Climate Sensitivity and Feedbacks of BCC-CSM to Idealized CO2 Forcing from CMIP5 to CMIP6

Climate sensitivity represents the response of climate system to doubled CO2 concentration relative to the preindustrial level, which is one of the sources of uncertainty in climate projections. It is unclear how the climate sensitivity and feedbacks will change as a model system is upgraded from the Coupled Model Intercomparison Project Phase 5(CMIP5) to CMIP6. In this paper, we address this issue by comparing two versions of the Beijing Climate Center Climate System Model(BCC-CSM) participating in CMIP6 and CMIP5, i.e., BCC-CSM2-MR and BCC-CSM1.1 m,which have the same horizontal resolution but different physical parameterizations. The results show that the equilibrium climate sensitivity(ECS) of BCC-CSM slightly increases from CMIP5(2.94 K) to CMIP6(3.04 K). The small changes in the ECS result from compensation between decreased effective radiative forcing(ERF) and the increased net feedback. In contrast, the transient climate response(TCR) evidently decreases from 2.19 to 1.40 K, nearly the lower bound of the CMIP6 multimodel spread. The low TCR in BCC-CSM2-MR is mainly caused by the small ERF overly even though the ocean heat uptake(OHU) efficiency is substantially improved from that in BCC-CSM1.1 m.Cloud shortwave feedback(λSWCL) is found to be the major cause of the increased net feedback in BCC-CSM2-MR,mainly over the Southern Ocean. The strong positive λSWCL in BCC-CSM2-MR is coincidently related to the weakened sea ice-albedo feedback in the same region. This result is caused by reduced sea ice coverage simulated during the preindustrial cold season, which leads to reduced melting per 1-K global warming. As a result, in BCCCSM2-MR, reduced surface heat flux and strengthened static stability of the planetary boundary layer cause a decrease in low-level clouds and an increase in incident shortwave radiation. This study reveals the important compensation between λSWCL and sea ice-albedo feedback in the Southern Ocean.

Hydrothermal pretreatment of rice straw at relatively lower temperature to improve biogas production vict anaerobic digestion

Although the degradation mechanism of straw anaerobic digestion is still obscure,lower temperature thermop hysical pretreatment might be a feasible way to improve biogas fermentation efficiency and net energy production in whole slurry.In this study,the performances of rice straw(RS)degradation and biogas production were examined at different pretreatment temperatures from 90 ℃ to 130℃ to identify the optimal process.With increasing pretreatment temperature,the change in cellulose and hemicellulose degradation in all the tests was directly related to volatile fatty acids(VFAs)content,but did not correspond to the variation in cumulative methane production.Both 100℃ and 130℃presented similar ideal digestion performances with highest methane yields of 127.6 and 124.6 mL/g TS,respectively,which were 22.80%and 19.83%higher than that noted in the control.Although test at 100 ℃pretreatment,which achieved 12.8%higher net energy production from RS than that observed in the control,could be considered as the optimal choice,the surplus biogas could only meet 75.9%of energy requirement for pretreated water temperature shift.Nevertheless,mesophilic or thermophilic fermentation,lower pretreatment water input,and reuse of excess heat are recommended as feasible working conditions for improving net biogas production.

Metabolic engineering using acetate as a promising building block for the production of bio‐based chemicals

The production of biofuels and biochemicals derived from microbial fermentation has received a lot of attention and interest in light of concerns about the depletion of fossil fuel resources and climatic degeneration.However,the economic viability of feedstocks for biological conversion remains a barrier,urging researchers to develop renewable and sustainable low-cost carbon sources for future bioindustries.Owing to the numerous advantages,acetate has been regarded as a promising feedstock targeting the production of acetyl-CoA-derived chemicals.This review aims to highlight the potential of acetate as a building block in industrial biotechnology for the production of bio-based chemicals with metabolic engineering.Different alternative approaches and routes com-prised of lignocellulosic biomass,waste streams,and C1 gas for acetate generation are briefly described and evaluated.Then,a thorough explanation of the metabolic pathway for biotechnological acetate conversion,cel-lular transport,and toxin tolerance is described.Particularly,current developments in metabolic engineering of the manufacture of biochemicals from acetate are summarized in detail,with various microbial cell factories and strategies proposed to improve acetate assimilation and enhance product formation.Challenges and future development for acetate generation and assimilation as well as chemicals production from acetate is eventually shown.This review provides an overview of the current status of acetate utilization and proves the great potential of acetate with metabolic engineering in industrial biotechnology.

CRISPR-mediated host genomic DNA damage is efficiently repaired through microhomology-mediated end joining in Zymomonas mobilis

CRISPR-Cas systems provide bacteria and archaea with adaptive immunity against mobile genetic elements(MGEs)through uptake of invader-derived spacers.De novo adaptation samples spacers from both invaders and hosts,whereas primed adaptation shows higher specificity to sample spacers from invaders in many model systems as well as in the subtype I-F system of Zymomonas mobilis.Self-derived spacers will lead to CRISPR self-interference.However,our in vivo study demonstrated that this species used the microhomology-mediated end joining(MMEJ)pathway to efficiently repair subtype I-F CRISPR-Cas system-mediated DNA breaks guided by the self-targeting spacers.MMEJ repair of DNA breaks requires direct microhomologous sequences flanking the protospacers and leads to DNA deletions covering the protospacers.Importantly,CRISPR-mediated genomic DNA breaks failed to be repaired via MMEJ pathway in presence of higher copies of short homologous DNA.Moreover,CRISPR-cleaved exogenous plasmid DNA was failed to be repaired through MMEJ pathway,probably due to the inhibition of MMEJ by the presence of higher copies of the plasmid DNA in Z.mobilis.Our results infer that MMEJ pathway discriminates DNA damages between in the host chromosome versus mobile genetic element(MGE)DNA,and maintains genome stability post CRISPR immunity in Z.mobilis.