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Methodsofscreening,culturing,improvementandstorageofmicroorganisms...
thatmakethemusefulinbiotechnologyhavebeenisolatedfor
years,fromthesoilenvironment.
Soilisanaturalhabitatformanyspeciesofmicroorganisms.
Itconsistsofmineralcompoundsandorganicsubstances(50%
ofthesoilcomposition),soilgas(about35%)andsoilsolution
(15%).Thesolidpartofthesoilconsistsmainlyofsoilcolloids.The
mostimportantfunctionisperformedbyorganiccolloids(humic
compounds),whichareformedasaresultofthedecomposition
oforganicmatterbymicroorganisms.Mineralcolloids,onthe
otherhand,determinewater-airrelations.Soilwater,containing
dissolvedorganicandmineralsubstances,iscalledsoilsolution.
ThissoilfractionhasbuferpropertiesanddeterminesthepHofthe
soil.Thespacebetweensoilparticles(unoccupiedbysoilsolution)
isfilledbythesoilgas.ThesoilgasconsistsmainlyofNH
3
,CO
2
,N
2
andO
2
,alsoofsmallerquantitiesofH
2
SandCH
4
.Soilstructureis
composedofmineralgrains,whicharegluedtogetherbyhumic
compoundsandmucous,forming0.5-5mmsizeparticles.The
microorganismsarelocatedonthesurfaceofparticlesinhumic
substances,aswellasinorgano-mineralcomplexes.
Soilisrichinmicrobiotainpartiallydecomposedorganic
matter(humus).Largerclusters,theso-calledsoilaggregates,
arebuiltfromsoilparticles.Theexterioroftheseclustersis
inhabitedmainlybyspore-formingbacteria,actinomycetes
andfilamentousfungi.Theinnerpartiscolonisedbybacteria
assimilatingmineralnitrogencompounds,other(mainlyGram-
negative)bacteria,andFusariummoulds.
Soilmicrobiotaareabundantanddependonthetypeof
soil,includingchemicalcomposition(inorganicandorganic
compounds),pH,oxygenavailability,humidity,temperature,
depth,geographicalzone,presenceofplants.Ingeneral,
soilmicrobiotaaredividedinto:autochthonousmicrobiota
(constantlypresentinthesoil)andzymogenousmicrobiota
(introducedperiodically).Thesourceofcarbonandenergyfor
theautochthonousmicrobiotaarehumussubstances(compounds
formedfromthedecompositionoforganicmatterofplantand
animalorigin).Thedevelopmentofthezymogenousmicrobiota
dependsontheinflowofeasilyassimilableorganicmatter.
Filamentousfungiandasignificantproportionofbacteriaprefer
moistenvironments.Microorganismswithlowwaterrequirements
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