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

Comparison of Toxicity and Cellular Uptake of CdSe/ZnS and Carbon Quantum Dots for Molecular Tracking Using Saccharomyces cerevisiae as a Fungal Model

Plant resource sharing mediated by mycorrhizal fungi has been a subject of recent debate, largely owing to the limitations of previously used isotopic tracking methods. Although CdSe/ZnS quantum dots (QDs) have been successfully used for in situ tracking of essential nutrients in plant-fungal systems, the Cd-containing QDs, due to the intrinsic toxic nature of Cd, are not a viable system for larger-scale in situ studies. We synthesized amino acid-based carbon quantum dots (CQDs; average hydrodynamic size 6 ± 3 nm, zeta potential -19 ± 12 mV) and compared their toxicity and uptake with commercial CdSe/ZnS QDs that we conjugated with the amino acid cysteine (Cys) (average hydrodynamic size 308 ± 150 nm, zeta potential -65 ± 4 mV) using yeast Saccharomyces cerevisiae as a proxy for mycorrhizal fungi. We showed that the CQDs readily entered yeast cells and were non-toxic up to 100 mg/L. While the Cys-conjugated CdSe/ZnS QDs were also not toxic to yeast cells up to 100 mg/L, they were not taken up into the cells but remained on the cell surfaces. These findings suggest that CQDs may be a suitable tool for molecular tracking in fungi (incl. mychorrhizal fungi) due to their ability to enter fungal cells.

Revealing Potential Genes Affecting Flocculation and/or Viability of Saccharomyces pastorianus by Comparative Genomic Analysis

Yeast flocculation and viability are critical factors in beer production. Adequate flocculation of yeast at the end of fermentation helps to reduce off-flavors and cell separation, while high viability is beneficial for yeast reuse. In this study, we used comparative genomics to analyze the genome information on Saccharomyces pastorianus W01, and its spontaneous mutant W02 with appropriate weakened flocculation ability (better off-flavor reduction performance) and unwanted decreased viability, to investigate the effect of different gene expressions on yeast flocculation or/and viability. Our results indicate that knockout of CNE1, CIN5, SIN3, HP-3, YPR170W-B, and SCEPF1_0274000100 and overexpression of CNE1 and ALD2 significantly decreased the flocculation ability of W01, while knockout of EPL1 increased the flocculation ability of W01. Meanwhile, knockout of CIN5, YPR170W-B, OST5, SFT1, SCEPF1_0274000100, and EPL1 and overexpression of SWC3, ALD2, and HP-2 decreased the viability of W01. CIN5, EPL1, SCEPF1_0274000100, ALD2, and YPR170W-B have all been shown to affect yeast flocculation ability and viability.

Reusable flexible poly(vinyl alcohol)/chitosan-based polymer carbon dots composite film for acid blue 93 dye adsorption

The design and synthesis of water-insoluble chitosan-based polymer carbon dots [P(CS-g-CA)CDs] are described. A polyvinyl alcohol/chitosan-based polymer carbon dot [PVA/P(CS-g-CA)CDs] composite film was prepared using a simple casting method to be used in dye adsorption. The composite film was characterized using FT-IR, XPS, transparency, contact angle, and mechanical properties tests, which showed the successful incorporation of P(CS-g-CA)CDs into the film and also revealed that hydrogen bonding improved the mechanical properties of the PVA film. Furthermore, the composite film displayed substantially enhanced hydrophobicity, making it suitable for use in aqueous environments. In addition, the composite film exhibited stable adsorption of acid blue 93 (AB93) at pH 2-9, with an enhanced adsorption capacity of 433.24 mg/g. The adsorption obeyed Langmuir law with an efficiency of more than 89% even after five cycles. Therefore, the PVA/P(CS-g-CA)CDs film is a promising material for the treatment of organic dye-polluted wastewater.

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.

Sustainable agronomic response of carbon quantum dots on Allium sativum: Translocation, physiological responses and alternations in chromosomal aberrations

The revolutionary growth in the usage of carbon quantum dots (CQDs) in different areas have ultimately directed their discharge in the environment and further augmented the exposure of agricultural crops to these released particles. Therefore, the aim of current study is to evaluate the uptake, translocation and phytotoxicity of blue emissive CQDs on Allium sativum plant. The genotoxicity and cytotoxicity assessment of CQDs towards Allium sativum roots was estimated as function of three different concentrations. Considering the role of CQDs in promoting seed germination at 50 ppm concentration, a greenhouse experiment was performed to evaluate their effect on plant growth. Systematic investigations have shown the translocation of CQDs and their physiological response in terms of increased shoot length wherein P-CQDs exhibited more accumulation into Allium sativum parts. Our investigations unfold the opportunity to utilize Aegle marmelos fruit derived CQDs as a growth regulator in variety of other food plants.

Rose Bengal-Derived Ultrabright Sulfur-Doped Carbon Dots for Fast Discrimination between Live and Dead Cells

The discrimination between dead and live cells is crucial for cell viability evaluation. Carbon dots (CDs), with advantages like simple and cost-effective synthesis, excellent biocompatibility, and high photostability, have shown potential for realizing selective live/dead cell staining. However, most of the developed CDs with the live/dead cell discrimination capacity usually have low photoluminescence quantum yields (PLQYs) and excitation wavelength-dependent fluorescence emission (which can cause fluorescence overlap with other fluorescent probes and make dual-color live/dead staining impossible), and hence, developing ultrabright CDs with excitation wavelength-independent fluorescence emission property for live/dead cell discrimination becomes an important task. Here, using a one-pot hydrothermal method, we prepared ultrasmall (∼1.6 nm), ultrabright (PLQY: ∼78%), and excitation wavelength-independent sulfur-doped carbon dots (termed S-CDs) using rose bengal and 1,4-dimercaptobenzene as raw materials and demonstrated that the S-CDs could rapidly (∼5 min) and accurately distinguish dead cells from live ones for almost all the cell types including bacterial, fungal, and animal cells in a wash-free manner. We confirmed that the S-CDs could rapidly pass through the dead cell surfaces to enter the interior of the dead cells, thus visualizing these dead cells. In contrast, the S-CDs could not enter the interior of live cells and thus could not stain these live cells. We further verified that the S-CDs presented better biocompatibility and higher photostability than the commercial live/dead staining dye propidium iodide, ensuring its bright application prospect in cell imaging and cell viability assessment. Overall, this work develops a type of CDs capable of realizing the live/dead cell discrimination of almost all the cell types (bacterial, fungal, and animal cells), which has seldom been achieved by other fluorescent nanoprobes.

B- and N-doped carbon dots by one-step microwave hydrothermal synthesis: tracking yeast status and imaging mechanism

Background

Carbon dots (CDs) are widely used in cell imaging due to their excellent optical properties, biocompatibility and low toxicity. At present, most of the research on CDs focuses on biomedical application, while there are few studies on the application of microbial imaging.

Results

In this study, B- and N-doped carbon dots (BN-CDs) were prepared from citric acid, ethylenediamine, and boric acid by microwave hydrothermal method. Based on BN-CDs labeling yeast, the dead or living of yeast cell could be quickly identified, and their growth status could also be clearly observed. In order to further observe the morphology of yeast cell under different lethal methods, six methods were used to kill the cells and then used BN-CDs to label the cells for imaging. More remarkably, imaging of yeast cell with ultrasound and antibiotics was significantly different from other imaging due to the overflow of cell contents. In addition, the endocytosis mechanism of BN-CDs was investigated. The cellular uptake of BN-CDs is dose, time and partially energy-dependent along with the involvement of passive diffusion. The main mechanism of endocytosis is caveolae-mediated.

Conclusion

BN-CDs can be used for long-term stable imaging of yeast, and the study provides basic research for applying CDs to microbiol imaging.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-01211-w.