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ABSTRACT Bacterial motility plays a crucial role in biofilm development, yet the underlying mechanism remains not fully understood. Here, we demonstrate that the flagellum-driven motility ofPseudomonas aeruginosaenhances biofilm formation by altering the orientation of bacterial cells, an effect controlled by shear stress rather than shear rate. By tracking wild-typeP. aeruginosaand its non-motile mutants in a microfluidic channel, we demonstrate that while non-motile cells align with the flow, many motile cells can orient toward the channel sidewalls, enhancing cell surface attachment and increasing biofilm cell density by up to 10-fold. Experiments with varying fluid viscosities further demonstrate that bacterial swimming speed decreases with increasing fluid viscosity, and the cell orientation scales with the shear stress rather than shear rate. Our results provide a quantitative framework to predict the role of motility in the orientation and biofilm development under different flow conditions and viscosities.IMPORTANCEBiofilms are ubiquitous in rivers, water pipes, and medical devices, impacting the environment and human health. While bacterial motility plays a crucial role in biofilm development, a mechanistic understanding remains limited, hindering our ability to predict and control biofilms. Here, we reveal how the motility ofPseudomonas aeruginosa, a common pathogen, influences biofilm formation through systematically controlled microfluidic experiments with confocal and high-speed microscopy. We demonstrate that the orientation of bacterial cells is controlled by shear stress. While non-motile cells primarily align with the flow, many motile cells overcome the fluid shear forces and reorient toward the channel sidewalls, increasing biofilm cell density by up to 10-fold. Our findings provide insights into how bacterial transition from free-swimming to surface-attached states under varying flow conditions, emphasizing the role of cell orientation in biofilm establishment. These results enhance our understanding of bacterial behavior in flow environments, informing strategies for biofilm management and control. 

Cells use DNA photolyases to protect their DNA from the damaging effects of UV radiation. Marine cyanobacteria possess many genes that appear to encode photolyases, but the function of the proteins encoded by these genes is unclear. 

Chromatic acclimation (CA) encompasses a diverse set of molecular processes that involve the ability of cyanobacterial cells to sense ambient light colors and use this information to optimize photosynthetic light harvesting. The six known types of CA, which we propose naming CA1 through CA6, use a range of molecular mechanisms that likely evolved independently in distantly related lineages of the Cyanobacteria phylum. Together, these processes sense and respond to the majority of the photosynthetically relevant solar spectrum, suggesting that CA provides fitness advantages across a broad range of light color niches. The recent discoveries of several new CA types suggest that additional CA systems involving additional light colors and molecular mechanisms will be revealed in coming years. Here we provide a comprehensive overview of the currently known types of CA and summarize the molecular details that underpin CA regulation. 

MarineSynechococcus, a globally important group of cyanobacteria, thrives in various light niches in part due to its varied photosynthetic light-harvesting pigments. ManySynechococcusstrains use a process known as chromatic acclimation to optimize the ratio of two chromophores, green-light–absorbing phycoerythrobilin (PEB) and blue-light–absorbing phycourobilin (PUB), within their light-harvesting complexes. A full mechanistic understanding of howSynechococcuscells tune their PEB to PUB ratio during chromatic acclimation has not yet been obtained. Here, we show that interplay between two enzymes named MpeY and MpeZ controls differential PEB and PUB covalent attachment to the same cysteine residue. MpeY attaches PEB to the light-harvesting protein MpeA in green light, while MpeZ attaches PUB to MpeA in blue light. We demonstrate that the ratio ofmpeYtompeZmRNA determines if PEB or PUB is attached. Additionally, strains encoding only MpeY or MpeZ do not acclimate. Examination of strains ofSynechococcusisolated from across the globe indicates that the interplay between MpeY and MpeZ uncovered here is a critical feature of chromatic acclimation for marineSynechococcusworldwide.