By Pooja Toshniwal PahariaReviewed by Lexie CornerJun 5 2025A recent study published in Nature Microbiology examined the motility behavior of copiotrophic marine bacteria under starvation.
The researchers found that some bacterial strains stop moving to conserve biomass, while others continue moving by converting biomass into energy. This behavioral split may help predict microbial nutrient-seeking strategies and improve models of oceanic carbon cycling.
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Copiotrophs are marine bacteria that thrive in nutrient-rich, especially carbon-rich, environments. They contribute to carbon cycling in the ocean by remineralizing organic molecules. Because organic particles are patchy in distribution, a bacterium’s role in particle degradation depends on its ability to locate and colonize these particles.
Including bacterial motility in carbon flow models could enhance their predictive accuracy and deepen our understanding of marine ecosystems.
About the Study
Researchers assessed how copiotrophic marine bacteria respond to carbon starvation. They tested 26 bacterial strains from 18 species within the Gamma-proteobacteria class.
To simulate starvation, the team first cultured the bacteria in carbon-rich marine broth. They then transferred the cells to a carbon-depleted medium, mimicking the sudden loss of nutrients that occurs when bacteria leave nutrient hotspots.
They tracked motility over time at six key intervals: one hour, three hours, seven hours, 22 hours, 30 hours, and 46 hours after starvation began. Video microscopy and cell tracking were used to measure movement. Kernel density estimates (KDE) helped identify which strains stopped moving and which remained motile.
To support their findings, the researchers also used scanning electron microscopy (SEM) to measure flagella, and quantitative phase imaging (QPI) to monitor single-cell biomass. Optical density (OD) indicated overall biomass changes, and flow cytometry provided cell counts.
The genetic basis of motility behavior was investigated using Bayesian classifiers and recursive feature elimination (RFE). The model was then applied to the Global Ocean Microbiomes dataset to predict motility patterns across marine environments.
Results
The study revealed a trade-off in motility under starvation. While movement helps bacteria locate nutrients, it requires energy. This trade-off leads to two distinct behaviors: limostatic strains stop moving to conserve energy, while limokinetic strains continue moving by using internal resources.
Limokinetic strains converted about 9.4 % of their biomass each day into energy for movement, resulting in a 62 % biomass loss over one week. Despite this loss, total cell counts remained stable, suggesting that the bacteria underwent reductive division, producing smaller daughter cells.
The energy use of limokinetic strains dropped by more than threefold during starvation, from 4.1 × 10⁴ to 1.2 × 10⁴ ATP molecules per second. This shows that although the bacteria kept moving, they did so at a reduced energy cost.
Even closely related species showed different responses. For example, Vibrio splendidus FF-500 reduced its movement speed from 29 μm/s to 4.0 μm/s within one hour of starvation. In contrast, Vibrio anguillarum 12B09 maintained high speeds at around 31 μm/s.
Bayesian classifiers accurately distinguished between motility types with 88 % accuracy and predicted behavior in other species, with 86 % accuracy.
Flagellar differences also supported the dichotomy. In limostatic strains, the fraction of flagellated cells dropped from 0.65 to 0.04 within 24 hours. In limokinetic strains, it increased from 0.69 to 0.75. This suggests that limostatic bacteria shed their flagella, while limokinetic bacteria retained them, temporarily pausing movement without losing the ability to resume.
Environmental data supported these lab findings. In the Global Ocean Microbiomes dataset, strains predicted to favor the limostatic strategy were more common in the euphotic zone (average depth 70 m), suggesting that environmental context influences motility behavior.
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Conclusions
The study shows that motility behavior in copiotrophic marine bacteria involves a trade-off between energy conservation and nutrient-seeking. Under carbon starvation, some strains stop moving (limostatic), while others continue to search for resources (limokinetic).
Limostatic strains may be better suited to environments with intermittent nutrient hotspots, such as algal blooms. By conserving biomass, they survive until conditions improve. In contrast, limokinetic strains actively seek new nutrient sources, even at the cost of reduced biomass. This strategy may help them shorten search times in nutrient-poor areas.
The researchers suggest that further studies should explore how widespread this behavioral split is among marine microbes. Future work could examine the environmental and genetic factors that influence motility strategies in different parts of the ocean.
Journal reference
Keegstra, J.M., et al. (2025). Risk–reward trade-off during carbon starvation generates dichotomy in motility endurance among marine bacteria. Nat Microbiol, DOI: 10.1038/s41564-025-01997-7, https://www.nature.com/articles/s41564-025-01997-7
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