The role of photodegradation on the mineralization of permafrost DOM

<p>Permafrost thaw leads to the formation of shallow water bodies in which large quantities of terrestrial organic carbon are mobilized as dissolved organic matter (DOM), partly turned into greenhouse gases (GHG). DOM comes from ancient carbon pools trapped in frozen soils for hundreds to thousands of years but also from present-day primary producers. Determining the fate of these pools is fundamental to evaluate the potential of these water bodies to amplify climate warming through their GHG emissions. In addition to the microbial degradation pathways producing CO<sub>2</sub> and CH<sub>4</sub>, DOM can be directly mineralized into CO<sub>2</sub> by sunlight. The CO<sub>2</sub> production rates from photodegradation vary extensively across Arctic regions. The controlling factors and interactions with the microbial communities are not well understood, while photodegradation is likely to rise as the open-water season extends. Determining the photo- and bio-lability of the carbon pools available on thawing permafrost landscapes is needed to predict to what extent these systems can affect the global carbon cycle.</p><p>Various DOM and environmental characteristics are considered in my PhD project, including mixing regime, seasonal exposure and light attenuation, as well as the microbial community response to photo-induced chemistry changes in DOM. Study sites include subarctic and arctic peatland areas of Eastern Canada, rich in thaw ponds and where organic matter started to accumulate between 3700 and 5600 years BP. These are non-Yedoma systems that have been poorly studied despite the large amount of organic carbon they store. This presentation will show the results of a lab experiment using a solar simulator where DOM of various origins and ages were tested: thaw pond water and leachates from plants, permafrost active layer, and previously unthawed permafrost. Short term incubations were carried out under five treatments: exposure to light without bacteria (0.2 µm filtration), exposure to light followed by a dark incubation with a bacterial inoculum, dark incubation with a bacterial inoculum, dark incubation with the whole bacterial community (2.7 µm filtration), and dark control without bacteria. A set of optical, biological and chemical characteristics were measured at the beginning and end of incubation. DOM losses (DOC, CDOM, and FDOM) and CO<sub>2</sub> production vary extensively among treatments and DOM pools. They were the highest in dark bacterial incubations of plants leachates. DOM of the subarctic area was quite refractory to degradation in general, except for the biodegradation of the unthawed permafrost leachate (- 50%). Photodegradation was observed in all water types, with DOM losses faster than biodegradation ones for the Arctic soils leachates and all the ponds waters. The highest CO<sub>2</sub> photoproduction was measured in Arctic unthawed permafrost leachates. Finally, the enhancement of DOM lability to microbes caused by photodegradation was generally observed for unthawed permafrost leachates. Incoming biological and 14C data, along with multivariate analyses, will improve the characterisation of the trends.</p>

Effects of the Photosystem II Inhibitors CCCP and DCMU on Hydrogen Production by the Unicellular Halotolerant CyanobacteriumAphanothece halophytica

The unicellular halotolerant cyanobacteriumAphanothece halophyticais a potential dark fermentative producer of molecular hydrogen (H2) that produces very little H2under illumination. One factor limiting the H2photoproduction of this cyanobacterium is an inhibition of bidirectional hydrogenase activity by oxygen (O2) obtained from splitting water molecules via photosystem II activity. The present study aimed to investigate the effects of the photosystem II inhibitors carbonyl cyanide m-chlorophenyl hydrazone (CCCP) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on H2production ofA.halophyticaunder light and dark conditions and on photosynthetic and respiratory activities. The results showed thatA.halophyticatreated with CCCP and DCMU produced H2at three to five times the rate of untreated cells, when exposed to light. The highest H2photoproduction rates,2.26 ± 0.24and3.63 ± 0.26 μmol H2 g−1dry weight h−1, were found in cells treated with 0.5μM CCCP and 50μM DCMU, respectively. Without inhibitor treatment,A.halophyticaincubated in the dark showed a significant increase in H2production compared with cells that were incubated in the light. Only CCCP treatment increased H2production ofA.halophyticaduring dark incubation, because CCCP functions as an uncoupling agent of oxidative phosphorylation. The highest dark fermentative H2production rate of39.50 ± 2.13 μmol H2 g−1dry weight h−1was found in cells treated with 0.5μM CCCP after 2 h of dark incubation. Under illumination, CCCP and DCMU inhibited chlorophyll fluorescence, resulting in a low level of O2, which promoted bidirectional hydrogenase activity inA.halophyticacells. In addition, only CCCP enhanced the respiration rate, further reducing the O2level. In contrast, DCMU reduced the respiration rate inA.halophytica.

Investigation of the post-cryogenic regeneration ability of potato varieties under different cultivation conditions

Cryopreservation provides long-term storage of the gene pool of potato varieties in cryobanks at extremely low temperatures. Currently, droplet vitrification is the most widely used method for cryopreservation of potato varieties, which is constantly improving to increase the regeneration rates of the stored plant material. Different modifications of this method are used in the world’s leading potato genebanks. This paper presents the results of studying the effect of cultivation conditions after plunging into liquid nitrogen and thawing of shoots tips and axillary buds of in vitro plants on their postcryogenic recovery. The droplet-vitrification method modified at VIR was used for cryopreservation. The factor “prolonged dark incubation of explants” did not have a significant effect on the frequency of post-cryogenic regeneration of the studied varieties except for one variety (Krepysh), for which a significant increase in the regeneration rate was observed for the shoot tips cultivated in the darkness compared to the cultivation under the photoperiod 16/8 hours (light/darkness). The frequency of post-cryogenic regeneration of shoot tips was higher than that of the axillary buds for all varieties; however, these differences were significant (p < 0.05) only in two cases: for the variety Udacha (a photoperiod of 16/8 hours) and for the variety Krepysh (the dark incubation). The results of two-factor analysis of variance indicate that there is no effect of interaction of factor 1 (prolonged dark incubation) and factor 2 (explant type) on the ability of varieties to post-cryogenic recovery. Taking into account the obtained results, the further cryopreservation of an extended subset of 9 varieties was carried out using shoot tips, which, after freezing-thawing, were cultivated under the photoperiod of 16/8 hours. The frequency of post-cryogenic regeneration of these varieties varied from 30 to 60 %. A significant effect of genotype on postcryogenic recovery has been established. The ability of varieties to regenerate shoots after freezing and thawing was not related to the values of morphogenic indices of in vitro plants. The age of the meriklons (2–4 years) did not significantly affect either the morphogenic indices or the frequency of post-cryogenic regeneration.

Influence of titanium dioxide modification on the antibacterial properties

Antibacterial properties of 15 titania photocatalysts, mono- and dual-modified with nitrogen and carbon were examined. Amorphous TiO2, supplied by Azoty Group Chemical Factory Police S.A., was used as titania source (Ar-TiO2, C-TiO2, N-TiO2 and N,C-TiO2 calcined at 300°C, 400°C, 500°C, 600°C, 700°C). The disinfection ability was examined against Escherichia coli K12 under irradiation with UV and artificial sunlight and in dark conditions. It has been found the development of new photocatalysts with enhanced interaction ability with microorganisms might be a useful strategy to improve disinfection method conducted under artificial sunlight irradiation. The efficiency of disinfection process conducted under artificial sunlight irradiation with carbon (C-TiO2) and carbon/nitrogen (N,C-TiO2) photocatalysts was similar as obtained under UV irradiation. Furthermore, during dark incubation, any toxicity of the photocatalyst was noted.

Influence of light on growth, conidiation and the mutual regulation of fumonisin B2 and ochratoxin A biosynthesis by Aspergillus niger

Aspergillus niger is a fungus able to produce the carcinogenic mycotoxins ochratoxin A (OTA) and fumonisins. We analysed the influence of light of various wavelengths on growth, conidiation, fumonisin B2 (FB2) and OTA biosynthesis by A. niger ITEM 7097. Light from both sides of the spectrum, from long (627 nm) to short wavelengths (470-455 nm), had a stimulating effect on growth, with the highest stimulation under blue (455 nm, 1,700 Lux) and short-wave blue light (390 nm). Conidiation was reduced by 40% under a short blue wavelength (455 nm, 200 Lux), but strongly promoted under light at an even shorter wavelength (390 nm), with an increase of about 200 fold in comparison to the dark. Production of FB2 and OTA was mutually regulated by light. FB2 production was promoted under light conditions: red and blue light in particular increased FB2 biosynthesis by 40%. Conversely, OTA production was greatly inhibited under red and blue light in comparison to dark incubation, with a mean reduction of about 40 fold, indicating a reverse regulation of both biosynthetic pathways. Incubation under a 390 nm wavelength repressed the production of both toxins to non-detectable levels.

A Two Bioreactor Treating Brewery Wastewater

A two stage bioreactor was employed in bioremediation study of laboratory simulated brewery wastewater. Two weeks anaerobic dark incubation of the artificial brewery wastewater without external seeding resulted in an effluent with 138mgl-1VFA; the chemical oxygen demand decreased from 10,000 to 7,814mgl-1 total nitrogen and total phosphorus recorded 18.63 and 18.95% reductions. Further treatment of the anaerobic effluent with a photobacterium named Z08, reduced both the pollutants (COD, TN, TP) and high energy molecules (VFA) significantly by 36.8, 67.5, 27.0, and 60% respectively. Addition of 200mgl-1 NH2-CO-NH2 to the effluent yielded the best result, reducing COD, TN, TP and VFA by 67.5, 68.9, 34.2 and 82%.