Quorum Sensing Influences Burkholderia thailandensis Biofilm Development and Matrix Production

ABSTRACTMembers of the genusBurkholderiaare known to be adept at biofilm formation, which presumably assists in the survival of these organisms in the environment and the host. Biofilm formation has been linked to quorum sensing (QS) in several bacterial species. In this study, we characterizedBurkholderia thailandensisbiofilm development under flow conditions and sought to determine whether QS contributes to this process.B. thailandensisbiofilm formation exhibited an unusual pattern: the cells formed small aggregates and then proceeded to produce mature biofilms characterized by “dome” structures filled with biofilm matrix material. We showed that this process was dependent on QS.B. thailandensishas three acyl-homoserine lactone (AHL) QS systems (QS-1, QS-2, and QS-3). An AHL-negative strain produced biofilms consisting of cell aggregates but lacking the matrix-filled dome structures. This phenotype was rescued via exogenous addition of the three AHL signals. Of the threeB. thailandensisQS systems, we show that QS-1 is required for proper biofilm development, since abtaR1mutant, which is defective in QS-1 regulation, forms biofilms without these dome structures. Furthermore, our data show that the wild-type biofilm biomass, as well as the material inside the domes, stains with a fucose-binding lectin. ThebtaR1mutant biofilms, however, are negative for fucose staining. This suggests that the QS-1 system regulates the production of a fucose-containing exopolysaccharide in wild-type biofilms. Finally, we present data showing that QS ability during biofilm development produces a biofilm that is resistant to dispersion under stress conditions.IMPORTANCEThe saprophyteBurkholderia thailandensisis a close relative of the pathogenic bacteriumBurkholderia pseudomallei, the causative agent of melioidosis, which is contracted from its environmental reservoir. Since most bacteria in the environment reside in biofilms,B. thailandensisis an ideal model organism for investigating questions inBurkholderiaphysiology. In this study, we characterizedB. thailandensisbiofilm development and sought to determine if quorum sensing (QS) contributes to this process. Our work shows thatB. thailandensisproduces biofilms with unusual dome structures under flow conditions. Our findings suggest that these dome structures are filled with a QS-regulated, fucose-containing exopolysaccharide that may be involved in the resilience ofB. thailandensisbiofilms against changes in the nutritional environment.

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Malleilactone Is a Burkholderia pseudomallei Virulence Factor Regulated by Antibiotics and Quorum Sensing

Journal of Bacteriology ◽

10.1128/jb.00008-18 ◽

2018 ◽

Vol 200 (14) ◽

Cited By ~ 19

Author(s):

Jennifer R. Klaus ◽

Jacqueline Deay ◽

Benjamin Neuenswander ◽

Wyatt Hursh ◽

Zhe Gao ◽

...

Keyword(s):

Transcription Factor ◽

Caenorhabditis Elegans ◽

Quorum Sensing ◽

Virulence Factor ◽

Mammalian Cells ◽

Burkholderia Pseudomallei ◽

Gene Clusters ◽

Close Relative ◽

Burkholderia Thailandensis ◽

Content Type

ABSTRACT Burkholderia pseudomallei , the causative agent of melioidosis, encodes almost a dozen predicted polyketide (PK) biosynthetic gene clusters. Many of these are regulated by LuxR-I-type acyl-homoserine (AHL) quorum-sensing systems. One of the PK gene clusters, the mal gene cluster, is conserved in the close relative Burkholderia thailandensis . The B. thailandensis mal genes code for the cytotoxin malleilactone and are regulated by a genetically linked LuxR-type transcription factor, MalR. Although AHLs typically interact with LuxR-type proteins to modulate gene transcription, the B. thailandensis MalR does not appear to be an AHL receptor. Here, we characterize the mal genes and MalR in B. pseudomallei . We use chemical analyses to demonstrate that the B. pseudomallei mal genes code for malleilactone. Our results show that MalR and the mal genes contribute to the ability of B. pseudomallei to kill Caenorhabditis elegans . In B. thailandensis , antibiotics like trimethoprim can activate MalR by driving transcription of the mal genes, and we demonstrate that some of the same antibiotics induce expression of B. pseudomallei malR . We also demonstrate that B. pseudomallei MalR does not respond directly to AHLs. Our results suggest that MalR is indirectly repressed by AHLs, possibly through a repressor, ScmR. We further show that malleilactone is a B. pseudomallei virulence factor and provide the foundation for understanding how malleilactone contributes to the pathology of melioidosis infections. IMPORTANCE Many bacterially produced polyketides are cytotoxic to mammalian cells and are potentially important contributors to pathogenesis during infection. We are interested in the polyketide gene clusters present in Burkholderia pseudomallei , which causes the often-fatal human disease melioidosis. Using knowledge gained by studies in the close relative Burkholderia thailandensis , we show that one of the B. pseudomallei polyketide biosynthetic clusters produces a cytotoxic polyketide, malleilactone. Malleilactone contributes to B. pseudomallei virulence in a Caenorhabditis elegans infection model and is regulated by an orphan LuxR family quorum-sensing transcription factor, MalR. Our studies demonstrate that malleilactone biosynthesis or MalR could be new targets for developing therapeutics to treat melioidosis.

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LitR of Vibrio salmonicida Is a Salinity-Sensitive Quorum-Sensing Regulator of Phenotypes Involved in Host Interactions and Virulence

Infection and Immunity ◽

10.1128/iai.06038-11 ◽

2012 ◽

Vol 80 (5) ◽

pp. 1681-1689 ◽

Cited By ~ 22

Author(s):

Ane Mohn Bjelland ◽

Henning Sørum ◽

Daget Ayana Tegegne ◽

Hanne C. Winther-Larsen ◽

Nils Peder Willassen ◽

...

Keyword(s):

Quorum Sensing ◽

Biofilm Formation ◽

Molecular Mechanisms ◽

Cold Water ◽

Bacterial Species ◽

Cell Communication ◽

Cell Aggregation ◽

Fish Host ◽

Content Type ◽

Vibrio Salmonicida

ABSTRACTVibrio(Aliivibrio)salmonicidais the causal agent of cold-water vibriosis, a fatal bacterial septicemia primarily of farmed salmonid fish. The molecular mechanisms of invasion, colonization, and growth ofV. salmonicidain the host are still largely unknown, and few virulence factors have been identified. Quorum sensing (QS) is a cell-to-cell communication system known to regulate virulence and other activities in several bacterial species. The genome ofV. salmonicidaLFI1238 encodes products presumably involved in several QS systems. In this study, the gene encoding LitR, a homolog of the master regulator of QS inV. fischeri, was deleted. Compared to the parental strain, thelitRmutant showed increased motility, adhesion, cell-to-cell aggregation, and biofilm formation. Furthermore, thelitRmutant produced less cryptic bioluminescence, whereas production of acylhomoserine lactones was unaffected. Our results also indicate a salinity-sensitive regulation of LitR. Finally, reduced mortality was observed in Atlantic salmon infected with thelitRmutant, implying that the fish were more susceptible to infection with the wild type than with the mutant strain. We hypothesize that LitR inhibits biofilm formation and favors planktonic growth, with the latter being more adapted for pathogenesis in the fish host.

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AbaM Regulates Quorum Sensing, Biofilm Formation and Virulence in Acinetobacter baumannii

Journal of Bacteriology ◽

10.1128/jb.00635-20 ◽

2021 ◽

Author(s):

Mario López-Martín ◽

Jean-Frédéric Dubern ◽

Morgan R. Alexander ◽

Paul Williams

Keyword(s):

Quorum Sensing ◽

Acinetobacter Baumannii ◽

Biofilm Formation ◽

Plant Pathogens ◽

Galleria Mellonella ◽

Homoserine Lactone ◽

Infection Model ◽

Wild Type ◽

Surface Motility ◽

Biofilm Development

Acinetobacter baumannii possesses a single divergent luxR/luxI-type quorum sensing (QS) locus named abaR/abaI. This locus also contains a third gene located between abaR and abaI which we term abaM that codes for an uncharacterized member of the RsaM protein family known to regulate N-acylhomoserine lactone (AHL) dependent QS in other β- and γ-proteobacteria. Here we show that disruption of abaM via a T26 insertion in A. baumannii strain AB5075 resulted in increased production of N-(3-hydroxydodecanoyl)-L-homoserine lactone (OHC12) and enhanced surface motility and biofilm formation. In contrast to the wild type and abaI::T26 mutant, the virulence of the abaM::T26 mutant was completely attenuated in a Galleria mellonella infection model. Transcriptomic analysis of the abaM::T26 mutant revealed that AbaM differentially regulates at least 76 genes including the csu pilus operon and the acinetin 505 lipopeptide biosynthetic operon, that are involved in surface adherence, biofilm formation and virulence. A comparison of the wild type, abaM::T26 and abaI::T26 transcriptomes, indicates that AbaM regulates ∼21% of the QS regulon including the csu operon. Moreover, the QS genes (abaI/abaR) were among the most upregulated in the abaM::T26 mutant. A. baumannii lux-based abaM reporter gene fusions revealed that abaM expression is positively regulated by QS but negatively auto-regulated. Overall, the data presented in this work demonstrates that AbaM plays a central role in regulating A. baumannii QS, virulence, surface motility and biofilm formation. Importance Acinetobacter baumanni is a multi-antibiotic resistant pathogen of global healthcare importance. Understanding Acinetobacter virulence gene regulation could aid the development of novel anti-infective strategies. In A. baumannii, the abaR and abaI genes that code for the receptor and synthase components of an N-acylhomoserine (AHL) lactone-dependent quorum sensing system (QS) are separated by abaM. Here we show that although mutation of abaM increased AHL production, surface motility and biofilm development, it resulted in the attenuation of virulence. AbaM was found to control both QS-dependent and QS-independent genes. The significance of this work lies in the identification of AbaM, an RsaM ortholog known to control virulence in plant pathogens, as a modulator of virulence in a human pathogen.

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The CpAL Quorum Sensing System Regulates Production of Hemolysins CPA and PFO To Build Clostridium perfringens Biofilms

Infection and Immunity ◽

10.1128/iai.00240-15 ◽

2015 ◽

Vol 83 (6) ◽

pp. 2430-2442 ◽

Cited By ~ 18

Author(s):

Jorge E. Vidal ◽

Joshua R. Shak ◽

Adrian Canizalez-Roman

Keyword(s):

Quorum Sensing ◽

Clostridium Perfringens ◽

Biofilm Formation ◽

Extracellular Dna ◽

Wild Type ◽

Content Type ◽

Type C ◽

Enteritis Necroticans ◽

Biofilm Structure

Clostridium perfringensstrains produce severe diseases, including myonecrosis and enteritis necroticans, in humans and animals. Diseases are mediated by the production of potent toxins that often damage the site of infection, e.g., skin epithelium during myonecrosis. In planktonic cultures, the regulation of important toxins, such as CPA, CPB, and PFO, is controlled by theC. perfringensAgr-like (CpAL) quorum sensing (QS) system. Strains also encode a functional LuxS/AI-2 system. AlthoughC. perfringensstrains form biofilm-like structures, the regulation of biofilm formation is poorly understood. Therefore, our studies investigated the role of CpAL and LuxS/AI-2 QS systems and of QS-regulated factors in controlling the formation of biofilms. We first demonstrate that biofilm production by reference strains differs depending on the culture medium. Increased biomass correlated with the presence of extracellular DNA in the supernatant, which was released by lysis of a fraction of the biofilm population and planktonic cells. Whereas ΔagrBmutant strains were not able to produce biofilms, a ΔluxSmutant produced wild-type levels. The transcript levels of CpAL-regulatedcpaandpfoAgenes, but notcpb, were upregulated in biofilms compared to planktonic cultures. Accordingly, Δcpaand ΔpfoAmutants, in type A (S13) or type C (CN3685) backgrounds, were unable to produce biofilms, whereas CN3685Δcpbmade wild-type levels. Biofilm formation was restored in complemented Δcpa/cpaand ΔpfoA/pfoAstrains. Confocal microscopy studies further detected CPA partially colocalizing with eDNA on the biofilm structure. Thus, CpAL regulates biofilm formation inC. perfringensby increasing levels of certain toxins required to build biofilms.

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Novel Role for the Streptococcus pneumoniae Toxin Pneumolysin in the Assembly of Biofilms

mBio ◽

10.1128/mbio.00655-13 ◽

2013 ◽

Vol 4 (5) ◽

Cited By ~ 39

Author(s):

Joshua R. Shak ◽

Herbert P. Ludewick ◽

Kristen E. Howery ◽

Fuminori Sakai ◽

Hong Yi ◽

...

Keyword(s):

Streptococcus Pneumoniae ◽

Hemolytic Activity ◽

Biofilm Formation ◽

Early Time ◽

Wild Type ◽

Knockout Mutant ◽

Content Type ◽

Biofilm Development ◽

Almost All

ABSTRACTStreptococcus pneumoniaeis an important commensal and pathogen responsible for almost a million deaths annually in children under five. The formation of biofilms byS. pneumoniaeis important in nasopharyngeal colonization, pneumonia, and otitis media. Pneumolysin (Ply) is a toxin that contributes significantly to the virulence ofS. pneumoniaeand is an important candidate as a serotype-independent vaccine target. Having previously demonstrated that aluxSknockout mutant was unable to form early biofilms and expressed lessplymRNA than the wild type, we conducted a study to investigate the role of Ply in biofilm formation. We found that Ply was expressed in early phases of biofilm development and localized to cellular aggregates as early as 4 h postinoculation.S. pneumoniae plyknockout mutants in D39 and TIGR4 backgrounds produced significantly less biofilm biomass than wild-type strains at early time points, both on polystyrene and on human respiratory epithelial cells, cultured under static or continuous-flow conditions. Ply’s role in biofilm formation appears to be independent of its hemolytic activity, asS. pneumoniaeserotype 1 strains, which produce a nonhemolytic variant of Ply, were still able to form biofilms. Transmission electron microscopy of biofilms grown on A549 lung cells using immunogold demonstrated that Ply was located both on the surfaces of pneumococcal cells and in the extracellular biofilm matrix. Altogether, our studies demonstrate a novel role for pneumolysin in the assembly ofS. pneumoniaebiofilms that is likely important during both carriage and disease and therefore significant for pneumolysin-targeting vaccines under development.IMPORTANCEThe bacteriumStreptococcus pneumoniae(commonly known as the pneumococcus) is commonly carried in the human nasopharynx and can spread to other body sites to cause disease. In the nasopharynx, middle ear, and lungs, the pneumococcus forms multicellular surface-associated structures called biofilms. Pneumolysin is an important toxin produced by almost allS. pneumoniaestrains, extensively studied for its ability to cause damage to human tissue. In this paper, we demonstrate that pneumolysin has a previously unrecognized role in biofilm formation by showing that strains without pneumolysin are unable to form the same amount of biofilm on plastic and human cell substrates. Furthermore, we show that the role of pneumolysin in biofilm formation is separate from the hemolytic activity responsible for tissue damage during pneumococcal diseases. This novel role for pneumolysin suggests that pneumococcal vaccines directed against this protein should be investigated for their potential impact on biofilms formed during carriage and disease.

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O-Mannosylation in Candida albicans Enables Development of Interkingdom Biofilm Communities

mBio ◽

10.1128/mbio.00911-14 ◽

2014 ◽

Vol 5 (2) ◽

Cited By ~ 41

Author(s):

Lindsay C. Dutton ◽

Angela H. Nobbs ◽

Katy Jepson ◽

Mark A. Jepson ◽

M. Margaret Vickerman ◽

...

Keyword(s):

Cell Wall ◽

Candida Albicans ◽

Biofilm Formation ◽

Early Stage ◽

Growth Conditions ◽

Wild Type ◽

Content Type ◽

Subsequent Performance ◽

Biofilm Development ◽

Mutant Cells

ABSTRACTCandida albicansis a fungus that colonizes oral cavity surfaces, the gut, and the genital tract.Streptococcus gordoniiis a ubiquitous oral bacterium that has been shown to form biofilm communities withC. albicans. Formation of dual-speciesS. gordonii-C. albicansbiofilm communities involves interaction of theS. gordoniiSspB protein with the Als3 protein on the hyphal filament surface ofC. albicans. Mannoproteins comprise a major component of theC. albicanscell wall, and in this study we sought to determine if mannosylation in cell wall biogenesis ofC. albicanswas necessary for hyphal adhesin functions associated with interkingdom biofilm development. AC. albicans mnt1Δmnt2Δ mutant, with deleted α-1,2-mannosyltransferase genes and thus defective inO-mannosylation, was abrogated in biofilm formation under various growth conditions and produced hyphal filaments that were not recognized byS. gordonii. Cell wall proteomes of hypha-formingmnt1Δmnt2Δ mutant cells showed growth medium-dependent alterations, compared to findings for the wild type, in a range of protein components, including Als1, Als3, Rbt1, Scw1, and Sap9. Hyphal filaments formed bymnt1Δmnt2Δ mutant cells, unlike wild-type hyphae, did not interact withC. albicansAls3 or Hwp1 partner cell wall proteins or withS. gordoniiSspB partner adhesin, suggesting defective functionality of adhesins on themnt1Δmnt2Δ mutant. These observations imply that early stageO-mannosylation is critical for activation of hyphal adhesin functions required for biofilm formation, recognition by bacteria such asS. gordonii, and microbial community development.IMPORTANCEIn the human mouth, microorganisms form communities known as biofilms that adhere to the surfaces present.Candida albicansis a fungus that is often found within these biofilms. We have focused on the mechanisms by whichC. albicansbecomes incorporated into communities containing bacteria, such asStreptococcus. We find that impairment of early stage addition of mannose sugars toC. albicanshyphal filament proteins deleteriously affects their subsequent performance in mediating formation of polymicrobial biofilms. Our analyses provide new understanding of the way that microbial communities develop, and of potential means to controlC. albicansinfections.

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Forward Genetic Dissection of Biofilm Development byFusobacterium nucleatum: Novel Functions of Cell Division Proteins FtsX and EnvC

mBio ◽

10.1128/mbio.00360-18 ◽

2018 ◽

Vol 9 (2) ◽

Cited By ~ 10

Author(s):

Chenggang Wu ◽

Abu Amar Mohamed Al Mamun ◽

Truc Thanh Luong ◽

Bo Hu ◽

Jianhua Gu ◽

...

Keyword(s):

Electron Microscopy ◽

Cell Division ◽

Cell Surface ◽

Biofilm Formation ◽

Cell Biology ◽

Associated Factors ◽

Surface Dynamics ◽

Wild Type ◽

Content Type ◽

Biofilm Development

ABSTRACTFusobacterium nucleatumis a key member of the human oral biofilm. It is also implicated in preterm birth and colorectal cancer. To facilitate basic studies of fusobacterial virulence, we describe here a versatile transposon mutagenesis procedure and a pilot screen for mutants defective in biofilm formation. Out of 10 independent biofilm-defective mutants isolated, the affected genes included the homologs of theEscherichia colicell division proteins FtsX and EnvC, the electron transport protein RnfA, and four proteins with unknown functions. Next, a facile new gene deletion method demonstrated that nonpolar, in-frame deletion offtsXorenvCproduces viable bacteria that are highly filamentous due to defective cell division. Transmission electron and cryo-electron microscopy revealed that the ΔftsXand ΔenvCmutant cells remain joined with apparent constriction, and scanning electron microscopy (EM) uncovered a smooth cell surface without the microfolds present in wild-type cells. FtsX and EnvC proteins interact with each other as well as a common set of interacting partners, many with unknown function. Last, biofilm development is altered when cell division is blocked by MinC overproduction; however, unlike the phenotypes of ΔftsXand ΔenvCmutants, a weakly adherent biofilm is formed, and the wild-type rugged cell surface is maintained. Therefore, FtsX and EnvC may perform novel functions inFusobacteriumcell biology. This is the first report of an unbiased approach to uncover genetic determinants of fusobacterial biofilm development. It points to an intriguing link among cytokinesis, cell surface dynamics, and biofilm formation, whose molecular underpinnings remain to be elucidated.IMPORTANCELittle is known about the virulence mechanisms and associated factors inF. nucleatum, due mainly to the lack of convenient genetic tools for this organism. We employed two efficient genetic strategies to identifyF. nucleatumbiofilm-defective mutants, revealing FtsX and EnvC among seven biofilm-associated factors. Electron microscopy established cell division defects of the ΔftsXand ΔenvCmutants, accompanied with a smooth cell surface, unlike the microfold, rugged appearance of wild-type bacteria. Proteomic studies demonstrated that FtsX and EnvC interact with each other as well as a set of common and unique interacting proteins, many with unknown functions. Importantly, blocking cell division by MinC overproduction led to formation of a weakly adherent biofilm, without alteration of the wild-type cell surface. Thus, this work links cell division and surface dynamics to biofilm development and lays a foundation for future genetic and biochemical investigations of basic cellular processes in this clinically significant pathogen.

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Role ofrpoSin Escherichia coli O157:H7 Strain H32 Biofilm Development and Survival

Applied and Environmental Microbiology ◽

10.1128/aem.02149-12 ◽

2012 ◽

Vol 78 (23) ◽

pp. 8331-8339 ◽

Cited By ~ 16

Author(s):

Jessica R. Sheldon ◽

Mi-Sung Yim ◽

Jessica H. Saliba ◽

Wai-Hong Chung ◽

Kwok-Yin Wong ◽

...

Keyword(s):

Escherichia Coli ◽

Lake Water ◽

Biofilm Formation ◽

Survival Rates ◽

Confocal Scanning Laser Microscopy ◽

Wild Type ◽

Minimal Growth ◽

Content Type ◽

Biofilm Development

ABSTRACTThe protein RpoS is responsible for mediating cell survival during the stationary phase by conferring cell resistance to various stressors and has been linked to biofilm formation. In this study, the role of therpoSgene inEscherichia coliO157:H7 biofilm formation and survival in water was investigated. Confocal scanning laser microscopy of biofilms established on coverslips revealed a nutrient-dependent role ofrpoSin biofilm formation, where the biofilm biomass volume of therpoSmutant was 2.4- to 7.5-fold the size of itsrpoS+wild-type counterpart in minimal growth medium. The enhanced biofilm formation of therpoSmutant did not, however, translate to increased survival in sterile double-distilled water (ddH2O), filter-sterilized lake water, or unfiltered lake water. TherpoSmutant had an overall reduction of 3.10 and 5.30 log10in sterile ddH2O and filter-sterilized lake water, respectively, while only minor reductions of 0.53 and 0.61 log10in viable counts were observed for the wild-type form in the two media over a 13-day period, respectively. However, the survival rates of the detached biofilm-derivedrpoS+andrpoSmutant cells were comparable. Under the competitive stress conditions of unfiltered lake water, the advantage conferred by the presence ofrpoSwas lost, and both the wild-type and knockout forms displayed similar declines in viable counts. These results suggest thatrpoSdoes have an influence on both biofilm formation and survival ofE. coliO157:H7 and that the advantage conferred byrpoSis contingent on the environmental conditions.

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σBInhibits Poly-N-Acetylglucosamine Exopolysaccharide Synthesis and Biofilm Formation inStaphylococcus aureus

Journal of Bacteriology ◽

10.1128/jb.00098-19 ◽

2019 ◽

Vol 201 (11) ◽

Cited By ~ 6

Author(s):

Jaione Valle ◽

Maite Echeverz ◽

Iñigo Lasa

Keyword(s):

Staphylococcus Aureus ◽

Biofilm Formation ◽

Flow Conditions ◽

Content Type ◽

Environmental Signals ◽

General Stress Response ◽

Biofilm Development ◽

Type Strains ◽

Complex Regulatory Network

ABSTRACTStaphylococcus aureusclinical strains are able to produce at least two distinct types of biofilm matrixes: biofilm matrixes made of the polysaccharide intercellular adhesin (PIA) or poly-N-acetylglucosamine (PNAG), whose synthesis is mediated by theicaADBClocus, and biofilm matrixes built of proteins (polysaccharide independent). σBis a conserved alternative sigma factor that regulates the expression of more than 100 genes in response to changes in environmental conditions. While numerous studies agree that σBis required for polysaccharide-independent biofilms, controversy persists over the role of σBin the regulation of PIA/PNAG-dependent biofilm development. Here, we show that genetically unrelatedS. aureusσB-deficient strains produced stronger biofilms under both static and flow conditions and accumulated higher levels of PIA/PNAG exopolysaccharide than their corresponding wild-type strains. The increased accumulation of PIA/PNAG in the σBmutants correlated with a greater accumulation of the IcaC protein showed that it was not due to adjustments inicaADBCoperon transcription and/oricaADBCmRNA stability. Overall, our results reveal that in the presence of active σB, the turnover of Ica proteins is accelerated, reducing the synthesis of PIA/PNAG exopolysaccharide and consequently the PIA/PNAG-dependent biofilm formation capacity.IMPORTANCEDue to its multifaceted lifestyle,Staphylococcus aureusneeds a complex regulatory network to connect environmental signals with cellular physiology. One particular transcription factor, named σB(SigB), is involved in the general stress response and the expression of virulence factors. For many years, great confusion has existed about the role of σBin the regulation of the biofilm lifestyle inS. aureus. Our study demonstrated that σBis not necessary for exopolysaccharide-dependent biofilms and, even more, thatS. aureusproduces stronger biofilms in the absence of σB. The increased accumulation of exopolysaccharide correlates with higher stability of the proteins responsible for its synthesis. The present findings reveal an additional regulatory layer to control biofilm exopolysaccharide synthesis under stress conditions.

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Quorum sensing in Bacillus subtilis slows down biofilm formation by enabling sporulation bet hedging

10.1101/768671 ◽

2019 ◽

Author(s):

Mihael Spacapan ◽

Tjaša Danevčič ◽

Polonca Štefanic ◽

Ines Mandic-Mulec

Keyword(s):

Bacillus Subtilis ◽

Quorum Sensing ◽

Biofilm Formation ◽

Bet Hedging ◽

Wild Type ◽

Master Regulator ◽

Matrix Components ◽

Sporulation Initiation ◽

Biofilm Development ◽

Biofilm Matrix

1.2ABSTRACTThe ComQXPA quorum sensing (QS) system of Bacillus subtilis, a Gram-positive, industrially relevant, endospore forming bacterium, promotes surfactin production. This lipopeptide increases transcription of several genes involved in biofilm matrix synthesis via the Spo0A-P master regulator. We hypothesized that the inactivation of the QS system will therefore result in decreased rates of floating biofilm formation. We find that this is not the case and that the QS deficient mutant forms pellicles with a faster rate and produces more biofilm matrix components than the wild type. As Spo0A-P is the master regulator of sporulation initiation we hypothesized that the ComQXPA dependent signaling promotes sporulation and consequently slows the growth rate of the wild type strain. Indeed, our results confirm that cells with the inactive QS initiate endospore formation in biofilms later and more synchronously than the wild type, as evidenced by spore frequencies and the PspoIIQ promoter activity. We argue, that the QS system acts as a switch that promotes stochastic sporulation initiation and consequently bet hedging behavior. By committing a subpopulation of cells to sporulation early during growth, wild type population grows slower and produces thinner biofilms but also assures better survival under stressful conditions.1.1IMPORTANCEBacillus subtilis is widely employed model organism to study biofilm formation and sporulation in Gram-positive bacteria. The ComQXPA quorum sensing (QS) system indirectly increases the transcription of genes involved in biofilm matrix formation, which predicts a positive role of this QS in biofilm development Here we show that QS mutants actually form more matrix components per pellicle than the wild type and that their pellicles are thicker and form with a faster rate. We explain this, by showing that cells with an inactive QS exhibit a delay in sporulation entry, which is also more synchronous relative to the wild type. We argue, that the ComQXPA QS system acts as a switch that contributes to the stochastic sporulation initiation and though this path promotes bet hedging behavior. This finding is important in terms of “quorum quenching” strategies aiming to down modulate biofilm development through inhibition of QS signaling and underscores the richness of QS regulated phenotypic outcomes among bacterial species.

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