Inoculation concentration modulating the secretion and accumulation pattern of exopolysaccharides.pdf

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 James 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 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 to 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 inoculationconcentration.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 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 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 environmental 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,Peoples 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 Institute,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,microalgalcultivation 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 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 1,6;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 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 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 16,17.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 substancessuch 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 wate