RESUMO
The adaptive response of the archaeon Sulfolobus acidocaldarius BC65 to phosphate starvation was studied. When cells were subjected to phosphate limitation, their growth was affected. In addition, the levels of synthesis and/or the degree of phosphorylation of several proteins changed, as detected by two-dimensional nonequilibrium pH gradient electrophoresis of cells labelled in vivo with [35S]methionine and [35S]cysteine, or H3 32PO4. After another growth-restricting treatment, a heat shock, a general inhibition of protein synthesis was observed. Under phosphate starvation conditions, a 36 kDa protein became phosphorylated without its synthesis being significantly modified, suggesting a probable regulatory role during adaptation of the cell to the change in the external environment. In Southern blot analysis with specific probes from very conserved regions of the phoR and phoB genes from Escherichia coli, a positive hybridization with S. acidocaldarius BC65 chromosomal DNA fragments was found. This suggested the presence in S. acidocaldarius BC65 of genes related to the E. coli genes involved in the phosphate starvation response system. This appears to be the first evidence of the possible existence of a two-component sensory system in a micro-organism from the archaeal kingdom Crenarchaeota.