A History of Iron Metabolism in the Mycobacteria - Iron Acquisition by the Genus Mycobacterium - page 20

the mycobactins according to differences in the R 2 , R 3 , R 4 and R 5 nuclear sub-
stituents (Fig. 2.4 ) and HPLC separated them mainly on the basis of differences in
the length of the alkyl chain at R1. Bosne et al. [ 54 ] subsequently simplified this
procedure by adding EDDA as an iron chelating agent into liquid culture medium
to produce iron-deficient growth conditions and thus a stimulation of mycobactin
production. They used this method to identify 65 strains of M. fortuitum and M.
chelonae according to the type of mycobactin being produced [ 55 ].
Using their simplified method of cultivation, Hall and Ratledge [ 56 ] analyzed
the mycobactins of 39 strains of mycobacteria, principally as a means to determine
if the mycobactins “…may be useful as a chemotaxonomic marker in the myco-
bacteria”. They were indeed able to confirm the validity of the hypothesis and
found that the mycobactins were strongly conserved molecules showing strong
intra-species consistency and could be therefore used as chemotaxonomic charac-
ters of high discriminatory power. The structures of the new mycobactins were not
determined, however. Using the same method, Leite et al. [ 57 ] were able to iden-
tify various clinical mycobacterial isolates from their mycobactins and Barclay et
al. [ 58 ] were able to suggest an even more rapid method of detecting and identify-
ing mycobacteria using 55 Fe-labelling of the mycobactins. A list of species pro-
ducing mycobactin is given in Table 2.2 ; it is probably reasonable to conclude that
most species of mycobacteria will be found to produce a mycobactin but there are
some exceptions.
Rich Hall went on to apply his techniques to other groups of mycobacteria,
showing equivalence of the mycobactins from M. senegalense, M. farcinogenes
and M. fortuitum but a distinction from that from Nocardia farcinica [ 59 ]. He also
examined the mycobactins from seven strains of armadillo-derived mycobacte-
ria (ADM) [ 59 ] that were of interest because of the association of M. leprae with
the armadillo and because, but unlike M. leprae , these bacteria could be grown in
laboratory medium. The ADM were found to be a heterogeneous group; four of
them produced materials that resembled the mycobactins from M. avium - intracel-
lulare - scrofulaceum (MIAS) complex of mycobacteria suggesting that they could
be assigned to this taxonomic grouping.
The MIAS group of mycobacteria had earlier been studied by Barclay and
Ratledge [ 61 ] for their mycobactins which were of particular interest as some
freshly isolated strains of M. avium had been reported as being dependent on
mycobactin for growth [ 62 ]. The presence of mycobactins in strains of M. avium
had, though, been initially reported by Ratledge and McCready [ 63 ]. Barclay and
Ratledge [ 61 ] found that only those strains of M. avium that could grow with-
out mycobactin could produce it themselves but three strains, initially unable to
grow unless mycobactin was added to the growth medium, were eventually able
to grow without it and now produced small quantities themselves. This indi-
cated that mycobactin biosynthesis was being strongly repressed and then slowly
reversed during the subsequent adaptation rather than being indicative of a perma-
nent genetic deletion. The structure of mycobactin Av from M. avium and other
MIAS strains was subsequently determined by Barclay et al. [ 64 ] (Fig. 2.4 ). In
addition, the same type of mycobactin was also isolated from three strains of M.