The Zymomonas mobilis genes encoding the glucose facilitator (glf), glucokinase (glk), or fructokinase (frk) were cloned and expressed in a lacI q -Ptac system using Escherichia coli K-12 mutants deficient in uptake and phosphorylation of glucose and fructose. Growth on glucose or fructose was restored when the respective genes (glf-glk or glf-frk) were expressed. In E. coli glf ؉ strains, both glucose and fructose were taken up via facilitated diffusion (K m , 4.1 mM for glucose and 39 mM for fructose; V max at 15؇C, 75 and 93 nmol min ؊1 mg ؊1 [dry weight] for glucose and fructose, respectively). For both substrates, counterflow maxima were observed.Glucose can be transported in bacteria by carrier systems which belong either to the phosphoenolpyruvate-dependent phosphotransferase system (PTS) type, to proton-or cationlinked permeases, or to ATP-binding cassette (ABC)-type carriers (4, 17). A rare case is the facilitator-type transport (uniport) of glucose in bacteria, exemplified by the system of the gram-negative, strictly fermentative bacterium Zymomonas mobilis. This type of sugar uptake does not use metabolic energy in the form of a proton potential or phosphoenolpyruvate (10, 17). Biochemical evidence for facilitated diffusion of glucose in this organism came from earlier studies (10, 26) and from in vivo nuclear magnetic resonance measurements using 13 C-labeled glucose and xylose as substrates (22). Mainly on the basis of competition studies, it was stated that the glucose facilitator (GLF) of Z. mobilis is a low-affinity, high-velocity carrier which in addition to glucose also transports fructose, xylose, or nonmetabolizable glucose analogs, such as 2-deoxyglucose (10,22,26). The sequence of a presumptive glf gene from Z. mobilis was reported (6), and on the basis of sequence comparison, this open reading frame was found to be a member of a superfamily of sugar transporters from both prokaryotes and eukaryotes (for a recent review, see reference 3). Recently, it was shown that the glf plus glk genes of Z. mobilis complemented an Escherichia coli mutant strain, which was deficient in glucokinase and in glucose uptake, to growth on glucose (23). However, detailed glucose uptake studies using this heterologous system have not yet been reported, nor was the substrate range of this carrier studied further.Plasmid constructions. DNA preparation, cloning, restriction analysis, and transformation were done according to established methods (20). Chromosomal DNA from Z. mobilis ZM6 (27) was prepared according to the lysozyme freeze-thaw method (12). The Z. mobilis gene glf from strain CP4 (15) had been fortuitously cloned in our laboratory as a 2.3-kb HindIII DNA fragment (pZY600) and shown to confer Glf activity to E. coli Glc Ϫ strains (18). DNA sequencing established the identity with the glf sequence reported earlier (6). The glf gene was amplified by PCR (16) using plasmid pZY600 as a template, and glk (6) and frk (31) genes were amplified from chromosomal DNA of Z. mobilis ZM6. The PCR primers for glf wer...

Summary — Although pesticides are assessed before registration for whether or not they are harmful to bees there is little information available about the exposure of individual bees during pesticide application under practical conditions. We investigated the exposure of bees in real application situations in flowering apple orchards and Phacelia fields (Phacelia tanacetifolia Benth) in the years 1992-1997. In application trials we used a fluorescent tracer (sodium-fluorescein) at a dose rate of 20 g per 10 000 m 2 sprayed area. Bees were collected at the closed hive entrance over a period of 20-30 min in 5-min intervals. The deposit was individually measured on about 100 individual bees per sampling point. Mean initial deposit per trial varied from 1.62 to 20.84 ng/bee in apple orchards (nine trials) and from 6.34 to 35.77 ng/bee in Phacelia crops (five trials) with very few highly contaminated individuals. Earlier investigations prove these magnitudes to be realistic. The data give information concerning maximum exposure of individual bees. Results contribute to the discussion of altering concentration-based dose recommendations to product quantities related to the sprayed area.Apis mellifera / pesticides / spraying / exposure

The vegetation of the Nylsvley Nature Reserve in the Transvaal Mixed Bushveld is classified hierarchically by the Braun-Blanquet Method of vegetation survey. The vegetation is seasonal grassland and deciduous savanna with four floristically distinct major groups of plant communities: (I) grasslands and broad-leaved savannas on non calcareous sandy soils on elevated sandstone and felsite areas; (2) microphyllous thorn savannas on calcareous, clayey, bottomland alluvial soils and termitaria thickets; (3) grassland and thorn savanna on calcareous self-mulching vertic soils; and (4) secondary communities on long abandoned native settlements and recently ploughed land. Seven primary communities with 12 community variations and 4 subvariations, and three secondary communities are described on the basis of 216 releves. The survey was carried out at two levels of detail, an ecosystem study area in the broad-leaved savanna being surveyed in more detail, floristically and structurally, than the rest of the Reserve.

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