Regulation of seawater dissolved carbon pools by environmental changes in Ulva prolifera originating sites: A new perspective on the contribution of U. prolifera to the seawater carbon sink function.

The Ulva prolifera bloom is considered one of the most serious ecological disasters in the Yellow Sea in the past decade, forming a carbon sink in its source area within a short period but becoming a carbon source at its destination. To explore the effects of different environmental changes on seawater dissolved carbon pools faced by living U. prolifera in its originating area, U. prolifera were cultured in three sets with different light intensity (54, 108, and 162 µmol m-2 s-1), temperature (12, 20, and 28 °C) and nitrate concentration gradients (25, 50, and 100 µmol L-1). The results showed that moderate light (108 µmol m-2 s-1), temperature (20 °C), and continuous addition of exogenous nitrate significantly enhanced the absorption of dissolved inorganic carbon (DIC) in seawater by U. prolifera and most promoted its growth. Under the most suitable environment, the changes in the seawater carbonate system were mainly dominated by biological production and denitrification, with less influence from aerobic respiration. Facing different environmental changes, U. prolifera continuously changed its carbon fixation mode according to tissue δ13C results, with the changes in the concentrations of various components of DIC in seawater, especially the fluctuation of HCO3- and CO2 concentrations. Enhanced light intensity of 108 µmol m-2 s-1 could shift the carbon fixation pathway of U. prolifera towards the C4 pathway compared to temperature and nitrate stimulation. Environmental conditions at the origin determined the amount of dissolved carbon fixed by U. prolifera. Therefore, more attention should be paid to the changes in marine environmental conditions at the origin of U. prolifera, providing a basis for scientific management of U. prolifera.

Improving key gene expression and di-n-butyl phthalate (DBP) degrading ability in a novel Pseudochrobactrum sp. XF203 by ribosome engineering.

Di-n-butyl phthalate (DBP) is one of the important phthalates detected commonly in soils and crops, posing serious threat to human health. Pseudochrobactrum sp. XF203 (XF203), a new strain related with DBP biodegradation, was first identified from a natural habitat lacking human disturbance. Genomic analysis coupled with gene expression comparison assay revealed this strain harbors the key aromatic ring-cleaving gene catE203 (encoding catechol 2,3-dioxygenase/C23O) involved DBP biodegradation. Following intermediates identification and enzymatic analysis also indicated a C23O dependent DBP lysis pathway in XF203. The gene directed ribosome engineering was operated and to generate a desirable mutant strain XF203R with highest catE203 gene expression level and strong DBP degrading ability. The X203R removed DBP in soil jointly by reassembling bacterial community. These results demonstrate a great value of XF203R for the practical DBP bioremediation application, highlighting the important role of the key gene-directed ribosome engineering in mining multi-pollutants degrading bacteria from natural habitats where various functional genes are well conserved.

Spatial distributions and environmentally-mediated factors of dimethylsulfoxide off the northern Antarctic Peninsula in summer.

Spatial distributions of dissolved and particulate dimethylsulfoxide (DMSOd and DMSOp) were investigated off the northern Antarctic Peninsula during the austral summer of 2018, an ecologically and climatically important region of the world. In the upper waters, DMSOd was concentrated in the ice-melt zone because DMSO functions physiologically as an intracellular osmolyte and cryoprotectant. DMSOd concentrations had a weak positive correlation with temperature but a negative correlation with nutrients. This highlighted the importance of temperature-dependent biological activities and photolysis in DMSOd production and the important role of the intracellular antioxidation system in phytoplankton cells. The decrease of average DMSOp:Chl-a ratios in upper waters from west to east, along with decreasing temperatures and increasing diatoms proportions in the phytoplankton, illustrates how seawater DMSO production capacities depend on ambient temperatures and the composition of phytoplankton assemblages. DMSOp were accumulated in deep waters through bio-debris accumulation and microbial activity.

Occurrence, distribution, and sea-air fluxes of volatile halocarbons in the upper ocean off the northern Antarctic Peninsula in summer.

We studied the spatial variations of six volatile halocarbons (VHCs), namely, iodomethane (CH3I), chloroform (CHCl3), tetrachloroethylene (C2Cl4), bromodichloromethane (CHBrCl2), dibromomethane (CH2Br2), and carbon tetrachloride (CCl4), and the environmental influencing factors involved in the cycling of VHCs in the upper ocean (0-500 m) off the Northern Antarctic Peninsula (NAP) during the summer of 2018. About 5%-10% of the total biogenic VHCs in the upper ocean were accumulated in the assemblage layer (AL) with high chlorophyll a. However, higher VHCs levels were observed in the dicothermal layer (DL) compared with the AL because of the preservation from winter and production from dinoflagellates and chlorophytes. Owing to the co-existence occurrence of sharp seasonal pycnocline and thick permanent pycnocline, DL could be an important VHCs reservoir in the upper water column during summer. In response to melting of sea ice and glacier, decreased salinity was responsible for ca. 50% of the variation in the CH2Br2 and CCl4 concentrations, which corresponded with increased CH2Br2 and CCl4 concentrations in the less saline water mass. Anthropogenic CCl4 was found with an average concentration of 44.9 pmol/L, and there was a strong positive relationship between CCl4 and CHCl3 in the upper water, indicating their similar source of pollutant transport caused by anthropogenic activities. Calculated sea-to-air fluxes of CCl4, C2Cl4, CHBrCl2, and CH2Br2 averaged 478.7, 93.7, 33.7, and 61.8 nmol/(m2·d) in summer, respectively, indicating that the waters off the NAP are important sources of VHCs for the atmosphere and exert potentially adverse impacts on the Antarctica ozone depletion.