Antibiotics as a silent driver of climate change? A case study investigating methane production in freshwater sediments

Methane (CH4) is the second most important greenhouse gas after carbon dioxide (CO2) and is inter alia produced in natural freshwater ecosystems. Given the rise in CH4 emissions from natural sources, researchers are investigating environmental factors and climate change feedbacks to explain this increment. Despite being omnipresent in freshwaters, knowledge on the influence of chemical stressors of anthropogenic origin (e.g., antibiotics) on methanogenesis is lacking. To address this knowledge gap, we incubated freshwater sediment under anaerobic conditions with a mixture of five antibiotics at four levels (from 0 to 5000 mu g/L) for 42 days. Weekly measurements of CH4 and CO2 in the headspace, as well as their compound-specific delta C-13, showed that the CH4 production rate was increased by up to 94% at 5000 mu g/L and up to 29% at field-relevant concentrations (i.e., 50 mu g/L). Metabarcoding of the archaeal and eubacterial 16S rRNA gene showed that effects of antibiotics on bacterial community level (i.e., species composition) may partially explain the observed differences in CH4 production rates. Despite the complications of transferring experimental CH4 production rates to realistic field conditions, the study indicated that chemical stressors contribute to the emissions of greenhouse gases by affecting the methanogenesis in freshwaters

Higher temperatures exacerbate effects of antibiotics on methanogenesis in freshwater sediment

<jats:title>Abstract</jats:title><jats:p>Methane (CH<jats:sub>4</jats:sub>) emissions from natural systems are rising in a concerning manner with an incomplete understanding of its drivers. Recently, chemical stressors such as antibiotics have been suggested as a thus far overlooked factor increasing methanogenesis in freshwaters. Since usage and toxicological impact of antibiotics could increase in a warming climate, we assessed the temperature-dependence of antibiotic effects on methanogenesis. In this light, we conducted anaerobic incubations with freshwater sediment at 10, 15, and 20 °C in presence of a mixture of five antibiotics at field-relevant concentrations. Weekly measurements of CH<jats:sub>4</jats:sub> showed a strong temperature dependence of antibiotic effects by changing effect sizes, directions and dynamics. While antibiotics reduced CH<jats:sub>4</jats:sub> production at 10 °C, methanogenesis was elevated at 15 °C with the most pronounced increase occurring at 20 °C. Furthermore, antibiotics changed the prokaryotic assemblage at all temperatures and effect patterns of CH<jats:sub>4</jats:sub> producing Methanomicrobia strongly followed the patterns observed for methanogenesis. While analyses of compound-specific stable isotopes and the metatranscriptome suggest the acetoclastic pathway as most relevant, linking prokaryotic structure to function remains one of the most significant research challenges. Nevertheless, the evidence provided by this study suggests a positive relationship between temperature and the stimulating effects of antibiotics on CH<jats:sub>4</jats:sub> production.</jats:p&gt

The ER protein Ema19 facilitates the degradation of non-imported mitochondrial precursor proteins

For the biogenesis of mitochondria, hundreds of proteins need to be targeted from the cytosol into the various compartments of this organelle. The intramitochondrial targeting routes these proteins take to reach their respective location in the organelle are well understood. However, the early targeting processes, from cytosolic ribosomes to the membrane of the organelle, are still largely unknown. In this study, we present evidence that an integral membrane protein of the endoplasmic reticulum (ER), Ema19, plays a role in this process. Mutants lacking Ema19 show an increased stability of mitochondrial precursor proteins, indicating that Ema19 promotes the proteolytic degradation of non-productive precursors. The deletion of Ema19 improves the growth of respiration-deficient cells, suggesting that Ema19-mediated degradation can compete with productive protein import into mitochondria. Ema19 is the yeast representative of a conserved protein family. The human Ema19 homolog is known as sigma 2 receptor or TMEM97. Though its molecular function is not known, previous studies suggested a role of the sigma 2 receptor as a quality control factor in the ER, compatible with our observations about Ema19. More globally, our data provide an additional demonstration of the important role of the ER in mitochondrial protein targeting

The ER protein Ema19 facilitates the degradation of nonimported mitochondrial precursor proteins

Ema19 is an integral endoplasmic reticulum (ER) protein with relevance for mitochondrial biogenesis. This yeast, representative of the TMEM97/sigma 2 receptor family, serves as quality control factor which supports the degradation of nonimported mitochondrial proteins. This study again demonstrates the important role of the ER in mitochondrial protein targeting. </jats:p

Marine microbes and climate change - a Qatari prospective

Overwhelming scientific evidence has emphasized that climate change is a serious global threat driven by human activity and requires a global response. The importance of marine microbial diversity and the involvement of microbes in processes such as the carbon and nitrogen cycles, production and consumption of greenhouse gasses such as carbon dioxide and methane has been highlighted in the past. Qatari marine environment is unique with an unusual harsh and arid climate, which influences sea salinity and temperature, thus influencing the water density and currents. Of economic importance, these waters are heavily influenced through anthropogenic use. Thus, Qatar's marine flora including the exotic phytoplankton and zooplankton species have adapted and developed a tolerance for extreme conditions. However, despite their relevance for ecosystem functioning, little is known about smaller size classes of organisms (bacteria, archaea, protists, fungi) in coastal habitats, their diversity, their distribution, biological interactions and how they cope with environmental changes. Therefore, a QNRF funded study, a first step towards an understanding and protection of the Qatari marine biosphere, established a baseline of microbial life in the waters surrounding Qatar, in order to monitor and react to the effect of global changes in these waters. Our multi-collaboration project established a comprehensive understanding of microbial biodiversity in Qatari coastal waters using the culture and metagenomic approaches. Results will be presented and the future perspectives discussed.Acknowledgement: This Research was supported by grant (NPRP-6-647-1-127) from the Qatar National Research Fund (a member of Qatar Foundation) to Rashmi Fotedar, Teun Boekhout, Jack. W. Fell, and Thorsten Stoeck.</jats:p