S. Ramirezarcos et al., A THERMOPHILIC NITRATE REDUCTASE IS RESPONSIBLE FOR THE STRAIN-SPECIFIC ANAEROBIC GROWTH OF THERMUS-THERMOPHILUS HB8, Biochimica et biophysica acta, N. Gene structure and expression, 1396(2), 1998, pp. 215-227
T. thermophilus HB8 contains a nitrate reductase gene cluster which is
absent from closely related strains. This cluster encodes 4 ORFs (a-d
) similar in organization and protein sequence to those encoded by res
piratory nitrate reductase operons (narGHJI) of Escherichia coli, Baci
llus subtilis, Pseudomonas fluorescens, and Thiosphaera pantothropha.
The highest similarity is shown between the proteins encoded by the OR
Fa, ORFb and ORFd, and the structural components of the mesophilic nit
rate reductases NarG(alpha), NarH(beta), and NarI(gamma) proteins, whi
lst ORFc encodes a protein which showed lower similarity to NarJ, a pr
otein of unknown function encoded between narH and narI genes in all t
he nar cluster so far sequenced. This T. thermophilus HB8 narGHJI clus
ter is strongly induced by the combined effect of nitrate and low oxyg
en concentration, giving rise to the synthesis of an enzyme whose opti
mal temperature and pH was determined to be 80 degrees C, and pH 10, r
espectively. We also demonstrate that insertional inactivation of the
narG and narH genes of this cluster results in strictly aerobic mutant
s, showing its sale responsibility in the strain specific ability of T
. thermophilus HB8 to grow anaerobically. (C) 1998 Elsevier Science B.
V.