1492Ch06

Manahan,StanleyE.AQUATICMICROBIALBIOCHEMISTRYEnvironmentalChemistryBocaRaton:CRCPressLLC,20006AQUATICMICROBIALBIOCHEMISTRY____________________________________________________6.1.AQUATICBIOCHEMICALPROCESSESMicroorganisms—bacteria,fungi,protozoa,andalgae—arelivingcatalyststhatenableavastnumberofchemicalprocessestooccurinwaterandsoil.Amajorityoftheimportantchemicalreactionsthattakeplaceinwater,particularlythoseinvolvingorganicmatterandoxidation-reductionprocesses,occurthroughbacterialintermediaries.Algaearetheprimaryproducersofbiologicalorganicmatter(biomass)inwater.Microorganismsareresponsiblefortheformationofmanysedimentandmineraldeposits;theyalsoplaythedominantroleinsecondarywastetreatment.SomeoftheeffectsofmicroorganismsonthechemistryofwaterinnatureareillustratedinFigure6.1.Pathogenicmicroorganismsmustbeeliminatedfromwaterpurifiedfordomesticuse.Inthepast,majorepidemicsoftyphoid,cholera,andotherwater-bornediseasesresultedfrompathogenicmicroorganismsinwatersupplies.Eventoday,constantvigilanceisrequiredtoensurethatwaterfordomesticuseisfreeofpathogens.Althoughtheyarenotinvolvedinaquaticchemicaltransformations,whichcons-titutemostofthischapter,specialmentionshouldbemadeofvirusesinwater.Virusescannotgrowbythemselves,butreproduceinthecellsofhostorganisms.Theyareonlyabout1/30-1/20thesizeofbacterialcells,andtheycauseanumberofdiseases,suchaspolio,viralhepatitis,andperhapscancer.Itisthoughtthatmanyofthesediseasesarewaterborne.Becauseoftheirsmallsize(0.025-0.100µm)andbiologicalcharacteristics,virusesaredifficulttoisolateandculture.Theyoftensurvivemunicipalwatertreat-ment,includingchlorination.Thus,althoughviruseshavenoeffectupontheoverallenvironmentalchemistryofwater,theyareanimportantconsiderationinthetreatmentanduseofwater.Microorganismsaredividedintothetwobroadcategoriesofprokaryotesandeukaryotes;thelatterhavewell-definedcellnucleienclosedbyanuclearmem-brane,whereastheformerlackanuclearmembraneandthenucleargeneticmaterial©2000CRCPressLLCismorediffuseinthecell.Otherdifferencesbetweenthesetwoclassesoforganismsincludelocationofcellrespiration,meansofphotosynthesis,meansofmotility,andreproductiveprocesses.Allclassesofmicroorganismsproducespores,metabolicallyinactivebodiesthatformandsurviveunderadverseconditionsina“resting”stateuntilconditionsfavorableforgrowthoccur.CO2tobiomassbyalgaeinsunlight.pHmayriseenoughtoproduceCaCO3.{CH2O}degradedtoCO2bybacteriainpresenceofO2.DeadalgalbiomassdegradedbybacteriaReducedformsofsomeelementsproducedbybacteriainabsenceofO2;forexample,SO4-H2S,whichproducessulfideminerals.CH4maybeproduced.2Fungiandbacteriaonlandconvertdeadbiomasstoinorganicmaterialanddegradation-resistantorganicslikefulvicacids.Someofthesepro-ductsenterwater.Figure6.1.Effectsofmicroorganismsonthechemistryofwaterinnature.Fungi,protozoa,andbacteria(withtheexceptionofphotosyntheticbacteriaandprotozoa)areclassifiedasreducers,whichbreakdownchemicalcompoundstomoresimplespeciesandtherebyextracttheenergyneededfortheirgrowthandmetabolism.Algaeareclassifiedasproducersbecausetheyutilizelightenergyandstoreitaschemicalenergy.Intheabsenceofsunlight,however,algaeutilizechem-icalenergyfortheirmetabolicneeds.Inasense,therefore,bacteria,protozoa,andfungimaybelookeduponasenvironmentalcatalysts,whereasalgaefunctionasaquaticsolarfuelcells.Allmicroorganismscanbeputintooneofthefourfollowingclassificationsbasedonthesourcesofenergyandcarbonthattheyutilize:chemoheterotrophs,chemoautotrophs,photoheterotrophs,andphotoautotrophs.Theseclassificationsarebasedupon(1)theenergysourceand(2)thecarbonsourceutilizedbytheorganism.Chemotrophsusechemicalenergyderivedfromoxidation-reductionreactionsofsimpleinorganicchemicalspeciesfortheirenergyneeds.Phototrophsutilizelightenergyfromphotosynthesis.Heterotrophsobtaintheircarbonfromotherorganisms;autotrophsusecarbondioxideandioniccarbonatesfortheCthattheyrequire.Figure6.2summarizestheclassificationsintowhichmicroorganismsmaybeplacedwiththesedefinitions.©2000CRCPressLLCEnergysourceCarbonsourcesChemicalPhotochemical(light)ChemoheterotrophsPhotoheterotrophsOrganicmatterInorganiccarbon(CO2,HCO3)-ChemoautotrophsPhotoautotrophsUseCO2forbiomassandoxidizesubstancessuchasH2(Pseudomonas),NH4(Nitrosomonas),S(Thio-bacillus)forenergyAlgae,cyanobacteria(“blue-greenalgae”),photosyntheticbacteriathatuselightenergytoconvertCO2(HCO3)tobiomassbyphotosynthesis-+Allfungiandprotozoans,mostbacteria.Chemoheter-otrophsuseorganicsourcesforbothenergyandcarbon.Afewspecializedbacteriathatusephotoenergy,butaredependentonorganicmatterforacarbonsourceFigure6.2.Classificationofmicroorganismsamongchemoheterotrophs,chemoautotrophs,photo-heterotrophs,andphotoautotrophs.MicroorganismsatInterfacesAquaticmicroorganismstendtogrowatinterfaces.Manysuchmicroorganismsgrowonsolidsthataresuspendedinwaterorarepresentinsediments.Largepopulationsofaquaticbacteriatypicallyresideonthesurfaceofwaterattheair-waterinterface.1Inadditiontobeingincontactwithairthataerobicmicroorganismsneedfortheirmetabolicprocesses,thisinterfacealsoaccumulatesfoodintheformoflipids(oils,