The steady-state levels of zinc in Candida utilis yeast grown in continuous culture under conditions of zinc limitations are <1nmol Zn2+/mg dry weight of cells. Unlike carbon-limited cells, zinc-depleted cells from a zinc-limited chemostat possess the capacity to accumulate and store zinc at levels far in excess of the steady-state level of 4 nmol/mg dry biomass observed in carbon-limited chemostat cultures. Zinc uptake is energy-dependent and apparently undirectional since accumulated 65Zn neither exists from preloaded cells nor exchanges with cold Zn2+. The transport system exhibits a high affinity for Zn2+ (Km =.36micrM) with a Vmaxof 2.2 nmol per minute per milligram dry weight of cells. Growth during the period of the uptake assay is responsible for the apparent plateau level of 35 nmol Zn2+/mg dry weight of cells achieved after 20-30 min in the presence of 65Zn at pH 4.5 and 30 degrees C. Inhibition of growth during the uptake assay by cycloheximide results in a biphasic linear pattern of zinc accumulation where the cellular zinc is about 60 nmol/mg dry weight after 1 h. The enhanced level of accumulated zinc is not inhibtory to growth. Zinc-depleted C. utilis contains elevated amounts of polyphosphate and this anionic evidence does not allow discrimination between possible regulation of zinc homestasis either by inhibitions of zinc efflux through control of the membrane carrier or by control of the synthesis of a cytoplasmic zinc-sequestering macromolecule.

Candida utilis NRRLY -900 was grown in aerobic continuous culture in a minimal salts medium with sucrose (1% w/v) as the carbon source. increasing the concentration of zinc in the medium from 2.3 microM results in an increase in the apparent critical dilution rate from 0.3 to 0.47h-1, and in the maximum biomass productivity form 1.5g dry weight per litre per hour (at D=0.33-1) to 2.56g per litre per hour (at D = 0.45-1). The maximum steady-state level of cell-associated zinc (at D = 0.4-1) is 4nmol Zn2+/mg dry weight, during carbon-limited growth, and about 9mumol Zn2+/mg dry weight when FeCI3 is omitted form the medium. At input zinc concentrations <20microM, the cellular zinc concentration decreases linearly in proportion to the input zinc concentration and at <4.5microM Zn2+ the culture becomes zinc-limited. Zinc-limitation results in a decrease iun the growth yield Ysurcosefrom 0.54 to 0.38 cells/g sucrose consumed, and Y0 from 22 to 13g cells/g-atom 02, suggesting an altered efficiency of energy metabolism. The composition of the culture biomass with respect to protein and RNA content is not affected by zinc limitation.

The biosynthesis of a thermogelable, extracellular homo-beta-(1 leads to 3)-glucan called "curdlan," has been studied in batch and continuous cultures of Alcaligenes faecalis var. myxogenes. Curdlan production is associated with the poststationary phase of a nitrogen-depleted, aerobic batch culture. Exopolymer is not detected in single-stage, carbon-limited continuous cultures but curdlan can be isolated from the effluent of a nitrogen-limited chemostat operating at a dilution rate (D) of less than 0.1 h-1. A spontaneous variant of strain ATCC 21680 was isolated and found to be compatible with long-term, nitrogen-limited chemostat culture. The specific rate of curdlan production is approximately four times higher in poststationary batch cultures than in single-stage continuous fermentations. The product yield (Yp/S) associated with batch processing (nongrowing cultures) is approximately 0.5 g curdlan/g glucose, with CO2 being the only detectable by-product.

Lysophosphatidylinositol acyltransferase utilizing arachidonoyl CoA and lysophosphatidylcholine acyltransferase utilizing linoleoyl CoA were measured in subcellular fractions of rat brain. In general, the distribution of activities paralleled that of NADPH--cytochrome c reductase. It is concluded that the endoplasmic reticulum is the major site of these acyltransferase activities in rat brain.

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