186 PBOVASOLl [CHAP. 8 



which are the ecologically important species ; type culture collections are still 

 grossly inadequate, and the species ill-identified at best. 



a. Antibiotics of bacterial origin 



Two of the most important groups which produce antibiotics in the soil, the 

 actinomycetes and the fungi imperfect!, seem scarce in sea-water. We do not 

 know whether any truly marine representatives of them exist. As a con- 

 sequence the antibiotic picture of the ocean should be quite different from the 

 soil. The predominant flora of the sea is composed of Gram-negative and 

 pleomorphic Gram-positive bacteria ; the commonest genera are Pseudcnnonas. 

 Vibrio, Flavobacterium, Achromobacter , Bacterium, and corynebacteria (Zobell, 

 1946; Wood, 1950). However, our knowledge of the bacterial flora of the seas 

 may be entirely biased by the enrichment media employed. If some marine 

 bacteria shared the nutritional characteristics of the marine algae, they could 

 never be isolated with the extremely rich media in current use: the marine 

 algae, many of which are quite euryhaline, are particularly sensitive to con- 

 centrations of organic substances (10-30 mg % of "peptones" drastically 

 inhibit their growth). The only criterion to ensure the qualitative and quantitive 

 appreciation of the marine flora is the matching of microscope counts with 

 colony counts. 



A few actinomycetes (Nocardia, Micromonospora, Streptomyces) and 

 mycobacteria have been isolated from marine coastal sediments, nets, cordage 

 and rotting seaweeds. Grein and Meyers (1958), after a survey, consider that 

 the species isolated are probably of terrestrial origin : they are not different 

 morphologically from terrestrial species ; the halophilic tolerance of terrestrial 

 actinomycetes is as good as the one of the "marine" species; both types grow 

 better at sea-water concentrations of less than 50%. Several isolates of Grein 

 and Meyers exhibited antibiotic production in culture media. A few marine 

 Bacillus and Micrococcus (9 out of 58 marine species tested) had antibiotic 

 activity against non-marine forms (Rosenfeld and Zobell, 1947). A conclusion 

 is that marine bacteria may account for some of the observed antibacterial 

 action of sea-water on enteric and fresh-water forms (Greenberg, 1956). The 

 antagonism between marine micro-organisms is probable but unproven. 



b. Antibiotics of algal origin 



Extracts of several marine seaweeds are antibacterial (Pratt, Mautner et ah, 

 1951; Mautner, Gardner and Pratt, 1953; Vacca and Walsh, 1954; Chesters 

 and Scott, 1956; Allen and Dawson, 1959). This seems a widespread ability in 

 seaweeds : antibiotics were found in green, brown and red seaweeds, but it is 

 not known whether they are excreted in the sea or released after death. Anti- 

 biotic activity and antibacterial spectrum vary with species, and activity 

 within each species of seaweed varies in the different months and may even 

 be lacking (Chesters and Scott, 1956). The seaweeds tested by Allen and 

 Dawson inhibit only Gram-positive bacteria (Bacillus subtilis, Staphylococcus 



