Microorganisms and Plant Life 191 



Even though many different microorganisms able to 

 produce antibiotics on laboratory media can be obtained 

 from soil, this provides no indication that these same 

 organisms will produce antibiotics in soil. In fact, it is 

 difficult to demonstrate antibiotic production in soil (41). 

 In several cases, demonstrable amounts of antibiotics have 

 been produced in sterilized soil that was treated with 

 organic substances and inoculated with pure cultures of 

 the antibiotic-producing microorganisms. Antibiotic pro- 

 duction in unsterilized soil has been demonstrated infre- 

 quently. Gregory, Allen, Riker, and Peterson (13) achieved 

 production of antibiotics by various microorganisms in 

 unsterilized soil supplemented with alfalfa meal or straw. 

 Wright (48) obtained gliotoxin under similar conditions 

 when clover was added to the acidic podzol of the Wareham 

 Heath. These difficulties in producing antibiotics, even 

 under conditions which should be more favorable than 

 those common to soils in nature, suggest that antibiotics 

 are unlikely to be present in soils in appreciable amounts 

 except in micro areas. 



Under conditions where the amounts of antibiotics are 

 low and localized, the likelihood that antibiotics will ex- 

 clude certain elements of the soil population is small. 

 The relationships of bacteriophage in soil may be com- 

 parable. If a phage contained in a soil controlled the popu- 

 lation, one might expect to recover only phage-resistant 

 cells, if any. But phage-sensitive cultures are obtainable 

 from soils that contain the phage. Probably, biological 

 control by such factors as phage or antibiotics would be 

 localized, temporary, and limited in effect except under 

 unusual conditions. 



Furthermore, results obtained in our laboratories (31, 

 41) indicate that the amounts of antibiotics required to 

 affect microorganisms are much greater in soil than in 

 culture media, and that even streptomycin, which is very 

 resistant to decomposition in comparison with other anti- 



