A Retentive Memory of Tetrachloroethene Respiration in Sulfurospirillum halorespirans - involved Proteins and a possible link to Acetylation of a Two-Component Regulatory System. 
Organohalide respiration (OHR), comprising the reductive dehalogenation of halogenated organic compounds, is subject to a unique memory effect and long-term transcriptional downregulation of the involved genes in Sulfurospirillum multivorans.  Gene expression ceases slowly over approximately 100 generations in the absence of tetrachloroethene (PCE).  However, the molecular mechanisms of this regulation process are not understood.  We show here that Sulfurospirillum halorespirans undergoes the same type of regulation when cultivated without chlorinated ethenes for a long period of time.  In addition, we compared the proteomes of S. halorespirans cells cultivated in the presence of PCE with those of cells long- and short-term cultivated with nitrate as the sole electron acceptor.  Important OHR-related proteins previously unidentified in S. multivorans include a histidine kinase, a putative quinol dehydrogenase membrane protein, and a PCE-induced porin.  Since for some regulatory proteins a posttranslational regulation of activity by lysine acetylations is known, we also analyzed the acetylome of S. halorespirans, revealing that 32% of the proteome was acetylated in at least one condition.  The data indicate that the response regulator and the histidine kinase of a two-component system most probably involved in induction of PCE respiration are highly acetylated during short-term cultivation with nitrate in the absence of PCE.  The so far unique long-term downregulation of organohalide respiration is now identified in a second species suggesting a broader distribution of this regulatory phenomenon.  An improved protein extraction method allowed the identification of proteins most probably involved in transcriptional regulation of OHR in Sulfurospirillum spp.  Our data indicate that acetylations of regulatory proteins are involved in this extreme, sustained standby-mode of metabolic enzymes in the absence of a substrate.  This first published acetylome of Epsilonproteobacteria might help to study other ecologically or medically important species of this clade.