Metaproteomic Analysis of Sarracenia Purpurea Pitcher Fluid at Harvard Forest 2012-2017

Aquatic ecosystem enrichment can lead to distinct and irreversible changes to undesirable states. Understanding changes in active microbial community function and composition following organic-matter loading in enriched ecosystems can help identify biomarkers of such state changes. In a field experiment, we enriched replicate aquatic ecosystems in the pitchers of the northern pitcher plant, Sarracenia purpurea. Shotgun metaproteomics using a custom metagenomic database identified proteins, molecular pathways, and contributing microbial taxa that differentiated control ecosystems from those that were enriched. The number of microbial taxa contributing to protein expression was comparable between treatments; however, taxonomic evenness was higher in controls. Functionally active bacterial composition differed significantly among treatments and was more divergent in control pitchers than enriched pitchers. Aerobic and facultative anaerobic bacteria contributed most to identified proteins in control and enriched ecosystems, respectively. The molecular pathways and contributing taxa in enriched pitcher ecosystems were similar to those found in larger enriched aquatic ecosystems and are consistent with microbial processes occurring at the base of detrital food webs. Detectable differences between protein profiles of enriched and control ecosystems suggest that a time series of environmental proteomics data may identify protein biomarkers of impending state changes to enriched states.水体生态系统富集可引发不可逆的不良状态转变。探明富营养化生态系统中有机质负载后活性微生物群落功能与组成的变化，有助于识别此类状态转变的生物标志物。本研究开展野外实验，在北方猪笼草（*Sarracenia purpurea*）的捕虫笼中设置了多组重复的水体生态富集体系。利用定制宏基因组数据库（custom metagenomic database）开展鸟枪法宏蛋白质组学（shotgun metaproteomics）分析，鉴定出了可区分对照组与富营养化组生态系统的蛋白质、分子通路以及参与蛋白表达的微生物类群。两组处理间参与蛋白表达的微生物类群数量相当，但对照组的分类群均匀度显著更高。不同处理组的功能活性细菌组成存在显著差异，且对照组捕虫笼内的细菌组成相较于富营养化组更为分散。对照组与富营养化生态系统中，分别以需氧菌和兼性厌氧菌对鉴定蛋白的贡献占比最高。富营养化捕虫笼生态系统中的分子通路与贡献类群，与大型富营养化水体生态系统中的相关特征相似，且与碎屑食物网基部发生的微生物过程相符。富营养化组与对照组生态系统的蛋白质谱存在可检测差异，这表明环境蛋白质组学的时序数据可用于识别即将发生富营养化状态转变的蛋白质生物标志物。