Uptake and Metabolism of d-Glucose by Neocosmospora vasinfecta E. F. Smith

Abstract

Freshly harvested, nongrowing mycelium of Neocosmospora vasinfecta E. F. Smith rapidly absorbed exogenous glucose but converted a greater proportion to trehalose and glucan than to respiratory CO2. This effect was accentuated in mycelium preincubated for 3.5 hours in water before exposure to glucose. Glucose was absorbed via two uptake systems, both apparently constitutive, with apparent Km values for glucose of 0.02 mM (high affinity) and 2 mM (low affinity). The glucose derivative 3-0-methylgloucose (3-0-MG) was also absorbed by two apparently constitutive systems with apparent Km values for 3-0-MG of 0.065 mM and 1.9 mM. Absorption of 3-0-MG by both freshly harvested and preincubated mycelium led to its accumulation. Freshly harvested mycelium lost accumulated 3-0-MG rapidly to water, whereas preincubated mycelium showed reduced or no leakage. The reduction in leakage due to preincubation was prevented by 5 ag/nd cycloheximide in the preincubation medium. Glucose competitively inhibited 3-0-MG uptake via the high affinity system and induced loss of previously accumulated 3-0-MG from preincubated mycelium. The uptake of both glucose and 3-0-MG was associated with a transient alkalinization of the uptake medium. It is concladed that uptake of both glucose and 3-0-MG by at least the high affinity system is energy-linked and probably mediated by proton cotransport.Soluble sugars are among the most widely available carbon sources for the growth of microorganisms, and indeed for all living cells. The utilization of externally supplied sugars is dependent upon the presence of specialized sugar-absorption mechanisms in the cell-surface membrane, as well as on the presence of the appropriate intracellular enzymes. Such absorption mechanisms, intensively studied in bacterial cells and membrane preparations (e.g. refs. 2 and 9), have been described in a variety of plant cells and also in fungi (3, 14, 16, 20-23, 25, 28).Metabolic influences on sugar transport are evident from many of these studies. Conversely, sugar transport should influence, directly or indirectly, many other cellular processes. A novel interaction between absorbed sugars and fluxes of the chloride ion was recently observed in the mycelial ascomycete Neocosmospora vasinfecta (10,11,13). This, together with an almost total lack of information on glucose uptake and metabolism in this organism, prompted the present studies. MATERIALS AND METHODSThe organism and the methods of growth and harvesting were as previously described (6). The sole carbon source in the growth medium was i-glucose, provided at an initial level of 3% (167 ' Supported by Operating Grant NRC A2813 from the National Research Council of Canada. mM). The washed mycelium was resuspended in demineralized H20 at a density of 0.3 to 0.7 mg dry matter/ml and aerated with moist air. From this mycelial suspension, samples of about 30 to 70 mg dry weight were withdrawn either immediately ("fresh" mycelium) or after a period of aeration ("preincubated" mycelium). Normally, preincubation ...

Characteristics of glucose uptake by glucose- and NH4-limited grown Penicillium ochrochloron at low, medium and high glucose concentration

“…1a). This was also reported by other authors (Schneider and Wiley, 1971;Budd, 1976). For P. ochrochloron this was true for non-growing mycelium (doubled uptake rate after 6 h) as well as for growing mycelium (tripled uptake rate after 6 h).…”

“…To deplete the mycelium of extracellular glucose many authors used a starvation period from several minutes to a few hours before starting the glucose uptake assay (Budd, 1976;Torres et al, 1996;Papagianni et al, 1999;MacCabe et al, 2003). Our results show that the longer the starvation period the higher was the observed glucose uptake rate (Fig.…”