EFFECT ON PHYSIOLOGY OF BACTERIAL CELL 253 



coming spherical coccoids which burst j in the case of some bacteria, not 

 all the spores are killed j however, the great majority of them become 

 nonviable. In non-nutrient media the spores are little affected, even by 

 strong concentrations of penicillin. The conclusion was reached, there- 

 fore, that the action of penicillin on sensitive bacteria has little or no 

 connection with multiplication or division, although some abnormal 

 divisions were observed in certain sensitive organisms. The majority of 

 S. aureus and S. pyogenes growing on agar are checked or killed before 

 any visible growth or division has occurred. 



A growth-depressing substance, which altered the type of growth of 

 both fungi and bacteria, was also isolated (151) from yeast. Fungi 

 treated with this substance produced thick gnarled mycelia and formed 

 no conidia or pigment. Increasing the concentrations of the depressing 

 agent changed the nature of the colony of E. coli from smooth to rough 

 and finally to grainy; this was associated with an increase in the length 

 of the cell and the formation of filaments. When the cultures thus modi- 

 fied were placed in media free of the agent, normal, highly motile cells 

 were again produced. 



The mechanism of disintegration of the hyphae of a plant pathogenic 

 fungus Rhizoctonia by an antagonistic fungus Trichoderma as well as 

 by the antibiotic product of the latter has been described by Weindling 

 (989). The hyphae are usually killed in less than 10 hours, as shown by 

 loss of the homogeneous appearance of the protoplasm and of the 

 vacuolate structure of the hyphae, which become empty or appear to be 

 filled with granular material. This is brought out in Figure 29, p. 302. 



ANTIBIOTIC SUBSTANCES AND THE PHYSIOLOGY 

 OF THE BACTERIAL CELL 



Half a century ago Smith (867) emphasized that bacteria growing 

 in mixed cultures undergo temporary and even permanent physiologi- 

 cal modifications. Aside from cell proliferation, the important meta- 

 bolic processes commonly considered to be affected by antibiotic agents 

 were oxygen uptake, acid production, and dehydrogenase activity. Some 

 agents apparently can inhibit cell growth without destroying the viabil- 

 ity of the cells and their capacity for taking up oxygen. 



