Results Directory UMM :Data Elmu:jurnal:J-a:Journal of Experimental Marine Biology and Ecology:Vol256.Issue2.Jan2001:

K .W. Tang et al. J. Exp. Mar. Biol. Ecol. 256 2001 185 –198 189 The detection limit of the system was 0.4 pmol DMSP per ml injection, which would be equivalent to 2 nM DMSP per sample.

3. Results

All four types of homogenate from A . tonsa contained DMSP-consuming bacteria DCB Table 1. Bacteria were absent in the highest dilution in the MPN experiment, which is a prerequisite for the MPN method to be applicable DeMan, 1975. The MPN of DCB in the body of A . tonsa that had fed and A. tonsa that had voided guts, and in 4 21 fecal pellets ranged from 1.6 to 8 3 10 DCB copepod , and were not significantly 2 different from each other P . 0.05. Starved A . tonsa from the field had | 9 3 10 DCB 21 copepod , significantly less than the other three groups P , 0.05. Cells in enrichment 8 21 1 reached a plateau of | 3 3 10 ml after 12 days. The final cell densities in 8 21 enrichments 2 and 3 were similarly low, at | 2 3 10 ml at day 12. Cells in 8 21 enrichment 4 grew to a maximum of 4.7 3 10 ml after 7 days, then decreased to 8 21 3 3 10 ml at the end of the experiment Fig. 1. We estimated the average doubling time t in the enrichment cultures assuming an exponential growth between the initial d cell density and the maximum cell density. The doubling times for enrichments 1, 2 and 3 were similar, between 2.4 and 2.9 days Table 2. Enrichment 4 had a shorter doubling time of 1.1 days. Microscopy revealed that the composition of bacteria was slightly different among the enrichments Fig. 2. Enrichments 1, 2 and 3 were predominantly composed of thick rods and coccoids; Enrichment 4 was predominantly composed of thin rods. Almost all of the initial DMSP 5 mM was consumed in enrichment 4 after 12 days, with , 0.3 mM | 0 remained in the medium. Enrichments 1 and 3 contained , 0.1 mM final DMSP concentration after 12 days, equivalent to , 2 of the initial DMSP. 0.5 mM, or 10 of the initial DMSP remained in enrichment 2 after 12 days Table 3. In enrichments 1, 2 and 3, total DMSP 1 DMS concentrations were not different from dissolved DMSP 1 DMS concentrations, but significantly higher than dissolved DMSP concentrations one-way ANOVA, P , 0.05. This indicates that accumulation of DMSP in bacteria was negligible, and some DMSP had been converted to DMS. In enrichment 4, total DMSP 1 DMS concentration was significantly higher than dissolved DMSP 1 Table 1 Most probable number MPN of DMSP-consuming bacteria DCB from Acartia tonsa CV to female Normalized to number of copepods used in 2-h defecation 21 Inoculum Homogenate type MPN of DCB copepod Mean 95 C.I. 4 4 1 Copepods after feeding 1.6310 0.8–8.4310 4 4 2 Copepods after defecation 2.8310 0.8–11.2310 5 5 3 Fecal pellets 0.8310 0.4–4.2310 3 3 4 Starved copepods 0.92310 0.28–5.16310 190 K .W. Tang et al. J. Exp. Mar. Biol. Ecol. 256 2001 185 –198 Fig. 1. Growth curves for enrichment cultures. 1 Copepods after feeding; 2 copepods after defecation; 3 fecal pellets; 4 starved copepods. DMS and dissolved DMS concentrations one-way ANOVA, P , 0.05, suggesting an accumulation of DMSP in bacteria, and a negligible net production of DMS.

4. Discussion