Road to full bioconversion of biowaste to biochemicals centering on chain elongation: A mini review

Production of biochemicals from waste streams has been attracting increasing worldwide interest to achieve climate protection goals.Chain elongation(CE)for production of mediumchain carboxylic acids(MCCAs,especially caproate,enanthate and caprylate)from diverse biowaste has emerged as a potential economic and environmental technology for a sustainable society.The present mini review summarizes the research utilizing various synthetic or real waste-derived substrates available for MCCA production.Additionally,the microbial characteristics of the CE process are surveyed and discussed.Considering that a large proportion of recalcitrantly biodegradable biowaste and residues cannot be further utilized by CE systems and remain to be treated and disposed,we propose here a loop concept of bioconversion of biowaste to MCCAs making full use of the biowaste with zero emission.This could make possible an alternative technology for synthesis of value-added products from a wide range of biowaste,or even non-biodegradable waste(such as,plastics and rubbers).Meanwhile,the remaining scientific questions,unsolved problems,application potential and possible developments for this technology are discussed.

Control of ribosome synthesis in bacteria:the important role of rRNA chain elongation rate

Bacteria growth depends crucially on protein synthesis,which is limited by ribosome synthesis.Ribosomal RNA(rRNA)transcription is the rate-limiting step of ribosome synthesis.It is generally proposed that the transcriptional initiation rate of rRNA operon is the primary factor that controls the r RNA synthesis.In this study,we established a convenient GFP-based reporter approach for measuring the bacterial rRNA chain elongation rate.We showed that the rRNA chain elongation rate of Escherichia coli remains constant under nutrient limitation and chloramphenicol inhibition.In contrast,rRNA chain elongation rate decreases dramatically under low temperatures.Strikingly,we found that Vibrio natriegens,the fastest growing bacteria known,has a 50%higher rRNA chain elongation rate than E.coli,which contributes to its rapid ribosome synthesis.Our study demonstrates that r RNA chain elongation rate is another important factor that affects the bacterial ribosome synthesis capacity.

Microbial Electrosynthesis for Producing Medium Chain Fatty Acids

Microbial electrosynthesis(MES)employs microbial catalysts and electrochemistry to enhance CO_(2)bioconversion to organics with concurrent waste biorefining capability.The aim of this review is to comprehensively discuss the current state of the art and prospects of medium chain fatty acids(MCFAs)production in MES from CO_(2)and organic wastes.Fundamental mechanisms and development of MCFAs production via conventional fermentation are introduced as well.Studies on MCFAs production in MES are summarized,highlighting the strategy of multiple-electron donors(EDs).Challenges for MCFAs production in MES from CO_(2)are presented,and the primary discussions included methanogenesis inhibition,adenosine triphosphate(ATP)limitations of acetogens,and production of limited EDs via solventogenesis.Possible applications of electrochemical approaches to promote the bioconversion of actual waste materials with MCFAs production are analyzed.Finally,future directions are explored,including multi-stage reactions,substrate supply,product extraction,and microbial pathways.

Unraveling the serial glycosylation in the biosynthesis of steroidal saponins in the medicinal plant Paris polyphylla and their antifungal action

Sugar-sugar glycosyltransferases play important roles in constructing complex and bioactive saponins.Here,we characterized a series of UDP-glycosyltransferases responsible for biosynthesizing the branched sugar chain of bioactive steroidal saponins from a widely known medicinal plant Paris polyphylla var.yunnanensis.Among them,a 2'-O-rhamnosyltransferase and three 6'-O-glucosyltrasferases catalyzed a cascade of glycosylation to produce steroidal diglycosides and triglycosides,respectively.These UDP-glycosyltransferases showed astonishing substrate promiscuity,resulting in the generation of a panel of 24 terpenoid glycosides including 15 previously undescribed compounds.A mutant library containing 44 variants was constructed based on the identification of critical residues by molecular docking simulations and protein model alignments,and a mutant UGT91AH1^(Y187A)with increased catalytic efficiency was obtained.The steroidal saponins exhibited remarkable antifungal activity against four widespread strains of human pathogenic fungi attributed to ergosterol-dependent damage of fungal cell membranes,and 2'-O-rhamnosylation appeared to correlate with strong antifungal effects.The findings elucidated the biosynthetic machinery for their production of steroidal saponins and revealed their potential as new antifungal agents.