Characterization of the promoter and upstream activating sequence from the Pseudomonas alcaligenes lipase gene

The Regulatory Hierarchy Following Signal Integration by the CbrAB Two-Component System: Diversity of Responses and Functions

CbrAB is a two-component system, unique to bacteria of the family Pseudomonaceae, capable of integrating signals and involved in a multitude of physiological processes that allow bacterial adaptation to a wide variety of varying environmental conditions. This regulatory system provides a great metabolic versatility that results in excellent adaptability and metabolic optimization. The two-component system (TCS) CbrA-CbrB is on top of a hierarchical regulatory cascade and interacts with other regulatory systems at different levels, resulting in a robust output. Among the regulatory systems found at the same or lower levels of CbrAB are the NtrBC nitrogen availability adaptation system, the Crc/Hfq carbon catabolite repression cascade in Pseudomonas, or interactions with the GacSA TCS or alternative sigma ECF factor, such as SigX. The interplay between regulatory mechanisms controls a number of physiological processes that intervene in important aspects of bacterial adaptation and survival. These include the hierarchy in the use of carbon sources, virulence or resistance to antibiotics, stress response or definition of the bacterial lifestyle. The multiple actions of the CbrAB TCS result in an important competitive advantage.

Role of Two-Component System Networks in Pseudomonas aeruginosa Pathogenesis

Two-component systems (TCS) are the largest family of signaling systems in the bacterial kingdom. They enable bacteria to cope with a wide range of environmental conditions via the sensing of stimuli and the transduction of the signal into an appropriate cellular adaptation response. Pseudomonas aeruginosa possesses one of the richest arrays of TCSs in bacteria and they have been the subject of intense investigation for more than 20 years. Most of the P. aeruginosa TCSs characterized to date affect its pathogenesis, via the regulation of virulence factors expression, modulation of the synthesis of antibiotic/antimicrobial resistance mechanisms, and/or via linking virulence to energy metabolism. Here, we give an overview of the current knowledge on P. aeruginosa TCSs, citing key examples for each of the above-mentioned regulatory actions. We then conclude by mentioning few small molecule inhibitors of P. aeruginosa TCSs that have shown an antimicrobial action in vitro.

PmrA/PmrB Two-Component System Regulation of lipA Expression in Pseudomonas aeruginosa PAO1

Pseudomonas lipases are well-studied, but few studies have examined the mechanisms of lipase expression regulation. As a global regulatory protein, PmrA controls the expression of multiple genes such as the Dot/Icm apparatus, eukaryotic-like proteins, and secreted effectors. In this study, the effect of PmrA on expression of the lipase lipA in Pseudomonas aeruginosa PAO1 was investigated by knocking out or overexpressing pmrA, rsmY, and rsmA. PmrA regulated the expression of lipA at both the transcriptional and translational level although translation was the pivotal regulatory mechanism for lipA expression. PmrA also regulated the expression of rsmY. Using gel mobility shift assay and pmrA/rsmY double gene knock-out model, we showed that PmrA directly bound to the promoter sequence of rsmY to regulate lipA expression. Translation of lipA was activated by the PmrA/PmrB system via RsmA. Specifically, the Shine-Dalgarno (SD) sequence located at lipA mRNA was overlapped through combination between RsmA and the AGAUGA sequence, subsequently blocking the 30S ribosomal subunit to the SD sequence, leading to translational inhibition of lipA. Transcriptional repression of RsmY initiated translation of lipA through negative translational regulation of rsmA. In conclusion, this study demonstrated that in P. aeruginosa PAO1, PmrA mainly regulated rsmY expression at a translational level to influence lipA expression. RsmY primarily activated lipA translation via negative translational regulation of rsmA.

Cloning and characterization of a novel lipase from Stenotrophomonas maltophilia GS11: The first member of a new bacterial lipase family XVI

Bacterial lipases are an important group of enzymes that offer enormous potential in organic synthesis, and there is considerable interest in identifying and developing novel bacterial lipases. In previous studies, strains of the genus Stenotrophomonas were proved to be potential source of lipases, but there is little genetic information describing lipase from the genus Stenotrophomonas. We have cloned and characterized a novel lipase (LipSM54), the first lipase described from the genus Stenotrophomonas. Enzymatic study showed that LipSM54 was a cold-active, solvent-tolerant and alkaline lipase. Using bioinformatics tools, LipSM54 was found to be related only to several putative lipases from different bacterial origins, none of which could be assigned to any previously described bacterial lipase family. LipSM54 and these related putative lipases share four conserved motifs around the catalytic residues. These motifs clearly distinguish them from the known bacterial lipase families. Consequently, LipSM54 is the first characterized member of the novel bacterial lipase family.

EliA facilitates the induction of lipase expression by stearyl alcohol in Ralstonia sp. NT80

Extracellular lipase activity from Ralstonia sp. NT80 is induced significantly by fatty alcohols such as stearyl alcohol. We found that when lipase expression was induced by stearyl alcohol, a 14-kDa protein (designated EliA) was produced concomitantly and abundantly in the culture supernatant. Cloning and sequence analysis revealed that EliA shared 30% identity with the protein-like activator protein of Pseudomonas aeruginosa, which facilitates oxidation and assimilation of n-hexadecane. Inactivation of the eliA gene caused a significant reduction in the level of induction of lipase expression by stearyl alcohol. Furthermore, turbidity that was caused by the presence of emulsified stearyl alcohol, an insoluble material, remained in the culture supernatant of the ΔeliA mutant during the late stationary phase, whereas the culture supernatant of the wild type at 72 h was comparatively clear. In contrast, when lipase expression was induced by polyoxyethylene (20) oleyl ether, a soluble material, inactivation of eliA did not affect the extracellular lipase activity greatly. These results strongly indicate that EliA facilitates the induction of lipase expression, presumably by promoting the recognition and/or incorporation of the induction signal that is attributed to stearyl alcohol.

Analysis of the promoter region of the gene LIP1 encoding triglyceride lipase from Fusarium graminearum

Triglyceride lipases catalyze the reversible degradation of glycerol esters with long-chain fatty acids into fatty acids and glycerol. In silico analysis of 5'-end flanking sequence of the gene LIP1 encoding a triglyceride lipase from the wheat head blight pathogen Fusarium graminearum revealed the presence of several cis-regulatory elements. To delineate the function of these regulatory elements, we constructed a series of deletion mutants in the LIP1 promoter region fused to the open reading frame of a green fluorescent protein (GFP) and assayed the promoter activity. Analysis of GFP expression levels in mutants indicated that a 563-bp promoter sequence was sufficient to drive the expression of LIP1 and regulatory elements responsible for the gene induction were located within the 563-372bp region. To further investigate the regulatory elements, putative cis-acting elements spanned within the 563-372bp region were mutated using a targeted mutagenesis approach. A CCAAT box, a CreA binding site, and a fatty acid responsive element (FARE) were identified and confirmed to be required for the basal expression of LIP1, glucose suppression and fatty acid induction, respectively.

Promoter recognition and activation by the global response regulator CbrB in Pseudomonas aeruginosa

In Pseudomonas aeruginosa, the CbrA/CbrB two-component system is instrumental in the maintenance of the carbon-nitrogen balance and for growth on carbon sources that are energetically less favorable than the preferred dicarboxylate substrates. The CbrA/CbrB system drives the expression of the small RNA CrcZ, which antagonizes the repressing effects of the catabolite repression control protein Crc, an RNA-binding protein. Dicarboxylates appear to cause carbon catabolite repression by inhibiting the activity of the CbrA/CbrB system, resulting in reduced crcZ expression. Here we have identified a conserved palindromic nucleotide sequence that is present in upstream activating sequences (UASs) of promoters under positive control by CbrB and σ(54) RNA polymerase, especially in the UAS of the crcZ promoter. Evidence for recognition of this palindromic sequence by CbrB was obtained in vivo from mutational analysis of the crcZ promoter and in vitro from electrophoretic mobility shift assays using crcZ promoter fragments and purified CbrB protein truncated at the N terminus. Integration host factor (IHF) was required for crcZ expression. CbrB also activated the lipA (lipase) promoter, albeit less effectively, apparently by interacting with a similar but less conserved palindromic sequence in the UAS of lipA. As expected, succinate caused CbrB-dependent catabolite repression of the lipA promoter. Based on these results and previously published data, a consensus CbrB recognition sequence is proposed. This sequence has similarity to the consensus NtrC recognition sequence, which is relevant for nitrogen control.

Lipase expression in Pseudomonas alcaligenes is under the control of a two-component regulatory system

Preliminary observations in a large-scale fermentation process suggested that the lipase expression of Pseudomonas alcaligenes can be switched on by the addition of certain medium components, such as soybean oil. In an attempt to elucidate the mechanism of induction of lipase expression, we have set up a search method for genes controlling lipase expression by use of a cosmid library containing fragments of P. alcaligenes genomic DNA. A screen for lipase hyperproduction resulted in the selection of multiple transformants, of which the best-producing strains comprised cosmids that shared an overlapping genomic fragment. Within this fragment, two previously unidentified genes were found and named lipQ and lipR. Their encoded proteins belong to the NtrBC family of regulators that regulate gene expression via binding to a specific upstream activator sequence (UAS). Such an NtrC-like UAS was identified in a previous study in the P. alcaligenes lipase promoter, strongly suggesting that LipR acts as a positive regulator of lipase expression. The regulating role could be confirmed by down-regulated lipase expression in a strain with an inactivated lipR gene and a threefold increase in lipase yield in a large-scale fermentation when expressing the lipQR operon from the multicopy plasmid pLAFR3. Finally, cell extracts of a LipR-overexpressing strain caused a retardation of the lipase promoter fragment in a band shift assay. Our results indicate that lipase expression in Pseudomonas alcaligenes is under the control of the LipQR two-component system.