The number of aerobic, anaerobic, and sulfate-reducing marine bacteria was 

 determined in the laboratory on nutrient agar plates and in test tubes. Because of 

 the different nutritional requirements of marine bacteria and the limitation in the 

 enumeration procedure employed in this study, only a small percentage of the marine 

 bacterial population may have been determined from the bottom samples. The 

 following media were used for culturing marine microorganisms: 



1. The nutrient medium used with pour plates for determining the general 

 aerobic bacterial population consisted of" 



Bacto-peptone 5.0 gm 



Ferric phosphate 0.1 gm 



Yeast extract 1.0 gm 



Seawater (aged) 1,000 ml 



Bacto-agor 20 gm 



pH 7.5 



2. The general anaerobic bacterial population was determined by using the 

 Fisher-Spray anaerobic culture dishes with the above medium, which was 

 treated with sodium formaldehyde sulfoxylate (1.0 gm/l) to lower the 

 redox potential and with resazurin (0.001 gm/l) to serve as an indicator 

 of anaerobiosis. " 



3. The nutrient medium for determining the presence of sulfate-reducing 

 bacteria consisted of° 



Potassium phosphate dibasic 0.2 gm 



Magnesium sulfate hydrated 0.2 gm 



Sodium sulfite 0.1 gm 



Ferrous ammonium sulfate 0.1 gm 



Calcium lactate 3.5 gm 



Ascorbic acid 0.1 gm 



Bacto-peptone 1 .0 gm 



Yeast extract 1.0 gm 



Seawater (aged) 1,000 ml 



pH 7.5 



For this study, agar was deleted from the above medium. The medium 

 was placed in test tubes with screw caps and sterilized. The screw caps 

 were tightened when the medium was still warm to exclude atmospheric 

 oxygen. Small samples of bottom sediment from various depths were 

 placed in these test tubes and incubated for several days at 15°C. 



The sediment samples obtained with a scoop sampler were washed through a 

 plastic screen to collect mud-dwelling organisms. The animals were bottled and 

 preserved in a 5% glycerol -alcohol solution aboard ship for laboratory analysis. 



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