The traits monitored in this work are (1) bioluminescence (2) the production of the red anthroquinone–derived pigment and (3) culture pH.

 

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