Sphere-like Bacterial Cellulose Producing Strains Screening and Influence Factors and Forming Laws
Author:Bi Ji Cai
Supervisor:liu si xin li cong fa
Bacterial cellulose(BC)is a natural macromolecular biopolymer produced by some microorganisms,which shows such unique properties as high mechanical strength,high water-holding capacity,high purity nano-fibril,high crystallinity,biocompatibility,biodegradability.The sphere-like BCs can be used in modern bioseparation,cell immobilization,sewage treatment and drug delivery carrier and so on due to its higher specific surface area.Here we screened some strains producing sphere-like BC,and studied the influence factors and formation rule of sphere-like BC,with the results shown as following.(1)Screening of strains producing sphere-like BC.Three kinds of BCs such as flocky asterisk-like BC,irregular BC and solid sphere-like BC were obtained from 26 strains.Komagataeibacter nataicola Y19 was the best strain for sphere-like BC production.It produced solid sphere-like BC in either Hestrin-Schramm medium(HS)or fermented coconut water medium(FCW),with BC yield being 0.638 g/L in HS and 0.767 g/L in FCW and bioconversion rate being 13.9%.The microstructure of sphere-like BC was compact,the crystallization degree was 84.35%,and the Ia content was 70.17%.(2)Two kinds of BCs were obtained when K.nataicola Y19 was cultivated in agitated culture in HS and FCW,respectively.During the formation process,the size of internal pores decreased gradually,degree of crystallinity increased gradually from 76.44%to 84.23%(HS)or from 62.11%to 79.53%(FCW),Iα decreased gradually from 76.63%to 70.84%(HS)or from 70.69%to 55.74%(FCW)and Ip increased gradually,the thermal stability increased and the maximum decomposition temperature(Tmax)increased from 316.92℃ to 339.08℃(HS)or from 305.07℃ to 334.44℃(FCW).(3)We studied the effects of fermentation condition and medium components on the yield and degree of uniformity of sphere-like BC by K.nataicola Y19 in agitated culture.The highest yield was obtained when 3.0%glucose,1.5%nitrogen source(peptone and yeast extract),0.8%ethanol was used in the medium(pH3.5)and fermented for 15 days at 30 ℃ and 50r/min with the beaker diameter 40mm and medium depth 1.35cm,they were 0.556g/L,0.6g/L,0.671 g/L,0.688g/L,0.519g/L,0.621 g/L,0.693g/L,1.521 g/L and 0.6g/L,respectively.When glucose 4.0%and nitrogen source 0.5%,ethanol concentration 0.6%,fermentation time 6 days,30 ℃,pH5.00,liquid deep 2.75cm,rotate speed 130r/min and diameter beaker 60mm,the best uniformity of sphere-like BC was obtained,the proportion of median sphere-like BC and the quantity proportion of sphere-like BC were the highest.(4)Three kinds of sphere-like BCs,including mono sphere-like BC,double sphere-like BC and multi sphere-like BC,could be produced in modified HS and FCW by K.nataicola Y19.The distributions of cell concentrating area were different in the three types of sphere-like BC.Modified HS and different concentrations of FCW were used to further study the relationship between the formations of different morphologies of sphere-like BC and the initial BC productivity.The results show that the 3%glucose,pH3.5 had a lower initial BC productivity 0.0258g/L/d and 0.0175g/L/d,it could produce 100%mono sphere-like BC.And 0.8%ethanol and 1.5%nitrogen source had an initial BC productivity 0.032 1g/L/d and 0.0319g/L/d,it could further produced 11.11%,7.26%of the double sphere-like BC and the rest was mono sphere-like BC,respectively.And 20%-80%FCW had a higher initial BC productivity form 0.091g/L/d to 0.1219g/L/d,and it could produce 4.90%to 36.17%multi sphere-like BC,13.29%to 34.75%double sphere-like BC,81.82%to 29.08%mono sphere-like BC,respectively.A high BC productivity leaded multi sphere-like BC,a median BC productivity leaded double sphere-like BC and a low BC productivity leaded mono sphere-like BC(5)The effect of viscosity on the sphere-like BC production was studied.The BC yield increased with the viscosity increasing and peaked at 1.583g/L,1.6267g/L and 1.6125g/L,respectively at 3.8mPa·s by adding 0.64%agar,0.87%xanthan gum or 1.65%potato starch.The uniformity was the best.The proportion of meddle sphere-like BC was the highest,being 47.32%,51.25%and 52.03%,respectively.The quantity proportion of sphere-like BC were 47.32%,51.25%and 52.03%,respectively.The yield of meddle sphere-like BC were 1.583g/L,I.517g/L and 1.613g/L,respectively.