Stable Associations Masked by Temporal Variability in the Marine Copepod Microbiome

Copepod-bacteria interactions include permanent and transient epi- and endobiotic associations that may play roles in copepod health, transfer of elements in the food web, and biogeochemical cycling. Microbiomes of three temperate copepod species (Acartia longiremis, Centropages hamatus, and Calanus finmarchicus) from the Gulf of Maine were investigated during the early summer season using high throughput amplicon sequencing. The most prominent stable component of the microbiome included several taxa within Gammaproteobacteria, with Pseudoalteromonas spp. especially abundant across copepod species. These Gammaproteobacteria appear to be promoted by the copepod association, likely benefitting from nutrient enriched microenvironments on copepods, and forming a more important part of the copepod-associated community than Vibrio spp. during the cold-water season in this temperate system. Taxon-specific associations included an elevated relative abundance of Piscirickettsiaceae and Colwelliaceae on Calanus, and Marinomonas sp. in Centropages. The communities in full and voided gut copepods had distinct characteristics, thus the presence of a food-associated microbiome was evident, including higher abundance of Rhodobacteraceae and chloroplast sequences in the transient communities. The observed variability was partially explained by collection date that may be linked to factors such as variable time since molting, gender differences, and changes in food availability and type over the study period. While some taxon-specific and stable associations were identified, temporal changes in environmental conditions, including food type, appear to be key in controlling the composition of bacterial communities associated with copepods in this temperate coastal system during the early summer.

桡足类-细菌互作涵盖永久与暂时性的体表及体内共生关联，此类互作可对桡足类健康、食物网内元素传递以及生物地球化学循环产生重要影响。本研究于初夏季节，采用高通量扩增子测序技术，对采集自缅因湾（Gulf of Maine）的3种温带桡足类物种（Acartia longiremis、Centropages hamatus及Calanus finmarchicus）的微生物组展开调查分析。该微生物组中最显著的稳定类群包含γ-变形菌纲（Gammaproteobacteria）下的多个分类单元，其中假交替单胞菌属（Pseudoalteromonas spp.）在所有受试桡足类物种中均呈现较高丰度。这类γ-变形菌似乎因与桡足类的共生关系得以富集，大概率借助桡足体表面富营养化的微环境获取生存优势；在该温带系统的冷水季中，它们相较于弧菌属（Vibrio spp.），是桡足类关联菌群中更为核心的组成部分。物种特异性共生关联表现为：Calanus属桡足类体表相对丰度较高的鱼立克次体科（Piscirickettsiaceae）与科尔韦尔氏菌科（Colwelliaceae），以及Centropages属桡足类中的海单胞菌属（Marinomonas sp.）。肠道完整与肠道排空的桡足类其关联菌群群落特征存在显著差异，由此可见存在与食物相关的微生物组：在暂时性菌群中，红杆菌科（Rhodobacteraceae）与叶绿体序列的丰度显著更高。观测到的菌群群落变异可部分由采样日期予以解释，而采样日期可能与蜕皮后时长差异、性别差异以及研究期间食物可获得性与食物类型的变化等因素相关。尽管本研究已鉴定出部分物种特异性及稳定的共生关联，但在该温带近岸系统的初夏时节，环境条件（包括食物类型）的时间动态变化似乎是调控桡足类关联细菌群落组成的核心因素。