Foffi Riccardo, Brumley Douglas R, Peaudecerf François J, Stocker Roman, Słomka Jonasz
Institute of Environmental Engineering, Department of Civil, Environmental and Geomatic Engineering, ETH Zürich, Zürich 8093, Switzerland.
School of Mathematics and Statistics, The University of Melbourne, Parkville, VIC 3010, Australia.
Proc Natl Acad Sci U S A. 2025 Jan 14;122(2):e2411074122. doi: 10.1073/pnas.2411074122. Epub 2025 Jan 10.
Chemotaxis enables marine bacteria to increase encounters with phytoplankton cells by reducing their search times, provided that bacteria detect noisy chemical gradients around phytoplankton. Gradient detection depends on bacterial phenotypes and phytoplankton size: large phytoplankton produce spatially extended but shallow gradients, whereas small phytoplankton produce steeper but spatially more confined gradients. To date, it has remained unclear how phytoplankton size and bacterial swimming speed affect bacteria's gradient detection ability and search times for phytoplankton. Here, we compute an upper bound on the increase in bacterial encounter rate with phytoplankton due to chemotaxis over random motility alone. We find that chemotaxis can substantially decrease search times for small phytoplankton, but this advantage is highly sensitive to variations in bacterial phenotypes or phytoplankton leakage rates. By contrast, chemotaxis toward large phytoplankton cells reduces the search time more modestly, but this benefit is more robust to variations in search or environmental parameters. Applying our findings to marine phytoplankton communities, we find that, in productive waters, chemotaxis toward phytoplankton smaller than 2 μm provides little to no benefit, but can decrease average search times for large phytoplankton (∼20 μm) from 2 wk to 2 d, an advantage that is robust to variations and favors bacteria with higher swimming speeds. By contrast, in oligotrophic waters, chemotaxis can reduce search times for picophytoplankton (∼1 μm) up to 10-fold, from a week to half a day, but only for bacteria with low swimming speeds and long sensory timescales. This asymmetry may promote the coexistence of diverse search phenotypes in marine bacterial populations.
趋化作用使海洋细菌能够通过减少搜索时间来增加与浮游植物细胞相遇的机会，前提是细菌能够检测到浮游植物周围有噪声的化学梯度。梯度检测取决于细菌表型和浮游植物大小：大型浮游植物产生空间上扩展但较浅的梯度，而小型浮游植物产生更陡峭但空间上更受限的梯度。迄今为止，尚不清楚浮游植物大小和细菌游动速度如何影响细菌的梯度检测能力以及对浮游植物的搜索时间。在此，我们计算了仅因趋化作用相对于随机运动而言细菌与浮游植物相遇率增加的上限。我们发现，趋化作用可大幅减少对小型浮游植物的搜索时间，但这一优势对细菌表型或浮游植物泄漏率的变化高度敏感。相比之下，对大型浮游植物细胞的趋化作用对搜索时间的减少幅度较小，但这种益处对搜索或环境参数的变化更具稳健性。将我们的研究结果应用于海洋浮游植物群落，我们发现，在生产力较高的水域中，对小于2μm的浮游植物的趋化作用几乎没有益处，但可将对大型浮游植物（约20μm）的平均搜索时间从2周减少至2天，这一优势对变化具有稳健性，且有利于游动速度较高的细菌。相比之下，在贫营养水域中，趋化作用可将对微微型浮游植物（约1μm）的搜索时间最多减少10倍，从一周减至半天，但仅适用于游动速度较低且感官时间尺度较长的细菌。这种不对称性可能促进海洋细菌种群中多种搜索表型的共存。
