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A lipid antibiotic was extracted from whole cells of the marine diatom Chaetoceros lauderi (Ralfs) and roughly identified as an unsaturated fatty acid by thin layer chromatography. A number of Gram-positive terrestrial bacteria and several Gram-negative marine bacilli were sensitive to this antibiotic, whereas Gram-negative enteric bacteria were resistant. Solar irradiation led to its partial disappearance and to the production of more polar antibiotics with a stronger antibacterial activity. This observation is compared to similar data culled from literature, and its significance in a natural environment is discussed.

A strain of Byssochlamys nivea cultivated in a liquid medium (Saccharose: 50 g: NaNo3: 2 g; KH2PO4: 1 g; KCL: 0.5 g; MgSO4, 7H2O: 0.5 g; water to 1000 ml) produces, at 24 degrees C, an antibiotic substance which appears after several days of growth (10-12 days). Among 43 strains of Bacteria Gram (minus) belonging to 10 genera none was resistant. The most was susceptible, save Pseudomonas aeruginosa, Serratia marcescens, Moraxella glucidolytica. On the the great bulk of the Bacteria (Gram +) tested was little influenced, except certain strains of Bacillus. The filtrate is ineffectual against Mycobacteria and Fungi (yeast or mould) at the concentration used. This substance seemed to be different of those produced by Byssochlamys fluva (byssochlamic acid) and by some species of Paecilomyces (P. varioti, P. persicinus, P. elegans, P. variabilis, P. fusidioides).