  Green photosynthetic bacteria adjust the structure and functionality of the
chlorosome - the light absorbing antenna complex - in response to environmental
stress factors. The chlorosome is a natural self-assembled aggregate of
bacteriochlorophyll (BChl) molecules. In this study we report the regulation of
the biogenesis of the Chlorobaculum tepidum chlorosome by carbon assimilation
in conjunction with temperature changes. Our studies indicate that the carbon
source and thermal stress culture of Cba. tepidum grows slower and incorporates
less BChl c in the chlorosome. Compared with the chlorosome from other cultural
conditions we investigated, the chlorosome from the carbon source and thermal
stress culture displays: (a) smaller cross-sectional radius and overall size;
(b) simplified BChl c homologues with smaller side chains; (c) blue-shifted Qy
absorption maxima and (d) a sigmoid-shaped circular dichroism (CD) spectra.
Using a theoretical model we analyze how the observed spectral modifications
can be associated with structural changes of BChl aggregates inside the
chlorosome. Our report suggests a mechanism of metabolic regulation for
chlorosome biogenesis.
