Yeast biofilm colony as an orchestrated multicellular organism.

2012·0.97 MB·English

by  Stovicek, Vratislav

ARTICLEADDENDUM
Communicative&IntegrativeBiology5:2,203–205;March/April2012;G2012LandesBioscience
Yeast biofilm colony as an orchestrated multicellular organism
Vratislav Št’ovíček,1 Libuše Váchová1,2 and Zdena Palková1,*
1DepartmentofGeneticsandMicrobiology;FacultyofScience;CharlesUniversityinPrague;Prague,CzechRepublic;2InstituteofMicrobiologyASCR;
Prague,CzechRepublic
Although still often considered as differentiated cell subpopulations and
simple unicellular organisms, in also possesses a significant resistance to
natural settings yeast cells tend to environmental impacts. Pathogenic yeasts
organize into intricate multicellular com- (i.e., of Candida sp.) can colonise various
munities.Duetospecificmechanismsonly surfaceswithinthehumanbody,including
feasible at the population level, their host tissues and artificial medical devices,
capacityforsocialbehaviorisadvantageous and form biofilms that resist otherwise
for their survival in a harmful environ- effective drug therapy. Biofilms are thus
ment.FeralSaccharomycescerevisiaestrains very difficult to eliminate and serve as a
form complex structured colonies, which source of serious systemic infections.6,7
display many properties typical of natural The questions of how yeast multicellular
biofilms causing (among others) serious populations orchestrate their development
infections in the human body. In our and how they achieve their environmental
recent paper, we looked inside a growing protection are therefore also important in
colony using two-photon confocal micro- terms of medical care. However, as it is
scopy. This allowed us to elucidate its difficult to grow artificial biofilms in the
three-dimensional colony architecture and laboratory that have properties similar to
some mechanisms responsible for com- those of fully developed natural biofilms,
munity protection. Moreover, we showed manyaspects ofbiofilmformation arestill
how particular protective mechanisms rather elusive.
complement each other during colony Single cells of feral S. cerevisiae strains
development and how each of them plated on solid medium retain the ability
contributes to its defense against attacks to develop into structured colonies with
from the environment. Our findings typical “fluffy” morphology3,8 within a
broaden current understanding of micro- coupleofdaysofgrowth.Asshownbelow,
bial multicellularity in general and also such colonies share many properties with
shednewlightontheenormousresistance natural biofilms, and we therefore call
Keywords: structured colony,
ofyeastbiofilms. thembiofilmcolonies.Thebiofilmcolony
Saccharomyces cerevisiae, feral strains,
model enabled us to discover the spatio-
biofilm, drug efflux pumps,
temporal localization of specific cell sub-
extracellular matrix
Microbial multicellular communities can populations with different functions and
Submitted: 11/30/11 be found in various (even extreme) determine their impact on the protection
Accepted: 12/01/11 environments in the wild.1 Yeast cells can and survival of the whole colony.
form diverse structures when attached to After relatively few cell divisions occur
http://dx.doi.org/10.4161/cib.18912
solid surfaces (e.g., biofilms,2 colonies3), and a simple mound colony is formed,
*Correspondenceto:ZdenaPalková;
when growing at a liquid/air interface particular cell subpopulations begin to
Email:[email protected]
(e.g., cell films on the surface of sherry diverge and play different roles. Cells at
wine that are called “flors”4) or when they the colony base form elongatedcell chains
Addendumto:VáchováL,StovícekV,HlavácekO,
ChernyavskiyO,StĕpánekL,KubínováL,etal. mutually interact in a liquid environment called pseudohyphae.9 These filaments
Flo11p,drugeffluxpumps,andtheextracellular and form cell clumps called “flocs”5. Each invade the agar medium, anchoring the
matrixcooperatetoformbiofilmyeastcolonies.J of these structures possesses some level structure to the solid substrate. Cells in
CellBiol2011;194:679–87;PMID:21875945; of internal cell organization and comple- peripheral layers surrounding the entire
http://dx.doi.org/10.1083/jcb.201103129
xity connected with the formation of colony (including subsurface parts) are
www.landesbioscience.com Communicative&IntegrativeBiology 203
Figure1.InternalstructureofcolonyofferalSaccharomycescerevisiaestrain.Thirty-sixh-old(left)and72h-old(right)colony.Boxesinverticalcolony
cross-sectionssummarizestructureandfunctionofcellsubpopulationsinupperaerialandbottomsubsurfacecolonyparts;thelocalizationofdividing,
non-dividingandstationarycellsisdepicted,aswellascellswithactivedrugeffluxpumpsPdr5pandSnq2p.ThepresenceofECMismarkedwith
blacklinehatching.Flo11p-dependentfibersinterconnectcellsinbothaerialandsubsurfacecolonyparts.
equipped with drug-efflux pumps (Pdr5p biofilms and planktonic cells,11,12 without biofilms.2,13,14 Despite the sequestration
and Snq2p) localized to the plasma mem- more detailed information on the trans- potential of the ECM in clinical biofilms
brane, the expression of which is con- porter’s function over the course of being implied,15,16 its contribution to bio-
trolled by Pdr1p together with another, community development. In addition to film resistance is unclear and sometimes
as yet unidentified transcription factor the presence of these pumps, cells at the evendoubted.7,17Asacolonydevelops,the
(Fig.1). These proteins that belong to surfacelayersoftheaerialcolonypartenter area of cells embedded in ECM expands
the family of pleiotropic drug resistance the stationary phase and thus become (Fig.1); in later stages, the ECM encloses
membrane transporters are capable of more resistant to potential environmental almost all colony cells. Complementarily,
removing various (including toxic) sub- stress (Fig.1). Meanwhile, cells in inter- the layer of cells containing functional
stances from the cells10 and protect them nal colony areas start to produce extra- drug-effluxpumpssurroundingthecolony
(and thus also the whole colony) against cellularpolymericmatrix(ECM; Fig.1)of becomes thinner as the transporters are
external attacks. It has been demonstrated unknown composition and thus become degraded (Fig.1) and almost completely
that various drug-efflux pumps play a fully embedded in this matrix. The ECM disappears in an older, fully developed
role in yeast biofilm resistance against apparently adopts the role of a protective colony.Onlythetipsofthepseudohyphae
extracellularly added toxic compounds. barrier, because it blocks the penetration in the agar not covered with ECM still
However, this has usually been based on of even harmful compounds. ECM is one maintain functional drug efflux pumps on
the overall change in behavior of mutated of the defining components of many the membrane, thus enabling the active
strains or expression differences between yeast multicellular communities including defense of these exposed cells.
204 Communicative&IntegrativeBiology Volume5Issue2
From the early developmental stage areobservedthroughouttheentirecolony, colonies expanding predominantly in the
(34–42 h), a cell-free cavity in the colony including subsurface filamentous cells horizontaldirection.3,8,22Cellswithinsuch
interior is formed. As the timing of its invading the agar (Fig.1). Cell-cell and colonies are tightly packed and neither
formation correlates with the appearance cell-substrate adhesion is another feature pores nor cavities can be observed.3,22 In
of ECM, we can speculate that the cavity typical of multicellular communities18,19 contrast, the strategy of feral strains is to
couldbefilledwithECM.TheECMmay and is often ascribed as a function of cell quickly occupy territory ahead of com-
also be involved in the storage of water wall adhesive proteins, including the FLO petitors, to build a complex structure
and possibly nutrients, as the extracellular familyofS.cerevisiae.19,20Frommutantsin protected by several cooperating mecha-
material isolated from colonies possesses a individual FLO genes, only those lacking nismssoastoprovideashelteredspacefor
high water retention capacity.8 Moreover, FLO11areunabletodevelopa3Dcolony new cell generations. Despite the high
it may provide a porous nutrient-rich architecture and they form smooth and energy costs, it is advantageous to build
spacefordividingcellsinthecolonyinter- flat colonies.8,21 Dflo11 colonies also lack such a complicated structure, because it
ior. Together with the division of internal intercellular connections, suggesting that enables the community to effectively cope
cells, site-specific ECM production and Flo11p has a unique function in the for- with a hostile environment. Thus, a
its subsequent swelling can lead to rapid mationoffibrouscell-cellinterconnections structured biofilm yeast colony should be
colony expansion in both the horizontal in biofilm colonies. considered to be a multicellular organism,
andverticaldirection.Asaresult,theaerial In plentiful and stable laboratory con- where everything is subordinated to the
surface layer undulates and forms ridges ditions, colonies no longer need the traits success of the community, regardless of
containingothercavities,givingthecolony described above. They are therefore individual cell fate.
its typical “fluffy” appearance. switched off and energy, otherwise con-
In addition to ECM that may provide sumed in e.g., the production of an ECM Acknowledgments
stability to the 3-D colony structure, the rich in polysaccharides, could be used in This work was supported by the Grant
flexibility and undulation of the surface a more profitable way.1 Thus, laboratory Agency of the Czech Republic 204/08/
colony layer could be dependent on the and domesticated strains (those arising 0718 and the Ministry of Education
presence of fibrous interconnections after passages of feral strains on complex LC531, LC06063; MSM0021620858
between the cells. These interconnections media)3 form non-adhesive, smooth flat and AV0Z50200510.
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