ROW: Dissolved Organic Nitrogen Uptake by Autotrophic Plankton Studied with Flow Cytometry

溶解有机氮（DON）池正在成为海洋氮循环的一个动态组成部分。虽然DON可以代表海洋系统中最大的固定氮库，但由于缺乏合适的方法，关于其利用的信息主要局限于氨基酸或尿素等少数个别有机化合物。尽管对大部分未定义的DON池的利用缺乏了解，但细菌被认为是海洋系统中DON的主要使用者（尿素除外）。然而，最近在浮游植物酶学方面的研究表明，这种假设需要重新评估。现在已知一些浮游植物具有细胞表面氧化酶，使它们能够从氨基酸、原胺和潜在的其他有机化合物中切割氨基。已知具有这些氧化酶的浮游植物是较小的自养生物，在传统的大小分馏实验中可能包括在“细菌”大小部分中。这个Row Planning Grant项目将结合流式细胞术的强大工具和新开发的15N示踪技术来区分DON的自养和异养摄取。该计划拨款的目标是：(1)完善现有的细胞分选技术，将自养生物从异养生物中分离出来，使其数量足够大，从而可以测量15N原子%的富集程度，从而可以测量自养生物对DON的吸收率；(2)获得东热带北太平洋自养生物对DON的吸收的初步数据，用于支持NSF的全面提案。＊＊＊

9416634 Bronk The dissolved organic nitrogen (DON) pool is emerging as a dynamic component of marine nitrogen cycles. Though DON can represent the largest pool of fixed nitrogen in marine systems, the lack of suitable methods has kept information on its utilization largely limited to a few individual organic compounds such as amino acids or urea. Despite the lack of knowledge on utilization of the bulk of the undefined DON pool, bacteria are considered the primary users of DON in marine systems (with the exception of urea). Recent work in phytoplankton enzymology, however, suggests this assumption needs to be reevaluated. Some phytoplankton are now known to posses cell surface oxidases which allow them to cleave amino groups from amino acids, primary amines, and potentially other organic compounds. The phytoplankton known to posses these oxidases are smaller autotrophs which could potentially be included in the "bacterial" size fraction in traditional size fractionation experiments. This Row Planning Grant project will combine the powerful tools of flow cytometry and newly developed 15N tracer techniques to discriminate autotrophic from heterotrophic uptake of DON. The objectives of this Planning Grant are to (1) refine existing cell sorting techniques for separating autotrophs from heterotrophs in large enough numbers to allow the measurement of 15N atom % enrichments and thus allow the measurement of DON uptake rates by autotrophs, and (2) to obtain preliminary data on uptake of DON by autotrophs in the Eastern Tropical North Pacific to be used in support of a full scale NSF proposal. ***