Biology subjects

Dauvillee, D.

Publications and source records attributed to Dauvillee, D..

8 recordsLinked to original sources

bioRxiv2026

Delayed onset and heterogeneous collective organization characterize twitching motility in Acinetobacter baumannii

Type IV pili (T4P) mediate twitching motility and contribute to surface colonization, biofilm formation, and host interactions in Acinetobacter baumannii. However, the prevalence, dynamics, and diversity of twitching motility across A. baumannii populations remain poorly understood. Here, we compared twitching motility in a collection of 35 A. baumannii strains originating from clinical, environmental, and animal sources, using Pseudomonas aeruginosa PAO1 as a reference. Standardization of assay conditions revealed a strong influence of agar composition on twitching motility, with Eiken agar supporting the most robust surface translocation. Under these conditions, 14 of 35 A. baumannii isolates exhibited detectable twitching motility. Time-lapse microscopy revealed major differences between A. baumannii and P. aeruginosa. Whereas PAO1 initiated twitching within minutes after inoculation and formed characteristic multicellular rafts, motile A. baumannii strains displayed a prolonged non-motile phase before movement initiation and exhibited distinct patterns of collective organization. Two major expansion phenotypes were identified, termed Homogeneous Front (HF) and Raft-Like Front (RLF), together with Early-Onset Motility (EOM) and Delayed-Onset Motility (DOM) subgroups. Quantitative analyses further revealed substantial variation in speed, directional persistence, and migration dynamics among strains. Because a majority of isolates were non-motile, we investigated the contribution of the minor pilin FimT. Although deletion of fimT abolished twitching motility and specific substitutions modulated motility efficiency, sequence variation in FimT alone could not account for the observed phenotypic diversity. Collectively, these findings reveal extensive heterogeneity in T4P-mediated surface motility in A. baumannii and identify delayed twitching activation and distinct collective migration strategies as key features of surface colonization in this species. HighlightsO_LIPopulation analysis reveals extensive twitching diversity in A. baumannii C_LIO_LIDelayed motility onset distinguishes A. baumannii from P. aeruginosa C_LIO_LIHomogeneous and raft-like fronts define distinct migration strategies C_LIO_LIFimT contributes to motility but not all non-motile phenotypes C_LI

microbiology↗

bioRxiv2024

PII1/MRC interaction with Starch Synthase 4 (SS4) from Arabidopsis thaliana inhibits SS4 enzymatic activity

Starch is the major energy storage compound in plants. It accumulates in the form of insoluble, partly crystalline granules whose number and shape are specific to each plant species. These characteristics are defined very early in starch biosynthesis, at the initiation stage. Starch biosynthesis initiation is a complex process that relies on the coordinated action of several proteins that interact together in the so-called complex of initiation. Starch Synthase 4 (SS4) is the only initiation protein with enzymatic activity. It catalyzes the formation of glucan primers, which serve as substrates for the enzymatic machinery that synthesizes starch granules. Previous studies have highlighted the importance of interactions between SS4 and regulatory proteins in this process. Among them, Protein Involved in Initiation 1 (PII1) interacts with SS4 but its function is not yet established. In this study, we explored the structural and functional implications of PII1 on SS4s enzymatic activity. Our findings reveal that PII1 contains a long coiled-coil domain that specifically interacts with SS4, leading to significant inhibition of SS4s glucan elongation activity. Importantly, this inhibition is specific to SS4 and does not affect other known synthases, suggesting a targeted regulatory mechanism. This work describes the structural specificities of PII1 and SS4 and reveals a function for PII1 in the initiation complex. These results allow us to re-examine these complex mechanisms and propose new hypotheses about the important steps in the initiation of starch biosynthesis.

plant biology↗

bioRxiv2024

Starch granule initiation doesnt require a starch synthase 4 isoform in Chlamydomonas reinhardtii.

The initiation of starch granule synthesis remains a relatively poorly understood phenomenon. Recent advances enabled the establishment of a model explaining the synthesis of new starch granules in Arabidopsis thaliana. These characterizations revealed the involvement of both a specific starch synthase isoform (SS4) and of several non-enzymatic proteins in this process. In this work, we investigated whether the initiation of starch synthesis in the green microalga Chlamydomonas reinhardtii involves the same machinery as those uncovered in the plant model. Our extensive phylogenetic analysis revealed that most of the key players that were identified in higher plants are not found in microalgae suggesting that a different pathway is taking place. We showed that restoration of ADP-glucose synthesis in a mutant strain devoid of any endogenous primers allowed normal starch synthesis, revealing the existence of an initiation mechanism in Chlamydomonas. Our biochemical characterizations revealed that starch synthase isoform 3 possesses the intrinsic capacity to initiate polysaccharide synthesis in vitro and could be one of the functions involved in starch initiation. Our work suggests that the initiation of starch synthesis in Chlamydomonas involves a different pathway to that described in Arabidopsis and that further efforts will be required to identify the proteins involved in this process.

biochemistry↗

bioRxiv2024

From raw microalgae to bioplastics: conversion of Chlorella vulgaris starch granules into thermoplastic starch

Microalgae are emerging as a promising feedstock for bioplastics, with Chlorella vulgaris yielding significant amounts of starch. This polysaccharide is convertible into thermoplastic starch (TPS), a biodegradable plastic of industrial relevance. In this study, we developed a pilot-scale protocol for extracting and purifying starch from starch-enriched Chlorella vulgaris biomass. From 430.3 {+/-} 0.5 g (dry weight - DW) of microalgae biomass containing 42.2 {+/-} 3.4 % of starch, we successfully extracted 205.8 {+/-} 1.2 gDW of purified starch extract containing 86.9 {+/-} 3.0 % of starch, resulting in a final recovery yield of 98.5%. We have characterized this extracted starch and processed it into TPS using twin-screw extrusion and injection molding. Microalgal starch showed similar properties to those of native plant starch, but with smaller granules. We compared the mechanical properties of microalgal TPS with two controls, namely a commercial TPS and a TPS prepared from commercial potato starch granules. TPS prepared from microalgal starch showed a softer and more ductile behavior compared to the reference materials. This study demonstrates the feasibility of recovering high-purity microalgal starch on a pilot scale with high yields, and highlights the potential of microalgal starch for the production of TPS using industrially relevant processes. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=77 SRC="FIGDIR/small/589749v1_ufig1.gif" ALT="Figure 1"> View larger version (44K): org.highwire.dtl.DTLVardef@f2f7fcorg.highwire.dtl.DTLVardef@176dc8corg.highwire.dtl.DTLVardef@8989d3org.highwire.dtl.DTLVardef@1b7b978_HPS_FORMAT_FIGEXP M_FIG C_FIG

plant biology↗

bioRxiv2023

The PP1 phosphatase exhibits pleiotropic roles controlling both the tachyzoite cell cycle and amylopectin-steady state levels in Toxoplasma gondii.

Virulence of apicomplexan parasites is based on their ability to divide rapidly to produce significant biomass. The regulation of their cell-cycle is therefore key to their pathogenesis. Phosphorylation is a crucial post-transcriptional modification that regulates many aspects of the eucaryotic cell cycle. The phosphatase PP1 is known to play a major role in the phosphorylation balance in eukaryotes. We explored the role of TgPP1 during the cell cycle of the tachyzoite form of the apicomplexan parasite Toxoplasma gondii. Using a conditional mutant strain, we show that TgPP1 regulates many aspects of the cell cycle including the proper assembly of the daughter cells inner membrane complex (IMC), the segregation of organelles and nuclear division. Unexpectedly, depletion of TgPP1 also results in the accumulation of amylopectin, a storage polysaccharide that is normally found in the latent bradyzoite form of the parasite. Using transcriptomics and phosphoproteomics, we show that TgPP1 mainly acts through post-transcriptional mechanisms by dephosphorylating target proteins including IMC proteins. TgPP1 also dephosphorylate a protein bearing a starch binding domain. Mutagenesis analysis reveals that the targeted phospho-sites are linked to the ability of the parasite to regulate amylopectin steady-state levels. Therefore, we show that TgPP1 has pleiotropic roles during the tachyzoite cell cycle regulation, but also regulates amylopectin accumulation.

microbiology↗

bioRxiv2023

Structural basis of the interaction between ESV1 and LESV from Arabidopsis thaliana with starch glucans.

Starch is the major energy storage compound in plants. Whether it is transient or stored, it is accumulated in the form of insoluble, semi-crystalline granules. The structure of these granules is related to the structure of the main component: amylopectin. Amylopectin consists of linear polymers of glucose units linked by -1,4 bonds, forming double helices that combine to form the semi-crystalline lamellae of the granules, and -1,6 branching points that form the amorphous lamellae. This particular structure of amylopectin is linked to the action of isoamylases, which cut the excess of branching points and allow the granules to be structured. For a long time, it was thought that the action of these enzymes was responsible for the structuring of starch granules. Recently, two new proteins, LESV and ESV1, have been characterized and are involved in the phase transition of amylopectin (LESV) or in the maintenance of the granule structure (ESV1). These proteins share a tryptophan-rich domain folded into an antiparallel {beta}-sheet that is particularly well suited to bind amylopectin double helices. In this paper we present the structural study of these interactions using integrative structural biology approaches and show that LESV, in contrast to ESV1 can intervenes during amylopectin biosynthesis.

biophysics↗

bioRxiv2023

BE3 is the major branching enzyme isoform required for amylopectin synthesis in Chlamydomonas reinhardtii

Starch-branching enzymes (BEs) are essential for starch synthesis in both plants and algae where they influence the architecture and physical properties of starch granules. Within Embryophytes, BEs are classified as type 1 and type 2 depending on their substrate preference. In this article, we report the characterization of the three BE isoforms encoded in the genome of the starch producing green algae Chlamydomonas reinhardtii: two type 2 BEs (BE2 and BE3) and a single type 1 BE (BE1). Using single mutant strains, we analyzed the consequences of the lack of each isoform on both transitory and storage starches. The transferred glucan substrate and the chain length specificities of each isoform were also determined. We show that only BE2 and BE3 isoforms are involved in starch synthesis and that, although both isoforms possess similar enzymatic properties, BE3 is critical for both transitory and storage starch metabolism. Finally, we propose putative explanations for the strong phenotype differences evidenced between the C. reinhardtii be2 and be3 mutants, including functional redundancy, enzymatic regulation or alterations in the composition of multimeric enzyme complexes.

plant biology↗

bioRxiv2018

PII1: a protein involved in starch initiation that determines granule number and size in Arabidopsis chloroplast.

The initiation of starch granule formation is still poorly understood. However, soluble starch synthase 4 (SS4) appears to be a major component of this process since it is required to synthetize the correct number of starch granules in the chloroplasts of Arabidopsis thaliana plants. A yeast-2-hybrid screen allowed the identification of several putative SS4 interacting partners. We identified the product of At4g32190 locus as a chloroplast-targeted PROTEIN INVOLVED IN STARCH INITIATION (named PII1). Arabidopsis mutants devoid of PII1 display an alteration of starch initiation process and accumulate, on average, one starch granule per plastid instead of the 5 to 7 granules found in plastids of wild-type plants. These granules are larger than in wild type and they remain flat and lenticular. pii1 mutants display wild-type growth rates and accumulate standard starch amounts. Moreover, starch characteristics, such as amylopectin chain length distribution, remain unchanged. Our results reveal the involvement of PII1 in starch priming process in Arabidopsis leaves through interaction with SS4.

plant biology↗