Steady-State Effects of 2,5,2',5'-Tetrachlorobiphenyl on Growth, Photosynthesis, and P Uptake in Selenastrum capricornutum.

The steady-state effect of 2,5,2',5'-tetrachlorobiphenyl (TCBP) on the green alga Selenastrum capricornutum was investigated in a P-limited two-stage chemostat system. The partition coefficient of this polychlorinated biphenyl congener was 5.9 x 10 in steady-state cultures. At a cellular TCBP concentration of 12.2 x 10 ng . cell, growth rate was not affected. However, photosynthetic capacity (P(max)) was significantly enhanced by TCBP (56 x 10 mumol of C . cell . h versus 34 x 10 mumol of C . cell . h in the control). Photosynthetic efficiency, or the slope of the photosynthesis-irradiance curve, was also significantly higher. There was little difference in the cell chlorophyll a content, and therefore the difference in these photosynthetic characteristics was the same even when they were expressed on a per-chlorophyll a basis. Cell C content was higher in TCBP-containing cells than in TCBP-free cells, but approximately 36% of the C fixed by cells with TCBP was not incorporated as cell C. The maximum P uptake rate was also enhanced by TCBP, but the half-saturation concentration appeared to be unaffected.