Psychrotolerant Paenibacillus tundrae isolates from barley grains produce new cereulide-like depsipeptides (paenilide and homopaenilide) that are highly toxic to mammalian cells.

Paenilide is a novel, heat-stable peptide toxin from Paenibacillus tundrae, which colonizes barley. P. tundrae produced 20 to 50 ng of the toxin mg(-1) of cells (wet weight) throughout a range of growth temperatures from +5°C to +28°C. Paenilide consisted of two substances of 1,152 Da and 1,166 Da, with masses and tandem mass spectra identical to those of cereulide and a cereulide homolog, respectively, produced by Bacillus cereus NS-58. The two components of paenilide were separated from those of cereulide by high-performance liquid chromatography (HPLC), showing a structural difference suggesting the replacement of O-Leu (cereulide) by O-Ile (paenilide). The exposure of porcine spermatozoa and kidney tubular epithelial (PK-15) cells to subnanomolar concentrations of paenilide resulted in inhibited motility, the depolarization of mitochondria, excessive glucose consumption, and metabolic acidosis. Paenilide was similar to cereulide in eight different toxicity endpoints with porcine and murine cells. In isolated rat liver mitochondria, nanomolar concentrations of paenilide collapsed respiratory control, zeroed the mitochondrial membrane potential, and induced swelling. The toxic effect of paenilide depended on its high lipophilicity and activity as a high-affinity potassium ion carrier. Similar to cereulide, paenilide formed lipocations, i.e., lipophilic cationic compounds, with K(+) ions already at 4 mM [K(+)], rendering lipid membranes electroconductive. Paenilide-producing P. tundrae was negative in a PCR assay with primers specific for the cesB gene, indicating that paenilide was not a product of plasmid pCER270, encoding the biosynthesis of cereulide in B. cereus. Paenilide represents the first potassium ionophoric compound described for Paenibacillus. The findings in this paper indicate that paenilide from P. tundrae is a potential food-poisoning agent.

Biofilm-forming bacteria with varying tolerance to peracetic acid from a paper machine.

Biofilms cause runnability problems in paper machines and are therefore controlled with biocides. Peracetic acid is usually effective in preventing bulky biofilms. This study investigated the microbiological status of a paper machine where low concentrations (≤ 15 ppm active ingredient) of peracetic acid had been used for several years. The paper machine contained a low amount of biofilms. Biofilm-forming bacteria from this environment were isolated and characterized by 16S rRNA gene sequencing, whole-cell fatty acid analysis, biochemical tests, and DNA fingerprinting. Seventy-five percent of the isolates were identified as members of the subclades Sphingomonas trueperi and S. aquatilis, and the others as species of the genera Burkholderia (B. cepacia complex), Methylobacterium, and Rhizobium. Although the isolation media were suitable for the common paper machine biofoulers Deinococcus, Meiothermus, and Pseudoxanthomonas, none of these were found, indicating that peracetic acid had prevented their growth. Spontaneous, irreversible loss of the ability to form biofilm was observed during subculturing of certain isolates of the subclade S. trueperi. The Sphingomonas isolates formed monoculture biofilms that tolerated peracetic acid at concentrations (10 ppm active ingredient) used for antifouling in paper machines. High pH and low conductivity of the process waters favored the peracetic acid tolerance of Sphingomonas sp. biofilms. This appears to be the first report on sphingomonads as biofilm formers in warm water using industries.