Transcriptional regulation of ectoine catabolism in response to multiple metabolic and environmental cues

Abstract

Ectoine and hydroxyectoine are effective microbial osmostress protectants, but can also serve as versatile nutrients for bacteria. We have studied the genetic regulation of ectoine and hydroxyectoine import and catabolism in the marine Roseobacter species Ruegeria pomeroyi and identified three transcriptional regulators involved in these processes: the GabR/MocR-type repressor EnuR, the feast and famine-type regulator AsnC and the two-component system NtrYX. The corresponding genes are widely associated with ectoine and hydroxyectoine uptake and catabolic gene clusters (enuR, asnC), and with microorganisms predicted to consume ectoines (ntrYX). EnuR contains a covalently bound pyridoxal-5'-phosphate as a co-factor and the chemistry underlying the functioning of MocR/GabR-type regulators typically requires a system-specific low molecular mass effector molecule. Through ligand binding studies with purified EnuR, we identified N-(alpha)-L-acetyl-2,4-diaminobutyric acid and L-2,4-diaminobutyric acid as inducers for EnuR that are generated through ectoine catabolism. AsnC/Lrp-type proteins can wrap DNA into nucleosome-like structures, and we found that the asnC gene was essential for use of ectoines as nutrients. Furthermore, we discovered through transposon mutagenesis that the NtrYX two-component system is required for their catabolism. Database searches suggest that our findings have important ramifications for an understanding of the molecular biology of most microbial consumers of ectoines.

Screening and Whole-Genome Sequencing of TwoStreptomycesSpecies from the Rhizosphere Soil of Peony Reveal Their Characteristics as Plant Growth-Promoting Rhizobacteria

“…Both MIB and teleocidin B were important terpenoids and they were synthetized by terpene synthases[ 35 , 38 ]. Ectoine was an effective microbial osmostress protectant, which could also serve as a versatile nutrient[ 39 ]. Furthermore, the similarities of cluster 7, cluster 10, cluster 22, cluster 30, cluster 31, and cluster 34 with their similar and known gene clusters were all more than 60%, which might indicate the biosynthesis ability of hopene, lantipeptide, cyclooctatin (a kind of siderophore), albachelin, and candicidin.…”

“…Some gene clusters in these two strains might improve the resistance of peony for the environmental stress. For example, the presence of synthetic gene cluster of ectoine [ 39 ] in both strains might improve the salt stress of peony in saline-alkali land. At present, the research on Streptomyces strains as PGPR has been carried out [ 16 , 17 ], but there were relatively little biocontrol study and genome research about species S. albireticuli and S. alboflavus.…”

The MocR‐like transcription factors: pyridoxal 5′‐phosphate‐dependent regulators of bacterial metabolism

“…Microscale thermophoresis experiments demonstrated that R. pomeroi EnuR binds two metabolites of ectoine catabolism N‐(α)‐ADABA ( K d = 1.7 μ m ) and DABA ( K d = 457 μ m ), which act as effector molecules, whereas it does not bind N‐(γ)‐ADABA, an intermediate in ectoine biosynthesis. These results demonstrated that EnuR is a key regulator for microorganisms that use ectoines as nutrient because it showed high affinity for N ‐α‐ADABA, an ectoine‐catabolism‐specific metabolite, low affinity for DABA, that is an intermediate in other metabolic and biosynthetic processes, including the biosynthesis of ectoine, and has no affinity for N‐(γ)‐ADABA, which serves as the main substrate for the ectoine synthase .…”

“…EnuR is transcribed from its own promoter and, in fact, its transcriptional level is low and independent from the available substrates, whereas the uehABC‐eutABC ‐ eutDE‐ssd‐atf transcript is strongly up‐regulated in cells grown on a medium containing either ectoine or 5‐hydroxyectoine. The loss of the EnuR regulator does not affect expression from the enuR promoter but results in a constitutive expression from the substrate‐inducible uehA promoter, demonstrating that EnuR acts as a repressor .…”

With a pinch of extra salt—Did predatory protists steal genes from their food?

“…Finally, ectoines are not only effective osmostress protectants but they are also valuable nutrients for microorganisms [ 24 ]. The physiology and genetics of the catabolism of these nitrogen-rich compounds ( Fig 2 ) have been intensively studied in the marine bacterium Ruegeria pomeroyi [ 53 ]. A unique ectoine-derived metabolite (N-α-L-acetyl-2,4-diaminobutyric acid), and not ectoine or hydroxyectoine themselves, serves as the inducer for the GabR/MocR-type regulatory protein EnuR that controls the transcription of the ectoine/5-hydroxyectoine import and catabolic gene clusters present in many microorganisms [ 53 ].…”