Analysis of natural diatom communities reveals novel insights into the diversity of long chain polyamine (LCPA) structures involved in silica precipitation

Abstract

The intricately nanopatterned siliceous frustules of diatoms are formed under the control of template organic molecules, some of which are tightly incorporated into the frustule during formation. Long chain polyamines (LCPAs) attract dissolved silicic acid species, enhance silica precipitation and play a role in frustule nanopattern formation. LCPAs thus play a central biogeochemical role, linking the cycling of organic matter with the cycling of silicic acid in the photic zone of the upper ocean. Their distribution and molecular diversity in the environment are as yet unknown. We used high performance liquid chromatography electrospray ionization–mass spectrometry (HPLC–ESI–MSn) to investigate the distribution and molecular diversity of aliphatic LCPAs extracted from the frustules of diatoms in mixed marine plankton communities collected within the euphotic zone of the northeastern Pacific coast, Bering Sea, and Puget Sound estuary. An astonishing variety of over 100 natural LCPAS with complex distribution patterns was found in each sample. Structural variation included degree of methylation, overall chain length, presence of secondary amine functionalities, incorporation of quaternary ammonium and occurrence of sulfonated derivatives. Putrescine-based LCPAs with various degrees of methylation and N-methyl propylamine repeat units were ubiquitous. Although some LCPA species overlapped between samples, there were regional differences in composition and structural characteristics. The structural variety of LCPAs employed by diatoms to produce their nanopatterned silicified exoskeleton could inform biomimetic studies of silica precipitation.