| Abstract: | Navicula pelliculosa and an associated Flavobacterium sp. were isolated from the epiphyton of Scirpus maritimus, an emergent macrophyte growing in a brackish drainage dyke. Both micro-organisms possessed active transport systems for glucose uptake. In N. pelliculosa the transport system was fully induced in the dark in the absence of glucose, and subsequently inactivated when transferred to the light in the absence of the substrate. The presence of glucose during the dark induction period prevented the achievement of maximum specific activity of the transport system, while incubation at a high light intensity with or without the presence of the substrate resulted in a very marked inhibition of glucose uptake. Inhibition in the light was partially offset by blocking photosynthetic electron flow with 3'(3,4 dichlorophenyl)1'1' dimethyl urea. The transport system accumulated 3-O-methyl glucose against a concentration gradient and was highly specific for glucose as there was no competition by most of the other sugars tested. However, 6-deoxyglucose was taken up instead of glucose and this suggested that glucose was transported in a non-phosphorylated state, whereas inhibition of glucose transport activity with dicyclohexylcarbodimide implicated the involvement of an adenosine triphosphatase on the cell membrane. Inhibitors of oxidative phosphorylation tetrachlorosalicylaniline and carbonylcyanide m-chlorophenylhydrazone also inhibited glucose transport activity. The affinity of the diatom for glucose was greater than that shown by the bacterium, but the Km for glucose transport, 1.5x10-5M was too high to allow effective removal of glucose at in situ concentrations. |
