Inoculation concentration modulating the secretion and accumulation pattern of exopolysaccharides.pdf
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1、Inoculation concentration modulating thesecretion and accumulation pattern ofexopolysaccharides in desert cyanobacteriumMicrocoleus vaginatusLong Qian1Li Wu1Lie Yang1Zulin Zhang1,21School of Resources and Environmental Engineering,Wuhan University ofTechnology,Wuhan,Peoples Republic of China2The Jam
2、es Hutton Institute,Craigiebuckler,Aberdeen,UKAbstractCyanobacterial exopolysaccharides(EPS)accumulated duringmicroalgal cultivation have significant application potential inantioxidation,pharmaceutical products,and so on.Inoculationconcentration strongly affects the cultivation cost,biomass,and EPS
3、 accumulation.In this study,a high-EPS-excreteddesert cyanobacterium Microcoleus vaginatus was isolated,and the effects of inoculation concentration on biomass,photosynthetic activity,and EPS accumulation were explored.The results showed that the original fluorescence(Fo)provided a good indication t
4、o cyanobacterial biomass,whenChl-a concentration was lower than 10 mg L1.Inoculationconcentration significantly affected cyanobacterial biomassand EPS concentration(P 0.05).The two fractions ofEPS,capsular exopolysaccharides(CPS)and releasedexopolysaccharides(RPS)were strongly affect by inoculationc
5、oncentration.Other than forming thick sheath(CPS)surrounded the filaments,M.vaginatus excreted higherproportions of RPS to culture medium,and the ratio of RPS toCPS ranged from 1.08 to 1.58 depending on the inoculationconcentration.Additionally,although the biomass and EPSaccumulation increased with
6、 inoculation concentration,theincreasing inoculation concentration did not bring to theproportionate increase of the final biomass and EPS yield.Altogether,comprehensively considering the EPS yield andproductivity,inoculation concentration of 0.04 mg Chl-a L1isrecommended for M.vaginatus to produce
7、EPS,with an EPSyield of 94.32 mg L1and EPS productivity of 184.86 mg(mg Chl-a)1L1d1at the end of experiment.2020International Union of Biochemistry and Molecular Biology,Inc.Volume 68,Number 2,Pages 330337,2021Keywords:microalgae,biomass,exopolysaccharides,desert,crust1.IntroductionAs resource and e
8、nvironmental problems became more andmore serious,the healthy development of human society,in-cluding human health,is seriously threatened.Under suchAddress for correspondence:Li Wu,Associate Professor of School ofResources and Environmental Engineering,Wuhan University ofTechnology,Wuhan 430072,Peo
9、ples Republic of China.Tel.:00862787651816;e-mail:;or Lie Yang,AssociateProfessor ofSchool of Resources and Environmental Engineering,WuhanUniversity of Technology,Wuhan,Peoples Republic of China.Tel.:00862787792151;Fax:0086 2787792151;e-mail:;orand Zulin Zhang,Professor of The James Hutton Institut
10、e,Craigiebuckler,Aberdeen ABI5 8QH,UK.Tel.:0044 344 9285428;Fax:0044 344 9285429;e-mail:Zulin.Zhanghutton.ac.uk.Received 26 December 2019;accepted 21 April 2020DOI:10.1002/bab.1930Published online 17 May 2020 in Wiley Online Library()circumstances,as a sustainable industrial model,microalgalcultivat
11、ion is considered as an ideal way to deal with both theincreasingly prominent resource and environmental issues.That is because in the process of microalgal cultivation,mi-croalgae not only fix atmospheric CO2to reduce the greenhouseeffect,but also can use some high nutritional waste water orgas as
12、nutrient source for growth,achieving simultaneouslyboth the economic and environmental aims 1,2.When thecultivated microalgae are harvested,microalgal biomass cannot only be used as biofertilizer 3,4 and desertification controlinocula 5;but also can be deeply processed into various foodsand feeds 1,
13、6;as well the lipid and other high added-valueproducts in microalgae can be used for bioenergy and healthindustries 7,8.Especially,during the process of microal-gal cultivation,microalgae would excrete a large amount ofexopolysaccharides(EPS),which have a very broad applica-tion prospect because of
14、their antioxidation,pharmaceuticalactivities,and other chemical and rheological properties9-12.330As the earliest photosynthetic organisms on the Earth,cyanobacteria not only have an important influence on theatmospheric composition,but also provide a basis for theorigin and evolution of the Earth s
15、 aerobic organisms13.Cyanobacteria are widely distributed in various habitats onthe Earth,even dry stones and hot spring over 60 C 14,15.That cyanobacteria can adapt to a variety of harshenvironmental conditions,may be attributed to their variousecological strategies and special metabolic mechanisms
16、 16,17.One of them,the excreted EPS play an important role intheir environmental adaptability:(1)as a protective layer outof cyanobacterial cells,the excreted EPS prevent the entranceof external toxic and harmful substances into cells 16,18;(2)the EPS provide a matrix for other extracellular substan
17、cessuch as trehalose and sucrose,which can lower the phasetransition temperature(Tm)of plasma membrane and form thecarbohydrate glass to prevent fusion of membrane vesicles 17,19;(3)some specific water stress proteins and UV-absorbingsubstances accumulated in EPS can ensure the stability of cellstru
18、cture and alleviate the radiation damage 17,20.Cyanobacterial EPS are a type of polysaccharide sub-stances,which are excreted during the process of cyanobac-terial growth and metabolism 14,19,21,22.Because of theimportant role in environment adaptation and applicationprospects,cyanobacterial EPS hav
19、e recently received a greatdeal of attention 4,912,21.However,for the time being,allthe prospects can only be stayed at laboratory stage,just be-cause the exopolysaccharide yield is limited.So how to improvecyanobacterial exopolysaccharide yield is an important issueto promote exopolysaccharide appl
20、ication.Many studies haveconfirmed that environmental factors,such as light and tem-perature,have significant effects on the excretion of EPS 16,18,21,23.Especially as the energy source of photosyntheticorganisms,light has a particularly important effect on theexcretion of EPS 22,24,and it was found
21、 that cyanobacterialEPS accumulation increased with the increasing light intensityin the range of 2080 E m2Sec124.In the current microalgal cultivation,for most of the con-ditions,it is always provided as the surface light intensity(onthe closest photoreactor surface from the light source)18,25.Howe
22、ver,the actual light energy absorbed by microalgalcells may be obviously different from each other in differentcultivations because the self-shading effect caused by differentconcentration will seriously affect the light energy absorption,even if the surface light intensity is consistent and same.Th
23、ere-fore,we speculate that different inoculation concentrationwould not only affect microalgal growth and biomass accumu-lation,but also might have a significant effect on the secretionof EPS.Therefore,in this study,the growth,photosyntheticactivity and EPS secretion were monitored under differentin
24、oculation concentrations of Microcoleus vaginatus,whichhas been wildly found as the dominant species of biological soilcrusts in global arid and semiarid areas 26,27,and is alsoused as the inoculum in desertification control 27.The effectsof inoculation concentration on the secretion and accumulatio
25、nof EPS were further discussed from the points of microalgalcultivation,biomass,and exopolysaccharide accumulation.Theresults will not only provide guidance for adjusting light inten-sity in the process of microalgal cultivation,but also provideimportant theoretical basis for improving microalgal EP
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