Glucose transport in isolated prosthecae of Asticcacaulis biprosthecum

Abstract

Active transport of glucose in prosthecae isolated from cells of Asticcacaulis biprosthecum was stimulated by the non-physiological electron donor N,N,N',N'-tetramethyl-p-phenylenediamine dihydrochloride. Glucose uptake was mediated by two transport systems; the apparent Km of the high-affinity system was 1.8 ,tM and that of the low-affinity system was 34 ,uM. Free glucose accumulated within prosthecae at a concentration 60 to 200 times above that present externally, depending on the Km of the system being observed. The glucose transport system in prosthecae was stereospecific for 1-glucose, and neither methyl aD -glucopyranoside nor 2-deoxyglucose was transported. Uptake of glucose was inhibited by N-ethylmaleimide (NEM) and p-chloromercuribenzoate (PCMB), and the inhibition by PCMB but not by NEM was reversed by dithiothreitol. Glucose uptake was also inhibited by the uncoupling agents 5chloro-3-t-butyl-2'-nitrosalicylanilide (S-13), 5-chloro-3-(p-chlorophenyl)-4'-chlorosalicylanilide (S-6), and carbonyl-cyanide m-chlorophenylhydrazone (CCCP) and by the respiratory inhibitor KCN. Efflux of glucose from preloaded prosthecae was induced by PCMB and KCN, but not by S-13 or CCCP. Glucose uptake was not affected by arsenate or an inhibitor of membrane-bound adenosine triphosphatases, N,N'-dicyclohexylcarbodiimide. The lack of inhibition by these two compounds, combined with the extremely low levels of adenosine 5'-triphosphate present in prosthecae, indicates that adenosine 5'-triphosphate is not involved in the transport of glucose by prosthecae.

The caulobacters: ubiquitous unusual bacteria.

“…This was consistent with the later observation of Porter and Pate that exogenous glucose accumulated by prosthecae was not metabolized (226). The glucose uptake system was characterized in considerable detail with respect to specificity, kinetics, energy dependence, and sensitivity to inhibitors (153). Two systems were distinguished: a high-affinity system (Km = 1.8 ,uM) and a low-affinity system (Km = 34,M).…”

“…Third, the uptake systems (at least in prosthecae) were found to be of low substrate specificity (153). This would seem to allow economical biosynthesis of versatile transport systems suitable for uptake of nutrients available one by one at low concentrations.…”

“…Isolated prosthecae were found to contain some elements of the respiratory and citric acid cycle systems and respiratory energy-dependent uptake systems and to lack the capacity for initial catabolism of sugars and amino acids (122,153,226). The attached appendage is biosynthetically active only in the region of its juncture with the cell body (239).…”

“…On the basis of these studies, it was concluded (153,226) that the prostheca functions as an extension of the cell's absorptive surface and that within the prostheca the absorbed substrates are not dissimilated. In the dilute natural environment, the prostheca would establish a localized concentration gradient allowing diffusion of nutrients toward the catabolically active cytoplasm of the prosthecate cells.…”

Effect of Na + Concentration and Nutritional Factors on the Lag Phase and Exponential Growth Rates of the Marine Bacterium Deleya aesta and of Other Marine Species

“…It has been suggested that microorganisms possessing a limited number of relatively nonspecific transport systems would be better adapted for survival at low nutrient concentrations than ones with specific transport systems, since one system could thereby serve for any of a variety of structurally similar utilizable nutrients (16,24). The results presented here suggest that the opposite situation may prevail.…”