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Abstract: The major yeast plasma membrane H+-ATPase is encoded by the essential PMA 1 gene. The PMA 2 gene encodes an H+-ATPase that is functionally interchangeable with the one encoded by PMA 1 , but it is expressed at a much lower level than the PMA 1 gene and it is not essential. Using genetically manipulated strains of Saccharomyces cerevisiae that exclusively synthesize PMA1 ATPase or PMA2 ATPase under control of the PMA1 promoter, we found that yeast cultivation under mild copper stress leads to a similar activation of PMA2 and PMA1 isoforms. At high inhibitory copper concentrations (close to the maximum that allowed growth), ATPase activity was reduced from maximal levels; this decrease in activity was less important for PMA2 ATPase than for PMA1 ATPase. The higher tolerance to high copper stress of the artificial strain synthesizing PMA2 ATPase exclusively, as compared to that synthesizing solely PMA1 ATPase, correlated both with the lower sensitivity of PMA2 ATPase to the deleterious effects of copper in vivo and with its higher apparent affinity for MgATP, and suggests that plasma membrane H+-ATPase activity plays a role in yeast tolerance to copper.

Abstract: Cells of Saccharomyces cerevisiae exibited a more active plasma membrane H+-ATPase during growth in media supplemented with CuSO4 concentrations equal to or below 1 mM than did cells cultivated in the absence of copper stress. Maximal specific activities were found with 0.5 mM CuSO4. ATPase activity declined when cells were grown with higher concentrations up to 1.5 mM (the maximal concentration that allowed growth), probably due to severe disorganization of plasma membrane. Cu2+-induced maximal activation was reflected in an increase of V max (approximately threefold) and in the slight decrease of the K m for MgATP (from 0.93 ± 0.13 to 0.65 ± 0.16 mM). The expression of the gene encoding the essential plasma membrane ATPase (PMA1) was reduced with a dose-dependent pattern in cells grown with inhibitory concentrations of copper, while the weakly expressed PMA2 gene promoter was moderately more efficient in cells cultivated under mild copper stress (1.5-fold maximal activation). ATPase was activated by copper despite the slightly lower content of ATPase protein in the plasma membrane of Cu2+-grown cells and the powerful inhibitory effect of Cu2+ in vitro.

A: bstract: In the absence of inhibitory concentrations of copper, the photoautotrophic growth of Chlorella vulgaris INETI58C at 27°C exhibited a higher specific growth rate and reached a higher maximal concentration of biomass, under irradiance of 150 W m−2, compared with 100 W m−2. However, when the mineral growth medium was supplemented with CuSO4 (range 40–80 μM), algal growth was significantly affected at the higher light intensity. In the presence of Cu2+, the increase in dry biomass was uncoupled from the increase in cell concentration since more than 16 autospores gathered together, inside the enlarged mother cell, suggesting that copper arrested the normal bursting of the mother cell wall. At the higher irradiance, growth medium supplementation with 80 μM of CuSO4 led to bleaching of photosynthetic pigments. No growth was observed, while, under the lower irradiance, growth was only slightly inhibited. Results clearly showed that copper toxicity to growth of C. vulgaris was strongly influenced by light intensity. Higher light intensity elicits lethal or sublethal Cu2+ damage at concentrations lower than the threshold level for damage at lower light intensities. Cu2+ may elicit lethal or sublethal light damage at irradiances lower than the threshold level for unpolluted aquatic systems.

Ethanol-induced death rate was higher for cells ofSaccharomyces bayanusorKluyveromyces marxianusin spanse suspensions (2×104cells/ml) compared with dense suspensions (2×105–2×107cells/ml). Specific death rates of sparse suspensions decreased to values similar to dense suspensions if ethanol-induced death experiments were undertaken in the media obtained after harvesting the cells previously incubated with the same lethal concentration of ethanol.

Temperatures as high as 36°C and 40°C did not negatively affect the ethanol productivity of Jerusalem artichoke (J.a.) juice batch fermentation and the final concentrations of ethanol were close to those produced at lower temperatures. At higher process temperatures (36–40°C), ethanol toxicity inKluyveromycesmarxianuswas less important during the fermentation of J.a. juice as compared with a simple medium. In simple medium, the heat-sticking of fermentation was observed and the percentage of unfermented sugars steeply increased from 28°C up to 40°C.

A non-axenic strain of the microalgaBotryococcus brauniiKützing, isolated from a small lake in Portugal, when cultured at 25°C in mineral medium and under continuous illumination, showed a poor production of hydrocarbons (5% of the dry biomass) but excreted remarkably high quantities of an exopolysaccharide (4–4.5g/l) into the medium. The production of soluble polysaccharide with galactose, fucose and uronic acid residues, follows growth. The role of the mucoid contaminating bacteria in polysaccharide production in the mixed culture was unproven.

Ethanol inhibited in a non-competitive way the fructose transport system of Kluyveromyces fragilis (marxianus). Vmax, the transport capacity, decreased exponentially with ethanol concentration. The exponential inhibition constant, 0.75 l/mol, was higher than the one obtained earlier for Saccharoomyces cerevisiae.

The maximum temperature for growth of a strain of Kluyveromyces fragiliswas depressed by increasing ethanol concentration from its normal value around 45 °C to 26.5 °C at 6.4% (w/v) of ethanol. Ethanol enhanced thermal death by increasing ΔS≠, the entropy of activation of thermal death. Entropy coefficients of 7.6 entropy units per mol of ethanol per liter of medium for unadapted cells and of 5.7 for adapted cells ware obtained.

Seven Gram-negative bacterial strains, capable of using lupanine, the predominant quinolizidine alkaloid in white lupin, as sole carbon and energy source, were isolated from soil in whichLupinus albus andL. luteus had been grown. A metabolic profile system (BIOLOG) identified only three of the seven isolates, two asXanthomonas oryzae pvoryzae E and one asGluconobacter cerinus. The maximum specific growth rates of the seven isolates when incubated at 27°C in a medium containing as sole carbon source 2 g L-1 of lupanine, ranged from 0.05 to 0.13 h-1 and the concentration of dry biomass at the stationary phase ranged from 0.7 to 1.1 g L-1. Unidentified strains IST20B and IST40D exhibited the highest maximum specific growth rates (0.13h-1), removed 99% of the initial lupanine after 30 h of incubation, and the dry biomass yields did not exceed 0.4 g per g lupanine consumed. Strain IST20B is of potential use forL. albus debittering because, after 32 h growth in aqueous extracts ofL. albus, 85% of initial alkaloids were removed while the concentration of soluble protein was only reduced by 8%.

Summary: In strain IGC 4052 of the amylolytic yeast Lipomyces kononenkoae growing in starch-limited chemostat cultures the critical dilution rate was reduced to about half of its theoretical value due to severe catabolite repression of amylase formation while its value in a repression-resistant mutant was near its theoretical value. The enzyme yield coefficients and the specific production rates of α-amylase and glucoamylase passed through maxima at intermediate dilution rates. The shapes of the respective curves were partly determined by catabolite repression (parent strain) or its absence (mutant strain) while induction did not seem to play to role. An additional growth-linked regulatory mechanism seemed to be involved. The use of continuous culture as compared with batch culture, increased the maximum biomass productivity by a factor of 2.2 in the mutant strain and by a factor of 1.4 in the parent strain.