Visualization of subcellular organelles in vivo is critical for basic biomedical research and clinical applications. Two new flavonoids with an amide substituent were synthesized and characterized. The flavonoids were nearly non-fluorescent in aqueous environment, but exhibited two emission peaks (one λem at 495–536 nm and the other at 570–587 nm) in organic solvents, which were assigned to the excited normal (N*) and tautomer (T*) emission. When the dyes were examined on oligodendrocyte cells, they were found to selectively accumulate in the endoplasmic reticulum (ER), a eukaryotic organelle involved in lipid and protein synthesis, giving fluorescence turn-on. The ER-selective flavonoids could be a valuable tool due to its low molecular mass (<500), large Stokes’ shift, low toxicity, and biocompatibility.

Summary Most methanotrophic bacteria maintain intracytoplasmic membranes which house the methane‐oxidizing enzyme, particulate methane monooxygenase. Previous studies have primarily used transmission electron microscopy or cryo‐electron microscopy to look at the structure of these membranes or lipid extraction methods to determine the per cent of cell dry weight composed of lipids. We show an alternative approach using lipophilic membrane probes and other fluorescent dyes to assess the extent of intracytoplasmic membrane formation in living cells. This fluorescence method is sensitive enough to show not only the characteristic shift in intracytoplasmic membrane formation that is present when methanotrophs are grown with or without copper, but also differences in intracytoplasmic membrane levels at intermediate copper concentrations. This technique can also be employed to monitor dynamic intracytoplasmic membrane changes in the same cell in real time under changing growth conditions. We anticipate that this approach will be of use to researchers wishing to visualize intracytoplasmic membranes who may not have access to electron microscopes. It will also have the capability to relate membrane changes in individual living cells to other measurements by fluorescence labelling or other single‐cell analysis methods.

Alkyl- and N,N′-bisnaphthyl-substituted imidazolium salts were tested in vitro for their anti-cancer activity against four non-small cell lung cancer cell lines (NCI–H460, NCI–H1975, HCC827, A549). All compounds had potent anticancer activity with 2 having IC50 values in the nanomolar range for three of the four cell lines, a 17-fold increase in activity against NCI-H1975 cells when compared to cisplatin. Compounds 1–4 also showed high anti-cancer activity against nine NSCLC cell lines in the NCI-60 human tumor cell line screen. In vitro studies performed using the Annexin V and JC-1 assays suggested that NCI-H460 cells treated with 2 undergo an apoptotic cell death pathway and that mitochondria could be the cellular target of 2 with the mechanism of action possibly related to a disruption of the mitochondrial membrane potential. The water solubilities of 1–4 was over 4.4 mg/mL using 2-hydroxypropyl-β-cyclodextrin as a chemical excipient, thereby providing sufficient solubility for systemic administration.

Methane is a common industrial by-product that can be used as feedstock for production of the biopolymer polyhydroxybutyrate (PHB) by alphaproteobacterial methanotrophs. In vivo assessment of PHB production would shed light on the biosynthesis process and guide design of improved production strategies, but it is currently difficult to perform efficiently. In this study, the alphaproteobacterial methanotroph Methylocystis sp. Rockwell was grown on methane with three different nitrogen sources (ammonium, nitrate, and atmospheric nitrogen), and biomass samples were harvested at defined time points during lag, exponential, and stationary growth phases. PHB cell content was analyzed at these sampling points via a standard gas chromatography-flame ionization detector method, which requires hydrolysis of PHB and esterification of the resulting monomer under acidic conditions, and a novel, rapid, cost-effective approach based on fixation and staining of bacterial cells via Nile Blue A fluorescent dye enabling differential staining of cell membranes and intracellular PHB granules for single-cell analysis through fluorescence microscopy. Overall, the two PHB quantification approaches were in agreement at all stages of growth and in all three growing conditions tested. The PHB cell content was greatest with atmospheric nitrogen as a nitrogen source, followed by ammonium and nitrate. Under atmospheric nitrogen and ammonium conditions, PHB cell content decreased with growth progression, while under nitrate conditions PHB cell content remained unchanged in all growth phases. In addition to presenting a rapid, efficient method enabling in vivo quantification of PHB production, the present study highlights the impact of nitrogen source on PHB production by Methylocystis sp. Rockwell. Key points• A novel fluorescence microscopy method to quantify PHB in single cells was developed • The microscopy method was validated by the derivation/gas chromatography method • Methylocystis sp. Rockwell synthesizes PHB granules without nutrient stress Keywords Polyhydroxybutyrate • Methylocystis sp. Rockwell • Methanotroph • Fluorescence microscopy • Granule visualization • Gas chromatography Marina Lazic and Ravindra Gudneppanavar contributed equally to this work.