Research On The Production Of Ethanol By Light-Driven Syngas Fermentation In Clostridium Autoethanogenum

Clostridium autoethanogenum is a strictly anaerobic bacterium that produces high value-added products such as ethanol by fermentation of syngas（H₂,CO,CO₂）.Ethanol as a pharmaceutical excipient has a wide range of uses in the medical and health industry,and it can be used for biofuels,which is an important organic substance.In this study,by monitoring bacterial growth,p H changes,and ethanol and acetate production changes under heterotrophic or autotrophic metabolism,we explored the reasons for the enhanced ethanol production capacity and the decreased acetic acid production capacity of bacteria under light.And evaluate the possibility of industrialized production of bacterial cellulose from syngas fermentation wastewater.The main findings are as follows:（1）In heterotrophic metabolism,both white light and blue light can enhance bacterial ethanol production capacity（ethanol production per unit OD value）,and acetate production is inhibited,while red light does not have this phenomenon.But white light at 3000-6000 Lux light intensity,the ethanol production differed little.The ethanol yield was 13.0±0.2 m M and the acetate yield was 72.5±1 m M under dark conditions.Taking the 4200 Lux as an example under light,the ethanol yield was 22.1±0.6 m M,and the acetate yield was only 25.4±2.0 m M.Bacterial ethanol production capacity increased by nearly 100%.Under different initial p H conditions,the growth of L-5.8 and D-5 were both inhibited,and the latter had a stronger inhibitory effect,but in terms of ethanol production capacity,the latter was much lower than the former,and the acetate production capacity was much higher than the former the latter.Therefore the reduction in acetate under light is not directly affected by growth.From the comprehensive analysis,we know that light can relate to direct synthesis of bacterial ethanol.（2）In autotrophic metabolism,similar to heterotrophic metabolism,both white light and blue light can enhance bacterial ethanol production while red light cannot.The difference is that autotrophic metabolism is more sensitive to light,and bacterial growth,acetate and ethanol metabolism are severely inhibited under 6000 Lux light intensity.The optimum light intensity under autotrophic metabolism was 4200 Lux.The results of changing the duration of light and darkness showed that light plays an important role in the entire metabolic process of bacteria,and plays a greater role in the bacterial growth stage.The observation of bacterial morphology between 0-120 h under light and dark showed that light did stress bacterial growth in the early stage of bacterial reproduction,but the re-transformation of spores indicated that the production of spores was reversible,and light did not damage bacteria.The autotrophic and heterotrophic metabolisms of bacteria at different initial acetic acid concentrations were similar.Under autotrophic conditions,low p H in the dark stimulates ethanol production,whereas heterotrophic metabolism does not.At the same time,the bacterial ethanol production did not continue to increase with the decrease of the initial p H under light,and the stimulatory effects of light and low p H did not produce a superimposed effect.Transcriptome data showed that the expression of the direct synthesis pathway of ethanol was enhanced by 2.6-4.5 times,and the expression of the indirect synthesis pathway was enhanced by about 3.7 times.（3）The production capacity of bacterial cellulose in sugar-containing waste liquid is 1.92 times that of HS medium under the same conditions,and the bacterial cellulose material produced in sugar-containing waste liquid has better mechanical strength,larger specific surface area,pore,volume,pore size and lower crystallinity.It is worth noting that Komagataeibacter sucrofermentans could not directly utilize the acetic acid in the waste liquid,but the presence of glucose activate the utilization of acetate in the waste liquid,prompting Komagataeibacter sucrofermentans to fully utilize the acetate.