Elena Polishchuk

A marine biogenic source of atmospheric ice-nucleating particles

The amount of ice present in clouds can affect cloud lifetime, precipitation and radiative properties. The formation of ice in clouds is facilitated by the presence of airborne ice-nucleating particles. Sea spray is one of the major global sources of atmospheric particles, but it is unclear to what extent these particles are capable of nucleating ice. Sea-spray aerosol contains large amounts of organic material that is ejected into the atmosphere during bubble bursting at the organically enriched sea–air interface or sea surface microlayer. Here we show that organic material in the sea surface microlayer nucleates ice under conditions relevant for mixed-phase cloud and high-altitude ice cloud formation. The ice-nucleating material is probably biogenic and less than approximately 0.2 micrometres in size. We find that exudates separated from cells of the marine diatom Thalassiosira pseudonana nucleate ice, and propose that organic material associated with phytoplankton cell exudates is a likely candidate for the observed ice-nucleating ability of the microlayer samples. Global model simulations of marine organic aerosol, in combination with our measurements, suggest that marine organic material may be an important source of ice-nucleating particles in remote marine environments such as the Southern Ocean, North Pacific Ocean and North Atlantic Ocean.

FGF signalling regulates bone growth through autophagy

Skeletal growth relies on both biosynthetic and catabolic processes. While the role of the former is clearly established, how the latter contributes to growth-promoting pathways is less understood. Macroautophagy, hereafter referred to as autophagy, is a catabolic process that plays a fundamental part in tissue homeostasis. We investigated the role of autophagy during bone growth, which is mediated by chondrocyte rate of proliferation, hypertrophic differentiation and extracellular matrix (ECM) deposition in growth plates. Here we show that autophagy is induced in growth-plate chondrocytes during post-natal development and regulates the secretion of type II collagen (Col2), the major component of cartilage ECM. Mice lacking the autophagy related gene 7 (Atg7) in chondrocytes experience endoplasmic reticulum storage of type II procollagen (PC2) and defective formation of the Col2 fibrillary network in the ECM. Surprisingly, post-natal induction of chondrocyte autophagy is mediated by the growth factor FGF18 through FGFR4 and JNK-dependent activation of the autophagy initiation complex VPS34–beclin-1. Autophagy is completely suppressed in growth plates from Fgf18−/− embryos, while Fgf18+/− heterozygous and Fgfr4−/− mice fail to induce autophagy during post-natal development and show decreased Col2 levels in the growth plate. Strikingly, the Fgf18+/− and Fgfr4−/− phenotypes can be rescued in vivo by pharmacological activation of autophagy, pointing to autophagy as a novel effector of FGF signalling in bone. These data demonstrate that autophagy is a developmentally regulated process necessary for bone growth, and identify FGF signalling as a crucial regulator of autophagy in chondrocytes.

The production of methylated organoantimony compounds by Scopulariopsis brevicaulis

Cultures of the fungus Scopulariopsis brevicaulis were grown in antimony-rich media. Although volatile compounds of other elements were readily detected in the culture headspace, volatile antimony compounds were formed irreproducibly and at only ultratrace levels. In order to monitor the media for nonvolatile methylantimony compounds, a method of sample preparation was developed, based on solid-phase extraction. This enabled the separation of large quantities of soluble inorganic antimony species from trace amounts of organoantimony compounds before speciation by HG–GC–AAS. By this methodology methylated antimony compounds were detected at concentrations of 0.8– 7.1 µg Sbl−1 in all media in which S. brevicaulis was grown in the presence of antimony(III) compounds. These methylantimony species were not detected in any of the nonliving or medium-only controls. Methylated compounds were not detected where S. brevicaulis was grown in the presence of antimony(V) compounds. This is the first study to show that antimony(III) compounds are biomethylated by S. brevicaulis under aerobic-only growth conditions. Copyright

Antimony biomethylation by Scopulariopsis brevicaulis: characterization of intermediates and the methyl donor.

The filamentous fungus Scopulariopsis brevicaulis biomethylates inorganic antimony(III) compounds to trimethylstibine, that can be detected in culture headspace gases. Dimethylantimony and trimethylantimony species have been detected in the medium of these cultures, but the origin of these species was controversial. We now show that the dimethylantimony species is a true intermediate on the pathway to trimethylstibine (rather than arising from trimethylstibine oxidation or as an analytical artifact) because no dimethylantimony species are formed on trimethylstibine oxidation, as determined by using HG-GC-AAS. Furthermore, the dimethylantimony and trimethylantimony species can be separated, by using anion exchange chromatography, and so the dimethylantimony species is not an analytical artifact, formed during the hydride generation process. The antimony biomethylation mechanism was further probed by measuring incorporation of the methyl group, from 13CD3-L-methionine and CD3-D-methionine, into methylantimony species and, for comparison, into methylarsenic species. The percentage incorporation of the labeled methyl group into methylarsenic and methylantimony species was not significantly different. The incorporation from 13CD3-L-methionine was 54% and 47% for antimony and arsenic, respectively. The incorporation from CD3-D-methionine was 20% and 16% for antimony and arsenic, respectively. It appears that the biomethylation of arsenic and antimony occur by very similar, perhaps identical, mechanisms.

Methylantimony compound formation in the medium of Scopulariopsis brevicaulis cultures: 13CD3-L-methionine as a source of the methyl group

The filamentous fungus Scopulariopsis brevicaulis produces nonvolatile methylantimony compounds (found in the medium) when grown in antimony(III)-rich medium. To investigate the methyl source, 13CD3-labelled L-methionine was added to the growth medium. After one month sodium borohydride reduction of media samples produced dimethylstibine and trimethylstibine. The methylstibines were separated on a packed GC column and obtained as gaseous fractions. Analysis of the methylstibines, in the gaseous fractions, by CGC–MS (ion-trap) established 13CD3 incorporation in both the trimethyl-and dimethyl-antimony compounds. Copyright

Confirmation of the aerobic production of trimethylstibine by Scopulariopsis brevicaulis

The filamentous fungus Scopulariopsis brevicaulis produces volatile trimethylstibine, found in the culture headspace, when grown in an antimony(III)-rich medium under aerobic conditions. The trimethylstibine was purged from cultures using a continuous flow of compressed air and trapped in a U-shaped tube containing Supelcoport SP 2100 at −78 °C. The trap contents were determined by using GC–ICP–MS methodology. Typically between 60 and 500 pg of trimethylstibine was trapped during sampling (12 h) from cultures containing 1000 g Sb ml−1 as potassium antimony tartrate. The total production of trimethylstibine over 18 days of growth was estimated at 10 ng. Trimethylarsine was produced in greater quantities than trimethylstibine, even though no arsenic compounds were added to the medium. Copyright

Synthesis, characterization, and evaluation of the antimicrobial potential of copper(II) coordination complexes with quinolone and p-xylenyl-linked quinolone ligands

The antimicrobial properties of copper have been known to mankind since the ancient times. In a coordination chemistry approach to develop novel antimicrobial agents, the quinolone antimicrobial agents ciprofloxacin (Hcipro) and pipemidic acid (Hpia), as well as dimers thereof (piperazinyl-linked with a p-xylenyl moiety) were complexed with copper(II). The synthesis and antimicrobial evaluation of bis(ciprofloxacino)copper(II) [Cu(cipro)2], bis(pipemido)copper(II) [Cu(pia)2], and the corresponding dimer complexes, [Cu2(ciproXcipro)2] and [Cu2(piaXpia)2], are reported. No combinational or synergistic effect between copper(II) and the respective quinolone ligands was observed in vitro.

The Effect of Phosphate on the Bioaccumulation and Biotransformation of Arsenic(V) by the Marine Alga Fucus gardneri

The phosphate concn. was varied to ascertain if the prodn. of arsenosugars by Fucus could be stimulated by a deficit of phosphate, which would encourage the uptake of arsenate, or by an excess of phosphate which would possibly increase metab. The results indicate that with a low phosphate concn. arsenate uptake is enhanced and as a result the concn. of the usual metabolites arsenite and dimethylarsenic acid are increased in the Fucus and the seawater.

Uroplakin traffic through the Golgi apparatus induces its fragmentation: new insights from novel in vitro models

Uroplakins (UPs) play an essential role in maintaining an effective urothelial permeability barrier at the level of superficial urothelial cell (UC) layer. Although the organization of UPs in the apical plasma membrane (PM) of UCs is well known, their transport in UCs is only partially understood. Here, we dissected trafficking of UPs and its differentiation-dependent impact on Golgi apparatus (GA) architecture. We demonstrated that individual subunits UPIb and UPIIIa are capable of trafficking from the endoplasmic reticulum to the GA in UCs. Moreover, UPIb, UPIIIa or UPIb/UPIIIa expressing UCs revealed fragmentation and peripheral redistribution of Golgi-units. Notably, expression of UPIb or UPIb/UPIIIa triggered similar GA fragmentation in MDCK and HeLa cells that do not express UPs endogenously. The colocalization analysis of UPIb/UPIIIa-EGFP and COPI, COPII or clathrin suggested that UPs follow constitutively the post-Golgi route to the apical PM. Depolymerisation of microtubules leads to complete blockade of the UPIb/UPIIIa-EGFP post-Golgi transport, while disassembly of actin filaments shows significantly reduced delivery of UPIb/UPIIIa-EGFP to the PM. Our findings show the significant effect of the UPs expression on the GA fragmentation, which enables secretory Golgi-outpost to be distributed as close as possible to the sites of cargo delivery at the PM.

Chapter 5 – Arsenic in Yellowknife, North West Territories, Canada

Publisher Summary In the Giant mine, Yellowknife, NWT, Canada, about 260,000 tons of arsenic (As) trioxide are stored underground in old mine workings and specially constructed chambers. The practice of storing the recovered mine dust underground began with the belief that the storage areas, initially abandoned mined-out sections, were either located in permafrost or in the areas that would revert to permafrost once human activity had ceased in the vicinity. Unfortunately, although permafrost conditions were never reestablished, the underground storage was continued and eventually special chambers were constructed to hold the mine dust. The stack gas, mainly As trioxide and sulfur dioxide, was initially released into the atmosphere. However, this undesirable practice was mitigated with the installation of an electrostatic precipitator to remove some of the As trioxide. The As recovery system was upgraded over the next decade in which the quantity released in 1949, 7300 kg/day, dropped to 75 kg/day in 1960.