grown to exponential phase or stationary phase in medium with a low initial concentration of haemin (0·25 μg/ml) was virtually devoid of cytochromes. Compared with bacteria grown in the presence of excess haemin (10 μg/ml), the haemin-limited organisms failed to respire formate and succinate and, generally, the respiratory rates with other substrates were reduced. However, growth rates were not affected by the haemin supply. Haemin-limited growth was associated with a reduced efficiency of glucose utilisation, in terms of glucose growth yields, and affected the net levels of excreted organic acids. Haemin limitation resulted in reduced acetate and increased succinate accumulation in the culture medium and the novel presence of d-lactate. These results indicate that, in contrast to the phenotype expressed during conventional cultivation of , the haemin-limited phenotype, which may be expressed , is characterised by a lack of cytochromes and a shift towards a more anaerobic type of metabolism.


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