Pfizer Handbook of Microbial Metabolites 6 



normal cell wall synthesis. Although we were unable to pursue 

 this fascinating topic, an appendix of literature titles on the 

 structure of higher molecular weight products of microorgan- 

 isms and their cell wall structures has been attached. 



In comparing the structures of the hundreds of microorgan- 

 ism metabolites which have been characterized thoroughly it is 

 well to remember that the statistical emphasis may be mislead- 

 ing. It is likely that insoluble compounds, lipophilic materials 

 easily extractible from aqueous cultures, organic acids which 

 can be precipitated as insoluble salts and pigments that are 

 easily observed have probably received a disproportionate degree 

 of attention. The same, of course, could be said for antibiotics, 

 which are conspicuous for their biological activity. The most 

 difficultly discoverable metabolites are the relatively inconspicu- 

 ous, low molecular weight, hydrophilic, perhaps phosphorylated 

 compounds. Eventually many of the precursors of more elabo- 

 rate metabolites will be found in this category. 



Also, the metabolites of certain microorganisms have re- 

 ceived disproportionate study. Examples are Mycobacterium 

 tuberculosis, the tuberculosis pathogen, and Claviceps purpurea, 

 the ergot fungus. By permission of Dr. Esmond R. Long and 

 the Williams and Wilkins Publishing Company a review of the 

 known metabolites of the former organism has been reproduced 

 as an appendix, although many of the compounds included in 

 this review are also to be found in the body of the text and others 

 in the text which were not in the review. Also an appendix 

 dealing with the confusing subject of microbial carotenoids has 

 been attached by permission of the Chemical Publishing Com- 

 pany and of Professor T. W. Goodwin of the University of Liver- 

 pool. 



Referencing is not exhaustive. It was kept on the lean side 

 intentionally, and we feel that it is more useful that way. On 

 some topics the literature is vast. It would have been virtually 

 impossible to offer complete referencing of, for example, acetic 

 acid, or even of some of the more complex substances such as 

 the gibberellins or ^-carotene. Much attention has been given 

 to choice of useful references, although no doubt there have 



