Succinate dehydrogenase (SDH) activity in single Paramecium caudatum cells

Single-cell microbiology: tools, technologies, and applications

The field of microbiology has traditionally been concerned with and focused on studies at the population level. Information on how cells respond to their environment, interact with each other, or undergo complex processes such as cellular differentiation or gene expression has been obtained mostly by inference from population-level data. Individual microorganisms, even those in supposedly "clonal" populations, may differ widely from each other in terms of their genetic composition, physiology, biochemistry, or behavior. This genetic and phenotypic heterogeneity has important practical consequences for a number of human interests, including antibiotic or biocide resistance, the productivity and stability of industrial fermentations, the efficacy of food preservatives, and the potential of pathogens to cause disease. New appreciation of the importance of cellular heterogeneity, coupled with recent advances in technology, has driven the development of new tools and techniques for the study of individual microbial cells. Because observations made at the single-cell level are not subject to the "averaging" effects characteristic of bulk-phase, population-level methods, they offer the unique capacity to observe discrete microbiological phenomena unavailable using traditional approaches. As a result, scientists have been able to characterize microorganisms, their activities, and their interactions at unprecedented levels of detail.

Quantitative cytochemical analysis of glucose-6-phosphate dehydrogenase activity in living isolated hepatocytes of European flounder for rapid analysis of xenobiotic effects

There is a great need for rapid but reliable assays to determine quantitatively effects of xenobiotics on biological systems in environmental research. Hepatocytes of European flounder are sensitive to low-dose toxic stress. Glucose-6-phosphate dehydrogenase (G6PDH) is the major source of NADPH in cells and is therefore of major importance for NADPH-dependent xenobiotic biotransformation and defense against toxic injury. These facts prompted us to develop a sensitive cytochemical method to detect G6PDH activity in living isolated flounder hepatocytes using the tetrazolium salt method. The intact plasma membrane did not appear to be a barrier for substrate, co-enzyme, and dye molecules because the intracellular enzyme reaction started immediately when incubation medium was added and could be monitored in real time per individual cell using image analysis. The reaction was effectively stopped for end point measurements by using 4% formaldehyde in 0.1 M phosphate buffer (pH 5.3). The final reaction product, formazan, was stable in hepatocytes for at least 12 days at 4C. This is the first time that a chromogenic histochemical assay is applied to living cells. This approach provides an easy tool for large-scale screening of xenobiotic metabolism and cellular stress defense.

Changes in succinate dehydrogenase (SDH) activity in Paramecium caudatum cells in culture as function of age

SDH activity and its frequency distributions were determined cytophotometrically to investigate the change in respiratory oxidative energy metabolism in Paramecium caudatum (P. caudatum) cell populations during their growth in cell culture. Cells from 3 separate cultures were examined on day 2, 5 and 11 post-inoculation as measures of logarithmic, early and late stationary phases, respectively. SDH activity per individual cell is expressed as the increase in total absorbance (TA) at 590 nm of nitroblue tetrazolium (Nitro BT) formazans per min per cell area in a specimen (deltaTA/min/microm2) to exclude the influence of cell size on the data. On day 5, the mean SDH activity was higher, being approx 140% of that on day 2 and decreased significantly to only approx 11% at day 11. As the mean SDH activity rose, a certain portion of the cells demonstrated a wider range of activity than on day 2 leading to an increase in the width of the SDH activity-frequency distribution. Moreover, on day 11, approx 85% of cells shifted toward the lowest range of activity with further increase in width of the distribution as the mean activity declined. These findings suggest that the respiratory oxidative energy metabolism in P. caudatum cells rise while the cells change from logarithmic to early stationary phases and decays during late stationary phase with increase in its extent of variety within cell populations.

Phosphohydrolytic activity in Paramecium caudatum at neutral pH

Phosphohydrolytic activity was cytochemically characterized in Paramecium caudatum, a ciliated protozoa, at neutral pH. We stained cells in the presence of several mononucleotides as substrates, namely adenosine 5'-monophosphate (5'-AMP), adenosine 2'-monophosphate, guanosine 5'-monophosphate (5'-GMP) and beta-glycerophosphate (beta-GLP) using a lead capture method at 37 degrees C. Cells were also incubated in the presence of 5'-AMP with the inhibitor for alkaline phosphatase, tetramisole. In all cases, varying amounts of final reaction product, lead sulfide, was observed in Paramecium cytoplasm. Tetramisole did not have any effect on Paramecium 5'-AMP hydrolytic activity. The phosphohydrolytic activity was measured as the increase in total absorbance of "test minus control" reactions at 440 nm per unit time after 20 min of incubation using a microphotometric system for image analysis that has been developed by us. From the relationship between the concentrations of 5'-AMP and activity, an apparent K(m) value was estimated to be 0.20 mM. These results suggest that mononucleotides and phosphate monoesters are hydrolyzed by one or more enzymes with wide substrate specificity in P. caudatum. All the activity distribution patterns in Paramecium cultures, that were tested, were monomodal. The mean activity for 5'-AMP hydrolysis widely varied in these cultures. To investigate substrate affinity, distribution patterns and mean activity with 5'-AMP as substrate were compared with those in the presence of 2 other substrates, 5'-GMP and beta-GLP. Affinity of the enzyme(s) was similar for 5'-AMP and 5'-GMP and lower for beta-GLP.