Differential expression of two bc_1 complexes in the strict acidophilic chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans suggests a model for their respective roles in iron or sulfur oxidation

摘要

Three strains of the strict acidophilic chemolithoautotrophic Acidithiobacillus ferrooxidans,including the type strain ATCC 23270,contain a petllABC gene cluster that encodes the three proteins,cytochrome c_1,cytochrome b and a Rieske protein,that constitute a bc_1 electron-transfer complex.RT-PCR and Northern blotting show that the petllABC cluster is co-transcribed with cycA,encoding a cytochrome c belonging to the c_4 family,sdrA,encoding a putative short-chain dehydrogenase,and hip,encoding a high potential iron-sulfur protein,suggesting that the six genes constitute an operon,termed the petll operon.Previous results indicated that A.ferrooxidans contains a second pef operon,termed the petl operon,which contains a gene cluster that is similarly organized except that it lacks hip.Real-time PCR and Northern blot experiments demonstrate that petl is transcribed mainly in cells grown in medium containing iron,whereas petll is transcribed in cells grown in media containing sulfur or iron.Primer extension experiments revealed possible transcription initiation sites for the petl and petll operons.A model is presented in which petl is proposed to encode the bc_1 complex,functioning in the uphill flow of electrons from iron to NAD(P),whereas petll is suggested to be involved in electron transfer from sulfur (or formate) to oxygen (or ferric iron).A.ferrooxidans is the only organism,to date,to exhibit two functional bc_1 complexes.