A strain isolated from a soil sample collected from a field at Origuchi, Akune City, Kagoshima-Ken was shake-cultured in a medium containing starch, glucose, peptone and meat extract, and the culture filtrate exhibited inhibition diameters of 13.5 mm to Staph. aureus 209P, 22.0 mm to Mycobacterium 607 and 19.0mm to M. phlei. As reported in another paper by Akita et al.¹⁾, the antibiotic was isolated and named labilomycin. This paper describes characters of the strain producing this antibiotic.

Antiprotozoal activities were reported on some antibacterial and antifungal antibiotics with strong toxicity. The antibiotic substances which inhibit or destroy protozoa are presumed to have general cytotoxicity. Antibiotics having a very broad spectrum, e.g. substances active against bacteria and protozoa can be expected to be more toxic than antibiotics with a specific activity only against protozoa. This presumption indicates the importance of including an antiprotozoal test already into the primary screening course. This paper reports the screening method which has been used in the authors laboratory.

Among fungi isolated from the sample of Chinese soil, several cultures exhibiting antiprotozal activity were selected by the specific screening method for antiprotozoal antibiotics¹⁾. One of these cultures was identified as Aspergillus fumigatus. We succeeded in isolating an antiprotozoal substance produced by this strain in pure, crystalline form. This antibiotic was confirmed to be a new antibiotic inhibiting Trypanosoma cruzi, and we named it trypacidin. Besides trypacidin, this strain produced at least one other antibiotic active against Bacillus subtilis, though we have not attempted to isolate or characterize this substance. In this paper are described the isolation method of trypacidin as well as some physical, chemical and biological properties of this substance.

After the discovery of trypacidin, which is an antibiotic with specific antiprotozoal activity^1,2), we studied the in vivo activity of this substance.

In the first preliminary experiments on the effect of trypacidin on the tissue culture of HeLa cells infected with Trypanosoma cruzi and Toxoplasma gondii, trypacidin exhibited a pronounced inhibitory effect on the intracellular forms of both parasites. The results of these experiments will be published elsewhere. This paper deals with the effect of trypacidin on experimental toxoplasmosis of mice. We are now also studying the effect of trypacidin on experimental Chagas’ disease and will publish the results later.

Angustmycins A and C, produced by Streptomyces hygroscopicus, are nucleoside antibiotics: angustmycin A is 6-amino-9-(L-1,2-fucopyranoseenyl)-purine and angustmycin C 6-amino-9-(β-D-psicofuranosyl)-purine.^1–4) They were observed to exhibit an inhibitory activity against experimental infections and transplantable tumors in animals⁶⁾.

The activity of angustmycins A and C was reversed by adenosine, guanosine, guanine and related substances. It indicated that both angustmycins may act as antimetabolites in purine biosynthesis. The inhibition index suggested that guanosine synthesis is more interfered than adenosine synthesis in the presence of angustmycins. ⁵⁾

This paper describes the results of further experiments concerning the mode of action of these nucleoside antibiotics, indicating that both angustmycins may inhibit the process of biosynthesis of guanosine monophosphate from xanthosine monophosphate.