Transport of d ‐Glucose and 3‐ O ‐Methyl‐ d ‐Glucose in the Cyanobacteria Aphanocapsa 6714 and Nostoc strain Mac

1 The cyanobacterium Aphanocapsa 6714 which grows in the dark on D‐glucose, will take up D‐glucose and the analogue 3‐ O ‐methyl‐D‐glucose; uptake of each of these compounds was inhibited competitively by the other and by 6‐deoxy‐D‐glucose. 2 This cyanobacterium accumulated 3‐ O ‐methyl‐D‐glucose up to 100‐fold relative to the medium but did not modify or metabolize it to a significant degree. 3 Intracellular 3‐ O ‐methyl‐D‐glucose was rapidly displaced from Aphanocapsa 6714 by exogenous D‐glucose and 3‐ O ‐methyl‐D‐glucose. 4 Although not characterized to the same extent, D‐glucose and 3‐ O ‐methyl‐D‐glucose uptake by Nostoc strain Mac, another cyanobacterium capable of growth in the dark on D‐glucose, was similar. 5 Other cyanobacteria that do not grow on D‐glucose take up this compound at much lower rates which were unaffected by analogues of D‐glucose that greatly reduced carbohydrate uptake by Aphanocapsa 6714 and Nostoc strain Mac. 6 It is therefore proposed that Aphanocapsa 6714 and Nostoc strain Mac possess a mechanism for the active transport of D‐glucose. The absence of this transport mechanism is suggested as the reason why other strains fail to grow in the dark on this substrate. These latter organisms are therefore naturally cryptic with respect to D‐glucose as a growth substrate.