Solemya reidii (Bernard, 1980) were collected by Van Veen grab near a sewage outfall in California, USA, in spring/early summer of 1984 and 1985. Fixation of carbon dioxide by symbiotic chemoautotrophic bacteria in the gills, followed by translocation of the fixed carbon to symbiontfree tissues of the clam has been demonstrated using NaH14CO3 in two types of experiments. The first approach used the technique of tissue autoradiography to determine the exact sites of fixation of carbon dioxide and subsequent utilization of the fixed carbon compounds. Initial deposition (>95% after 10 min) was in the well defined portion of the gill filaments where the symbiotic bacteria reside. The heaviest redeposition of labeled carbon after a 2 d chase period was in the various glandular tissues of the clams (8 to 38% of the gill level). Levels in two of these glandular tissues decreased after a 5 d chase period, probably due to secretion. Significant labeling of muscle tissue, gonads, and the tips of the gill filaments occurred only after the chase periods. In the second approach, rates of initial carbon fixation by symbiotic bacteria and translocation into clam tissues were determined using pulse-chase experiments followed by dissections and assay of the clam tissues for radioactivity. Freshly caught clams fixed carbon at an average rate of 0.8 μmol CO2 g-1 wet weight h-1. In these fresh clams, 88% of the fixed carbon was found in the gills after 2 min incubation periods, with only 44% remaining in the gills after 1 to 1.7 h incubations. Individuals maintained in the laboratory for 100 d had only 5.8% of the RuBP carboxylase (a diagnostic enzyme for autotrophs) activity in their gills compared to freshly caught clams. After 2 min incubations in NaH14CO3, only 21% of the carbon fixed by the "old" clams was found in their gills, and the rate of incoporation into gill tissue was 5.7% of the rate in fresh individuals. These experiments demonstrate that the symbiotic bacteria fix carbon at a high rate, that a significant portion of the carbon fixed by the symbiotic bacteria (>45%) is translocated to the host, and that the translocated carbon is used by the host.
All Science Journal Classification (ASJC) codes
- Ecology, Evolution, Behavior and Systematics
- Aquatic Science