Biology subjects

Modi, Z. K.

Publications and source records attributed to Modi, Z. K..

4 recordsLinked to original sources

bioRxiv2026

The construction and operation of type IV pili impose a variable energetic burden across phylogenetically distant bacteria

Type IV pili (T4P) are dynamic surface appendages that mediate essential biological functions and virulence traits, yet their energetic burden on cellular budgets in light of fluctuating host environments remains unexplored. Here, we present a comprehensive economic analysis of T4P construction and operation in ATP equivalents, following established frameworks of flagella analyses. Using Pseudomonas aeruginosa as a model system, we quantify the total cellular burden to synthesize the T4P machinery, maintain the inner-membrane pool of major pilin (PilA), and drive repeated cycles of pilus extension and retraction over a generation. We estimate that the T4P system consumes ~0.7% of the total cellular energy budget, dominated by PilA monomer production. Conversely, the operational cost of dynamic T4P fibers is negligible due to their intermittent activity - contrasting sharply with the high continuous cost of rotating a polar flagellum. Extending this framework across five phylogenetically diverse species (P. aeruginosa, Vibrio cholerae, Caulobacter crescentus, Neisseria spp., and Myxococcus xanthus) reveals that T4P investment varies tenfold (0.2 - 1.8% of the cellular budget), driven by differences in pilin size, machine number, pilus extension rates, and cell volume. Neisseria is a distinct outlier whose high extension rate makes operational costs approach construction costs, while in all other species construction dominates. These findings indicate that changes in nutrient availability or surface association may modulate pilus number and length as a strategy to optimize energetic burdens during host-pathogen interaction.

microbiology↗

bioRxiv2026

Pil-Chp orchestrates a multi-level regulatory system to control type IV pilus dynamics in Pseudomonas aeruginosa

The cyclical extension and retraction dynamics of type IV pili (T4P) mediate critical virulence traits in many bacterial species, yet how these dynamics are regulated remain poorly understood. Here, by analyzing individual pilus dynamics across mutants covering the entire T4P system of Pseudomonas aeruginosa, we identified active pili in several mutants previously classified as non-piliated. Correlating these dynamics with intracellular cAMP levels, transcriptional profiles, and T4P protein abundances reveals how the chemosensory Pil-Chp system controls T4P fiber length, count, extension rate, and polarity in surface-naive cells by modulating cAMP levels. Specifically, fiber length is tuned by modulating the effective association and dissociation rates of the extension ATPase PilB; fiber count is regulated by controlling machine abundance; and extension rate is limited by the abundance of the major pilin (PilA). Furthermore, we demonstrate that these regulatory mechanisms of T4P length and count differentially impact T4P-dependent functions: phage infection efficiency increases continuously with fiber count or length, whereas twitching motility exhibits step-like activation thresholding. This indicates that the functional output of T4P dynamics is strictly context dependent. Because the Pil-Chp system is conserved across diverse human and plant pathogens, this multi-level regulatory logic may represent a widespread mechanism controlling T4P-mediated virulence.

microbiology↗

bioRxiv2026

Rapid activation of dormant type IV pili enables a dispersal-infection tradeoff in environments with fluctuating nutrients

Bacteria in fluctuating environments must balance the high metabolic costs of motility against risks of bacteriophage predation and immune clearance. While flagellar trade-off mechanisms are well-documented, regulation of type IV pilus (T4P) activity during environmental transitions remains unclear. We show that Pseudomonas aeruginosa uses an energy-dependent idling strategy to synchronize T4P-mediated surface motility with nutrient availability. In nutrient-depleted stationary phase, T4P transcription and protein levels remain constant, pre-assembled machines persist at the cell pole, yet cells produce only sparse, truncated pili that extend and retract slowly. Using a single-cell ATP biosensor, we show that T4P dynamics respond directly to cellular adenylate energy charge. Carbon source addition rapidly elevates intracellular ATP, reactivating pre-assembled T4P within minutes. This bypasses de novo protein synthesis, restoring pilus number, length, and extension/retraction rates. This rapid response drives opportunistic biofilm dispersal but, at the same time, creates an immediate tradeoff: reactivated T4P restore susceptibility to pilus-specific phages upon nutrient upshift. Thus, energetic gating of T4P enables P. aeruginosa to minimize exposure to phages during starvation while remaining poised for rapid reactivation. Importantly, T4P promote resistance to opsonization and phagocytosis by macrophages and neutrophils. Upon nutrient upshift, full T4P activity therefore supports dispersal and host colonization while conferring immune protection, revealing a fundamental dispersal-infection tradeoff at the host- microbe interface in fluctuating environments such as the lung and gut.

microbiology↗

bioRxiv2026

Type IV pilus length determines virulence by regulating a hidden subpopulation of non-contributing filaments

Many clinically important bacterial pathogens, including Pseudomonas, Vibrio, Neisseria, and Acinetobacter species, employ dynamic extracellular appendages called type IV pili (T4P) to facilitate virulence through cyclical extension and retraction of pilus filaments. To dissect how T4P dynamics govern pathogenesis, we engineered a genetic system to precisely tune pilus length across a continuum. We demonstrate that pilus length critically determines four major T4P-dependent virulence traits in Pseudomonas aeruginosa (motility, surface sensing, biofilm formation, and phage infection) and reveal a hidden subpopulation of pili that are unable to interact with environmental substrates or host cells, rendering them non-contributing to any T4P-mediated function. Integrating molecular dynamics simulations, we show that low inner-membrane abundance of the major pilin forces the extension mechanism into transient idle states, restricting both velocity and final length. Molecularly, this finding reveals how two key biophysical parameters, pilin abundance and diffusion, impose a fundamental physical constraint on T4P assembly, and that regulating pilin abundance presents a strong lever over regulating pilus count for controlling the amount of functionally contributing filaments. Contrary to the prevailing view that retraction force generation primarily dictates T4P-mediated behaviors, our results establish extension dynamics as the overlooked bottleneck constraining all retraction-enabled virulence traits, with population heterogeneity in length enabling adaptive bet-hedging.

microbiology↗