Ntrb ntrc and phb production

APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Jan. 2000, p. 113–117
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Copyright © 2000, American Society for Microbiology. All Rights Reserved.

Vol. 66, No. 1

The ntrB and ntrC Genes Are Involved in the Regulation of
Poly-3-Hydroxybutyrate Biosynthesis by Ammonia in
Azospirillum brasilense Sp7
JUN SUN,1 XUAN PENG,2 JAN VAN IMPE,2

AND

JOS VANDERLEYDEN1*

F. A. Janssens Laboratory of Genetics1 and Bioprocess Technology and Control,2 K.U. Leuven,
B-3001 Heverlee, Belgium
Received 6 July 1999/Accepted 10 October 1999

Azospirillum brasilense Sp7 and its ntrA (rpoN), ntrBC, and ntrC mutants have been evaluated for their capabilities of poly-3-hydroxybutyrate (PHB) accumulation in media with high and low ammonia concentrations. It was observed that the ntrBC and ntrC mutants can produce PHB in both low- and high-C/N-ratio media, while no significant PHB production was observed for the wild type or the ntrA mutant in low-C/N-ratio media. Further investigation by fermentation analysis indicated that the ntrBC and ntrC mutants were able to grow and accumulate PHB simultaneously in the presence of a high concentration of ammonia in the medium, while little PHB was produced in the wild type and ntrA (rpoN) mutant during active growth phase. These results provide the first genetic evidence that the ntrB and ntrC genes are involved in the regulation of PHB synthesis by ammonia in A. brasilense Sp7. accumulation, and generally ammonia is considered the critical control factor decoupling the growth of cells and PHB production. However, some bacteria, such as Azotobacter vinelandii strain UWD (obtained by chemical mutagenesis [23]), Alcaligenes latus (8), and Pseudomonas putida KT2442 (9), are able to accumulate large amounts of PHB or polyhydroxyalkanoate
(PHA) during exponential growth. The inactivation of inhibition of ammonia of the accumulation of PHB has industrial potential for improvement of process control and productivity