Biology subjects

Arnaouteli, S.

Publications and source records attributed to Arnaouteli, S..

4 recordsLinked to original sources

bioRxiv2019

The majority of the matrix protein TapA is dispensable for biofilm formation by Bacillus subtilis

Biofilm formation is a co-operative behaviour where microbial cells become embedded in an extracellular matrix. This biomolecular matrix plays a key role in the manifestation of the beneficial or detrimental outcome mediated by the collective of cells. Bacillus subtilis is an important bacterium for understanding the general principles of biofilm formation and is a plant growth-promoting organism. The protein components of the B. subtilis matrix include the secreted proteins BslA, which forms a hydrophobic coat over the biofilm, and TasA, which forms protease-resistant fibres needed for structuring. A third protein TapA (for TasA anchoring and assembly protein) is needed for biofilm formation and helps TasA fibre formation in vivo but is dispensable for TasA-fibre assembly in vitro. Here we show that TapA is subjected to proteolytic cleavage in the biofilm and that only the first 57 amino acids of the 253-amino acid protein are required for biofilm architecture. However, through the construction of a strain which lacks all eight extracellular proteases, we show that proteolytic cleavage by these enzymes is not a prerequisite for TapA function. It remains unknown why TapA is synthesized at a full length of 253 amino acids when the first 57 are sufficient for biofilm structuring, but the findings do not exclude the core conserved region of TapA having a second role beyond that of structuring the B. subtilis biofilm.

microbiology↗

bioRxiv2019

Pulcherrimin formation controls growth arrest of the Bacillus subtilis biofilm

Biofilm formation by Bacillus subtilis is a communal process that culminates in the formation of architecturally complex multicellular communities. Here we reveal that the transition of the biofilm into a non-expanding phase constitutes a distinct step in the process of biofilm development. Using genetic analysis we show that B. subtilis strains lacking the ability to synthesize pulcherriminic acid form biofilms that sustain the expansion phase, thereby linking pulcherriminic acid to growth arrest. However, production of pulcherriminic acid is not sufficient to block expansion of the biofilm. It needs to be secreted into the extracellular environment where it chelates Fe3+ from the growth medium in a non-enzymatic reaction. Utilizing mathematical modelling and a series of experimental methodologies we show that when the level of freely available iron in the environment drops below a critical threshold, expansion of the biofilm stops. Bioinformatics analysis allows us to identify the genes required for pulcherriminic acid synthesis in other Firmicutes but the patchwork presence both within and across closely related species suggests loss of these genes through multiple independent recombination events. The seemingly counterintuitive self-restriction of growth led us to explore if there were any benefits associated pulcherriminic acid production. We identified that pulcherriminic acid producers can prevent invasion from neighbouring communities through the generation of an \"iron free\" zone thereby addressing the paradox of pulcherriminic acid production by B. subtilis.\n\nSignificanceUnderstanding the processes that underpin the mechanism of biofilm formation, dispersal, and inhibition are critical to allow exploitation and to understand how microbes thrive in the environment. Here, we reveal that the formation of an extracellular iron chelate restricts the expansion of a biofilm. The countering benefit to self-restriction of growth is protection of an environmental niche. These findings highlight the complex options and outcomes that bacteria need to balance in order to modulate their local environment to maximise colonisation, and therefore survival.

microbiology↗

bioRxiv2017

Bifunctionality Of A Biofilm Matrix Protein Controlled By Redox State

Biofilms are communities of microbial cells that are encapsulated within a self-produced polymeric matrix. The matrix is critical to the success of biofilms in diverse habitats, but despite this many details of the composition, structure, and function remain enigmatic. Biofilms formed by the Gram-positive bacterium Bacillus subtilis depend on the production of the secreted film-forming protein BslA. Here we show that a gradient of electron acceptor availability through the depth of the biofilm gives rise to two distinct functional roles for BslA and that these can be genetically separated through targeted amino acid substitutions. We establish that monomeric BslA is necessary and sufficient to give rise to complex biofilm architecture, while dimerization of BslA is required to render the community hydrophobic. Dimerization of BslA, mediated by disulfide bond formation, depends on two conserved cysteine residues located in the C-terminal region. Our findings demonstrate that bacteria have evolved multiple uses for limited elements in the matrix, allowing for alternative responses in a complex, changing environment.\n\nSignificanceThe biofilm matrix is a critical target in the hunt for novel strategies to destabilise or stabilise biofilms. Knowledge of the processes controlling matrix assembly is therefore an essential prerequisite to exploitation. Here we highlight that the complexity of the biofilm matrix is even higher than anticipated with one matrix component making two independent functional contributions to the community. The influence the protein exerts is dependent on the local environmental properties, providing another dimension to consider during analysis. These findings add to the evidence that bacteria can evolve multifunctional uses for the extracellular matrix components.

microbiology↗

bioRxiv2016

Evolutionary variations in the biofilm-associated protein BslA from the genus Bacillus

BslA is a protein secreted by Bacillus subtilis which forms a hydrophobic film that coats the biofilm surface and renders it water-repellent. We have characterised three orthologues of BslA from Bacillus amyloliquefaciens, Bacillus licheniformis and Bacillus pumilus as well as a paralogue from B. subtilis called YweA. We find that the three orthologous proteins can substitute for BslA in B. subtilis and confer a degree of protection, whereas YweA cannot. The degree to which the proteins functionally substitute for native BslA correlates with their in vitro biophysical properties. Our results demonstrate the use of naturally-evolved variants to provide a framework for teasing out the molecular basis of interfacial self-assembly.

microbiology↗