環境非目標溶解有機物濃度對海洋細菌化學趨向性之影響

Abstract

海洋細菌的化學趨向性在全球生物地球化學循環以及海洋生態系統的運作中扮演了關鍵角色，因此，深入探討影響其作用的相關因子具有重要意義。過去的研究表明，海洋中普遍存在的有機化合物可能干擾細菌的化學趨向性。然而，目前尚無研究探討海水中溶解有機質（DOM）濃度對海洋細菌化學趨向性的具體影響。本研究設計了一種方法，用於檢測海洋細菌在不同海水條件下化學趨向性強度的變化。我們首先將沿岸海水中的天然細菌群集與無菌的人工有機顆粒（幾丁質顆粒）共同培養，以獲得具化學趨向性的顆粒附著型海洋細菌。接著，分離這些培養後的有機顆粒，並將其置於含有新鮮人工幾丁質顆粒的海水中，設置不同的DOM濃度條件。新加入的幾丁質顆粒作為細菌的化學趨向目標。我們透過比較浮游於海水中與附著於新幾丁質顆粒上的細菌數量比例，量化細菌的相對化學趨向性強度。此外，為了區分那些不作為細菌化學趨向性目標的海水溶解有機質，我們將其定義為「非目標溶解有機質」（nt-DOM）。本研究測試了天然沿岸海水中的細菌群集在不同濃度nt-DOM條件下化學趨向性的變化。結果顯示，海水中的nt-DOM會顯著降低細菌群集的化學趨向性，且nt-DOM濃度與細菌化學趨向性之間呈現穩定的負相關。這種負相關性在不同海水來源的實驗中均有表現。我們的研究結果表明，海水中的非目標溶解有機質會干擾細菌群集的化學趨向性強度，從而可能改變生物地球化學循環的動態過程。

The chemotaxis of planktonic bacteria plays a crucial role in determining how efficiently these organisms can approach particles in marine environments, thereby facilitating the decomposition of particulate organic matter. This process significantly influences marine microbial food webs and biogeochemical cycles. Understanding the factors that shape bacterial chemotaxis is therefore critical. Previous studies have demonstrated that ubiquitous organic molecules can interfere with bacterial chemosensory mechanisms. However, no research has specifically investigated how dissolved organic matter (DOM) in seawater impacts bacterial chemotaxis, despite the potential for environmental DOM to disrupt this process. In this study, we developed a methodology to evaluate changes in the chemotactic strength of bacterial assemblages under varying concentrations of DOM. To establish particle-attached bacteria with chemotactic capabilities, we incubated a natural bacterial assemblage, collected from a coastal environment, with organic particles (artificial chitin magnetic beads, or CMBs) suspended in seawater. The CMBs with attached bacteria were then isolated and incubated in seawater containing fresh synthetic chitin particles under different DOM concentrations. Using the synthetic particles as chemotactic targets, we quantified the ratio of attached (on the particles) to suspended (in seawater) bacterial abundance as an indicator of relative chemotactic strength. To clarify that the DOM in bulk seawater is not the target of bacterial chemotaxis, we introduced the term “non-target DOM” (nt-DOM). We investigated the chemotactic strength of naturally derived bacterial assemblages across seawater with varying nt-DOM concentrations. Our results reveal a robust negative relationship between chemotactic strength and nt-DOM concentration, regardless of the seawater source. This finding suggests that the nt-DOM concentration in bulk seawater interferes with bacterial chemotaxis, potentially altering biogeochemical fluxes.