Community metabolism of adenylates by microheterotrophs from the Los Angeles Harbor and Southern California coastal waters

Abstract

The natural concentration (Sn) of dissolved total adenylates TA(=AMP+ADP+ATP) in coastal seawater from a depth of 1 m at 5 stations (California, USA) sampled periodically for 1 yr had a mean value ±1 SD of 2.8±1.7 nmol TA1-1. The specific uptake rates of TA by microheterotrophs at a station inside the Los Angeles Harbor and at a station 1.5 km offshore in the San Pedro Channel were studied by simple uptake and saturation-type kinetic analysis using 3H-AMP as a tracer. Within the harbor, the specific uptake rate (nmol TA 109 cell-1 h-1) at Sn ranged 10-fold from 0.028 in December to 0.28 in August. Kt (half-saturation constant) values always exceeded theSn concentrations in any given month, and were greater in the harbor than in the channel. Generally, over 80% of biological uptake of 3H-AMP was associated with organisms <1.0 μm, a size class accounting for about 20% of the total particulate adenylate concentration in the 0.2 to 203 μm size fraction. Assuming steady-state conditions for the dissolved adenylate pool, we propose a model in which losses from this pool are balanced by inputs to the pool through inefficient feeding, lysis and decomposition of particulate adenylates.