Biology subjects

Kosta, A.

Publications and source records attributed to Kosta, A..

6 recordsLinked to original sources

bioRxiv2026

Multiscale oocyst wall mechanics govern coccidian resistance

Coccidian parasites spread through oocysts, environmental transmission stages that must survive harsh conditions yet rupture on cue inside the host to release infectious sporozoites. How the oocyst wall reconciles these opposing demands is unknown. Using single-oocyst microindentation, quantitative imaging and infection assays in Eimeria acervulina and Eimeria tenella, we show that the bilayered wall is functionally partitioned: the chemically fragile outer layer is mechanically dispensable, while the inner layer bears the mechanical load and remains impermeable to macromolecules and limiting osmotic exchange even after the outer layer is stripped. Oocysts behave as pressurised shells that fail preferentially at the anterior pole, a fixed mechanical weak point that channels sporocyst release regardless of where force is applied. Wall structure, autofluorescence, mechanics and infectivity prove dissociable: bleach removes the outer layer without weakening the wall or fully abolishing infectivity, whereas heat weakens the wall and abolishes infectivity while leaving the bilayered structure intact. These findings define a mechanical logic for coccidian oocyst resistance, disinfection and controlled excystation, and identify the inner wall as the critical target for inactivating environmentally transmitted parasites.

microbiology↗

bioRxiv2026

Aggregation-mediated microcolony shields bacteria from contact-dependent competition and maintains phenotypic heterogeneity

Bacteria are adaptable microorganisms capable of surviving in a wide variety of environments. One common strategy for persistence and attachment to surfaces is the formation of microcolonies, often controlled by cell surfaces structures that mediate adhesion such as fimbriae. In this study, we show that type 1 fimbriae, and other adhesins structures such as autotransporter adhesins, trigger microcolony formation which confer resistance against a broad range of short-range contact-dependent weapons (e.g. T6SS, T4SS, CDI) but not against long-range diffusible weapons (e.g. diffusible toxins like colicins). Interestingly, we identify "sheltered" bacteria within microcolonies that benefit from collective protection without expressing the adhesive structure. Our findings demonstrate that adhesive structures not only improve survival in hostile environments by promoting microcolony formation but also maintain phenotypic heterogeneity within the microcolony, highlighting the importance of social behavior in bacterial adaptation to changing environments.

microbiology↗

bioRxiv2025

CP12 controls ribulose 1,5 bisphosphate recycling and carbon acquisition in Chlamydomonas reinhardtii

The small chloroplastic protein CP12 has multiple functions, including the regulation of enzymes in the Calvin-Benson-Bassham cycle. Here, we investigated its role in the acclimation of Chlamydomonas reinhardtii to varying CO2 availability. This alga has a CO2 concentrating mechanism that increases the supply of CO2 to ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) and involves hallmarks such as HCO3- transporters and carbonic anhydrases as well as the condensation of RuBisCO within the pyrenoid via its interaction with a scaffold protein named Essential Pyrenoid Component 1 (EPYC1). We showed that compared to the wild type, at high CO2, C. reinhardtii CP12 deletion mutants, or partially complemented mutants, have less phosphoribulokinase and ribulose-1,5-bisphosphate (RuBP) indicating that the regeneration of RuBP is regulated by CP12. In the absence of CP12, the expected relocation of RuBisCO towards the pyrenoid was not observed upon transition from high to very low CO2, contrary to WT cells. The CP12 deletion mutants are a unique example where the induction of CO2 concentrating mechanism hallmarks at very low CO2 was not accompanied by RuBisCO relocation. Altogether, these results suggest that CP12 contributes to the coordination between RuBP regeneration, RuBisCO location and CO2 acquisition. HighlightCP12 regulates phosphoribulokinase amount and its product RuBP. The CP12 deletion mutants are unique example where the RuBisCO location was not correlated with the induction of CO2 concentration mechanism. This reveals a novel link between Calvin-Benson-Bassham cycle regulation and CO2 concentrating mechanisms in Chlamydomonas reinhardtii. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=115 SRC="FIGDIR/small/659560v1_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@1cdadb2org.highwire.dtl.DTLVardef@46ae27org.highwire.dtl.DTLVardef@538295org.highwire.dtl.DTLVardef@a214c7_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2023

Structure of a heteropolymeric type 4 pilus from a monoderm bacterium

Type 4 pili (T4P) are important virulence factors, which belong to a superfamily of nanomachines ubiquitous in prokaryotes, called type 4 filaments (T4F). T4F are defined as helical polymers of type 4 pilins. Recent advances in cryo-electron microscopy (cryo-EM) led to structures of several T4F. This revealed that the long N-terminal -helix, the trademark of pilins, packs in the centre of the filaments to form a hydrophobic core, which in bacteria is accompanied by the melting (unfolding) of a portion of 1. Since all available bacterial T4F structures are from diderm species, we tested whether this architecture is conserved in phylogenetically distant species by determining the structure of the T4P of the monoderm Streptococcus sanguinis. Our 3.7 A resolution cryo-EM structure of this heteropolymeric T4P, and the resulting full atomic model including all minor pilins, highlight universal features of bacterial T4F and have widespread implications in understanding their biology.

microbiology↗

bioRxiv2022

Membrane-remodeling protein ESCRT-III homologs incarnate the evolution and morphogenesis of multicellular magnetotactic bacteria

Endosomal sorting complex required transport (ESCRT) III proteins are essential for membrane remodeling and repair across all domains of life. Eukaryotic ESCRT-III and the cyanobacterial homologs PspA and Vipp1/Imm30 remodel membrane into vesicles, rings, filaments and tubular rods structures. Here our microscopy analysis showed that multicellular bacteria, referred to as magnetoglobules, possess multiple compartments including magnetosome organelles, polyphosphate granules, vesicles, rings, tubular rods, filaments and MVB-like structures. Therefore, membrane remodeling protein PspA might be required for the formation of these compartments, and contribute to the morphogenesis and evolution of multicellularity. To assess these hypotheses, we sequenced nine genomes of magnetoglobules and found a significant genome expansion compared to unicellular magnetotactic bacteria. Moreover, PspA was ubiquitous in magnetoglobules and formed a distinct clade on the tree of eubacterial and archaeal ESCRT-III. The phylogenetic feature suggested the evolution of magnetoglobules from a unicellular ancestor of deltaproteobacterium. Hetero-expression of ellipsoidal magnetoglobule pspA2 gene alone in Escherichia coli resulted in intracellular membrane aggregation. GFP fusion labeling revealed polar location of PspA2 in rod-shaped unicells and regular interval location in filamentous cells. Cryo-electron tomography analysis showed filament bundle, membrane sacculus, vesicles and MVB-like structure in the cells expressing PspA2. Moreover, electron-dense area with a similar distribution as GFP-PspA2 foci in filamentous cells changed the inward orientation of the septum, which might interfere with the cell division. Collectively, these results show the membrane remodeling function of magnetoglobule PspA proteins, which may contribute to morphogenesis and the evolution of multicellularity of magnetotactic bacteria.

microbiology↗

bioRxiv2021

Dynamic proton-dependent motors power Type IX secretion and gliding adhesin movement in Flavobacterium

Motile bacteria usually rely on external apparatus like flagella for swimming or pili for twitching. By contrast, gliding bacteria do not rely on obvious surface appendages to move on solid surfaces. Flavobacterium johnsoniae and other bacteria in the Bacteroidetes phylum use adhesins whose movement on the cell surface supports motility. In F. johnsoniae, secretion and helicoidal motion of the main adhesin SprB are intimately linked and depend on the type IX secretion system (T9SS). Both processes necessitate the proton motive force (PMF), which is thought to fuel a molecular motor that comprises the GldL and GldM cytoplasmic membrane proteins. Here we show that F. johnsoniae gliding motility is powered by the pH gradient component of the PMF. We further delineate the interaction network between the GldLM transmembrane helices (TMH) and show that conserved glutamate residues in GldL TMH are essential for gliding motility, although having distinct roles in SprB secretion and motion. We then demonstrate that the PMF and GldL trigger conformational changes in the GldM periplasmic domain. We finally show that multiple GldLM complexes are distributed in the membrane suggesting that a network of motors may be present to move SprB along a helical path on the cell surface. Altogether, our results provide evidence that GldL and GldM assemble dynamic membrane channels that use the proton gradient to power both T9SS-dependent secretion of SprB and its motion at the cell surface.

microbiology↗