Microbialspeciesinteractionscontrollitterdecomposition
EstherPlotnick1,CarolynA.Zeiner2,Caylon Yates2,JenniferM.Talbot2
LindenHall,Lititz,PA1;Dept.ofBiology,BostonUniversity,Boston,MA2
Abstract
Results
Acomplexcommunityofmicroorganismsdecomposeplantlitter(deadorganicmaterial),
releasingcarbon (C)fromthesoiltotheatmosphereinoneofthemostimportantstepsin
theglobalCcycle.However,itispoorlyunderstoodhowbiologicalinteractionsamong
microorganismsaffecttheprocessofdecompositionandmicrobialcarbonutilization.Inthis
study,wecharacterizedplantlittermassduringinteractionsamongpairsofmodel
decomposerfungiandbacteria.Tenspeciesoffungiandfivespeciesofbacteriawere
culturedtogetheronplantlitterinlaboratorymicrocosmsoverfourweeks.Decayrateof
litter(aspercentmassloss)wasmeasuredusingstandardprotocols.Fungal-bacterial
interactionsslowedlitterdecayrateswhilefungal-fungalinteractionsstimulatedlitterdecay.
Thisworkaidsourunderstandingofdecompositionatamicrobiallevelandtheroleof
species’interactionsincarboncycling.
Hypothesis1:Thepresenceofbacteriahindersplantlitterdecaybyfungi
Background
Average%MassLoss
perDay
1.40%
A
A
1.20%
P=.000,bars=standarderror
1.00%
Interestingly,fungalfungalcompetition
didnotsignificantly
promotelitterdecay
0.80%
0.60%
0.40%
B
0.20%
0.00%
FungiAlone
-0.20%
Fungiv.Fungi(Other)
Fungivs.Bacteria
• Fungal-fungalinteractionsmaystimulateorhinderdecay
becauseofinterspeciescompetitionforresources
• e.g.fungimayexpandtheirterritorytosequester
resourcesfromtheircompetitors
• Interactionsamongmicrobesofdifferenttypes(e.g.
Decompositioninthecarbon
bacteriaandfungi)maystimulateorhinderdecaybecause
cycle1
ofstrongantagonismamongthecompetingmicrobes
• e.g.fungiandbacteriamayproduceantimicrobialcompounds
• Though incrediblydiverse,decomposerfungiandbacteriahave evolvedtobe
as efficientaspossible atinducingdecay(andobtainingC resources) acrossspecies
• OBJECTIVE:Determineifmicrobialinteractionsamongdecomposerfungiandbacteria
affectrateofplantlitterdecomposition
Hypotheses
Average%MassLossperDay
• Howdecompositionoccursandtheeffectofmicrobial
interactionsondecayarenotwellunderstood
Average%MassLossperDay
Hypothesis2:Interactiontypedetermineslittermasslossinfungalspecies
• Fungiandbacteriaareapartofacomplexcommunityof
interactingmicrobesinthesoilthatdecomposeplantlitter
Fungivs.Fungi
1.75%
1.50%
1.25%
1.00%
0.75%
0.50%
0.25%
0.00%
1.25%
A
A
A
P=.184,bars=standarderror
A
Fungivs.Bacteria
1.00%
0.75%
A
0.50%
A
A
A
A
P=.090,bars=standarderror
A
A
A
A
A
0.25%
0.00%
-0.25%
1. Fungalspeciescompeteforresourcesà increased plantlittermassloss
bacterianegativelyaffectfungalgrowthà decreased plantlittermassloss
2. Interactiontypeistheprimarydeterminantofdecompositionrateoverspeciesà
different speciesdecomposelitterinsimilar waysregardinginteractiontype
Methods
StudySystem
• 10speciesofmodeldecomposerfungi
• 5speciesofco-occurringbacteria
• Arabidopsisthalianaplantlitter
ExperimentalDesign
• PetridisheswithModifiedMelin Norkrans
(MMN)media
• Speciesinoculatedinco-cultureand
monoculture(N=490)
• Harvestedafter30-35days
LitterMassLoss
• Comparisonoflitterdryweightsbeforeand
afterharvest
1
3
2
Cladosporium longipes
(fungus)incompetition
onplantlitterwith1:
Cladosporium longipes
(fungus) 2:Cladosporium
herbarum (fungus)3:
Sphingomonus wittichii
(bacterium)
DiscussionandConclusion
• Bacterialcompetitorshinderedlitterdecay,suggestingthatthebacteriareduce
fungalgrowthandabilitytodecomposethelitter
• Aloneandincompetition,fungitendedtogalvanizelitterdecay,suggestingthatfungi
drivethedecayprocess,notbacteria
• Competitiontyperatherthanspecies-specificinteractionsdeterminedplantlitter
massloss
• FutureResearchQuestions:
• Whatarethemechanismsbywhichinteractiontypeaffects
decomposition?
• Howmuchmicrobialbiomassaccumulatesonlitterinthesescenarios?
References
1.Mayes,Melanie. OakRidgeNationalLab.ORNL
researchersimprovesoilcarboncyclingmodels.
https://goo.gl/EwF8Nj(accessedJul26,2016).
Acknowledgements
RISE
TalbotLabofMicrobialEcology
Microbial species interactions drive litter decomposition
Esther Plotnick1, Carolyn A. Zeiner2, Caylon Yates2, Jennifer M. Talbot2
Linden Hall, Lititz, PA1; Department of Biology, Boston University, Boston, MA2
A complex community of microorganisms decompose plant litter (dead organic material),
releasing carbon from the soil to the atmosphere in one of the most important steps in the global
carbon cycle. However, it is poorly understood how biological interactions among fungi and
bacteria affect the process of decomposition and microbial carbon utilization. In this study, we
characterized plant litter mass loss and changes in litter chemical composition during interactions
among pairs of model decomposer fungi and bacteria. Ten species of fungi and five species of
bacteria were cultured together on plant litter in laboratory microcosms over four weeks. Decay
rate of litter (as percent mass loss) and changes in litter chemical composition were measured using
standard protocols. Fungal-bacterial interactions slowed litter decay rates, while fungal-fungal
interactions stimulated litter decay. Bacteria alone were ineffective at decomposing litter; however,
the fungal-bacterial interactions increased consumption of soluble sugars compared to species in
isolation. This work aids our understanding of decomposition at a microbial level and the role of
species’ interactions in carbon cycling.