The mitochondrial toxin produced by Streptomyces griseus strains isolated from an indoor environment is valinomycin

Actinomycete isolates from indoor air and dust in water-damaged schools and children's day care centers were tested for toxicity by using boar spermat ozoa as an indicator. Toxicity was detected in extracts of four strains whi ch caused a loss of sperm motility, and the 50% effective concentrations (E C50) were 10 to 63 ng (dry weight) mi of extended boar semen(-1). The four strains were identified as Streptomyces griseus strains by 16S ribosomal DN A and chemotaxonomic methods. The four S. griseus strains had similar effec ts on sperm cells, including loss of motility and swelling of mitochondria, but we observed no loss of plasma membrane integrity or depletion of cellu lar ATP, None of the effects was observed with sperm cells exposed to extra cts of other indoor actinomycete isolates at concentrations of greater than or equal to 5,000 to 72,000 ng ml(-1). The toxin was purified from all fou r strains and was identified as a dodecadepsipeptide, and the fragmentation pattern obtained by tandem mass spectrometry was identical to that of vali nomycin, Commercial valinomycin had effects in sperm cells that were identi cal to the effects of the four indoor isolates of S, griseus. The EC50 of p urified toxin from the S, griseus strains were 1 to 3 ng ml of extended boa r semen(-1), and the EC50 of commercial valinomycin was 2 ng ml of extended boar semen(-1). To our knowledge, this is the first report of the presence of ionophoric toxin producers in an indoor environment and the first repor t of valinomycin-producing strains identified as S, griseus.