Effect Of Oxygen Tension And Carbon Source On Bacterial Cellulose Synthesis

In order to study the effects of carbon source and oxygen partial pressure on BC synthesis and fiber structure,the fermentation was determined by single carbon source culture,composite carbon source culture,overexpression of FBP protein,and different carbon sources and oxygen partial pressure.Parameters,BC material properties and related enzyme activity levels,and further explore the effects of carbon source and oxygen partial pressure on bacterial cellulose synthesis mechanism through metabolomics techniques.The results obtained are as follows:(1)Synthetic bacterial cellulose was synthesized from glucose and glycerol as a single carbon source.Compared with glucose as a carbon source,G.xylinus CGMCC 2955 has a low cell concentration,a high pH value,a low by-product gluconic acid concentration,and a high BC yield,the yield is 4.930 g/L,and the source-BC conversion rate is high.With glycerol as the carbon source,the fermentation of the starting BC yield was low,and the final yield is high.This is due to the difference in bacterial metabolism and BC synthesis pathways when glucose and glycerol are carbon sources.(2)Based on the results of single carbon source synthesis BC experiment,the bacterial carbon fiber was synthesized by the composite carbon source of glucose and glycerol.The optimal composite carbon source ratio was glucose:glycerol was 1.5:1.The optimal composite carbon source synthetic BC yield was 5.994 g/L.Porosity,crystallinity and Young’s modulus of bacterial cellulose synthesized by composite carbon source increased.(3)It was determined that fructose-1,6-bisphosphatase(FBP)is the rate-limiting enzyme of the gluconeogenesis pathway.By overexpressing the fbp gene,a strain expressing the FBP protein was constructed.Compared with the fermentation parameters of G.xylinus CGMCC 2955,the cell concentration of G.xylinus-fbp+was increased,and the BC yield and carbon source-BC conversion were decreased.(4)G.xylinus CGMCC 2955 and G.xylinus-fbp+synthetic bacterial cellulose were studied by adjusting the carbon source and oxygen partial pressure from fermentation parameters,material properties,metabolomics and related enzyme activities.Under the condition of 15%oxygen partial pressure,glycerol was used as the carbon source,G.xylinus CGMCC 2955 had the highest BC yield,and glycerol as the carbon source could further reduce the effect of oxygen concentration on BC yield by reducing the by-product gluconic acid content.Under hypoxic culture conditions,overexpression of FBP protein promotes carboxy anabolism to BC.With the increase of oxygen partial pressure,the porosity increases,and the porosity of the BC film synthesized by G.xylinus-fbp+ increases and the crystallinity decreases.The results of metabolomics data and intracellular related enzyme activity analysis showed that with the increase of oxygen partial pressure,the key enzymes of EMP pathway and UGPase activity decreased,and the relative contents of amino acids and fatty acids increased.Overexpression of FBP protein promotes significant accumulation of D-xylose,D-(-)-tagatose,and pro line under 15%partial pressure of oxygen.