Chromate tolerance in strains of Rhodosporidium toruloides modulated by thiosulfate and sulfur amino acids

Cr(VI) tolerance was studied in four strains of Rhodosporidium toruloides and compared with that of a fifth strain, DBVPG 6662, isolated from metallurgical wastes and known to be Cr(VI) resistant. Tolerance was studied in relation to different species of sulfur (sulfates, thiosulfates, methionine, cysteine) at different concentrations. Djenkolic acid, a poor source of sulfur and an activator of sulfate transport, was also considered. In synthetic medium all strains except the Cr(VI)-resistant one started to be inhibited by 10 g ml^– (0.2 mm) Cr(VI) as K₂Cr₂O₇. DBVPG 6662 was inhibited by 100 g ml^– (2.0 mm) Cr(VI). In Yeast Nitrogen Base without amino acids (minimal medium), supplemented with varying concentrations of chromate, all Cr(VI)-sensitive strains accumulated concentrations of total chromium (from 0.8 to 1.0 g mg^– cell dry wt) after 18 h of incubation at 28 °C. In minimal medium supplemented with 10 g ml^– Cr(VI), the addition of sulfate did not significantly improve the yeast growth. Cysteine at m levels increased tolerance up to 10 g ml^–, whereas methionine only reduced the Cr(VI) toxicity in the strain DBVPG 6739. Additions of djenkolic acid resulted in increased Cr(VI) sensitivity in all strains. The best inorganic sulfur species for conferring high tolerance was thiosulfate at concentrations up to 1 mm. In all cases increased Cr(VI) tolerance was due to a significantly reduced uptake in the oxyanion by the cells and not to the chemical reduction of Cr(VI) to Cr(III) by sulfur compounds.     

Colourless sulfur bacteria and their role in the sulfur cycle

Summary The bacteria belonging to the families of the Thiobacteriaceae, Beggiatoaceae and Achromatiaceae are commonly called the colourless sulfur bacteria. While their ability to oxidize reduced inorganic sulfur compounds has clearly been established, it is still not known whether all these organisms can derive metabolically useful energy from these oxidations. During the last decades research has mainly focussed on the genus Thiobacillus. Bacteria belonging to this genus can oxidize a variety of reduced inorganic sulfur compounds and detailed information is available on the biochemistry and physiology of these energy-yielding reactions. The thiobacilli, most of which can synthesize all cell material from CO₂, possess a well-regulated metabolic machinery with high biosynthetic capacities, which is essentially similar to that of other procaryotic organisms. Although the qualitative role of colourless sulfur bacteria in the sulfur cycle is well documented, quantitative data are virtually absent. Activities of colourless sulfur bacteria in nature must be related to direct and indirect parameters, such as: the rate of oxidation of (S³⁵) sulfur compounds, the rate of C¹⁴O₂-fixation, the rate of acid production and numbers and growth rates of the bacteria. However, chemical reactions and similar activities of heterotrophic organisms mask the activities of the colourless sulfur bacteria to various extents, depending on the condition of the natural environment. This interference is minimal in regions where high temperature and/or low pH allow the development of a dominant population of colourless sulfur bacteria, such as hot acid sulfur springs, sulfide ores, sulfur deposits and some acid soils. The oxidation of inorganic sulfur compounds is carried out by a spectrum of sulfur-oxidizing organisms which includes: 1) obligately chemolithotrophic organisms 2) mixotrophs 3) chemolithotrophic heterotrophs 4) heterotrophs which do not gain energy from the oxidation of sulfur compounds but benefit in other ways from this reaction, and 5) heterotrophs which do not benefit from the oxidation of sulfur compounds. The spectrum is completed by a hypothetical group of heterotrophic organisms, which may have a symbiotic relationship with thiobacilli and related bacteria. Such heterotrophs may stimulate the growth of colourless sulfur bacteria and thereby contribute to the oxidation of sulfur compounds. Future research should focus in the first place on obtaining and studying pure cultures of many of the colourless sulfur bacteria. In the second place, studies on the physiological and ecological aspects of mixed cultures of colourless sulfur bacteria and heterotrophs may add to a better understanding of the role of the colourless sulfur bacteria in the sulfur cycle. Paper read at the Symposium on the Sulphur Cycle, Wageningen, May 1974.     

Chromate resistantBacillus cereus augments sunflower growth by reducing toxicity of Cr (VI)

Impact of four chromium resistant bacterial strains (S3, S4, S6, and S7) was studied on the different growth parameters of sunflower (Helianthus annuus var SF-187) in chromium free or under chromium stress. Strains used exhibited very high-level resistance to chromate (up to 50 mg ml^-1 on nutrient agar and 1-2 mg ml^-1 in minimal medium). Application of Cr(VI) salt adversely affected the seed germination, root and shoot length, and fresh weight of seedlings. Bacterial inoculations improved the growth parameters. The effects of Cr(VI) on the different biochemical parameters were also very severe but seedlings inoculated with bacteria showed much improvements as compared to non-inoculated controls. Uptake of Cr(VI) was higher than Cr(III) by the seedlings. Inoculated seedlings contained less chromium than non-inoculated seedlings. Much improvement in the internal region of root and shoot was observed in inoculated plants especially in guard cells.     

The role of maternal toxicity in lovastatin-induced developmental toxicity

The role of maternal toxicity in lovastatin-induced developmental toxicity in rats was examined in a series of studies. The first study administered lovastatin at 100, 200, 400, or 800 mg/kg/day (mkd) orally to mated rats from Gestation Day (GD) 6 through 20. Maternal toxicity was observed as transient dose-related body weight losses at the initiation of dosing; there were also deaths and/or morbidity at 400 and 800 mkd. These toxicities occurred in conjunction with forestomach lesions. Mean fetal weights were decreased in all groups (-5 to -16%), and the incidence of skeletal malformations, variations, and incomplete ossifications was increased. The 2 highest doses produced the most severe maternal and developmental effects. Using the same dosages, the second study avoided gestational maternal weight losses and morbidity by starting treatment 14 days before mating with dosing continued to GD 20. There were transient dose-related body weight losses after the start of dosing and deaths in the 400- and 800-mkd groups; however, there was no evidence of maternal toxicity during gestation. Developmental toxicity was evident only as slight, but generally significant (p< or =0.05) decreases in mean fetal weights in groups given > or =200 mkd (-2 to -5%). Significantly, no skeletal abnormalities were observed. A third study administered the pharmacologically active metabolite of lovastatin subcutaneously at dose levels that matched oral maternal drug exposures. In the high-dose group, maternal weight gain and mean fetal weight were slightly decreased but there were no treatment-related skeletal abnormalities. Finally, a series of toxicokinetic studies assessed whether the 2 different developmental toxicity profiles were due to differences in drug exposure between the developmentally toxic and non-toxic dosing regimes. The data showed that groups with no skeletal abnormalities had maternal and embryonic/fetal drug concentrations similar to or even greater than the groups with fetal abnormalities. These results indicate that fetal skeletal abnormalities observed at lovastatin dose levels > or =100 mkd are not due to a direct teratogenic effect, but are the result of excessive maternal toxicity, which most likely involves a nutritional deficiency associated with forestomach lesions and reduced maternal food intake.     

Zinc Chromate Modification of the Golgi Technic

A modification of the Golgi technic is described in which the reaction takes place in well fixed formalin material. Thin slices (whole sections of adult monkey, cat and rat cerebrum) 2 to 3 mm. thick, from brains fixed 3 to 4 months in 10% formalin, are chromated for two days in 3 g. of zinc chromate dissolved in 98 ml. of distilled water and 2 ml. of formic acid. Slices are then removed, blotted dry and immersed, suspended by a thread, in 0.75% silver nitrate solution for two days. Solution should be changed after the first day. After silvering, the slices are dehydrated rapidly (total time about one hour) in 95% and absolute alcohol, placed in xylene 10 minutes, in low melting point paraffin 10 minutes and embedded in low melting point paraffin. Only surface infiltration is necessary since sections are cut 90 to 100 u. Sections are collected in 95% alcohol, dehydrated in absolute alcohol, cleared in several changes of xylene and mounted in Fisher's Permount. Results with fetal and new born material were not good.     

Arsenic-induced toxicity and the ameliorative role of antioxidants and natural compounds

Arsenic (As) poisoning has proven to be a major threat worldwide because of its toxic effects on the human body. As toxicity through drinking water is a global health concern. The toxicity of As is known to affect the liver, kidney, lungs, muscles, cardiovascular system, and nervous system and can even induce diabetes. Further As can cause skin lesions leading to notable diseases in the skin like Bowen's disease. Chronic exposure to As has caused many tragedies in Eastern, and several Southeast Asian and Latin American countries. Long-term exposure to As makes it an immediate threat that should be dealt with as a priority, and one of the ways to handle it may be with the use of antioxidants. In this review, we have discussed the natural and anthropogenic sources of As, its metabolism, pathophysiology, and mechanism of toxicity. Besides, we have also discussed some of the synthetic chelators and the ameliorative role of antioxidants and natural compounds in reducing As toxicity.     

The role of calcium in the toxicity of the myocardium

Conclusion Localization studies of calcium both by light and electron microscopy, combined with biochemical quantification, may reveal valid adjuncts to histopathological and toxicological research of cardiac muscle. Although it is dificult to prove whether a direct relationship exists between the subcellular redistribution of calcium causing the activation of degradative enzymes and the structural damage, future research should investigate this interrelationship on a cytochemical and biochemical basis. The role of calcium as one of the causal factors that underlies myocardial degeneration in various pathological and toxicological conditions, as described here, is at lest highly suggestive and the abnormal accumulation of calcium might well be a common pathway of degeneration.Since toxicity to cells including the myocardium involves the entry of extracellular calcium through a perturbed sarcolemma, growing interest is developing in pharmacotherapy for the use of calcium-entry blockers. Histo- and cyto-chemistry remains a largely unexplored discipline in the field of cardiotoxicity and merits more attention from the histopathologist and toxicologist, for it may contribute in a substantial way to diagnostic and therapeutic research and may provide the missing link between morphology and biochemistry.     

Copper toxicity and sulfur metabolism in Chinese cabbage are affected by UV radiation

Biomass production, dry matter content, specific leaf area and pigment content of Chinese cabbage were all quite similar, when plants were grown in the absence or presence of UV-A + B (2.2 mW cm⁻²). Elevated Cu²⁺ concentrations (2–10 μM) in the root environment and UV radiation had negative synergistic effects for Chinese cabbage and resulted in a more rapid and stronger decrease in plant biomass production and pigment content. The quantum yield of photosystem II photochemistry (F_v/F_m) was only decreased at ≥5 μM Cu²⁺ in the presence of UV radiation, when leaf tissue started to become necrotic. The enhanced Cu toxicity in the presence of UV was largely due to a UV-induced enhanced accumulation of Cu in both roots and shoots. An enhanced Cu content strongly affected the uptake and assimilation of sulfur in plants. The total sulfur content of the root increased at ≥2 μM Cu²⁺ in presence of UV and at 10 μM Cu²⁺ in absence of UV and that of the shoot increased at ≥2 μM Cu²⁺ in presence of UV and at ≥5 μM Cu²⁺ in absence of UV. In the shoot it could be attributed mainly to an increase in sulfate content. Moreover, there was a strong increase in the water-soluble non-protein thiol content upon Cu²⁺ exposure in the root and, to a lesser extent in the shoot, both in the presence and absence of UV. The regulation of the uptake of sulfate responded to the occurrence of Cu toxicity directly, since it was more rapidly affected in the presence than in the absence of UV radiation. For instance, the expression and activity of the high affinity sulfate transporter, Sultr1;2, were enhanced at ≥2 μM in the presence of UV, and at ≥5 μM Cu²⁺ in the absence of UV. In the shoot, the expression of the vacuolar sulfate transporter, Sultr4;1, was upregulated at ≥5 μM Cu²⁺ in the presence and absence of UV whilst the expression of a second vacuolar sulfate transporter, Sultr4;2, was upregulated at 10 μM Cu²⁺ in the presence of UV. It is suggested that high Cu tissue levels may interfere/react with the signal compounds involved in the regulation of expression and activity of sulfate transporters. The expression of adenosine 5′-phosphosulfate reductase in the root was hardly affected and was slightly down-regulated at 2 μM in the presence of UV and at 10 μM in the absence of UV. The expression and activity of sulfate transporters were enhanced upon exposure at elevated Cu²⁺ concentrations; this may not be simply due to a greater sulfur demand at higher Cu levels, but more likely is the consequence of Cu toxicity, since it occurred more rapidly in the presence compared to the absence of UV.     

Methallothioneins and their role in the metabolism and toxicity of metals.

Recent investigations have provided considerable new information regarding the biological role of metallothioneins. The synthesis of this protein is induced in cells by certain metals. It can tightly bind with zinc, copper, cadmium, mercury or silver reducing the availability of diffusible forms of these metals within cells and therefore decreasing their toxic potential. The metallothioneins may also have an important role in regulating the normal absorption and homeostasis of zinc and copper. It is paradoxical, however, in that a protein synthesized within the cell to reduce toxicity, may, in itself, be toxic when excreted or leaked out from the cell to the extracellular space. Further studies are required to elucidate the mechanisms involved in these effects.     

The role of cysteine in tellurate reduction and toxicity

BioMetals - The tellurium oxyanion tellurate is toxic to living organisms even at low concentrations; however, its mechanism of toxicity is poorly understood. Here, we show that exposure of...     

The role of glutathione in copper metabolism and toxicity

Cellular copper metabolism and the mechanism of resistance to copper toxicity were investigated using a wild type hepatoma cell line (HAC) and a copper-resistant cell line (HAC600) that accumulates copper and has a highly elevated level of metallothionein (MT). Of the enzymes involved in reactive oxygen metabolism, only glutathionine peroxidase was elevated (3-4-fold) in resistant cells, suggestive of an increase in the cellular flux of hydrogen peroxide. A majority of the cytoplasmic copper (greater than 60%) was isolated from both cell lines as a GSH complex. Kinetic studies of 67Cu uptake showed that GSH bound 67Cu before the metal was complexed by MT. Depletion of cellular GSH with buthionine sulfoximine inhibited the incorporation of 67Cu into MT by greater than 50%. These results support a model of copper metabolism in which the metal is complexed by GSH soon after entering the cell. The complexed metal is then transferred to MT where it is stored. This study also indicates that resistance to metal toxicity in copper-resistant hepatoma cells is due to increases in both cellular GSH and MT. Furthermore, it is suggested that elevated levels of GSH peroxidase allows cells to more efficiently accommodate an increased cellular hydrogen peroxide flux that may occur as a consequence of elevated levels of cytoplasmic copper.