Publication details

Characteristics and growth of two-phased bacteria Photorhabdus luminescens



Year of publication 2020
Type Conference abstract
MU Faculty or unit

Faculty of Science

Description Gram-negative bacteria Photorhabdus luminescens of the family Morganellaceae live symbiotically in the gut of entomopathogenic nematodes Heterorhabditis bacteriophora. Their common life strategy is to find an insect host, kill it and proliferate in the cadaver. Penetration of the nematode into the insect host is performed through the natural openings or by disrupting the cuticle. Then the nematode releases bacteria from the gut into the haemocoel and together they cause insect death by producing toxins and other substances inhibiting host immunity. Nematodes and bacteria obtain nutrients from the decaying corpse and proliferate. P. luminescens forms two phases which are genetically identical, but morphologically different. Cells of phase I are known to be pathogenic, associated with nematodes and produce bioluminescence, toxins, pigments, enzymes or antibiotic substances. Phase II cells cannot produce many substances and do not show any light emission. However, they also produce pigments, but to a lesser extent than phase I cells. To discriminate both phases, the selective cultivation media are used. MacConkey and NBT agar contain dyes that cells of phase I absorb, but phase II do not. Phase I cells are deeply red on MacConkey and blue or green on NBTA. Cells of phase II are only pale or pink on MacConkey and red on NBTA medium. Phase differentiation is crucial because only phase I cells could kill insect and this property is utilized in bio-insecticide products in pest control management. Phase verification can be performed by measuring the bioluminescence of bacteria using luminometer, because only phase I cells emit light. Also growth of the cell culture could be measured by the light emission rate of the cells, because it increases as the bacterial culture grows. P. luminescens grows more slowly than other bacteria, colonies on the agar plates appears in 2-3 days. The exponential phase of the growth was not reached before 5-8 hours of cultivation.

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