MINERAL 

 SALT — 

 SOLUTION 







GAS 

 MIXTURE 



SOIL 

 SLURRY 



RESERVOIR 



REACTOR 



Figure 28-6. The simple apparatus shown here was used to incubate bacteria as a means 

 of measuring their density in the soil (Stravinski). 



In 1947 Bokova and others showed that certain strains of bacteria could 

 oxidize methane, pentane, and hexane, but not ethane or propane. Ethane- 

 oxidizing bacteria that were isolated could utilize propane, butane, and higher 

 hydrocarbons. He was also able to stimulate selectively the growth of a given 

 species by introducing a specific hydrocarbon gas into the circulating air cur- 

 rent. Concentrations of 0.019 percent methane and 0.001 percent propane were 

 found adequate to activate these bacteria strains. 



Stravinski (1955) described a simple apparatus for measuring the hydro- 

 carbon-consuming bacteria population. Soil samples were collected from about 

 24 inches in depth and about 25 feet apart. They were dried and sieved through 

 a U. S. stainless-steel series No. 18 sieve. A nutrient media, consisting of 1.0 

 gram of NH 4 N0 3 , 0.5 gram of K 2 HP0 4 , and 0.1 gram of CaS0 4 was diluted 

 with distilled water to 1 liter, with a resulting pH of 7.5. A pint of sample then 

 was mixed for one minute with 700 milliliters of the nutrient media, after which 

 a 50 milliliter slurry sample was transferred to a 250 milliliter reactor jar. This 

 jar, meanwhile, was filled with a prepared gas mixture containing 65 percent 

 hydrocarbon gas, 30 percent oxygen, and 5 percent carbon dioxide. The reservoir 

 of nutrient media was connected to the reactor jar so that it could be drawn free- 



631 



