Cell cycle operation during batch growth of fission yeast populations

Modeling synchronous growth of bacterial populations in phased cultivation

The phasing technique is a method for synchronizing cell populations in a bioreactor. Periodic changes of substrate supply and depletion can provoke a cell cycle phasing of originally stochastic scattered proliferation patterns. Synchronized cell populations characterized by changes in DNA content distribution can be monitored by flow cytometry. Thus, studies of the dynamics of single cells in specific cell cycle phases are facilitated. Here we present an age structured model framework investigating synchronized populations using delay differential equations. Applying the framework not only cell populations synchronously increasing under balanced growth conditions, but also synchronized cultures growing in continuous phasing experiments can be described. A process model developed for describing phased cultures was fitted to growth data obtained from a synchronous cultivation of Cupriavidus necator. Its potential utility is demonstrated by a quantitative process description and by its ability to identify ways in which the grade of synchrony could be improved.

mcl1+, the Schizosaccharomyces pombe homologue of CTF4, is important for chromosome replication, cohesion, and segregation

The fission yeast minichromosome loss mutant mcl1-1 was identified in a screen for mutants defective in chromosome segregation. Missegregation of the chromosomes in mcl1-1 mutant cells results from decreased centromeric cohesion between sister chromatids. mcl1+ encodes a beta-transducin-like protein with similarity to a family of eukaryotic proteins that includes Ctf4p from Saccharomyces cerevisiae, sepB from Aspergillus nidulans, and AND-1 from humans. The previously identified fungal members of this protein family also have chromosome segregation defects, but they primarily affect DNA metabolism. Chromosomes from mcl1-1 cells were heterogeneous in size or structure on pulsed-field electrophoresis gels and had elongated heterogeneous telomeres. mcl1-1 was lethal in combination with the DNA checkpoint mutations rad3delta and rad26delta, demonstrating that loss of Mcl1p function leads to DNA damage. mcl1-1 showed an acute sensitivity to DNA damage that affects S-phase progression. It interacts genetically with replication components and causes an S-phase delay when overexpressed. We propose that Mcl1p, like Ctf4p, has a role in regulating DNA replication complexes.

Flow cytometry of yeasts

This unit promotes increased interest in the use of flow cytometry in several new environments. The author provides protocols and descriptive detail on measurements of cell cycle, viability, respiratory activity, and beta-galactosidase activity. Many of these assays are described for other biological systems in CPC, but are now provided in detail for yeasts. Despite the increasing usefulness of digital imaging techniques, flow cytometry remains the method of choice for the resolution of population heterogeneities.

Applications of flow cytometry to clinical microbiology

Classical microbiology techniques are relatively slow in comparison to other analytical techniques, in many cases due to the need to culture the microorganisms. Furthermore, classical approaches are difficult with unculturable microorganisms. More recently, the emergence of molecular biology techniques, particularly those on antibodies and nucleic acid probes combined with amplification techniques, has provided speediness and specificity to microbiological diagnosis. Flow cytometry (FCM) allows single- or multiple-microbe detection in clinical samples in an easy, reliable, and fast way. Microbes can be identified on the basis of their peculiar cytometric parameters or by means of certain fluorochromes that can be used either independently or bound to specific antibodies or oligonucleotides. FCM has permitted the development of quantitative procedures to assess antimicrobial susceptibility and drug cytotoxicity in a rapid, accurate, and highly reproducible way. Furthermore, this technique allows the monitoring of in vitro antimicrobial activity and of antimicrobial treatments ex vivo. The most outstanding contribution of FCM is the possibility of detecting the presence of heterogeneous populations with different responses to antimicrobial treatments. Despite these advantages, the application of FCM in clinical microbiology is not yet widespread, probably due to the lack of access to flow cytometers or the lack of knowledge about the potential of this technique. One of the goals of this review is to attempt to mitigate this latter circumstance. We are convinced that in the near future, the availability of commercial kits should increase the use of this technique in the clinical microbiology laboratory.

Applications of flow cytometry to clinical microbiology

Classical microbiology techniques are relatively slow in comparison to other analytical techniques, in many cases due to the need to culture the microorganisms. Furthermore, classical approaches are difficult with unculturable microorganisms. More recently, the emergence of molecular biology techniques, particularly those on antibodies and nucleic acid probes combined with amplification techniques, has provided speediness and specificity to microbiological diagnosis. Flow cytometry (FCM) allows single- or multiple-microbe detection in clinical samples in an easy, reliable, and fast way. Microbes can be identified on the basis of their peculiar cytometric parameters or by means of certain fluorochromes that can be used either independently or bound to specific antibodies or oligonucleotides. FCM has permitted the development of quantitative procedures to assess antimicrobial susceptibility and drug cytotoxicity in a rapid, accurate, and highly reproducible way. Furthermore, this technique allows the monitoring of in vitro antimicrobial activity and of antimicrobial treatments ex vivo. The most outstanding contribution of FCM is the possibility of detecting the presence of heterogeneous populations with different responses to antimicrobial treatments. Despite these advantages, the application of FCM in clinical microbiology is not yet widespread, probably due to the lack of access to flow cytometers or the lack of knowledge about the potential of this technique. One of the goals of this review is to attempt to mitigate this latter circumstance. We are convinced that in the near future, the availability of commercial kits should increase the use of this technique in the clinical microbiology laboratory.

Intracellular compounds quantification by means of flow cytometry in bacteria: application to xanthan production by Xanthomonas campestris

The use of flow cytometry (FCM) to quantitatively analyze intracellular compounds is studied. FCM is a very useful technique for individual cell studies in microbial systems, and gives access to information which cannot be obtained in any other way. Nevertheless, it provides data in arbitrary units, that is, relative data. This analytical technique could be employed for kinetic modeling of microbial systems and even for internal phenomena analysis, but for this purpose, absolute data-that is concentration of intracellular compounds-must be used. In this work, relative flow cytometry data are transformed into absolute data by means of calibrations employing the same fluorochromes with another technique: spectrofluorymetry. Calibrations of DNA, RNA, and protein intracellular concentrations are presented for the bacteria, Xanthomonas campestris. Other analytical methods, based on biochemical determinations, were also employed to quantify intracellular compounds, but the results obtained are very poor compared with those achieved by means of spectrofluorymetry (SFM). Calibration equations and data obtained by both techniques are given. Evolutions of protein and nucleic acids during Xanthomonas campestris growth and xanthan gum production are shown.

Flow cytometric analysis of Saccharomyces cerevisiae autolytic mutants and protoplasts

Simple methods, based on the technique of flow cytometry, have been developed for the phenotypic characterization of yeast autolytic mutants and for the analysis of the formation and regeneration of the yeast protoplasts. The expression of lytic mutations determined uptake of the fluorescent dye propidium iodide, which could be carefully monitored by flow cytometry. Mixed populations of lysed and viable cells were precisely quantified and sorted, and the technique was also applied to demonstrate protection from lysis of mutant cells with cell wall defects, in the presence of osmotic stabilizers. Protoplast formation and regeneration was monitored by analysing relative cell size; this was facilitated by the preparation of homogeneous protoplast preparations. The technique of flow cytometry proved superior to other conventional methods for these types of study.

Flow cytometry analysis of recombinant Saccharomyces cerevisiae populations

A new fluorescent stain has been developed for detecting cloned beta-galactosidase activity in individual cells of Saccharomyces cerevisiae by flow cytometry. The staining reaction is based on enzymatic cleavage of alpha-naphthol-beta-D-galactopyranoside by intracellular beta-galactosidase and trapping of the liberated naphthol by hexazoniumpararosaniline yielding a fluorescent, insoluble end product. This stain, in connection with an appropriate host strain, has been applied for detecting plasmids encoding inducible beta-galactosidase in unstable recombinant cell populations carrying plasmids with different origins of replication. The method enables rapid determination of the fraction of plasmid-containing cells as well as quantitation of intracellular beta-galactosidase content by kinetic enzyme assay. Inducibility of the marker enzyme is important for maintaining correlation between enzyme and gene content.