Planktonic versus colony growth of Bacillus thuringiensis affects gene expression in vitro and infectivity against an insect host, Galleria mellonella

The entomopathogenic bacterium, Bacillus thuringiensis, can complete its life cycle in environments of varying densities like insects, cadavers and soil. The stationary growth phase of the bacterial lifecycle includes virulent, necrotrophic and sporulation stages, which are under the control of pleotropic regulators of quorum sensing. In addition to insecticidal Cry-toxins, B. thuringiensis can generate quorum-dependent virulence factors. Herein, we investigated the development of B. thuringiensis under conditions of planktonic and colony growth. Using an insect host, namely Galleria mellonella larvae, we observed distinct virulence profiles and differential expression of quorum regulatory genes between B. thuringiensis from liquid planktonic growth and those colonies on a solid surface/medium.