RESISTANCE OF MATERIALS TO MARINE BIOLOGICAL ATTACK 1101 



prescription bottle. About 1 gram of a finely divided test material is also 

 placed in the bottle which is then filled about three-quarters full of raw 

 sea water. To include as heterogeneous a population of marine bacteria 

 as possible, another inoculum is prepared for addition to the enrichment 

 culture. The additional inoculum is made by placing in a vial a small 

 particle of each of seven different sediments furnished by Dr. ZoBell of 

 the Scripps Institute of Oceanography. These sediments are identified 

 in Table II. Following this, one or two drops of liquid are added to the 

 same vial from each of twenty-nine different enrichment cultures which 

 also were provided by Dr. ZoBell. These cultures are identified in Table 

 III. Transfers from eight different cultui'es of marine sulfate-reducing 

 bacteria are included, and the vial shaken thoroughly. About five drops 

 of pooled inoculum are added to the eniichment culture prepared for 

 each test material. The completed enrichment cultures are incubated at 

 25° C for a minimum of six weeks prior to use. During the incubation 

 period those bacteria in the culture which are capable of utilizing the 

 test material tend to develop preferentially. 



The same enrichment culture is used whether the test procedure is 

 aerobic or anaerobic since both conditions prevail in this type of enrich- 

 ment cultiu'e — aerobic in the water and upper sediment, and anaerobic 

 in the deeper, compacted sediment. From this point on, in describing the 

 method used in the material tests, it is necessary to describe the aerobic 

 and anaerobic procedures separately. 



In the aerobic tests, 0.01 per cent ammonium phosphate is added to 

 sufficient sea water (usually about 7 liters) for a given test run. Oxygen 

 is bubbled through the sea water in a carboy for a minimum of sixteen 

 hours at which time the oxygen content of the sea water is about 25 

 ppm. Since as many as four or more test materials may be included in a 

 test run, the inoculum is prepared by combining in one vial a small 

 amount of liquid from the enrichment culture for each material to be 



Table II — Sources of Sediments* used in Preparing 

 Enrichment Cultures 



* Obtained from Dr. C. ZoBell, Scripps Institute of Oceanography 



