Abstract
Bacteria using toxic chemicals, such as detergents, as growth substrates face the challenge of exposing themselves to cell-damaging effects that require protection mechanisms, which demand energy delivered from catabolism of the toxic compound. Thus, adaptations are necessary for ensuring the rapid onset of substrate degradation and the integrity of the cells. Pseudomonas aeruginosa strain PAO1 can use the toxic detergent sodium dodecyl sulfate (SDS) as a growth substrate and employs, among others, cell aggregation as a protection mechanism. The degradation itself is also a protection mechanism and has to be rapidly induced upon contact to SDS. In this study, gene regulation of the enzymes initiating SDS degradation in strain PAO1 was studied. The gene and an atypical DNA-binding site of the LysR-type regulator SdsB1 were identified and shown to activate expression of the alkylsulfatase SdsA1 initiating SDS degradation. Further degradation of the resulting 1-dodecanol is catalyzed by enzymes encoded by laoCBA, which were shown to form an operon. Expression of this operon is regulated by the TetR-type repressor LaoR. Studies with purified LaoR identified its DNA-binding site and 1-dodecanoyl coenzyme A as the ligand causing detachment of LaoR from the DNA. Transcriptional studies revealed that the sulfate ester detergent sodium lauryl ether sulfate (SLES) induced expression of sdsA1 and the lao operon. Growth experiments revealed an essential involvement of the alkylsulfatase SdsA1 for SLES degradation. This study revealed that the genes for the enzymes initiating the degradation of toxic sulfate-ester detergents are induced stepwise by a positive and a negative regulator in P. aeruginosa strain PAO1.IMPORTANCE Bacterial degradation of toxic compounds is important not only for bioremediation but also for the colonization of hostile anthropogenic environments in which biocides are being used. This study with Pseudomonas aeruginosa expands our knowledge of gene regulation of the enzymes initiating degradation of sulfate ester detergents, which occurs in many hygiene and household products and, consequently, also in wastewater. As an opportunistic pathogen, P. aeruginosa causes severe hygienic problems because of its pronounced biocide resistance and its metabolic versatility, often combined with its pronounced biofilm formation. Knowledge about the regulation of detergent degradation, especially regarding the ligands of DNA-binding regulators, may lead to the rational development of specific inhibitors for restricting growth and biofilm formation of P. aeruginosa in hygienic settings. In addition, it may also contribute to optimizing bioremediation strategies not only for detergents but also for alkanes, which when degraded merge with sulfate ester degradation at the level of long-chain alcohols.