Brewing yeast viability measured using a novel fluorescent dye and image cytometer

Spectral origami: an angle-variable, wavelength-selective concept with a highly efficient filter-based sensing

This study demonstrates the concept of an angle-variable compact spectral module. As a key feature, the filter-based module enables highly efficient wavelength-selective light detection by applying the reflective beam path according to the origami example. It was accomplished through inclined mirrors, which allow for different incident angles on the wavelength separating interference filters used in a robust assembly with no moving parts. To experimentally verify the concept, a wavelength range between 550 and 700 nm was detected by 11 spectral channels. These initial results showed the potential to develop easily scalable and application-tailored sensors, which can overcome conventional filter-based sensor approaches that use upright or fixed-angle illumination.

Efficient imaging based on P - and N-codoped carbon dots for tracking division and viability assessment of lactic acid bacteria

Assessment of lactic acid bacteria (LAB) activity plays a key role in the fermented food industry. Fluorescence imaging method based on dye is facile to detect LAB viability. However, it is difficult to obtain stable fluorescence, non-toxic and low-cost dyes. In this study, we prepare P- and N-doped carbon dots (PN-CDs) via microwave-assisted hydrothermal synthesis. The properties of high quantum yield (60.36%) and excitation dependence allowed for multicolor imaging of LAB (Lactobacillus plantarum [L.p] and Streptococcus thermophilus [S.t]). The abundant functional groups and positive charges (+2.34 mV) on the surface of PN-CDs facilitated their quickly integrated into cell wall of live LAB with obvious fluorescence or into dead cells. As a result, PN-CDs can not only be used to rapidly and efficiently monitor bacterial viability (one minute), but can also be used to visualize LAB division using fluorescence imaging. Importantly, the PN-CDs have potential to rapidly detect LAB activity in LAB-fermented juices.

Simultaneous enumeration of CD34+ and CD45+ cells using EasyCounter image cytometer

Accurate counting of CD34-positive cells is important for successful hematopoietic stem cell transplantation that is applied to various diseases. The aim of this study was simultaneous counting of viable CD34⁺ (vCD34+) and CD45⁺ (vCD45+) cells in apheresis samples by automatic immunofluorescence counter - EasyCounter BC. CD34⁺ and CD45⁺ cells were counted using two conjugates anti-CD34 antibody - dR110 and anti-CD45 antibody - ATTO620, respectively. The conjugates were prepared by carbodiimide method. Dead nuclear cells were counted by using monomethine cyanine dye PO-TEDM 1. The linearity and reproducibility of EasyCounter BC for CD34⁺ cell counting were determined (R² = 0.99; CV values for vCD34+ cells were 6.8 ÷ 8.5% and for vCD45+ cells 4.1 ÷ 7.2%). The obtained results by EasyCounter BC were compared with those by other two standard methods - flow cytometry (Guava easyCyte 8HT) and fluorescence microscopic method (Olympus BX51) with the same conjugates. Passing-Bablok regression was performed to determine the relationship between the results of the three methods, analyzing 43 apheresis samples. Correlation coefficients for vCD45+ and vCD34+ between EasyCounter BC and Olympus microscope were 0.987 and 0.982, respectively (P < 0.0001). Better results were obtained between EasyCounter BC and flow cytometer Guava, 0.998 for vCD45+ and 0.998 for vCD34+ (P < 0.0001).

Enzymatic Analysis of Yeast Cell Wall-Resident GAPDH and Its Secretion

In yeast, many proteins are found in both the cytoplasmic and extracellular compartments, and consequently it can be difficult to distinguish nonconventional secretion from cellular leakage. Therefore, we monitored the extracellular glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity of intact cells as a specific marker for nonconventional secretion. Extracellular GAPDH activity was proportional to the number of cells assayed, increased with incubation time, and was dependent on added substrates. Preincubation of intact cells with 100 μM dithiothreitol increased the reaction rate, consistent with increased access of the enzyme after reduction of cell wall disulfide cross-links. Such treatment did not increase cell permeability to propidium iodide, in contrast to effects of higher concentrations of reducing agents. An amine-specific membrane-impermeant biotinylation reagent specifically inactivated extracellular GAPDH. The enzyme was secreted again after a 30- to 60-min lag following the inactivation, and there was no concomitant increase in propidium iodide staining. There were about 4 × 10⁴ active GAPDH molecules per cell at steady state, and secretion studies showed replenishment to that level 1 h after inactivation. These results establish conditions for specific quantitative assays of cell wall proteins in the absence of cytoplasmic leakage and for subsequent quantification of secretion rates in intact cells.IMPORTANCE Eukaryotic cells secrete many proteins, including many proteins that do not follow the classical secretion pathway. Among these, the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is unexpectedly found in the walls of yeasts and other fungi and in extracellular space in mammalian cell cultures. It is difficult to quantify extracellular GAPDH, because leakage of just a little of the very large amount of cytoplasmic enzyme can invalidate the determinations. We used enzymatic assays of intact cells while also maintaining membrane integrity. The results lead to estimates of the amount of extracellular enzyme and its rate of secretion to the wall in intact cells. Therefore, enzyme assays under controlled conditions can be used to investigate nonconventional secretion more generally.

Genetically Encoded Phase Contrast Agents for Digital Holographic Microscopy

Quantitative phase imaging and digital holographic microscopy have shown great promise for visualizing the motion, structure, and physiology of microorganisms and mammalian cells in three dimensions. However, these imaging techniques currently lack molecular contrast agents analogous to the fluorescent dyes and proteins that have revolutionized fluorescence microscopy. Here we introduce the first genetically encodable phase contrast agents based on gas vesicles. The relatively low index of refraction of the air-filled core of gas vesicles results in optical phase advancement relative to aqueous media, making them a "positive" phase contrast agent easily distinguished from organelles, dyes, or microminerals. We demonstrate this capability by identifying and tracking the motion of gas vesicles and gas vesicle-expressing bacteria using digital holographic microscopy, and by imaging the uptake of engineered gas vesicles by mammalian cells. These results give phase imaging a biomolecular contrast agent, expanding the capabilities of this powerful technology for three-dimensional biological imaging.

Genetically Encoded Phase Contrast Agents for Digital Holographic Microscopy

Quantitative phase imaging and digital holographic microscopy have shown great promise for visualizing the motion, structure, and physiology of microorganisms and mammalian cells in three dimensions. However, these imaging techniques currently lack molecular contrast agents analogous to the fluorescent dyes and proteins that have revolutionized fluorescence microscopy. Here we introduce the first genetically encodable phase contrast agents based on gas vesicles. The relatively low index of refraction of the air-filled core of gas vesicles results in optical phase advancement relative to aqueous media, making them a "positive" phase contrast agent easily distinguished from organelles, dyes, or microminerals. We demonstrate this capability by identifying and tracking the motion of gas vesicles and gas vesicle-expressing bacteria using digital holographic microscopy, and by imaging the uptake of engineered gas vesicles by mammalian cells. These results give phase imaging a biomolecular contrast agent, expanding the capabilities of this powerful technology for three-dimensional biological imaging.

Efficient Imaging of Saccharomyces cerevisiae Based on B- and N-Doped Carbon Dots

The estimation of yeast viability with B- and N-doped carbon dots (BN-CDs) was investigated in this paper. BN-CDs with a fluorescent quantum yield of 65.47% were prepared by a one-step hydrothermal method. The size distribution of BN-CDs was relatively narrow, with the majority falling within 7.5-8.5 nm, and they were mainly composed of carbon, oxygen, nitrogen, and boron. BN-CDs were shown to have strong and stable fluorescence. They exhibited excitation-independent photoluminescence property, which could avoid the autofluorescence and limitation of the excitation source. Dead and live yeast cells were distinguished well by BN-CD staining in a short time, and there was no strict requirement for light protection. The application of BN-CDs in beer brewing can solve the problem of estimation of yeast viability.