Treść książki

Przejdź do opcji czytnikaPrzejdź do nawigacjiPrzejdź do informacjiPrzejdź do stopki
Microbialbiotechnologyinthelaboratoryandinpractce
developindrysoils-theyarexerophilicmicroorganisms.
ActinomycetesandnitrifyingbacteriaoftheArthrobactergenus
alsoinhabitdrysoils.Wetsoils,whichhavealimitedamountof
nutrientsandoxygen,areabundantinanaerobicandfacultative
microorganism.Biodiversityofsoilmicrobiotaalsodependson
temperature.Thebesttimeofyearforthemicroorganism’sisolation
isspring.Inwinter,thesoilmicrobiotaissignificantlyreduced.
Animportantparameterthatdeterminesthedevelopmentof
microorganismsinthesoilispH.SoilswithalkalineorneutralpH
containseveraltimesmoremicroorganismsthanacidicsoils(e.g.
peatlands).Fertilesoil,richinhumussubstances,isalsorichin
microbiotacomparedtocompactedmeadowsoil.
Microorganismsareverysensitivetosunlight(UVsolar
radiation)andwind(drying),soveryfewdwellonthesoilsurface.
Mostmicroorganismsarepresentintherootzone
(rhizosphere)andontherootsurface(rhizoplane).Ontheother
hand,thenumberofmicroorganismsismuchsmallerindeeper
soillayers(atthedepthof1-2m).
102030Microbialscreening
Specialscreeningmethodshavebeendevelopedinordertoobtain
newstrainsfromtheenvironment.Thescreeningcanbedefinedas
asetofselectiveproceduresaimedatisolatingfromalargenumber
ofmicroorganisms,onlythosethatmeetspecifictechnological
requirements.Screeningalsoincludesapreliminaryassessment
oftheirsuitabilityforagivenprocess,e.g.assessmentoftheir
biodegradationpotential.Intheinitialstageofscreening,weare
dealingwithmicroorganismswithundefinedsystematicafliation,
whichmayalsoincludepathogenicstrains.Usuallystrains
isolateddirectlyfromtheenvironmentproducesmallamountsof
metabolitesofinterest.Onlyaftertheyhavebeenenhanced,using
geneticandmicrobiologicaltechniques(seeSection1.6),canstrains
beusedonanindustrialscale.Anefectiveandsimpletechnique
fortheisolationofmicroorganismsistheselectivemultiplication
ofcultures.Inthiscase,strictlydefinedmediaandspecificculture
conditionsareused,i.e.,mediumcomposition,temperature,pH,
osmoticpressure,lightavailability,oxygenavailability,whichallow
thegrowthofaspecificgroupofmicroorganisms(Table1.2.1).
24