THE MICROBIOLOGY OF THE ATMOSPHERE 



expected to increase the counts of earlier worliers by from lo to 20 times. 

 On these media gram-negative bacilH predominate, there are few cocci, 

 no vibrio or spirilla forms, and fewer than half were spore-formers. A pink 

 yeast has been reported from ocean air by several workers. This spora 

 contrasts strongly with the gram-positive rods, spore-formers, cocci, 

 Bacillaceae, and Micrococcaceae which, with mould spores, are normally 

 abundant in air over land (ZoBell, 1942). 



Rittenberg (1939) sampled in (presumably horizontal) Petri dishes 

 at 21 metres above the deck of the vessel E. W. Scripps off the Pacific 

 Coast of California. Contrasts between sea-water and fresh-water media 

 were not so clear as in previous tests, and the numbers varied widely at 

 different stations; but, on the average, moulds decreased in numbers with 

 increasing distance from land (Table XXII). 



TABLE XXII 



NUMBERS OF MICROBES AND DISTANCE FROM LAND. SUMMARY OF 25 PETRI 

 DISH EXPOSURES AT 21 METRES ABOVE DECK (Rittenberg, 1 939). 



Distance Average number of colonies per hour of 



from land exposure (on 4 Petri dishes of each inoculum). 



km. Sea-water Medium Tap-water Medium 



Bacteria Bacteria 



(and yeasts) Moulds (and yeasts) Moulds 



0-20 45 115 20 200 



20-300 48 79 13 69 



300-800 71 20 39 36 



Detailed examination of 100 bacterial and yeast cultures taken at 

 random by Rittenberg showed that 32 per cent were yeasts, 30 per cent 

 cocci, 15 per cent gram-negative rods, and the remaining 23 per cent 

 gram-positive spore-forming rods. They included: Bacillus subtilis^ 

 B. flavus^ B. megatherium^ B. mjcoides, B. tufnescens, B. cohaerens, B. 

 laterosporus, Flavobacterium aquatilis^ Achromobacter liquifaciens^ Staphylo- 

 coccus aureus, S. albus, S. citreus, Micrococcus Jlavus, M. candidus, and 

 Sarcina jlava* One hundred mould cultures included: Cladosporium 

 (Hormodendrum), 22 per cent; Penicillium, 18 per cent; Alternaria — 

 Macrosporium — Stetuphylium, 11 per cent; Cephalosporium, 7 per cent. 

 Others identified included : Plenozythia, Catenularia, Spicaria or Paecilo- 

 myces, and Trichoderma. To avoid the usual embarrassment of the micro- 

 biologist, all sampling in free air seems to have been done with sugar-free 

 media; otherwise, moulds might have been many times more abundant. 

 Rittenberg points out that this marine airborne flora is unlike that of sea 

 water itself, but resembles the air-spora over land. 



* But additional information by ZoBell (1942) indicates that these identifiable 

 species were all from fresh-water plates. 



126 



