Biology subjects

van Wijngaarden, E.

Publications and source records attributed to van Wijngaarden, E..

3 recordsLinked to original sources

bioRxiv2026

Diversification of biofilm architecture among freshwater Pararheinheimera isolates

Air-liquid interfaces (ALIs) at the upper layer of oceans, lakes and rivers cover the majority of the earths surface. Microbes are known to accumulate at these resource-rich boundaries, but the mechanisms of ALI colonization are often assumed to mirror the formation of pellicle biofilms by non-aquatic organisms. Here, we analyzed ALI colonization by natural aquatic bacteria. We used samples from a freshwater lake to enrich for microbes that colonize the ALI in liquid growth medium. Mixed-species pellicles formed rapidly in these enrichments, were structurally stable for weeks and displayed a pronounced ecological succession. We isolated 31 members of the genus Pararheinheimera from early stages of mixed-species pellicle maturation. Five phylogenetically distinct Pararheinheimera clades were identified, each with a shared colony morphology. We used representative isolates to show that only one Pararheinheimera clade formed thin, adherent films at the ALI resembling classical pellicles. Isolates from the four remaining clades formed floating structures that could be categorized either as non-adhesive films or large viscous masses. Viscous mass (VM) pellicle formation was a polyphyletic trait that correlated with a highly mucoid appearance on agar plates, suggesting that the process is driven by copious secretion of extracellular matrix. Matrices from VM biofilms were largely non-adhesive, contained a mixture of acidic polysaccharides and proteins and formed thermally stable, shear-thinning hydrogels. Our results demonstrate that ALI colonization strategies vary widely even among closely related aquatic bacteria and identify VM pellicles as a distinct biofilm architecture with unique mechanical properties. ImportanceLakes, rivers and oceans contain a boundary between the air and the waters surface known as the air-liquid interface (ALI). Microbial communities that populate the ALI play crucial roles in nutrient cycling, but how aquatic microbes partition to these sites remains poorly characterized. Our study investigated how bacteria from a freshwater lake accumulate at the ALI. Lake water samples incubated in nutrient medium formed a layer of cells known as a pellicle biofilm at the ALI, and we isolated 31 different bacteria from a genus (Pararheinheimera) that was abundant during the early stages of pellicle formation. Only a subset of Pararheinheimera isolates formed traditional pellicle biofilms. Most formed either thin, non-adhesive films or large, gelatinous aggregates that appeared to persist at the ALI due to buoyancy. These findings expand our understanding of biofilm diversity in aquatic systems and suggest that the production of buoyant hydrogels may play an important role in structuring microbial communities at air-water boundaries.

microbiology↗

bioRxiv2025

A load-bearing function for the cytoplasmic membrane of Escherichia coli

The structural integrity of bacterial cells is traditionally attributed to the peptidoglycan cell wall, and more recently to the outer membrane, with the cytoplasmic membrane assumed to be mechanically passive. Cells lacking filaments of the actin homolog MreB are more bendable, suggesting a role for the cytoskeleton in cell stiffness. Here, we show that MreB does not stiffen the envelope directly, but instead mechanically couples the cell wall to the cytoplasmic membrane through its role in peptidoglycan synthesis, increasing resistance to bending. Under hyperosmotic stress, MreB relocalized to the poles, forming linkages that prevent membrane detachment from the cell wall and attenuate cytoplasmic contraction. Disruption of MreB filament formation, nutrient starvation, or inactivation of glycan elongation factors abolished or reduced this coupling, revealing that peptidoglycan biosynthesis actively mediates stress distribution across surface layers. Our findings redefine the bacterial envelope as a mechanically integrated composite, with the cytoplasmic membrane having substantial load-bearing capacity.

microbiology↗

bioRxiv2022

Mechanical stimuli activate gene expression via a cell envelope stress sensing pathway

In tissues with mechanical function, the regulation of remodeling and repair processes is often controlled by mechanosensitive mechanisms; damage to the tissue structure is detected by changes in mechanical stress and strain, stimulating matrix synthesis and repair. While this mechanoregulatory feedback process is well recognized in animals and plants, it is not known whether such a process occurs in bacteria. In Vibrio cholerae, antibiotic-induced damage to the load-bearing cell wall promotes increased signaling by the two-component system VxrAB, which stimulates cell wall synthesis. Here we show that changes in mechanical stress and strain within the cell envelope are sufficient to stimulate VxrAB signaling in the absence of antibiotics. We applied mechanical forces to individual bacteria using three distinct loading modalities: extrusion loading within a microfluidic device, compression, and hydrostatic pressure. In all three cases, VxrAB signaling, as indicated by a fluorescent protein reporter, was increased in cells submitted to greater magnitudes of mechanical loading, hence diverse forms of mechanical stimuli activate VxrAB signaling. Mechanosensitivity of VxrAB signaling was lost following removal of the VxrAB stimulating endopeptidase ShyA, suggesting that VxrAB may not be directly sensing mechanical forces, but instead relies on other factors including lytic enzymes in the periplasmic space. Our findings suggest that mechanical signals play an important role in regulating cell wall homeostasis in bacteria. Significance StatementBiological materials with mechanical function (bones, muscle, etc.) are often maintained through mechanosensitive mechanisms, in which damage-induced reductions in stiffness stimulate remodeling and repair processes that restore mechanical function. Here we show that a similar process can occur in bacteria. We find that mechanical stresses in the bacterial cell envelope (the primary load-bearing structure in bacteria) regulate signaling of a two-component system involved in cell wall synthesis. These findings suggest that the mechanical stress state within the cell envelope can contribute to cell wall homeostasis. Furthermore, these findings demonstrate the potential to use mechanical stimuli to regulate gene expression in bacteria.

microbiology↗