SECT. 2] ORGANIC REGULATION OF PHYTOPLANKTON FERTILITY 187 



aureus and Mycobacterium smegmatis) and not Escherichia coli 1 while the 

 species tested by Chesters and Scott inhibited also Gram -negative fresh-water 

 bacteria (Escherichia coli and Pseudomonas aeroginosa, etc.) ; marine bacteria 

 are mostly Gram-negative. 



Unicellular fresh-water algae also produce antibiotics : antibacterial sub- 

 stances are present in old cultures of Protosiphon and Stichococcus (Harder and 

 Oppermann, 1953) and in Chlorella extracts (Spoehr et al., 1949). Photooxidized 

 unsaturated fatty acids are responsible for the antibacterial action of Chlorella 

 and, apparently, also for Protosiphon and Stichococcus (the evidence is scanty). 

 Unsaturated fatty acids produced and liberated upon death by Chlamydomonas 

 reinhardii are apparently responsible for the antibiosis of C. reinhardii on 

 Haematococcus pluvialis (Proctor, 1957). Since unsaturated fatty acids are 

 produced by algae, including the seaweeds (Collyer and Fogg, 1955, for green 

 algae, and table in Fogg, 1953), one wonders whether some antibacterial effects 

 of seaweeds are not due to fatty-acid toxicity, especially in the alkaline range. 

 This possibility was not considered in the work on seaweeds. 



Several laboratories are now testing a variety of marine unicellular algae for 

 antibacterial activity. The only published report is the very instructive story of 

 Phaeocystis sp. Arctic birds were known to have a reduced gastro-intestinal 

 microflora; this was confirmed for Antarctic birds by Sieburth (1959), who 

 found that blood serum of penguins was active against Gram -positive bacteria. 

 The antibiotic activity was traced through the food chain : from the crustacean 

 Euphausia superba, which is the staple diet of penguins, to Phaeocystis -like 

 algae which bloom in the Antarctic and are a food for Euphausia (Sieburth, 

 1959a). The antibacterial substance of Phaeocystis inhibits Gram-positives more 

 than Gram-negatives ; it is water- and ethanol-soluble and is soluble in non- 

 polar solvents, stable to heat and alkali, but inactivated by heat-drying and 

 mineral acids (Sieburth and Burkholder, 1959). The substance was finally 

 identified as acrylic acid (Sieburth, 1960). 



c. Antibiotics of invertebrate origin 



Water homogenates of living sponges from the temperate and subtropical 

 zones contain substances which inhibit a variety of marine bacteria (isolated 

 from sponges and sea-water) and the usual forms employed for antimicrobial 

 assays (Jakowska and Nigrelli, 1960). This activity was found in species of 

 Microciona, Halichondria, Cliona, Tedania, Haliclona, Dysidea and Oligocera. 

 The active substances are heat-stable and can be selectively extracted with 

 solvents, also from frozen and heat-dried sponges. The activity ranges from 

 inhibition of marine bacteria to "broad-spectrum antibiosis" ("ectyonin" 

 extracted from Microciona prolifera) and specific action against Pseudomonas 

 pyocyanea and Candida albicans. 



Extracts of several gorgonian (horny) corals had a strong antibiotic action 

 against both the usual fresh-water assay species and marine bacteria. On the 



1 Gram-positive bacteria are notoriously more sensitive to antibiotics, on the whole, 

 than are Gram-negative. 



