Data from: The contribution of marine aggregate-associated bacteria to the accumulation of pathogenic bacteria in oysters: an agent-based model

Bivalves process large volumes of water, leading to their accumulation of bacteria, including potential human pathogens (e.g., vibrios). These bacteria are captured at low efficiencies when freely suspended in the water column, but they also attach to marine aggregates, which are captured with near 100% efficiency. For this reason, and because they are often enriched with heterotrophic bacteria, marine aggregates have been hypothesized to function as important transporters of bacteria into bivalves. The relative contribution of aggregates and unattached bacteria to the accumulation of these cells, however, is unknown. We developed an agent-based model to simulate accumulation of vibrio-type bacteria in oysters. Simulations were conducted over a realistic range of concentrations of bacteria and aggregates and incorporated the dependence of pseudofeces production on particulate matter. The model shows that the contribution of aggregate-attached bacteria depends strongly on the unattached bacteria, which form the colonization pool for aggregates and are directly captured by the simulated oysters. The concentration of aggregates is also important, but its effect depends on the concentration of unattached bacteria. At high bacterial concentrations, aggregates contribute the majority of bacteria in the oysters. At low concentrations of unattached bacteria, aggregates have a neutral or even a slightly negative effect on bacterial accumulation. These results provide the first evidence suggesting that the concentration of aggregates could influence uptake of pathogenic bacteria in bivalves and show that the tendency of a bacterial species to remain attached to aggregates is a key factor for understanding species-specific accumulation.

双壳纲动物（Bivalves）可滤过大量水体，进而在体内积累细菌，其中包括潜在的人类致病菌，例如弧菌（vibrios）。这类细菌在自由悬浮于水柱中时，被捕食的效率极低，但它们也会附着于海洋团聚体（marine aggregates）之上，而牡蛎对附着有细菌的团聚体的捕获效率近乎100%。基于这一特性，加之海洋团聚体通常会富集异养细菌（heterotrophic bacteria），学界已提出假说：海洋团聚体是将细菌转运至双壳类体内的重要载体。然而，团聚体与游离细菌对这类细菌在双壳类体内积累的相对贡献，目前仍不明确。本研究构建了基于智能体的模型（agent-based model），以模拟牡蛎体内弧菌类细菌的积累过程。模拟实验在符合自然场景的细菌与团聚体浓度范围内开展，且纳入了伪粪（pseudofeces）产生量对颗粒物的依赖关系。模型结果显示，附着于团聚体的细菌的贡献程度，高度依赖于游离细菌：游离细菌既是团聚体的定殖菌群来源，同时也会被模拟牡蛎直接捕获。团聚体的浓度同样会产生影响，但其作用效果取决于游离细菌的浓度。当细菌总浓度较高时，团聚体携带的细菌会成为牡蛎体内细菌的主要来源；当游离细菌浓度较低时，团聚体对细菌积累的影响则呈中性，甚至会产生轻微的负面作用。本研究结果首次证实，海洋团聚体的浓度可影响双壳类对致病菌的摄取，同时表明，细菌物种保持附着于团聚体的倾向，是理解物种特异性细菌积累机制的关键因素。