Regulation of the Expression of the Photosynthetic Apparatus of Rhodobacter capsulatus Grown in Nitrogen-Limited Chemostat Cultures |
| |
Authors: | Jorge E Teppaz Norma L Pucheu Augusto F García |
| |
Institution: | (1) CIByF—CONICET and Cátedra de Microbiología, Facultad de Agronomía, UBA, Av. San Martín 4453, 1417 Capital Federal, Argentina , AR |
| |
Abstract: | Rhodobacter capsulatus was grown in chemostat cultures under different dilution rates and with ammonium ions as the limiting nutrient. The maximal
growth rate (μmax) and the Monod cell growth saturation coefficient (Ks), were calculated from batch cultures grown at different concentrations of NH4
+. The experiments in chemostat were carried out at 0.25 mM (NH4)2SO4, and the dilution rates were varied between 38% and 75% of μmax. The results indicated that under continuous culture conditions
the cell yield coefficient (Y) (mg dry weight × μmol consumed ammonium sulfate−1) decreased with increasing dilution rate (D). On the contrary, the cell yield was constant when expressed as mg cellular
protein ×μmol consumed ammonium sulfate−1. This occurred as a consequence of both an increase in the consumed ammonium sulfate and a simultaneous decrease in the cell
biomass production at increasing growth rates. The cells produced at higher growth rates had a higher protein content per
cell. The specific content of bacteriochlorophyll (Bchl) decreased (between 3 and 4 times) with increasing growth rates measured
in either cells or chromatophores. However, the absorption spectra of the cells indicated that the ratio LHI (light-harvesting
complex I) to LHII (light-harvesting complex II) Bchl complexes did not change. The reaction center (RC) complex content varied
in parallel with the total Bchl content, yielding a constant photosynthetic unit of 65 mol Bchl × mol RC−1 at different Ds. On the other hand, the uncoupled ATPase-specific activity measured in chromatophores was usually between
30% and 40% higher at the highest growth rates reached in these experiments.
Received: 22 January 1996 / Accepted: 9 March 1996 |
| |
Keywords: | |
本文献已被 PubMed SpringerLink 等数据库收录! |
|