Journal of Bacteriology, March 2001, p. 1568-1576, Vol. 183, No. 5
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.5.1568-1576.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Department of Biological Sciences, Oakland University, Rochester, Michigan 48309
Received 25 September 2000/Accepted 6 December 2000
The common precursor to all tetrapyrroles is 5-aminolevulinic acid
(ALA), and in Rhodobacter sphaeroides its formation occurs via the Shemin pathway. ALA synthase activity is encoded by two differentially regulated genes in R. sphaeroides 2.4.1:
hemA and hemT. In our investigations of
hemA regulation, we applied transposon mutagenesis under
aerobic conditions, followed by a selection that identified transposon
insertion mutants in which hemA expression is elevated. One
of these mutants has been characterized previously (J. Zeilstra-Ryalls
and S. Kaplan, J. Bacteriol. 178:985-993, 1996), and here we describe
our analysis of a second mutant strain. The transposon inserted into
the coding sequences of hbdA, coding for
S-(+)-
-hydroxybutyryl-coenzyme A dehydrogenase and
catalyzing an NAD-dependent reaction. We provide evidence that the
hbdA gene product participates in polyhydroxybutyrate (PHB)
metabolism and, based on our findings, we discuss possibilities as to
how defective PHB metabolism might alter the level of hemA expression.
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