RESULTS OF IRRADIATING SACCHAROMYCES WITH MONOCHROMATIC ULTRA-VIOLET LIGHT : II. THE INFLUENCE OF MODIFYING FACTORS

Possible variation in the probability that absorbed quanta of ultra-violet energy will produce observable inhibitory and lethal effects in the yeast cell, due to non-uniformity in sensitivity of the different regions of the cell, may be further modified by the reproductive stage of the cell at the time of irradiation. Tests of the survival of yeast cells of 15 day and 24 hour cultures indicate that the older resting cells are more resistant to ultra-violet irradiation effects than cells undergoing rapid cell division. The effects of temperature changes within the range of normal growth are evidently small, as judged from the temperature coefficient (1.10). Possible inhibitory effects due to the action of ultra-violet radiation on the malt agar medium and to toxic substances diffused from cells killed by irradiation were not found under the conditions of the experiments. Tests of the validity of the Bunsen-Roscoe reciprocity law for variation in the intensity of the incident ultra-violet radiation up to 30 per cent indicate that for this range the rate of absorption of quanta by the cell does not produce any marked change in the lethal effects observed.     

Elucidation of toxicity of organic acids inhibiting growth of Escherichia coli W

The toxic effects of 3-hydroxypropionic acid (3-HP) at high concentrations on cell growth and cellular metabolism are a great challenge to its commercial production. This study has examined and compared the toxic effects of 3-HP on cell growth with other similar weak acids, especially lactic acid, under various concentrations, temperatures and pH using Escherichia coli W as the test strain. 3-HP was approximately 4.4-times more toxic than lactic acid due to the 4.4-fold weaker acidity or 0.64 higher pKa value. The two acids presented no appreciable difference when the growth inhibition was correlated with the undissociated or protonated free acid concentration calculated by the Henderson-Hasselbalch equation. The growth inhibition by other small organic acids, such as acetic acid, pyruvic acid, propionic acid, 2-hydroxybutyric acid (2-HB) and 3-hydroxybutyric acid (3-HB), was also well correlated with their pKa values or protonated free acid concentrations. This study suggests that the growth inhibition by small weak acids is mainly caused by the socalled proton effect (rather than the anion effect), i.e., an increase in the intracellular proton concentration. An appropriate increase in the medium pH was suggested to alleviate the acid toxicity by reducing the free acid concentration in the culture medium.     

Extended Monod equation for batch cultures with multiple exponential phases

The batch growth curves of Laclobacillus delbreuckii exhibit several exponential phases. From the results of a series of shaker flask experiments, the position of the slope changes in the growth curve and the overall bacterial yield is affected by the initial amount of yeast extract in the medium. It is postulated that this behavior is due to several growth enhancing substances that are initially in the yeast extract and are consumed by the bacteria during the course of the fermentation. Using a Monod-type expression to represent the effect of growth enhancing components in a proposed growth rate expression, a mathematical model of the system is set up and solved on the analog computer.     

Pathway of oxidation of pyruvic oxime by a heterotrophic nitrifier of the genus Alcaligenes: evidence against nitroethane as an intermediate

The role of nitroethane as an intermediate in the oxidation of pyruvic oxime to nitrate by an Alcaligenes sp. was examined. Unlike pyruvic oxime, which serves as a sole source of C and N for the bacterium, nitroethane was incapable of supporting the growth of the microbe. Nitroethane was metabolized and diauxic growth did occur, however, if the nitroethane medium was amended with yeast extract. Alcaligenes sp. resting cells and cell-free extracts were prepared from nitroethane-yeast extract grown cultures and the maximum rate of nitrite synthesis when nitroethane was the substrate was 6.8 nmol min-1 mg cell protein-1, a 10-fold lower rate than that previously noted for pyruvic oxime oxidation. These cell-free extracts were unable to metabolize pyruvic oxime. Resting cells and cell-free extracts prepared from Alcaligenes sp. cells grown in a pyruvic oxime medium were, conversely, incapable of metabolizing nitroethane. Collectively, these results indicate that nitroethane is not an intermediate in the pathway of pyruvic oxime oxidation and that two separate enzyme systems exist in the Alcaligenes sp. for the metabolism of pyruvic oxime and nitroethane.     

Formation of the yeast mitochondrial membrane. 3. Accumulation of mitochondrial proteins synthesized in both the cytoplasm and mitochondria in yeast undergoing glucose depression

The inhibitors of protein synthesis, chloramphenicol and cycloheximide, were added to cultures of yeast undergoing glucose derepression at different times during the growth cycle. Both inhibitors blocked the increase in activity of coenzyme QH₂-cytochrome c reductase, suggesting that the formation of complex III of the respiratory chain requires products of both mitochondrial and cytoplasmic protein synthesis.The possibility that precursor proteins synthesized by either cytoplasmic or mitochondrial ribosomes may accumulate was investigated by the sequential addition of cycloheximide and chloramphenicol (or the reverse order) to cultures of yeast undergoing glucose derepression. When yeast cells were grown for 3 hr in medium containing cycloheximide and then transferred to medium containing chloramphenicol, the activity of cytochrome oxidase increased at the same rate as the control during the first hour in chloramphenicol. These results suggest that some accumulation of precursor proteins synthesized in the mitochondria had occurred when cytoplasmic protein synthesis was blocked during the growth phase in cycloheximide. In contrast, essentially no products of mitochondrial protein synthesis accumulated as precursors for either oligomycin-sensitive ATPase or complex III of the respiratory chain during growth of the cells in cycloheximide.When yeast were grown for 3 hr in medium containing chloramphenicol followed by 1 hr in cycloheximide, the activities of cytochrome oxidase and succinate-cytochrome c reductase increased at the same rate as the control, while the activities of oligomycin-sensitive ATPase and NADH or coenzyme QH₂-cytochrome c reductase were nearly double that of the control. These data suggest that a significant accumulation of mitochondrial proteins synthesized in the cytoplasm had occurred when the yeast cells were grown in medium containing sufficient chloramphenicol to block mitochondrial protein synthesis. The possibility that proteins synthesized in the cytoplasm may act to control the synthesis of mitochondrial proteins for both oligomycin-sensitive ATPase and complex III of the respiratory chain is discussed.     

Symbiotic Relationship of Bacteroides cellulosolvens and Clostridium saccharolyticum in Cellulose Fermentation

In coculture, Bacteroides cellulosolvens and Clostridium saccharolyticum fermented 33% more cellulose than did B. cellulosolvens alone. Also, cellulose digestion continued at a maximum rate 48 h longer in coculture. B. cellulosolvens hydrolyzes cellulose and supplies C. saccharolyticum with sugars and a growth factor replaceable by yeast extract. Alone, B. cellulosolvens exhibited an early cessation of growth which was not due to nutrient depletion, low pH, or toxic accumulation of acetic acid, ethanol, lactic acid, H₂, CO₂, cellobiose, glucose, or xylose. However, a 1-h incubation of B. cellulosolvens spent-culture medium with C. saacharolyticum cells starved for growth factor allowed a resumption of B. cellulosolvens growth. The symbiotic relationship of this naturally occurring coculture is one of mutualism, in which the cellulolytic microbe supplies the saccharolytic microbe with nutrients, and in turn the saccharolytic microbe removes a secondary metabolite toxic to the primary microbe.     

Alcohol fermentation in olive oil extraction effluents

Eight culture-collection yeast strains of various species and five newly isolated strains were tested for both growth in olive oil extraction effluents and fermentation of the sugars in the same media. The culture-collection yeast strains did not grow in an effluent containing 2·86% sugar (w/v), 8 g/litre phenolic substances, 4·58 g/litre titratable acidity and pH 4·96, whereas the newly isolated strains of Torulopsis sp. MK-1, Saccharomyces norbensis MC-1, S. oleaceus MC-2 and S. oleaginosus grew well and fermented the sugars. In the medium mentioned above, they produced alcohol in amounts of 1·63 to 1·38%, respectively. None of the yeasts grew in an olive oil extraction effluent vacuum-concentrated to over 13–14% of dry matter. The strain of T. sp. MK-1 showed a hogher stability.     

Oxygen Requirements of the Food Spoilage Yeast Zygosaccharomyces bailii in Synthetic and Complex Media

Most yeast species can ferment sugars to ethanol, but only a few can grow in the complete absence of oxygen. Oxygen availability might, therefore, be a key parameter in spoilage of food caused by fermentative yeasts. In this study, the oxygen requirement and regulation of alcoholic fermentation were studied in batch cultures of the spoilage yeast Zygosaccharomyces bailii at a constant pH, pH 3.0. In aerobic, glucose-grown cultures, Z. bailii exhibited aerobic alcoholic fermentation similar to that of Saccharomyces cerevisiae and other Crabtree-positive yeasts. In anaerobic fermentor cultures grown on a synthetic medium supplemented with glucose, Tween 80, and ergosterol, S. cerevisiae exhibited rapid exponential growth. Growth of Z. bailii under these conditions was extremely slow and linear. These linear growth kinetics indicate that cell proliferation of Z. bailii in the anaerobic fermentors was limited by a constant, low rate of oxygen leakage into the system. Similar results were obtained with the facultatively fermentative yeast Candida utilis. When the same experimental setup was used for anaerobic cultivation, in complex YPD medium, Z. bailii exhibited exponential growth and vigorous fermentation, indicating that a nutritional requirement for anaerobic growth was met by complex-medium components. Our results demonstrate that restriction of oxygen entry into foods and beverages, which are rich in nutrients, is not a promising strategy for preventing growth and gas formation by Z. bailii. In contrast to the growth of Z. bailii, anaerobic growth of S. cerevisiae on complex YPD medium was much slower than growth in synthetic medium, which probably reflected the superior tolerance of the former yeast to organic acids at low pH.     

FORMATION OF AUXIN IN YEAST CULTURES

We have found far more auxin in the culture media of bakers'' yeast than was obtained by Kögl and Kostermans from the cells themselves. The production of auxin by yeast cells resembles the formation observed in other organisms such as Rhizopus and Rhizobium which also form auxins in their culture media. The auxin yield was found to increase with the concentration of sucrose and to decrease with the concentration of peptone. An inverse relation with the rate of cell multiplication was observed. Enlarged and elongated cells appeared only in those media which contained considerable amounts of auxin. The total auxin yield in the various cultures was found to be directly proportional, below pH 5, to the hydrogen ion concentration. Thus, it was proposed that certain growth conditions favor the breakage of the link between auxin and its protein carrier (Skoog and Thimann) 1940) and consequently accelerate the rate of excretion of auxin into the growth medium.     

Uncoupling of Methanogenesis from Growth of Methanosarcina barkeri by Phosphate Limitation

Production of methane by Methanosarcina barkeri from H₂-CO₂ was studied in fed-batch culture under phosphate-limiting conditions. A transition in the kinetics of methanogenesis from an exponentially increasing rate to a constant rate was due to depletion of phosphate from the medium. The period of exponentially increasing rate of methanogenesis was extended by increasing the initial concentration of phosphate in the medium. Addition of phosphate during the constant period changed the kinetics to an exponentially increasing rate of methanogenesis, indicating the reversibility of phosphate depletion. The relation between methanogenesis and growth of M. barkeri was investigated by measuring the incorporation of phosphorus, supplied as KH₂³²PO₄, in the medium. At a low (1 μM) initial concentration of phosphate in the medium and during the constant period of methanogenesis, there was no net cell growth. At a higher (10 μM) initial concentration of phosphate, cell growth proceeded linearly with time after phosphate had been removed from the medium by uptake into cells.     

Penicillinamidohydrolase inEscherichia coli

The differential rate of synthesis of penicillinamidohydrolase (penicillin acylase — EC 3.5.1.11) was studied inEscherichia coli growing in some chemically defined media and in a complex medium. The enzyme is synthesized at a constant rate only during the exponential phase of growth of cells. Its synthesis is induced most effectively (with respect to quantity) by phenylacetic acid. The induction lag of the enzyme synthesis in a medium with acetate corresponds to two generation times. The highest rate of the enzyme synthesis is reached in a medium containing phenylacetic acid as the only source of carbon and energy. The enzyme synthesis is fully repressed by an increased concentration of dissolved oxygen in the medium, even whenEscherichia coli is cultivated in the medium with phenylacetic acid as the only carbon and energy source.     

THE ACTION OF SULFONAMIDES ON THE RESPIRATION OF BACTERIA AND YEAST : INHIBITION OF BACTERIAL AND YEAST CARBOXYLASES BY SULFONAMIDE DRUGS STRUCTURALLY RELATED TO COCARBOXYLASE

The inhibiting effects of sulfonamide drugs and their derivatives on the anaerobic decarboxylation of pyruvic acid by Staphylococcus aureus, Escherichia coli, baker''s and brewer''s yeast, and a carboxylase preparation from brewer''s yeast have been investigated. These drugs are: sulfanilamide, sulfapyridine, sulfadiazine, sulfamethyldiazine, sulfathiazole, sulfamethylthiazole, sulfanilamido-5-ethyl-4-thiazolone, 2-aminopyrimidine, 2-aminothiazole, and 2-aminopyridine. The sulfathiazole ring appears to exercise decidedly greater specific inhibiting effect on the carboxylases of Staph. aureus and E. coli. The inhibiting effect on yeast carboxylase is non-differentiable among all the substances tried, except sulfamethyldiazine which is completely ineffective on the carboxylases of the organisms studied. The specific inhibitory effect of sulfathiazole on the carboxylases of Staph. aureus and E. coli in comparison to sulfanilamide, sulfapyridine, and sulfadiazine is in harmony with in vivo and in vitro experimental results of other investigators. The results of the present investigation appear to support the hypothesis (1) that sulfonamides exert their bacteriostatic action through chemical affinity for the carrier proteins of certain respiratory enzymes of the bacterial cell, and that this affinity may in part be related to structural similarity between components of the drugs and the corresponding respiratory coenzymes.     

Trans effects in cell membrane transport

The efflux of a substrate from preloaded cells may be decelerated by an inhibitor in the external medium or accelerated by a compatible substrate in the external medium. The derivations of rate equations for the initial velocity of the zero-trans reaction, trans efflux inhibition, and accelerated exchange diffusion are described for steady state conditions. The rate constants making up the Michaelis constant for the trans inhibition reaction are the same as the corresponding parameters in the zero-trans reaction. The rate constants making up the Michaelis constant for the accelerated exchange reaction, however, are different from the corresponding parameters in the zero-trans reaction. The rate equation for trans inhibition shows that the velocity constant for recovery of the unloaded carrier may be determined with steady state experimental data. It is suggested that the observed recovery constant is independent of the substrates and trans inhibitors chosen for an assay of a particular carrier system. An experiment is briefly described to show a determination of a tentative value for the recovery constant of the unloaded nucleoside carrier in yeast cells and the apparent inhibition constant for a trans inhibitor.     

Use of PMA1 as a Housekeeping Biomarker for Assessment of Toxicant-Induced Stress in Saccharomyces cerevisiae

The brewer's yeast Saccharomyces cerevisiae has emerged as a versatile and robust model system for laboratory use to study toxic effects of various substances. In this study, toxicant-induced stresses of pure compounds were investigated in Saccharomyces cerevisiae utilizing a destabilized version of the green fluorescent protein optimized for expression in yeast (yEGFP3) under control of the promoter of the housekeeping plasma membrane ATPase gene PMA1. The responses of the biomarker upon increasing test compound concentrations were monitored by determining the decrease in fluorescence. The reporter assay deployed a simple and robust protocol for the rapid detection of toxic effects within a 96-well microplate format. Fluorescence emissions were normalized to cell growth determined by absorption and were correlated to internal reference standards. The results were expressed as effective concentrations (EC₂₀). Dose-response experiments were conducted in which yeast cells were exposed in minimal medium and in the presence of 20% fetal calf serum to sublethal concentrations of an array of heavy metals, salt, and a number of stress-inducing compounds (Diclofenac, Lindane, methyl-N-nitro-N-nitrosoguanidine [MNNG], hydroxyurea, and caffeine). Long-term exposure (7 h) played a considerable role in the adaptive response to intoxication compared to early responses at 4 h exposure. The data obtained after 4 h of exposure and expressed as EC₂₀ were compared to 50% inhibitory concentration values derived from cell line and ecotoxicological tests. This study demonstrates the versatility of the novel biomarker to complement existing test batteries to assess contaminant exposure and effects.     

REACTIONS OF VALONIA AND OF HALICYSTIS TO COLLOIDS

From the results of these tests it is clear that both Halicystis and Valonia have a high degree of tolerance for animal peptone, and a very high degree of tolerance for animal proteose and for egg albumen. The products of bacterial growths fostered by these proteins have a deleterious effect upon both species of algae; but, if it were possible to prevent bacterial growth entirely and at the same time supply proper food, it is probable that Halicystis and Valonia would show normal growth indefinitely in the presence of these three colloids. This is not true where exposure is made to yeast nucleic acid dissolved in sea water containing 0.00093 gm. per cc. of NaOH. Valonia is markedly less tolerant of this medium (perhaps of NaOH rather than the colloid used) than Halicystis. Such differential effects, however, reach a high point in the case of the solutions of diphtheria toxin and of edestin. Halicystis has a very high tolerance for diphtheria toxin, and Valonia a very low tolerance. In the case of edestin, the relationship is reversed. Here Halicystis has a very low tolerance, and Valonia a very high tolerance. In fact, it may be said that diphtheria toxin has no appreciable effect upon Halicystis, and edestin a very slight effect upon Valonia; while diphtheria toxin is extremely toxic to Valonia, and edestin is extremely toxic to Halicystis. We can offer no suggestions, at present, as to the way in which these effects are produced. It is probable that the very thin protoplasmic layer of these species, which is certainly no thicker than 8µ, is sufficient to obstruct the passage of proteins having large molecules, like egg albumen, with a degree of efficiency that is extraordinary. In the tests we have reported, areas of from 20 sq. cm. to 40 sq. cm. have been submitted to the action of a relatively high concentration of egg albumen for several days without permitting the passage of sufficient amounts to give definable tests either with Spiegler''s or with Tanret''s method,— presumably less than 1 part in 250,000. In the tests of the proteins having much smaller molecules (though the size may not be the explanation), there is some probability that the membranes exhibit a little permeability. The peptone and the proteose of animal origin, or biuret-positive substances derived from them, apparently pass the protoplasmic membranes occasionally in quantities sufficient to give biuret tests. The most probable case of protein passage, however, was that of the proteose of the scarlet runner bean, where specific detection of less than 1 part per 80,000 was possible. In this instance the proteose appeared to pass membranes that were healthy and were functioning normally. But since the cells of the algae had to be destroyed in making the tests, one cannot maintain this point. All one can say is that protein passage was indicated in carefully examined cells of both species, where no breaks in the protoplasmic membrane were discernible, and where samples of the treated cells behaved normally after treatment.     

A KINETIC ANALYSIS OF THE ENDOGENOUS RESPIRATION OF BAKERS' YEAST

The process of endogenous respiration of two strains of bakers'' yeast, Saccharomyces cerevisiae, was examined kinetically. The rate of respiration with respect to time in a non-nutrient medium was found to exhibit two phases: (a) a period of constant rate of O₂ consumption and CO₂ production (R.Q. = 1) characteristic of cells with ample concentrations of stored material; (b) a first order decline in rate of respiration with respect to time, where the rate was proportional to the concentration of some substrate, S. (R.Q. = 1 throughout second phase.) The nature of this substrate was reexamined and the evidence summarized confirms the notion that it is a carbohydrate, probably glycogen. These phases of endogenous respiration were shown to depend upon the age of the culture and the amount of substrate available.     

Effect of ferrihydrite on 2,4,6-trinitrotoluene biotransformation by an aerobic yeast

This study investigated the impact of ferrihydrite on the pathway and rate of 2,4,6-trinitrotoluene (TNT) transformation by Yarrowia lipolytica AN-L15. The presence of ferrihydrite in the culture medium decreased the rate of TNT biotransformation but resulted in the accumulation of the same TNT metabolites as in the absence of ferrihydrite, albeit at slightly different concentrations. Transformation products observed included aromatic ring reduction products, such as hydride-Meisenheimer complexes, and nitro group reduction products, such as hydroxylamino- and amino-dinitrotoluenes. Independently of the presence of ferrihydrite the subsequent degradation of the hydride complex(es) resulted in the release of nitrite followed by its conversion to nitrate and nitric oxide at the low pH values observed during yeast cultivation. Nitric oxide generation was ascertained by electron spin resonance spectroscopy. In addition, increased Fe³⁺-reduction was observed in the presence of TNT and Y. lipolytica. This study demonstrates that in the presence of yeast cells, TNT-hydride complexes were formed at approximately the same level as in the presence of ferrihydrite, opening up the possibility of aromatic ring cleavage, instead of promoting the production of potentially toxic nitro group reduction products in the presence of iron minerals.     

THE INFLUENCE OF ELECTROLYTES UPON THE ELECTROPHORETIC MIGRATION OF BACTERIA AND OF YEAST CELLS

1. It seems first of all clear from our results that the effect of electrolytes upon electrophoretic charge is essentially the same, whether one is dealing with silica dust, bacteria, or yeast cells, although certain quantitative differences appear which will later be discussed. 2. The normal negative charge on the suspended particles appears to be slightly increased by very low concentrations of electrolytes, markedly so in the case of yeast cells. Increase in charge due to minimal concentrations of electrolytes has been recorded by Loeb (1922) for collodion particles. 3. Higher concentrations of electrolytes cause a marked and progressive decrease in negative charge, sometimes leading to an isopotential condition and sometimes to a complete reversal of charge with active migration toward the cathode. This effect is apparently due to the cation alone and increases with the valency of the cation, except that the H ion shows specially marked activity, between that of bivalent and trivalent ions. Since NaOH behaves like an ordinary univalent salt, increased alkalinity of a solution does not further depress the charge already depressed by salts; but, since the H ion is much more active than other univalent or bivalent ions, increased acidity does cause a further progressive depression of charge, even in salt solutions. Certain electrolytes appear to show individual peculiarities due to something else than their valency. Thus KCl for example is distinctly more effective than NaCl. Sodium chloride in general appears to exert less influence upon electrophoretic charge, either in low or high dilution, than do other compounds of univalent ions studied. This depressing effect of moderately high concentrations of electrolytes is much less marked with yeast cells than with Bacterium coli. Silica dust is still less affected by monovalent and bivalent ions than are the yeast cells but appears to be more affected than either yeast or Bacterium coli by AlCl₃. 4. Very high concentrations of AlCl₃ (above 10^–2 M) show a third effect, a decrease of the positive charge produced by concentrations of moderate molar strength. This is analogous to phenomena observed for trivalent salts by Northrop and De Kruif (1921–22) and for acid by Winslow, Falk, and Caulfield (1923–24). 5. Organic substances, such as glucose, glycerol, and saponin produce no effect on electrophoretic velocity until they reach a concentration at which viscosity changes are involved. 6. The first two results observed,—(a) the increase in charge as a result of slight additions of electrolytes, and (b) the marked decrease in charge with further concentration of electrolytes, depending on the valency of the cation, so far as vegetable cells are concerned, are entirely in accord with the theory of the Donnan equilibrium as worked out by Loeb (1922). We might assume in explaining such phenomena that the plant cell contains a certain proportion of unbound protein material and that the first modicum of cation which enters the cell is bound by the protein, leading to an increase in the relative negative charge of the cell as compared with its menstruum, while subsequent increments of cation remain unbound in the cell and thus lower its charge. When we find, however, that the same phenomena are apparent with collodion particles, as shown by Loeb, and with silica dust, it seems difficult to apply such a theory, involving the conceptions of a permeable membrane and unbound organic compounds. Loeb (1923–24) suggests that the primary increase may be due to an aggregation of anions in the part of the electrical double layer adjacent to the suspended particles; but why there should be first an aggregation of anions and later (with increasing concentration) an aggregation of cations, is not easy to conceive. The third result,—the reversion to a more negative charge in the presence of a marked excess of trivalent ions,—is again difficult to explain. Loeb, in this connection, postulates the existence of complex ion-protein compounds, which can scarcely be assumed in the case of the silica particles.     

THE EFFECT OF RADIOACTIVE RADIATIONS AND X-RAYS ON ENZYMES : IV. THE EFFECT OF RADIATIONS FROM RADIUM EMANATION ON SOLUTIONS OF INVERTASE.

The radiochemical inactivation of invertase by beta radiation from the radioactive products in equilibrium with radium emanation can be explained quantitatively on the same basis as that of trypsin and pepsin previously reported; namely, the rate of change in the logarithm of the concentration of the active enzyme with respect to the variable, W, is constant, under the conditions of irradiation described, when the volume of solution exposed is constant. When, within the limits stated in this paper, this volume (V) is varied, the rate of radiochemical change is inversely proportional to V; i.e., See PDF for Equation     

Microcalorimetry coupled with chemometric techniques for toxicity evaluation of Radix Aconiti Lateralis Preparata (Fuzi) and its processed products on Escherichia coli

As a widely used traditional Chinese medicine (TCM), Radix Aconiti Lateralis Preparata (Fuzi) is not only efficacious but also poisonous. Its toxicity and processed products should be taken into account and effectively evaluated. In this study, a non-invasive and non-destructive microcalorimetric method was employed to evaluate and compare the toxicity of Fuzi and its three processed products including Yanfupian, Heifupian, and Danfupian on Escherichia coli (E. coli). Some important metabolic information, such as the power–time curves and some quantitative thermokinetic parameters including growth rate constant k, heat output power P, inhibitory ratio I, and half inhibitory concentration IC₅₀, of E. coli growth affected by various concentrations of Fuzi and its processed products were obtained. Combined with chemometric techniques including multivariate analysis of variance and principal component analysis on this information, it could be seen that Fuzi and its processed products could be distinguished according to their toxic effects on E. coli. The IC₅₀ values of 14.6 mg/mL for Fuzi, 59.2 mg/mL for Yanfupian, 118.3 mg/mL for Heifupian, and 182.7 mg/mL for Danfupian illustrated that the sequence of toxicity on E. coli was Fuzi > Yanfupian > Heifupian > Danfupian. This study provided a useful method and idea of the combination of microcalorimetry and chemometrics for studying the toxic effects of TCMs and other substances.