Determination of microbial activity of estuarine detritus by relative rates of lipid biosynthesis 1

Microorganisms colonizing allochthonous detritus (live oak leaves) incubated in a north Florida estuary show metabolic activity that can be assayed reproducibly by the incorporation of [ super(32)P]H sub(3)PO sub(4) and [1- super(14)C] sodium acetate into the lipids in a 2-h period without introducing subculture bias. Relatively uncolonized live oak leaves show only about 1% of the biosynthetic capacity of leaves incubated in the estuary for 1 week. Lipid synthesis is proportional to time for at least 2 h and also to detrital mass. Random sampling from pooled portions of many leaves greatly reduces the variance of activities from individual leaves. Rates of phospholipid synthesis paralleled the total extractable ATP and the alkaline phosphatase activity during a 6-week incubation of live oak leaves in Apalachicola Bay. Rates of super(14)C incorporation into lipids paralleled the respiratory and the alpha -d-mannosidase