ADAPTIVE RESPONSE OF THE ARCHAEON SULFOLOBUS-ACIDOCALDARIUS BC65 TO PHOSPHATE STARVATION

The adaptive response of the archaeon Sulfolobus acidocaldarius BC65 t o phosphate starvation was studied. When cells were subjected to phosp hate limitation, their growth was affected. In addition, the levels of synthesis and/or the degree of phosphorylation of several proteins ch anged, as detected by two-dimensional nonequilibrium ph gradient elect rophoresis of cells labelled in vivo with [S-35]methionine and [S-35]c ysteine, or H-3 (PO4)-P-32. 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 phosp horylated without its synthesis being significantly modified, suggesti ng a probable regulatory role during adaptation of the cell to the cha nge in the external environment. In Southern blot analysis with specif ic probes from very conserved regions of the phoR and phoB genes from Escherichia coil, a positive hybridization with S. acidocaldarius BC65 chromosomal DNA fragments was found. This suggested the presence in 5 . acidocaldarius BC65 of genes related to the E. coil genes involved i n the phosphate starvation response system. This appears to be the fir st evidence of the possible existence of a two-component sensory syste m in a micro-organism from the archaeal kingdom Crenarchaeota.