Biology subjects

Novion Ducassou, J.

Publications and source records attributed to Novion Ducassou, J..

3 recordsLinked to original sources

bioRxiv2021

Micrarchaeota are covered by a proteinaceous S-Layer

In previous publications, it was hypothesized that Micrarchaeota cells are covered by two individual membrane systems. This study proofs that at least the recently cultivated "Candidatus Micrarchaeum harzensis A_DKE" possesses an S-layer covering its cytoplasmic membrane. The potential S-layer protein was found to be among the proteins with the highest abundance in A_DKE and in silico characterization of its primary structure indicated homologies to other known S-layer proteins. Homologs of this protein were found in other Micrarchaeota genomes, which raises the question, whether the ability to form an S-layer is a common trait within this phylum. The S-layer protein seems to be glycosylated and the Micrarchaeum expresses genes for N-glycosylation under cultivation conditions, despite not being able to synthesize carbohydrates. Electron micrographs of freeze-etched samples of a previously described co-culture, containing Micrarchaeum A_DKE and a Thermoplasmatales member as its host organism, verified the hypothesis of an S-layer on the surface of A_DKE. Both organisms are clearly distinguishable by cell size, shape and surface structure.

microbiology↗

bioRxiv2021

Extracellular riboflavin induces anaerobic biofilm formation in Shewanella oneidensis

Some microorganisms can respire with extracellular electron acceptors using an extended electron transport chain to the cell surface. These organisms apply flavin molecules as cofactors to facilitate one-electron transfer catalysed by the terminal reductases and as endogenous electron shuttles. In the model organism Shewanella oneidensis, riboflavin production and excretion triggers a specific biofilm formation response that is initiated at a specific threshold concentration, similar to canonical quorum sensing molecules. Riboflavin-mediated messaging is based on the overexpression of the gene encoding the putrescin decarboxylase speC which leads to posttranscriptional overproduction of proteins involved in biofilm formation. Using a model of growth-dependent riboflavin production under batch and biofilm growth conditions, the number of cells necessary to produce the threshold concentration per time was deduced. Furthermore, our results indicate that specific retention of riboflavin in the biofilm matrix leads to localized concentrations which by far exceed the necessary threshold value. ImportanceFerric iron is the fourth most abundant element of the earth crust. It occurs at neutral pH in the form insoluble iron minerals. The dissimilatory reduction of these minerals is an import part of global geological cycles and is catalyzed by microorganisms through extended respiratory chains to the cell surface. Shewanella oneidensis is one of the best understood model organisms for this kind of extracellular respiration. Flavins are important for the reduction of extracellular electron acceptors by S. oneidensis. since they have a function as (I) cofactors of the terminal reductases and (II) electron shuttles. In this study we reveal that flavin molecules are further employed as quorum sensing molecules. They are excreted by the organisms in a growth dependent manner and lead to anaerobic biofilm formation as a specific response at a certain threshold concentration. Although we know multiple examples of quorum sensing mechanisms, the use of riboflavin was so far not described and at least in S. oneidensis proceeds via a new regulatory routine that proceeds on the trancriptomic and posttranscriptomic level.

microbiology↗

bioRxiv2020

The PopN gate-keeper complex acts on the ATPase PscN to regulate the T3SS secretion switch from early to middle substrates in Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic bacterium of which the main virulence factor is the Type III Secretion System. The ATPase of this machinery, PscN (SctN), is thought to be localized at the base of the secretion apparatus and to participate in the recognition, chaperone dissociation and unfolding of exported T3SS proteins. In this work, a protein-protein interaction ELISA revealed the interaction of PscN with a wide range of exported T3SS proteins including the needle, translocator, gate-keeper and effector. These interactions were further confirmed by Microscale Thermophoresis that also indicated a preferential interaction of PscN with secreted proteins or protein-chaperone complex rather than with chaperones alone, in line with the release of the chaperones in the bacterial cytoplasm after the dissociation from their exported proteins. Moreover, we suggest a new role of the gate-keeper complex and the ATPase in the regulation of early substrates recognition by the T3SS. This finding sheds a new light on the mechanism of secretion switching from early to middle substrates in P. aeruginosa. HighlightsO_LIT3SS substrates are secreted sequentially but information on the switches are missing C_LIO_LIInteraction of the T3SS ATPase with secreted proteins were investigated by different approaches C_LIO_LIMicroscale Thermophoresis revealed a lower affinity for chaperones alone compared to complexes C_LIO_LIThe Gate-keeper complex binds to the ATPase and increases its affinity for the needle complex C_LIO_LIA new role of the Gate-keeper complex is proposed, directly acting on the T3SS ATPase C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=103 SRC="FIGDIR/small/224923v2_ufig1.gif" ALT="Figure 1"> View larger version (15K): org.highwire.dtl.DTLVardef@1e6803corg.highwire.dtl.DTLVardef@1ed155aorg.highwire.dtl.DTLVardef@14faf6org.highwire.dtl.DTLVardef@1685ec8_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗