Department of Earth and Planetary Sciences, McGill University, 3450 University St, Montréal, Quebec H3A 0E8, Canada.
Department of Civil Engineering, McGill University, 817 Rue Sherbrooke Ouest, Montréal, Quebec H3A 0C3, Canada.
ISME J. 2024 Jan 8;18(1). doi: 10.1093/ismejo/wrae018.
Growing evidence suggests that interactions among heterotrophic microorganisms influence the efficiency and rate of organic matter turnover. These interactions are dynamic and shaped by the composition and availability of resources in their surrounding environment. Heterotrophic microorganisms inhabiting marine environments often encounter fluctuations in the quality and quantity of carbon inputs, ranging from simple sugars to large, complex compounds. Here, we experimentally tested how the chemical complexity of carbon substrates affects competition and growth dynamics between two heterotrophic marine isolates. We tracked cell density using species-specific polymerase chain reaction (PCR) assays and measured rates of microbial CO2 production along with associated isotopic signatures (13C and 14C) to quantify the impact of these interactions on organic matter remineralization. The observed cell densities revealed substrate-driven interactions: one species exhibited a competitive advantage and quickly outgrew the other when incubated with a labile compound whereas both species seemed to coexist harmoniously in the presence of more complex organic matter. Rates of CO2 respiration revealed that coincubation of these isolates enhanced organic matter turnover, sometimes by nearly 2-fold, compared to their incubation as mono-cultures. Isotopic signatures of respired CO2 indicated that coincubation resulted in a greater remineralization of macromolecular organic matter. These results demonstrate that simple substrates promote competition whereas high substrate complexity reduces competitiveness and promotes the partitioning of degradative activities into distinct niches, facilitating coordinated utilization of the carbon pool. Taken together, this study yields new insight into how the quality of organic matter plays a pivotal role in determining microbial interactions within marine environments.
越来越多的证据表明，异养微生物之间的相互作用会影响有机物的转化效率和速率。这些相互作用是动态的，并受其周围环境中资源的组成和可利用性的影响。栖息在海洋环境中的异养微生物经常会遇到碳输入质量和数量的波动，从简单的糖到大型复杂化合物。在这里，我们通过实验测试了碳底物的化学复杂性如何影响两种海洋异养分离物之间的竞争和生长动态。我们使用种特异性聚合酶链反应（PCR）测定法跟踪细胞密度，并测量微生物 CO2 产生的速率以及相关的同位素特征（13C 和 14C），以量化这些相互作用对有机物再矿化的影响。观察到的细胞密度揭示了底物驱动的相互作用：一种物种在与不稳定化合物孵育时表现出竞争优势，并迅速超过另一种物种，而在更复杂的有机物存在下，两种物种似乎和谐共存。CO2 呼吸速率表明，与作为单培养物孵育相比，这些分离物的共培养增强了有机物的转化，有时可增加近 2 倍。呼吸 CO2 的同位素特征表明，共培养导致了更大的高分子有机物的再矿化。这些结果表明，简单的底物促进竞争，而高底物复杂性降低竞争力，并促进降解活性在不同小生境中的分配，从而促进碳库的协调利用。总之，这项研究提供了新的见解，即有机物的质量如何在决定海洋环境中微生物相互作用方面起着关键作用。
