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Fig. 2.6 The accumulation
of salicylic acid during
iron-deficient growth of
Mycobacterium smegmatis .
Light bars iron-sufficient
growth conditions (controls)
and dark bars iron-deficient
growth [ 73 , 113 ]
salicylic acid. Alan Snow then wrote to us to ask if the detected acid was indeed
salicylate; could it not be 6-methylsalicylate? And, indeed, so it turned out to be.
Snow's concern over the correct identification of salicylic acid arose from his
realization that, although salicylate was a common moiety in most mycobactins,
in some mycobactins (see Fig. 2.4 ) and notably in mycobactin P from M phlei ,
it was 6-methylsalicylate that occurred. It therefore seemed odd to Snow that
we had recorded finding salicylate in the extracellular medium of this species as
this would imply a metabolic puzzle. However, by using more selective solvent
systems for paper chromatography, we then showed that the original conclusion
had been too hasty. We had failed to double-check; M. phlei did indeed secrete
6-methylsalicylate into the culture medium and not salicylic acid.
This useful contact with Alan Snow then immediately brought our attention to
the mycobactins which, at that point, were just emerging as probably having sig-
nificant roles in iron metabolism. Although the biochemical connection between
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