A new study published on October 8 in the journal Science by researchers at the University of California San Diego’s Scripps Institution of Oceanography and the University of Lincoln offers a strikingly simple answer to part of that puzzle: the gooier the particle, the better it performs. The team found that the viscosity of marine snow—its thickness, its stickiness, its sheer sliminess—can have a decisive impact on how quickly bacteria break the particles down and how far they ultimately sink. According to the researchers’ estimates, high-viscosity marine snow can shuttle more than six times as much carbon into the deep ocean as its runnier, less viscous counterparts. In a field where global carbon budgets hinge on precisely these kinds of particle-level details, a sixfold difference tied to a single physical property is the sort of result that forces modelers and field scientists alike to rethink their assumptions about how the biological carbon pump actually works.

The breakthrough began, as many do, with a technical frustration. In 2021, Bryce Inman, then a postdoctoral scholar at Scripps Oceanography, set out to visualize what he describes as the muscoscape—the intricate, microscopic world of bacteria living within and upon mucus. The obstacle was fundamental: no one had ever directly observed individual bacteria interacting with the physical structure of mucus, whether in the ocean or anywhere else. For four years, Inman and his colleagues, including Farooq Azam, a microbiologist and professor emeritus at Scripps, attempted and failed to make such observations possible. Mucus is transparent, delicate, and notoriously difficult to image without destroying the very architecture researchers hoped to study. It was not until 2025 that the team finally cracked the problem, developing a method that allowed them to see, for the first time, the hidden topography of a particle that sinks past billions of microbes every day.

The solution combined 3D confocal microscopy with specialized fluorescent molecules designed to label the mucus itself. With this toolkit, the researchers could map the physical terrain of individual clumps of marine snow in three dimensions and watch how bacteria navigated that landscape in real time. The technical details of the imaging method are described in a companion paper published in Nature Communications. What the technique revealed was unexpected: marine snow is not a homogeneous blob of slime but a structured habitat, riddled with bulges, crevasses, and regions of dramatically different consistency. Mucus, Inman noted, has a surprising amount of structure at a scale smaller than bacteria—a physical microenvironment that scientists had never previously been able to examine directly. The finding effectively opens a new window onto a habitat that covers much of the living world.

That structure matters because it shapes the battle between sinking particles and the bacteria that consume them. Like snowflakes on land, no two marine snow particles are alike; each is assembled from a different combination of organic and inorganic molecules, and each differs in its gooeyness. Using their new imaging approach, the researchers determined that bacteria can colonize the less viscous zones near a particle’s surface far more easily than the denser, more viscous regions deeper inside. Bacteria, Inman explained, can latch onto the less viscous portions of each particle but cannot reach the more viscous regions until they break them down first. He offered a vivid analogy: it is like a worm in an apple, where the flesh is easy to penetrate but the core is tough to chew through. The outer layers of a marine snow particle are an open buffet; the interior is a fortress.

The consequences of that microbial siege are profound for the carbon cycle. In a series of laboratory experiments, the team found that more viscous marine snow takes significantly longer for bacteria to degrade and fragment. Every hour a particle resists consumption is another hour it spends sinking, and every additional meter of descent moves its carbon cargo further from the surface reservoir where it could quickly return to the atmosphere. Computer simulations extended the laboratory findings, suggesting that the more viscous a particle is, the deeper it will ultimately sink. When Inman and his colleagues translated those results into global terms, they estimated that high-viscosity marine snow can carry more than six times the carbon to the deep ocean compared with low-viscosity particles. How far marine snow can sink, Inman observed, is a surprisingly complicated problem, and the new work adds another—very gooey—piece to the puzzle.

The study is also notable for being the first time scientists have examined live bacteria interacting with the physical structure of marine snow, or with any mucus for that matter. That gap in knowledge was never trivial. Interactions between mucus and bacteria are critical to maintaining the health of life across the planet: coral reefs depend on their surface mucus layers to host protective microbial communities, kelp forests rely on similar partnerships, land plant root systems negotiate with bacteria through mucilaginous coatings, and animal and human digestive tracts function only because of the finely tuned relationships between gut mucus and resident microbes. A method that finally makes the muscoscape visible therefore has implications far beyond oceanography, offering researchers in medicine, microbiology, and ecology a new way to study how bacteria behave inside the slimy matrices they inhabit.

For ocean and climate scientists, the findings arrive at a moment of intense scrutiny of the biological carbon pump, the suite of processes by which marine life exports carbon from the surface ocean. Global carbon models have long struggled to reconcile the enormous annual flux of marine snow with the much smaller fraction that reaches long-term storage depths. Viscosity, the new work suggests, is a variable that has been largely absent from those calculations, yet it may help explain why some particles survive the gauntlet of degradation while others dissolve into remineralized carbon within the upper ocean. If the distribution of particle gooeyness varies across ocean regions, seasons, or warming-driven changes in plankton communities, then the efficiency of the ocean’s carbon sink may be far more sensitive to microbial ecology than current models assume. Incorporating viscosity into future estimates could sharpen predictions of how much atmospheric carbon the ocean will continue to absorb as the climate changes.

The research was supported in part by additional funding from the Simons Foundation and the Engineering and Physical Sciences Research Council, and it reflects a broader shift in marine science toward treating microscopic processes as the engines of planetary-scale phenomena. What began as an effort to image slime in a laboratory dish has ended up quantifying a property that helps determine the fate of gigatons of carbon each year. As Inman and his colleagues continue to explore the muscoscape, the message of the new study is clear: the ocean’s carbon future may depend, in no small part, on how sticky its snow turns out to be. In the deep sea, where the snow never stops falling, gooiness is not a curiosity—it is climate machinery.

Subject of Research: The role of marine snow viscosity in microbial degradation and deep-ocean carbon transport

Article Title: The gooier marine snow is, the better it is at transporting carbon, new study finds

Article References: The gooier marine snow is, the better it is at transporting carbon, new study finds. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: marine snow, carbon cycle, ocean carbon sink, viscosity, bacteria, mucus, Scripps Institution of Oceanography, biological carbon pump, confocal microscopy, deep ocean, biogeochemistry, Science journal

The study, published in Advanced Science, tackles a problem that has frustrated the field for years. Researchers have extensively studied how nanoparticle size, shape, and surface chemistry influence transport through mucus, but two factors have remained comparatively neglected: the mechanical flexibility of the particle itself, and the biological variability of the mucus barrier across different organs and physiological states. The difficulty is that flexibility is nearly impossible to tune in isolation. Modifying a particle’s mechanical properties typically changes its geometry or surface chemistry at the same time, making it hard to know whether observed effects stem from deformability or from some other confounding variable.

DNA origami offered a way out of this impasse. The technique folds a long single-stranded DNA scaffold, in this case from the M13mp18 bacteriophage, using hundreds of short complementary staple strands into precisely defined nanoscale shapes. The researchers built a rod-shaped structure called a 14-helix bundle, roughly 150 nanometers long—a size deliberately chosen to match the reported mesh size of mucus, which ranges from about 100 to 200 nanometers. By selectively removing staples from a central hinge region, the team could systematically increase the structure’s bending flexibility while keeping its overall dimensions and surface chemistry essentially unchanged.

The result was a family of five variants, designated Hinge 0 through Hinge 4, ranging from fully rigid to maximally flexible. Transmission electron microscopy confirmed that all five assembled correctly and retained their rod-like geometry, with only modest and statistically insignificant differences in effective length. The bending angles told a clear story: the rigid Hinge 0 structures remained nearly linear at close to 180 degrees, while the most flexible Hinge 4 constructs averaged around 120 degrees, with individual particles bending as far as 75 degrees. The most compliant designs also showed pronounced twisting, a sign of increased rotational freedom.

Before introducing the structures to biological samples, the team measured their diffusion in simple buffer and in a viscous polyethylene glycol solution that mimics mucus’s viscosity without any specific biochemical interactions. In both inert environments, flexibility paid off. The most flexible rods diffused roughly 45 percent faster than the rigid ones in buffer, and about 48 percent faster in the viscous medium. The explanation is hydrodynamic: bending and shape fluctuations reduce the effective drag a rod experiences as it moves through fluid, making it easier to translate forward even before any biological interactions come into play.

The real test came in mucus. The researchers tracked fluorescently labeled particles in three physiologically distinct porcine mucus environments: fasted intestinal mucus, fed intestinal mucus, and stomach mucus. In fasted intestinal mucus, the trend from the inert media held—more flexible rods moved farther and faster than rigid ones, supporting the idea that deformability helps particles squeeze through the sterically heterogeneous mucus mesh. Surprisingly, coating the particles with bovine serum albumin, a common surface-passivation strategy, actually reduced diffusion of all variants, likely because the protein layer increases hydrodynamic size and adds steric interactions at the particle-mucus interface. Yet even with this burden, flexible rods retained a measurable advantage over rigid ones.

The other two mucus environments revealed a more complicated picture. Fed intestinal mucus and stomach mucus both slowed particle diffusion overall, suggesting stronger adhesive interactions. To understand why, the team characterized each mucus sample using cryogenic scanning electron microscopy, rheology, and proteomics. The two intestinal samples, regardless of feeding state, looked structurally similar under the microscope, with elongated, oval-shaped pores, while stomach mucus displayed a distinctly different architecture of predominantly circular pores. Rheological measurements confirmed that stomach mucus was significantly stiffer than either intestinal sample. Proteomics identified roughly 6,300 proteins per sample, with about 88 percent shared across all three sources—but stomach mucus contained 258 unique proteins, compared with just 15 and 30 for the fasted and fed intestinal samples.

Single-particle tracking then exposed a critical mechanistic divide that bulk measurements would have missed. In stomach and fasted intestinal mucus, particles moved mostly as individuals, and their transport appeared limited by steric hindrance within the polymer network—conditions under which flexibility clearly helps. In fed intestinal mucus, however, particles clustered into aggregates, indicating that adhesive surface interactions, including electrostatic and hydrophobic binding to mucins, dominated the transport behavior. Under those conditions, adding flexibility alone accomplished little. Instead, BSA passivation was needed first to suppress aggregation and restore mobility—and once that happened, flexibility again provided an additional boost to diffusion. In other words, the right design strategy depends entirely on which barrier mechanism dominates in a given mucus environment.

The team also probed a scenario closer to real oral drug delivery: sequential exposure to intestinal fluid followed by mucus. Particles first incubated in intestinal fluid—a complex soup of enzymes, bile salts, and macromolecules—showed reduced mobility compared with particles introduced directly from buffer, and their subsequent diffusion in mucus was further diminished. Prior work has shown that DNA origami structures remain stable in intestinal mucus, so structural degradation was not the culprit; instead, fluid components appear to alter particle surface properties or create transient binding events that hinder movement. Crucially, the relative advantage of flexible designs persisted even after this fluid preconditioning, suggesting that mechanical compliance remains valuable under physiologically realistic conditions.

The findings carry practical weight for nanomedicine. Widely used surface-passivation strategies such as PEGylation can improve mucus penetration but may simultaneously compromise targeting and cellular uptake, so complementary approaches are needed. By decoupling flexibility from geometry and surface chemistry, this work establishes structural mechanics as a legitimate, independently tunable design parameter for mucosal drug carriers. The authors suggest the principle may extend beyond the gastrointestinal tract to pulmonary, nasal, and cervical mucus, though its impact will always depend on whether a given barrier is governed primarily by mechanical confinement or by surface-driven interactions. The broader message is that rational nanocarrier design demands a mechanistic diagnosis first: identify whether steric obstruction, interfacial adhesion, or aggregation is the limiting factor, and only then choose between flexibility, passivation, or a combination of both.

Subject of Research: Effect of DNA origami mechanical flexibility on nanoparticle transport through gastrointestinal mucus

Article Title: Mechanical Flexibility Enables DNA Origami to Overcome Steric Confinement in Mucus

Article References: Tollemeto, M., Tsang, E., Hong Lin, M. K. T., Mannino, L., Gothelf, K. V., & Boisen, A. (2026). Mechanical Flexibility Enables DNA Origami to Overcome Steric Confinement in Mucus. Advanced Science, 13(55), Article e76493. https://doi.org/10.1002/advs.76493

Image Credits: AI Generated

DOI: 10.1002/advs.76493

Keywords: DNA origami, mucus, nanoparticle transport, drug delivery, mechanical flexibility, single-particle tracking, mucosal barriers, surface passivation, 14-helix bundle, proteomics, rheology, gastrointestinal mucus