Lu Zhiying, Entwistle Elizabeth, Kuhl Matthew D, Durrant Alexander R, Barreto Filho Marcelo Malisano, Goswami Anuradha, Morris J Jeffrey
Department of Biology, University of Alabama at Birmingham, Birmingham, AL 35294, United States.
ISME J. 2025 Jan 2;19(1). doi: 10.1093/ismejo/wrae259.
As a result of human activity, Earth's atmosphere and climate are changing at an unprecedented pace. Models based on short-term experiments predict major changes will occur in marine phytoplankton communities in the future ocean, but rarely consider how evolution or interactions with other microbes may influence these changes. Here, we experimentally evolved several phytoplankton in coculture with a heterotrophic bacterium, Alteromonas sp. EZ55, under either present-day or predicted future pCO2 conditions. Growth rates of phytoplankton generally increased over time under both conditions, but only Thalassiosira oceanica had evidence of a growth rate tradeoff in the ancestral environment after evolution at elevated pCO2. The growth defects observed in ancestral Prochlorococcus cultures at elevated pCO2 and in axenic culture were diminished after evolution, possibly due to regulatory mutations in antioxidant genes. Except for Prochlorococcus, mutational profiles suggested phytoplankton experienced primarily purifying selection, but most Alteromonas lineages showed evidence of directional selection, where evolution appeared to favor a metabolic switch between growth on small organic acids with cyanobacteria versus catabolism of more complex carbon substrates with eukaryotic phytoplankton. Evolved Alteromonas were also poorer "helpers" for Prochlorococcus, consistent with that interaction being a competitive Black Queen process rather than a true mutualism. This work provides new insights on how phytoplankton will respond to increased pCO2 and on the evolutionary mechanisms governing phytoplankton:bacteria interactions. It also clearly demonstrates that both evolution and interspecies interactions must be considered to predict future marine biogeochemistry.
由于人类活动，地球的大气和气候正以前所未有的速度发生变化。基于短期实验的模型预测，未来海洋中的海洋浮游植物群落将发生重大变化，但很少考虑进化或与其他微生物的相互作用可能如何影响这些变化。在这里，我们在当今或预测的未来pCO₂条件下，将几种浮游植物与异养细菌Alteromonas sp. EZ55进行共培养实验进化。在这两种条件下，浮游植物的生长速率通常随时间增加，但只有海洋硅藻在高pCO₂条件下进化后，在原始环境中有生长速率权衡的证据。在高pCO₂条件下的原始原绿球藻培养物和无菌培养物中观察到的生长缺陷在进化后有所减轻，这可能是由于抗氧化基因的调控突变。除了原绿球藻，突变谱表明浮游植物主要经历了纯化选择，但大多数交替单胞菌谱系显示出定向选择的证据，即进化似乎有利于在以蓝细菌为食的小分子有机酸上生长与以真核浮游植物为食的更复杂碳底物的分解代谢之间的代谢转换。进化后的交替单胞菌对原绿球藻来说也是更差的“帮手”，这与这种相互作用是一个竞争性的黑皇后过程而不是真正的互利共生一致。这项工作为浮游植物如何应对pCO₂增加以及控制浮游植物与细菌相互作用的进化机制提供了新的见解。它还清楚地表明，必须考虑进化和种间相互作用来预测未来的海洋生物地球化学。
