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Cereulide, produced by certain Bacillus cereus strains, is a lipophilic cyclic peptide of 1152 Da that binds K(+) ions with high specificity and affinity. It is toxic to humans, but its role for the producer organism is not known. We report here that cereulide operates for B. cereus to scavenge potassium when the environment is growth limiting for this ion. Cereulide-producing B. cereus showed higher maximal growth rates (µ(max)) than cereulide non-producing B. cereus in K(+)-deficient medium (K(+) concentration ~1 mM). The cereulide-producing strains grew faster in K(+)-deficient than in K(+)-rich medium with or without added cereulide. Cereulide non-producing B. cereus neither increased µ(max) in K(+)-deficient medium compared with K(+)-rich medium, nor benefited from added cereulide. Cereulide-producing strains outcompeted GFP-labelled Bacillus thuringiensis in potassium-deficient (K(+) concentration ~1 mM) but not in potassium-rich (K(+) concentration ~30 mM) medium. Exposure to 2 µM cereulide in potassium-free medium lacking an energy source caused, within seconds, a major efflux of cellular K(+) from B. cereus not producing cereulide as well as from Bacillus subtilis. Cereulide depleted the cereulide non-producing B. cereus and B. subtilis cells of a major part of their K(+) stores, but did not affect cereulide-producing B. cereus strains. Externally added 6-10 µM cereulide triggered the generation of biofilms and pellicles by B. cereus. The results indicate that both endogenous and externally accessible cereulide supports the fitness of cereulide-producing B. cereus in environments where the potassium concentration is low.

Transcriptional profiling highlighted a subset of genes encoding putative multidrug transporters in the pathogen Bacillus cereus that were up-regulated during stress produced by bile salts. One of these multidrug transporters (BC4707) was selected for investigation. Functional characterization of the BC4707 protein in Escherichia coli revealed a role in the energized efflux of xenobiotics. Phenotypic analyses after inactivation of the gene bc4707 in Bacillus cereus ATCC14579 suggested a more specific, but modest role in the efflux of norfloxacin. In addition to this, transcriptional analyses showed that BC4707 is also expressed during growth of B. cereus under non-stressful conditions where it may have a role in the normal physiology of the bacteria. Altogether, the results indicate that bc4707, which is part of the core genome of the B. cereus group of bacteria, encodes a multidrug resistance efflux protein that is likely involved in maintaining intracellular homeostasis during growth of the bacteria.

A rod-shaped, non-spore-forming, non-motile, aerobic, oxidase and catalase-positive and radiation-resistant bacterium (designated strain K4.1(T)) was isolated from biofilm collected from a Finnish paper mill. The bacterium grew as pale pink colonies on oligotrophic medium at 12 to 50 °C (optimum 37 to 45 °C) and at pH 6 to 10.3. The DNA G+C content of the strain was 66.8 l%. According to 16S rRNA gene sequence analysis, strain K4.1(T) was distantly related to the genus Deinococcus, sharing highest similarity with Deinococcus pimensis (90.0  %). In the phylogenetic tree, strain K4.1(T) formed a separate branch in the vicinity of the genus Deinococcus. The peptidoglycan type was A3β with L-Orn-Gly-Gly and the quinone system was determined to be MK-8. The polar lipid profile of strain K4.1(T) differed markedly from that of the genus Deinococcus. The predominant lipid of strain K4.1(T) was an unknown aminophospholipid and it did not contain the unknown phosphoglycolipid predominant in the polar lipid profiles of deinococci analysed to date. Two of the predominant fatty acids of the strain, 15 : 0 anteiso and 17 : 0 anteiso, were lacking or present in small amounts in species of the genus Deinococcus. Phylogenetic distinctness and significant differences in the polar lipid and fatty acid profiles suggest classification of strain K4.1(T) as a novel genus and species in the family Deinococcaceae, for which we propose the name Deinobacterium chartae gen. nov., sp. nov. The type strain is K4.1(T) (=DSM 21458(T) =HAMBI 2721(T)).