PRODUCTION OF DISSOLVED ORGANIC MATTER FROM DEAD GREEN ALGAL CELLS. I. AEROBIC MICROBIAL DECOMPOSITION

Abstract

The green alga, Scenedesmus sp., killed by freeze‐drying, was experimentally decomposed by microflora extracted from lake mud under aerobic conditions. The production of dissolved organic matter was about 7% as carbon and about 6% as nitrogen by the 30th day. These amounts probably were minimal. The dissolved organic product was fractionated between butanol and acidified water. One fraction was insolubilized when mixed with butanol, became suspended at the interface between the two solutions, and gave a white amorphous solid after vacuum drying. Its infrared spectrum showed it was proteinaceous; it contained more than 14 kinds of amino acids. The other was extracted with butanol and gave a dark brown viscous substance on drying. Aerobic microbial decomposition of Scenedesmus can be approximated to a first‐order reaction during the first 30 days under laboratory conditions. Kinetic considerations of the decomposition pattern of the cell nitrogen and the production of dissolved organic nitrogen suggest that dead algal cell substance may be divided into labile and refractory constituents by their relative resistance to the action of bacteria. The dissolved organic nitrogenous material produced is composed of two major fractions: One is produced with the decomposition of algal cells and the other is probably excreted by bacteria through reassimilation of mineralized nitrogen.