Effect of extracellular polymeric substances (EPS) on Pb2+ accumulation by Aureobasidium pullulans

In Pb²⁺ accumulation by Aureobasidium pullulans, the time to reach an equilibrium state was not dependent on the initial cell dry weight. The Pb²⁺ accumulation capacity was increased from 56.9 to 215.6 mg Pb²⁺/g cell dry weight as the biomass was stored from 1 to 53 days, and correlated with the amount of excreted extracellular polymeric substances (EPS). It was observed that Pb²⁺ accumulated only on the surface of the intact cells of A. pullulans due to the existence of EPS, whereas Pb²⁺ penetrated into the inner cellular parts of the EPS-extracted cells.     

A novel fiber optic probe for on-line monitoring of biomass concentrations

A fiber optic biomass probe for on-line measurement of biomass concentration was designed. Results of biomass concentration monitoring experiments with suspended cells of baker's yeast as well as an experimental cultivation of S. cerevisiae are presented. The device was able to observe biomass concentrations of 14 g l^у S. cerevisiae. By means of correlations the capability of estimating the biomass concentration from the probe signal is demonstrated.     

Improved extracellular transferase enzyme production by Aspergillus foetidus for synthesis of isooligosaccharides

Aspergillus foetidus was used to produce transferases that can be utilized in the synthesis of isooligosaccharides. Maltose and corn steep liquor were found to be the best carbon and nitrogen substrates at optimum concentration of 1% and 3% respectively. Surfactant Tween 80 and metal ions including Fe²⁺, Zn²⁺, Mg²⁺ and Cu²⁺ were found to have no obvious effect on the enzyme productivity. Uncontrolled pH starting with an initial value of 5.0 gave the highest transferase productivity compared with pH controlled at constant levels and control after natural fall. The optimum temperature was found to be 30v°C. Enzyme activity increased 8 fold in reactors, with better aeration and agitation condition, as compared to shake flask. The morphology of the organism was highly dependent on the nitrogen source and had great influence on enzyme productivity.     

Joint aerobic biodegradation of wastewater from table olive manufacturing industries and urban wastewater

Wastewater generated in the elaboration of table olives has been treated using activated sludge from a municipal wastewater plant after adequate acclimation. To avoid bactericide properties of some chemical structures present in this type of effluents, synthetic urban wastewater has been used to dilute the original wastewater. The main parameters affecting efficiency of biological processes have been studied. Thus, initial biomass concentration, temperature up to 303 K (upper working temperature limit = 313 K) and initial substrate concentration exerted a positive influence on COD degradation rate. The optimum pH was found to be around 7, experiencing a slight inhibition on cell activity at pH 4. Under the experimental conditions investigated other parameters like polyphenol content, absorbance at 254 nm and total organic carbon were also reduced to some extent. Only nitrates amount was increased after the biological process took place. A kinetic model based on Monod equation was proposed and applied to experimental results. The maximum specific growth rate was calculated by means of the aforementioned kinetic model. The value of this parameter as a function of temperature was fitted to an Arrhenius expression, w_max = 9.43 2 10¹⁰ exp(72021/RT) h^у (R in J mol^у K^у283 K < T < 303 K, pH , 7-10).     

Cation (K+, Mg2+, Ca2+) exchange in Pb2+ accumulation by Saccharomyces cerevisiae

The relationship between Pb²⁺ accumulation and cation (K⁺, Mg²⁺, Ca²⁺) release in Saccharomyces cerevisiae was extensively investigated. As Pb²⁺ accumulation proceeded, the release of cellular metal ions such as K⁺, Mg²⁺ and Ca²⁺ was concomitantly released within 24 h, thereafter Pb²⁺ penetrated into the inner cellular parts and consequently plasmolysis of the cell was observed by TEM analysis. Pb²⁺ accumulation process in S. cerevisiae after 24 h was metabolism-independent because of the absence of cell viability. As the cell storage time was prolonged, the released amount of K⁺ was markedly increased, while the amount of accumulated Pb²⁺ was nearly constant regardless of cell storage time and the time required to reach an equilibrium state was shortened. The autoclaved cells had less Pb²⁺ accumulation capacity than the untreated cells, and the amounts of released K⁺ and Mg²⁺ were very low due to the denaturation of cell surface and cell membrane.     

Elevated CO2 influences nutrient availability in young beech-spruce communities on two soil types

The objectives of this study were to investigate how different soil types and elevated N deposition (0.7 vs 7 g N m^-2a^-1) influence the effects of elevated CO₂ (370 vs 570 µmol CO₂ mol^-1) on soil nutrients and net accumulation of N, P, K, S, Ca, Mg, Fe, Mn, and Zn in spruce (Picea abies) and beech (Fagus sylvatica). Model ecosystems were established in large open-top chambers on two different forest soils: a nutrient-poor acidic loam and a nutrient-rich calcareous sand. The response of net nutrient accumulation to elevated atmospheric CO₂ depended upon soil type (interaction soil 2 CO₂, P<0.05 for N, P, K, S, Ca, Mg, Zn) and differed between spruce and beech. On the acidic loam, CO₂ enrichment suppressed net accumulation of all nutrients in beech (P<0.05 for P, S, Zn), but stimulated it for spruce (P<0.05 for Fe, Zn) On the nutrient-rich calcareous sand, increased atmospheric CO₂ enhanced nutrient accumulation in both species significantly. Increasing the N deposition did not influence the CO₂ effects on net nutrient accumulation with either soil. Under elevated atmospheric CO₂, the accumulation of N declined relative to other nutrients, as indicated by decreasing ratios of N to other nutrients in tree biomass (all ratios: P<0.001, except the N to S ratio). In both the soil and soil solution, elevated CO₂ did not influence concentrations of base cations and available P. Under CO₂ enrichment, concentrations of exchangeable NH₄⁺ decreased by 22% in the acidic loam and increased by 50% in the calcareous sand (soil 2 CO₂, P<0.001). NO₃^- concentrations decreased by 10-70% at elevated CO₂ in both soils (P<0.01).     

Salt, nutrient uptake and transport, and ABA of Populus euphratica; a hybrid in response to increasing soil NaCl

The uptake and transport of salt ions (Na⁺, Cl^-), macronutrients (K⁺, Ca²⁺, Mg²⁺) and abscisic acid (ABA) response to increasing soil salinity were examined in 2-year-old seedlings of Populus euphratica and a hybrid, P. talassica Kom 2 (P. euphratica + Salix alba L.). Leaf burn symptoms appeared in the hybrid after 8 days of exposure to salinity when soil NaCl concentration increased to 206 mM, whereas P. euphratica exhibited leaf damage after day 21 when soil NaCl exceeded 354 mM. Leaf necrosis was the result of excess salt accumulation since the injury followed an abrupt increase of endogenous salt levels. Compared with the hybrid, P. euphratica exhibited a greater capacity to exclude salt ions from leaves under increasing salinity, especially Cl^-. Salt treatment altered nutrient balance of the hybrid, leaf K⁺, Ca²⁺ and Mg²⁺ concentrations significantly declined and the same trends were observed in roots with the exception of K⁺. Although K⁺ levels decreased in salinised P. euphratica, increasing salinity did not affect the levels of Ca²⁺ and Mg²⁺ in leaves, but did increase the uptake of these nutrients when salt stress was initiated. NaCl-induced increase of ABA concentration in xylem sap [ABA] was observed in the two tested genotypes, however xylem [ABA] increased more rapidly in P. euphratica and a fivefold increase of xylem [ABA] was recorded after the first day of exposure to salt stress. Therefore, we conclude that the increase of Ca²⁺ uptake may be associated with the rise of ABA, and thus contributes to membrane integrity maintenance, which enables P. euphratica to regulate uptake and transport of salt ions under high levels of external salinity in the longer term.     

外源一氧化氮对铅胁迫下小麦种子萌发及幼苗生理特性的影响

利用室内水培实验,研究了外源一氧化氮（NO）供体硝普钠（SNP）对Pb²⁺处理下小麦（Triticum aestivum L.）种子萌发、幼苗生长及相关生理指标变化的影响。结果表明,Pb²⁺处理使小麦种子发芽势、发芽率、幼苗根长和茎长均显著降低,诱导叶绿素a、叶绿素b含量减少及叶绿素荧光参数F_v/F_m和F_v/F_o的比值减小,25 μmol·L^-1 SNP明显缓解Pb²⁺胁迫对种子萌发及幼苗生长的抑制作用,提高Pb²⁺胁迫下叶绿素a、叶绿素b含量及F_v/F_m和F_v/F_o的比值,而100 μmol·L^-1SNP无明显缓解作用。此外,25和100 μmol·L^-1SNP诱导Pb²⁺胁迫下小麦幼苗叶片过氧化氢酶（CAT）活性增强和可溶性蛋白含量增多,但100 μmol·L^-1SNP处理降低了过氧化物酶（POD）活性。结果说明,外源NO促进Pb²⁺胁迫下小麦种子萌发及幼苗生长,提高叶绿素和可溶性蛋白含量,诱导CAT活性升高,从而增强小麦对Pb²⁺胁迫的适应性。     

沉水植物菹草在低温条件下对重金属Cu、Pb、Zn的吸附和富集

在10℃的较低温度条件下,研究了冬春季节生长旺盛的沉水植物菹草(Potamogeton crispus L.)对重金属离子Cu²⁺,Pb²⁺,Zn²⁺的生物吸附特征及解吸情况,对不同初始浓度重金属水体中的重金属离子去除率情况,以及在此过程中菹草各器官(叶、茎、根茎、根)对重金属离子的富集情况。结果表明,菹草对Cu²⁺,Zn²⁺的吸附在20 min内达到平衡,对Pb²⁺的吸附在50 min内达到平衡,吸附动力学结果符合伪二级动力学方程,决定系数分别达1,1,0.997 8。Freundlich等温线可较好地拟合菹草吸附Cu²⁺,Pb²⁺,Zn²⁺的过程,Cu²⁺,Pb²⁺,Zn²⁺的吸附容量分别达到66.900 6,26.543 0,30.371 8 mg·L^-1。以去离子水作洗脱剂,解吸液中3种重金属离子浓度均低于仪器检出限(0.01 mg·L^-1),解吸程度微弱。投放菹草后,随着初始处理浓度的升高,水体Cu²⁺的去除率先降低后升高,Pb²⁺的去除率的变化趋势与Cu²⁺类似。Zn²⁺去除率则随水体Zn²⁺初始浓度的升高而逐渐升高。菹草各器官对水体3种重金属离子的富集能力不同,排序为Cu²⁺＞Zn²⁺＞Pb²⁺。不同器官对同一种重金属离子的富集量差异显著,叶是富集重金属离子的主要器官。水体重金属离子的初始浓度会影响菹草各器官富集重金属离子的能力,一般随水体重金属初始浓度升高,菹草各器官的重金属离子富集量虽有不同程度的增加但富集系数持续减小。     

Shoot δ15N and δ13C values of non-host Brassica rapa change when exposed to ±Glomus etunicatum inoculum and three levels of phosphorus and nitrogen

Glasshouse experiments were conducted to study the response of non-host Brassica rapa and host Sorghum bicolor to inoculation with the arbuscular mycorrhizal fungus (AMF) Glomus etunicatum when given different levels of N (0.9 mmol kg^-1 sand, 2.7 mmol kg^-1 sand, 8.1 mmol kg^-1 sand) and P (3.6 µmol kg^-1 sand, 10.7 µmol kg^-1 sand, 32.0 µmol kg^-1 sand) fertiliser. On both plant species, the presence of G. etunicatum inoculum (+AMF) was associated with significant changes of shoot '¹⁵N values, with +AMF plants having larger average '¹⁵N values than uninoculated plants (-AMF). These values are the largest average differences in shoot '¹⁵N yet recorded for AMF and nutrient effects. B. rapa shoot '¹⁵N average differences ranged from 1.67‰ to 2.70‰, while for S. bicolor they range between 2.07‰ and 4.40‰. For shoot '¹³C only the non-host B. rapa responded to -AMF and added N. Although the harvested dry weight biomass (-35.2% B. rapa; +39.8% S. bicolor) of both plant species responded to AMF inoculation, no direct relationship was observed between isotopic discrimination and growth inhibition for the non-host B. rapa. In this paper we discuss some implications regarding AMF inocula on the basis of our findings and current literature.     

Direct Transfer of Plasmid DNA from Intact Yeast Spheroplasts into Plant Protoplasts

We developed a polyethylene glycol (PEG)-mediated direct DNAtransfer method from intact Saccharomyces cerevisiae spheroplastsinto Arabidopsis thaliana protoplasts. To monitor the DNA transferfrom yeast to plant cells, ß-glucuronidase (GUS) reportergene in which a plant intron was inserted was used as a reporter.This intron-GUS reporter gene on a 2µm-based plasmid vectorwas not expressed in yeast transformants, while it expressedGUS activity when the plasmid DNA was introduced into plantcells. When a mixture of 1 x 10⁸ of S. cerevisiae spheroplastsharboring the plasmid and 2 x 10⁶ of A. thaliana protoplastswas treated with PEG and high pH-high Ca²⁺ solution (0.4 M mannitol,50 mM CaCl₂, 50 mM glycine-NaOH pH 10.5), GUS activity was detectedin the extract of the plant cells after a three-day culture.The GUS activity was higher than that of a reconstitution experimentin which the mixture of 1 x 10⁸ of S. cerevisiae spheroplastswhich did not carry the reporter gene, 2 x 10⁶ of A. thalianaprotoplasts and the same amount of the reporter plasmid DNAas that contained in 1 x 10⁸ of S. cerevisiae spheroplasts,was treated with PEG and high pH-high Ca²⁺ solution. Moreover,the GUS gene expression was resistant to micrococcal nucleasetreatment before and during PEG treatment. From these results,we concluded that plasmid DNA can be directly transferred fromintact yeast spheroplasts to plant protoplasts by a nuclease-resistantprocess, possibly by the cell fusion. ²Deceased on September 15, 1992.     

Mycorrhizal associations between Tuber melanosporum mycelia and transformed roots of Cistus incanus

We set out to establish root cultures of a host plant with the aim of obtaining dual cultures of Tuber melanosporum mycorrhiza on transformed roots. Seedlings of Cistus incanus germinated under sterile conditions from seeds collected in the wild were treated with Agrobacterium rhizogenes. Nine hairy roots collected from different seedlings were cultured individually by repeated subculturing. The hairy root clones differed in growth rates and in morphology (branching frequency and distance between side roots). Root growth in a liquid medium exhibited a lag phase of about 2 weeks and an exponential phase lasting about 12 days before the start of the stationary phase. Hairy roots could be kept alive on medium M, a special solid minimal medium (low in Fe²⁺, BO₄^3-, Ca²⁺, Cu²⁺ and Zn²⁺, very low in PO₄^3- and lacking MoO₄^2-, NH₄⁺ and Co²⁺), for more than 7 months. T. melanosporum could be grown on the same medium for long periods only by subculturing the fungus with the roots. A mycorrhizal association developed between the roots and the T. melanosporum mycelium within 3 months. The association consisted of elongated roots with a mantle and a Hartig net surrounding two to three layers of cortical cells. Swollen, club-like root tips were discernible 5 months after inoculation. The mycorrhized roots could be subcultured and propagated on medium M and maintain the mycorrhizal association.     

香根草对重金属铅离子的胁迫反应研究

研究了Pb²⁺对香根草生理生态指标的影响.结果表明, 随水培液中Pb²⁺浓度的增加(0～8 mmol·L^-1),香根草苗的生长受到严重影响;叶片电导率增大;SOD活性先上升后下降,但均高于对照,其活性与Pb ²⁺浓度呈正相关;POD和CAT活性虽也是先上升后下降,但在高浓度(＞4 mmol·L^-1)的Pb²⁺处理下,酶活性均低于对照,其酶活性与Pb²⁺浓度呈显著负相关.可以认为,酶活性升高是由于香根草苗对Pb2+胁迫做出的应激反应,而高浓度Pb²⁺却对香根草苗的保护酶活性有抑制作用.     

Sulphate and cation accumulation in mesophyll and endodermis vacuoles of spruce needles – effects on nutrient supply after SO<Subscript>2</Subscript> fumigation

Three 10-year-old spruces were excavated with their root balls from a typical rhyolite site in the eastern Erzgebirge. The trees were fumigated for 6 months in a plant growth chamber with an average of 92 ppb_v SO₂. Trees of similar age from the same site served as control. The accumulation of SO₄^2- and counter cations in vacuoles of the mesophyll and endodermis cells of spruce needles Picea abies (L.) Karst. was studied, applying low-temperature SEM and EDX. The element content in needles and the water-soluble proportions of the major nutrient elements were determined. The needles of the fumigated trees yielded 3-5 times higher S content than the control and increased total Mg and Mn values. The stomatal S uptake decreased with increasing needle age. The fumigation caused decreasing N, P, and S_org contents in the needles, and an increase of K⁺ in the youngest needles. Potassium, Mg²⁺, and traces of Mn²⁺ were identified as counter ions to the accumulated SO₄^2- in the mesophyll vacuoles of the fumigated spruce. S concentrations were 3-4 times higher in the endodermis than the mesophyll vacuoles. Magnesium was the dominant counter ion in the endodermis. The endodermic P content of the fumigated spruce was significantly reduced as compared to the control. Relative to normal values, the needles showed a sufficient K⁺ and Mg²⁺ nutrition. Nutrient deficiency became obvious in the needles of the SO₂-fumigated spruces when the cations fixed to SO₄^2- in the vacuoles were subtracted. Our method of using plants with large root balls for fumigation successfully simulated real-world conditions. The experiments clearly show that the investigation of total element contents in needles is not sufficient to judge the nutrient supply and underlined the importance of the relative Mg²⁺ and K⁺ depletion to explain damage symptoms in the Erzgebirge.     

Modeling of growth and energy metabolism of Pichia pastoris producing a fusion protein

A fusion protein composed of a cellulose binding domain from Neocallimastix patriciarum cellulase A and Candida antarctica lipase B (CBD-lipase) was produced by Pichia pastoris methanol utilization plus phenotype in high cell-density cultures. The genes expressing CBD-lipase were fused to the alpha-factor secretion signal sequence of Saccharomyces cerevisiae and placed under the control of the alcohol oxidase gene (AOX1) promoter. To control the repression and induction of AOX1 and oxygen demand at high cell density, a four-stage process was used. Batch growth on glycerol was used in the first step to provide biomass (28 g L^-1) while product formation was prevented due to repression of the AOX1. The second stage was exponential fed-batch growth on glycerol, which caused a slight increase of the enzyme alcohol oxidase activity due to derepression of the AOX1. This procedure resulted in smooth transition to exponential fed-batch growth on methanol, the third stage, in which the AOX1 was strongly induced. The fourth stage was constant fed-batch growth on methanol used to control the oxygen demand at the high cell density. A kinetic model was developed that could predict biomass growth and oxygen consumption in processes with and without oxygen-enriched air. With oxygen enrichment to 34% O₂ in the inlet air the methanol feed rate could be increased by 50% and this resulted in 14% higher final cell density (from 140 to 160 g L^-1 cell dry weight). The increased methanol feed rate resulted in a proportionally increased specific rate of product secretion to the medium. After an initial decrease, the synthesis capacity of the cell was kept constant throughout the cultivation, which made the product concentration increase almost constantly during the process. The kinetic model also describes how the low maintenance demand of P. pastoris compared with E. coli enables this organism to grow to such high cell densities.     

Verticillium lecanii spore production in solid-state and liquid-state fermentations

Verticillium lecanii has been recognized as an entomopathogen with high potential in biological control of pests. Two types of cultivation methods, the solid-state fermentation (SSF) and the liquid-state fermentation (LSF), were examined for V. lecanii. In SSF, the substrate types including rice, rice bran, rice husk, and the mixtures of these components were tested. The results showed that both cooked rice with appropriate water addition and rice bran gave significantly higher spore production of 1.5 2 10⁹ spores/g substrate and 1.4 2 10⁹ spores/g substrate, respectively. In LSF, SMAY liquid medium was used as a base, and the effects of environmental conditions on the spore production of V. lecanii were investigated. From the time course study, on the 9th day the spore yield reached 1.2 2 10⁹ spores/ml of broth at 24v°C, 150 rpm for this strain. A series of medium volumes in the shaker-flask have been tested for the requirement of aeration. The largest surface aeration test, one tenth of the medium volume in the shaker-flask for cultivation, gave the highest spore count. The optimal pH value was tested and the initial pH 5 in the SMAY medium produced a high spore density. Finally, V. lecanii spores from SSF and LSF were different in size, shape, and size distribution; while mean spore length from SSF was 6.1 7m, and mean spore length from LSF was 5.0 7m.     

Characterization and theoretical analysis on toxicological threshold of mercuric ions to Pseudomonas aeruginosa PU21 (Rip64)

This study provides a novel attempt to put forward, in general terms and explanations, the toxicological threshold for Hg(II) detoxification. Quantitative analysis of mercuric ion toxicity to a mercury-resistant strain Pseudomonas aeruginosa PU21 and identification of the threshold phenomena are included. It is revealed that rate of cellular viability loss depends upon the ratio of Hg²⁺ concentration to cell population, (or "multiplicity of toxicity" - MOT). The threshold of unacclimated cells (or "non-growth cells" PU21_u) and hyperresistant strain (PU21_r) occurs at MOT of 1.6᎒¹⁰~3.2᎒¹⁰ and 1.7᎒¹¹~3.4᎒¹¹ molecules Hg²⁺/cfu, respectively. The threshold of PU21_r increase approx. 10-fold compared with unacclimated resistant strain PU21_u. This indicated that sequential treatment of culture with selection pressures (i.e. mercury-containing media) led to over 10-fold increase in mercury resistance. Thus, this quantitative evaluation of toxicity threshold among resistant populations can be used as a design criterion for long-term Hg²⁺ detoxification bioprocesses.     

星天牛幼虫肠道木聚糖酶的纯化和性质

星天牛Anoplophora chinensis (Frster)幼虫肠道匀浆液经80%丙酮沉淀、Q-Sepharose阴离子交换柱层析、PAGE制备电泳等方法纯化后,获得在SDS-PAGE上呈现单一区带的木聚糖酶。该酶的分子量约25 kD,等电点约4.0,最适温度50℃,最适pH 5.4,pH 3.0～7.8对酶活性的恢复无大的影响, 50℃保温2 h仍有60%酶活性。Hg²⁺、M_nO^-4、变性剂SDS完全抑制该酶活性, Cu²⁺、Mn²⁺、Ag⁺、Zn²⁺、Pb⁺、脲对酶活性有强烈的抑制作用。该酶具有水解纤维素的交叉活性,其K_m值为2.47 mg/mL,V_max为0.6 IU/mL。     

Sperm extract and inositol 1,4,5-triphosphate induce cytosolic calcium rise in the central cell of Torenia fournieri

Microinjection of soluble sperm extract and Calcium Green-1 10 kDa-dextran conjugate (CG-1) into the mature central cell of Torenia fournieri induced a significant rise in cytosolic free calcium concentration ([Ca²⁺]_i). The rise reached a maximum at 20 min after injection and then steadily declined. Nevertheless, a relatively high level of [Ca²⁺]_i was maintained even 40 min after injection. Microinjection of sperm extract of maize into Torenia central cells, however, did not trigger any increase in [Ca²⁺]_i, suggesting the possibility of distinct triggers in different species. We also injected caged inositol 1,4,5-triphosphate (InsP₃) and caged cyclic ADP-ribose (cADPR) into Torenia central cells to compare the pattern of Ca²⁺ rise induced by the sperm extract. The results showed that [Ca²⁺]_i elevation triggered by the release of InsP₃ after photolysis appears much faster than that induced by sperm extract. The increase in [Ca²⁺]_i reached a maximum at 70-80 s and dropped to the resting level within 300 s after photolysis. Microinjection of cADPR, however, did not induce any changes in [Ca²⁺]_i. The results indicate that sperm extract might contain factors triggering the release of Ca²⁺ in the central cell.     

Native Cadmium-Metallothionein from the Yeast Saccharomyces cerevisiae: Its Primary Structure and Function in Heavy-Metal Resistance

A Cd-resistant strain of yeast (Saccharomyces cerevisiae, strain30IN) accumulated Cd with the concomitant synthesis of a Cd-bindingprotein of low molecular weight when grown in Cd²⁺-containingmedium. Analysis of the amino acid composition, N-terminal sequenceand immunological properties of the protein revealed its structuralhomology to Cu-metallothionein (Cu-MT) in S. cerevisiae 2186,a Cu-resistant strain of yeast (Winge et al. 1985). The synthesisof MT in Cu-resistant strains of yeast is known to be underthe strict control of Cu²⁺ ions, while that in 301N was inducedboth by Cd²⁺ and Cu²⁺ ions. When 301N was precultured for 48h in the presence of 1 mM CuSO₄, its resistance to Cu²⁺ andthe synthesis of MT in response to Cu²⁺ were enhanced whileanalogous responses to Cd²⁺ were conversely reduced. These resultssuggest that the synthesis of MT is controlled by Cd²⁺ and Cu²⁺in a counteractive manner in strain 301N and, therefore, theregulation of the synthesis of MT plays a role in the adaptationof this strain to conditions when either metal is present. (Received November 1, 1990; Accepted February 22, 1991)