494 LIGHT AND LIFE 



and Engelmann (46, 47) discovered the purple bacteria that carried 

 on a kind of photosynthesis which apparently liberated no oxygen. 

 Neither discovery was fidly appreciated in its day; their effect was 

 not that of an explosive charge, but rather that of a time-bomb that 

 did its devastation later. 



The far-reaching consequences of Winogradsky's discovery were 

 ignored by most of his contemporaries, who persisted in their belief in 

 what Lebedev, one of Winogradsky's few adherents, called, with re- 

 markable insight, a "methodological error" (89) . Lebedev pointed 

 out that since the discovery of chemosynthetic bacteria revealed that 

 CO2 assimilation can also occur in the dark, it was no longer per- 

 missible to consider CO2 assimilation as peculiar to photosynthetic 

 cells. What was peculiar to these cells was their ability to use light 

 as a source of energy for that process, whereas chemosynthetic or- 

 ganisms obtained the needed energy by oxidation of chemical sub- 

 strates. COo assimilation itself was in both cases an endergonic process, 

 independent of light. 



But Lebedev's views were too advanced to gain wide acceptance. 

 This was delayed for over forty years. Only after the discovery of the 

 Wood-Werkman reaction and the use of tracer isotopes by many in- 

 vestigators in the past twenty years, did it become generally recognized 

 that all living cells, photosynthetic and non-photosynthetic, auto- 

 trophic and heterotrophic, assimilate COo, but differ as to the sources 

 of energy that must be expended during this process. 



The full impact of the discovery of photosynthetic bacteria was 

 also delayed for about forty years. There was at first no compelling 

 evidence for, and great resistance to, the notion that photosynthesis 

 could proceed without oxygen evolution. The view that CO2 assimila- 

 tion always involved a liberation of oxygen was so firmly entrenched 

 that it was even extended to the dark COo assimilation by chemo- 

 synthetic bacteria. For example, Lebedev's (87-89) early conclusion 

 about the fundamental similarity of COo assimilation in chemo- 

 synthetic and photosynthetic organisms rested on his belief that hy- 

 drogen bacteria use molecular oxygen, released by the decomposition 

 of COo for the oxidation of hydrogen gas. The idea, therefore, of 

 photosynthesis without oxygen evolution seemed a contradiction of 

 terms until the basic facts of bacterial photosynthesis were experi- 

 mentally unravelled ami clearly interjireted by the incisive work of 

 van Niel (158, 159) . It then became evident that bacterial photo- 

 synthesis proceeds anaerobically without oxygen evolution, and the 



