The peptide toxin amylosin of Bacillus amyloliquefaciens from moisture-damaged buildings is immunotoxic, induces potassium efflux from mammalian cells, and has antimicrobial activity.

Amylosin, a heat-stable channel-forming non-ribosomally synthesized peptide toxin produced by strains of Bacillus amyloliquefaciens isolated from moisture-damaged buildings, is shown in this paper to have immunotoxic and cytotoxic effects on human cells as well as antagonistic effects on microbes. Human macrophages exposed to 50 ng of amylosin ml(-1) secreted high levels of cytokines interleukin-1ß (IL-1ß) and IL-18 within 2 h, indicating activation of the NLRP3 inflammasome, an integral part of the innate immune system. At the same exposure level, expression of IL-1ß and IL-18 mRNA increased. Amylosin caused dose-dependent potassium ion efflux from all tested mammalian cells (human monocytes and keratinocytes and porcine sperm cells) at 1 to 2 µM exposure. Amylosin also inhibited the motility of porcine sperm cells and depolarized the mitochondria of human keratinocytes. Amylosin may thus trigger the activation of the NLRP3 inflammasome and subsequently cytokine release by causing potassium efflux from exposed cells. The results of this study indicate that exposure to amylosin activates the innate immune system, which could offer an explanation for the inflammatory symptoms experienced by occupants of moisture-damaged buildings. In addition, the amylosin-producing B. amyloliquefaciens inhibited the growth of both prokaryotic and eukaryotic indoor microbes, and purified amylosin also had an antimicrobial effect. These antimicrobial effects could make amylosin producers dominant and therefore significant causal agents of health problems in some moisture-damaged sites.

Streptomyces strains producing mitochondriotoxic antimycin A found in cereal grains.

Reasons for mammalian cell toxicity observed in barley and spring wheat grains were sought. Streptomyces sp. isolates from wheat and barley produced heat-stable methanol-soluble substances which inhibited the motility of exposed porcine spermatozoa used as a toxicity indicator. Several barley isolates produced antimycin A (2 to 5 ng/mg wet wt of biomass), a macrolide antibiotic known to block oxygen utilization in mitochondria. The antimycin-producing isolates were members of the Streptomyces albidoflavus group. In in vitro assays with porcine kidney tubular epithelial cells, the specific toxicity of antimycin A towards mitochondria was higher than that of the mycotoxin enniatin B but lower than that of the mitochondriotoxins cereulide and paenilide, produced by food-related Bacillus cereus and Paenibacillus tundrae, respectively. The toxic wheat isolates, related to Streptomyces sedi, did not produce antimycin A and or any other known toxin. Our results suggest that the presence of toxin-producing streptomycetes in stored cereal grains may pose a thus far unrecognized threat for food and feed safety.