Stationary phase-dependent accumulation of ectoine is an efficient adaptation strategy in Vibrio anguillarum against cold stress

The tropical marine actinomycete Nocardiopsis dassonvillei NCIM 5124 as novel source of ectoine: Genomic and transcriptomic insights

Since ectoine is a high-value product, overviewing strategies for identifying novel microbial sources becomes relevant. In the current study, by following a genome mining approach, the ectoine biosynthetic cluster in a tropical marine strain of Nocardiopsis dassonvillei (NCIM 5124) was located and compared with related organisms. Transcriptome analysis of Control and Test samples (with 0 and 5% NaCl, respectively) was carried out to understand salt induced stress response at the molecular level. There were 4950 differentially expressed genes with 25 transcripts being significantly upregulated in Test samples. NaCl induced upregulation of the ectoine biosynthesis cluster and some other genes (stress response, chaperone/Clp protease, cytoplasm, ribonucleoprotein and protein biosynthesis). The production of ectoine as a stress response molecule was experimentally validated via LCMS analysis. The investigation sheds light on the responses exhibited by this actinomycete in coping up with salt stress and provides a foundation for understanding salt induced molecular interactions.

Dynamic Transcriptional Landscape of Mycobacterium smegmatis under Cold Stress

Bacterial adaptation to cold stress requires wide transcriptional reprogramming. However, the knowledge of molecular mechanisms underlying the cold stress response of mycobacteria is limited. We conducted comparative transcriptomic analysis of Mycobacterium smegmatis subjected to cold shock. The growth of M. smegmatis cultivated at 37 °C was arrested just after exposure to cold (acclimation phase) but later (by 24 h) was resumed at a much slower rate (adaptation phase). Transcriptomic analyses revealed distinct gene expression patterns corresponding to the two phases. During the acclimation phase, differential expression was observed for genes associated with cell wall remodeling, starvation response, and osmotic pressure stress, in parallel with global changes in the expression of transcription factors and the downregulation of ribosomal genes, suggesting an energy-saving strategy to support survival. At the adaptation phase, the expression profiles were recovered, indicating restoration of the processes repressed earlier. Comparison of transcriptional responses in M. smegmatis with those in other bacteria revealed unique adaptation strategies developed by mycobacteria. Our findings shed light on the molecular mechanisms underlying M. smegmatis survival under cold stress. Further research should clarify whether the discovered transcriptional mechanisms exist in other mycobacterial species, including pathogenic Mycobacterium tuberculosis, which could be important for transmission control.

The phylogeny and metabolic potentials of an n-alkane-degrading Venatorbacter bacterium isolated from deep-sea sediment of the Mariana Trench

Recently, several reports showed that n-alkanes were abundant in the hadal zone, suggesting that n-alkanes could be an important source of nutrients for microorganisms in hadal ecosystems. To date, most of the published studies on the microbial capacity to degrade hydrocarbons were conducted only at atmospheric temperature and pressure (0.1 MPa), and little is known about whether and which microbes could utilize n-alkanes at in situ environmental conditions in the hadal zone, including low temperature and high hydrostatic pressure (especially >30 MPa). In this study, a piezotolerant bacterium, strain C2-1, was isolated from a Mariana Trench sediment at depth of 5,800 m. Strain C2-1 was able to grow at in situ temperature (4°C) and pressure (58 MPa) with n-alkanes as the sole carbon source. Phylogenetically, strain C2-1 and related strains (TMPB967, ST750PaO-4, IMCC1826, and TTBP476) should be classified into the genus Venatorbacter. Metagenomic analysis using ~5,000 publicly available datasets showed that Venatorbacter has a wide environmental distribution in seawater (38), marine sediments (3), hydrothermal vent plumes (2), Antarctic ice (1), groundwater (13), and marine sponge ecosystems (1). Most Venatorbacter species are non-obligate n-alkane degraders that could utilize, at a minimal, C16-C18 n-alkanes, as well as other different types of carbon substrates, including carbohydrates, amino acids, peptides, and phospholipids. The type II secretion system, extracellular proteases, phospholipase, and endonuclease of Venatorbacter species were robustly expressed in the metatranscriptomes of deep-sea hydrothermal vents, suggesting their important contribution to secondary productivity by degrading extracellular macromolecules. The identification of denitrifying genes suggested a genus-specific ecological potential that allowed Venatorbacter species to be active in anoxic environments, e.g., the oxygen-minimal zone (OMZ) and the deeply buried marine sediments. Our results show that Venatorbacter species are responsible for the degradation of hydrocarbon and extracellular macromolecules, suggesting that they may play an important role in the biogeochemistry process in the Trench ecosystems.

Performance and microbial mechanism of eletrotrophic bio-cathode denitrification under low temperature

Insufficient amount of carbon in wastewater and low temperatures hinder the use of biological nitrogen removal for purification of wastewaters. Nitrogen removal using cold-tolerant electrotrophic cathodic microbes is a novel and unique autotrophic denitrification technique in which electrical current, not chemicals, is used as a source of electrons. In this study, integrated MFC (R_W) and open-circuit MFC (R_O) were cultured and acclimatized in stages at a low temperature (10 °C) to impart cold tolerance to electrotrophic cathodic microbes, investigate the effectiveness of simultaneous nitrification and denitrification (SND) process, and address the possible mechanism of microbial action. The results showed that (i) microbial communities in the R_W system were successfully enriched with the cold-tolerant electrotrophic cathodic microbes after five stages, and (ii) the degree of NH₄⁺-N removal and SND were 75.50% and 81.91%, respectively, but the respective values in the R_O system were only 40.47% and 54.01%. The desirable SND efficiency was obtained in R_W at a DO of ∼0.6 mg/L, a current of ∼20 mA, and pH ∼7.0. In R_W, Thauera, Pesudomonas, and Hydrogenophaga were the main electrotrophic cathodic denitrifying bacteria with cold tolerance capable of degrading ammonia, nitrate, and nitrite through autotrophic denitrification and cathodic-driven bio-electrochemical denitrification. Besides, for R_W, results from high throughput sequencing analysis revealed that the abundance of genes related to energy production and conversion, amino acid transport, and metabolism, signal transduction, environmental adaptation, and enzymatic activity (AMO, HAO, NAR, NIR, NOR, and NOS) were significantly higher than the corresponding parameters of the R_O system. This may explain the reason behind R_W having excellent ammonia and TN removal performance at low temperatures.

Complete genome of Vibrio japonicus strain JCM 31412 T and assessment of the Nereis clade of the genus Vibrio

Clade-based taxonomy has become a recognised means of classifying members of the family Vibrionaceae. A multilocus sequence analysis (MLSA) approach based on eight housekeeping genes can be used to infer phylogenetic relationships, which then groups species into monophyletic clades. Recent work on the Vibrionaceae clades added newly described species and updated existing relationships; the Nereis clade currently includes Vibrio nereis and Vibrio hepatarius. A publication characterising Vibrio japonicus as a novel species placed it within the Nereis clade, but this strain was not included in a recently published taxonomic update because a genome sequence was not available for phylogenetic assessment. To resolve this discrepancy and assess the taxonomic position of V. japonicus within the updated clades, we sequenced the complete genome of V. japonicus JCM 31412 ^T and conducted phylogenetic and genomic analyses of this clade. Vibrio japonicus remains within the Nereis clade and phylogenomic, average nucleotide identity (ANI), and average amino acid identity (AAI) analyses confirm this relationship. Additional genomic assessments on all Nereis clade members found gene clusters and inferred functionalities shared among the species. This work represents the first complete genome of a member of the Nereis clade and updates the clade-based taxonomy of the Vibrionaceae family.

Complete genome sequence of a multiple-stress-tolerant bacterium Halomonas piezotolerans NBT06E8T isolated from a deep-sea sediment sample of the New Britain Trench

Halomonas piezotolerans NBT06E8T is a Gram-stain-negative, moderately halophilic, piezotolerant, H2O2 and heavy metal-resistant bacterium, isolated from a deep-sea sediment sample collected from the New Britain Trench at depth of 8900 m. Growth of the strain was observed at 4-45 °C (optimum 30 °C), at pH 5-11 (optimum 8-9) and in 0.5-21% (w/v) NaCl (optimum 3-7%). The optimum pressure for growth was 0.1-30 MPa (megapascal) with tolerance up to 60 MPa. Under optimum growth conditions, the strain could tolerant 15 mM H2O2. Here, we report the complete genome of H. piezotolerans NBT06E8T, which consists of 3,945,801 bp (G + C content of 57.93%) with a single chromosome, 3509 protein-coding genes, 60 tRNAs and 6 rRNA operons. Genomic analysis revealed the capability of utilizing various carbon and nitrogen sources, the presence of multiple toxin-antitoxin systems and strain-specific type VI secretion system benefitting its adaptation to the oligotrophic hadal environments. Multiple respiratory chain components, especially the strain-specific anaerobic enzymes, could allow its survival in both surficial and buried sediments with variable oxygen concentrations. Gene function and metabolic pathway analysis showed that strain NBT06E8T encodes a series of genes related to high hydrostatic pressure tolerance, antioxidative stress and heavy metal resistance, which could also contribute to its deep-sea adaptation strategies. The complete genome sequence of H. piezotolerans NBT06E8T provides further insights into the stress adaptation strategies of deep-sea bacteria and potential biotechnological application of Halomonas species.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03283-3.

Improving environmental monitoring of Vibrionaceae in coastal ecosystems through 16S rRNA gene amplicon sequencing

The Vibrionaceae family groups genetically and metabolically diverse bacteria thriving in all marine environments. Despite often representing a minor fraction of bacterial assemblages, members of this family can exploit a wide variety of nutritional sources, which makes them important players in biogeochemical dynamics. Furthermore, several Vibrionaceae species are well-known pathogens, posing a threat to human and animal health. Here, we applied the phylogenetic placement coupled with a consensus-based approach using 16S rRNA gene amplicon sequencing, aiming to reach a reliable and fine-level Vibrionaceae characterization and identify the dynamics of blooming, ecologically important, and potentially pathogenic species in different sites of the northern Adriatic Sea. Water samples were collected monthly at a Long-Term Ecological Research network site from 2018 to 2021, and in spring and summer of 2019 and 2020 at two sites affected by depurated sewage discharge. The 41 identified Vibrionaceae species represented generally below 1% of the sampled communities; blooms (up to ~ 11%) mainly formed by Vibrio chagasii and Vibrio owensii occurred in summer, linked to increasing temperature and particulate matter concentration. Pathogenic species such as Vibrio anguilllarum, Vibrio tapetis, and Photobacterium damselae were found in low abundance. Depuration plant samples were characterized by a lower abundance and diversity of Vibrionaceae species compared to seawater, highlighting that Vibrionaceae dynamics at sea are unlikely to be related to wastewater inputs. Our work represents a further step to improve the molecular approach based on short reads, toward a shared, updated, and curated phylogeny of the Vibrionaceae family.

Enhanced nitrogen removal from low-temperature wastewater by an iterative screening of cold-tolerant denitrifying bacteria

The biological process to remove nitrogen in winter effluent is often seriously compromised due to the effect of low temperatures (< 13 °C) on the metabolic activity of microorganisms. In this study, a novel heterotrophic nitrifying-aerobic denitrifying bacterium with cold tolerance was isolated by iterative domestication and named Moraxella sp. LT-01. The LT-01 maintained almost 60% of its maximal growth activity at 10 °C. Under initial concentrations of 100 mg/L, the removal efficiencies of ammonium, nitrate, nitrite by LT-01 were 70.3%, 65.4%, 61.7% respectively for 72 h incubation at 10 °C. Nitrogen balance analysis showed that about 46% of TN was released as gases and 16% of TN was assimilated for cell growth. The biomarker genes involved in nitrification and denitrification pathways were identified by gene-specific PCR and revealed that the LT-01 has nitrite reductase (NirS) but not hydroxylamine reductase (HAO), which implies the involvement of other genes in the process. The study indicates that LT-01 has the potential for use in low-temperature regions for efficient sewage treatment.

Regulated strategies of cold-adapted microorganisms in response to cold: a review

There are a large number of active cold-adapted microorganisms in the perennial cold environment. Due to their high-efficiency and energy-saving catalytic properties, cold-adapted microorganisms have become valuable natural resources with potential in various biological fields. In this study, a series of cold response strategies for microorganisms were summarized. This mainly involves the regulation of cell membrane fluidity, synthesis of cold adaptation proteins, regulators and metabolic changes, energy supply, and reactive oxygen species. Also, the potential of biocatalysts produced by cold-adapted microorganisms including cold-active enzymes, ice-binding proteins, polyhydroxyalkanoates, and surfactants was introduced, which provided a guidance for expanding its application values. Overall, new insights were obtained on response strategies of microorganisms to cold environments in this review. This will deepen the understanding of the cold tolerance mechanism of cold-adapted microorganisms, thus promoting the establishment and application of low-temperature biotechnology.

The ups and downs of ectoine: structural enzymology of a major microbial stress protectant and versatile nutrient

Ectoine and its derivative 5-hydroxyectoine are compatible solutes and chemical chaperones widely synthesized by Bacteria and some Archaea as cytoprotectants during osmotic stress and high- or low-growth temperature extremes. The function-preserving attributes of ectoines led to numerous biotechnological and biomedical applications and fostered the development of an industrial scale production process. Synthesis of ectoines requires the expenditure of considerable energetic and biosynthetic resources. Hence, microorganisms have developed ways to exploit ectoines as nutrients when they are no longer needed as stress protectants. Here, we summarize our current knowledge on the phylogenomic distribution of ectoine producing and consuming microorganisms. We emphasize the structural enzymology of the pathways underlying ectoine biosynthesis and consumption, an understanding that has been achieved only recently. The synthesis and degradation pathways critically differ in the isomeric form of the key metabolite N-acetyldiaminobutyric acid (ADABA). γ-ADABA serves as preferred substrate for the ectoine synthase, while the α-ADABA isomer is produced by the ectoine hydrolase as an intermediate in catabolism. It can serve as internal inducer for the genetic control of ectoine catabolic genes via the GabR/MocR-type regulator EnuR. Our review highlights the importance of structural enzymology to inspire the mechanistic understanding of metabolic networks at the biological scale.

Accumulation of Ectoines By Halophilic Bacteria Isolated from Fermented Shrimp Paste: An Adaptation Mechanism to Salinity, Temperature, and pH Stress

Shrimp paste is a traditional fermented food produced by many Asian countries. Bacteria play important roles in the shrimp paste fermentation process. In order to survive under the low water activity (A_w) conditions caused by the high salt concentration, the bacteria need to employ a special adaptation strategy. This study found that most halophilic bacteria isolated from shrimp paste accumulated ectoines (ectoine and hydroxyectoine) as protective osmotic agents. Five isolated bacteria, including three high ectoine producers and two high hydroxyectoine producers, were selected for further study. Based on their morphological and biochemical characteristics and 16S rRNA gene sequences, the five strains were classified into three genera: Salinivibrio (strains M7 and M316), Salimicrobium (strains M31 and M69), and Vibrio (strain M92). The accumulation of ectoines by Salimicrobium species is reported here for the first time. The effects of salinity, incubation temperature, and initial pH on the growth rate and accumulation of ectoines by the five strains were investigated. The results revealed that the bacterial growth rate was inhibited while the accumulation of ectoines by the five selected strains was triggered by an increase in the external salinity, incubation temperature, or initial pH. In addition, a high concentration of ectoine only (21.2 wt%) was produced by strain M316 at the optimum salinity and temperature, and under pressure of a high initial pH value. To the best of our knowledge, this is the first report demonstrating that the production of ectoines by bacterial strains can be enhanced by increasing the pH of the culture medium to induce pH stress. This finding suggests a new ectoine producer and fermentation strategy that may help to improve the production of ectoines in the future.

Physiological response of the moderately halophilic psychrotolerant strain Chromohalobacter sp. N1 to salinity change and low temperature

The available information on de novo synthesized compatible solutes in response to high medium salinity by bacteria of the Chromohalobacter genus is limited to studies of the mesophilic moderately halophilic strain Chromohalobacter salexigens DSM 3043^T. Therefore, there is a need for studies of representatives of other species of the Chromohalobacter genus of the Halomonadaceae family. A moderately halophilic psychrotolerant bacterium, strain N1, closely related to the species Chromohalobacter japonicus was isolated from the salt crust of a rock salt waste pile in Berezniki, Perm Krai, Russia. An intracellular pool of compatible solutes of strain N1 was investigated by NMR spectroscopy. Cells grown in the presence of 5% NaCl at optimal growth temperature (28 °C) accumulated ectoine, glutamate, N(4)-acetyl-l-2,4-diaminobutyrate (NADA), alanine, trehalose, hydroxyectoine, and valine. Such a combination of compatible solutes is unique and distinguishes the strain from C. salexigens DSM 3043^T. Hyperosmotic stress induced by 15% NaCl caused the accumulation of ectoine, NADA, and hydroxyectoine but led to a decrease in the amount of alanine, valine, and trehalose. The intracellular pool of glutamate was not significantly changed. A reduction of the growth temperature from 28 to 5 °C led to an increase in the amount of ectoine, NADA, trehalose, and hydroxyectoine. Ectoine was the major compatible solute.

Stressed out: Bacterial response to high salinity using compatible solute biosynthesis and uptake systems, lessons from Vibrionaceae

Bacteria have evolved mechanisms that allow them to adapt to changes in osmolarity and some species have adapted to live optimally in high salinity environments such as in the marine ecosystem. Most bacteria that live in high salinity do so by the biosynthesis and/or uptake of compatible solutes, small organic molecules that maintain the turgor pressure of the cell. Osmotic stress response mechanisms and their regulation among marine heterotrophic bacteria are poorly understood. In this review, we discuss what is known about compatible solute metabolism and transport and new insights gained from studying marine bacteria belonging to the family Vibrionaceae.

Exploring useful fermentation strategies for the production of hydroxyectoine with a halophilic strain, Halomonas salina BCRC 17875

Hydroxyectoine, an ectoine derivative, is the most common compatible solute in halophilic microorganisms for resisting harsh environments. Compatible solutes can be utilized in fields such as cosmetics, medicine, and biochemistry. Moderately halophilic microorganisms produce much less hydroxyectoine as compared with ectoine. In this study, we first evaluate the effect of medium formulation (i.e., yeast extract (YE) medium and high yeast extract (HYE) medium) on hydroxyectoine production. In addition, an investigation of hydroxyectoine production by Halomonas salina under optimal conditions for vital factors (i.e., iron and α-ketoglutarate) and hydroxylase activity was also carried out. As a result, hydroxyectoine production was obviously elevated (0.9 g/L to 1.8 g/L) when the HYE medium was utilized. Furthermore, hydroxyectoine production further increased to 2.4 g/L when both the α-ketoglutarate and iron factors were added to the HYE medium in the early stationary phase. In addition, we found that ectoine hydroxylase activity increased more when a combination of iron and α-ketoglutarate was used than when either was used alone. The results showed that the alteration of iron and α-ketoglutarate clearly stimulated the expression of ectoine hydroxylase, which in turn affected hydroxyectoine synthesis. This study also showed that hydroxyectoine production was further raised from 2.4 g/L to 2.9 g/L when 50 mM of α-ketoglutarate and 1 mM of iron were added to the HYE medium. Ultimately, the experimental results showed using the optimal conditions further elevated the hydroxyectoine production yield to 2.90 g/L, which was over 3-fold higher than the best results obtained from the original medium.

Survival, Virulent Characteristics, and Transcriptomic Analyses of the Pathogenic Vibrio anguillarum Under Starvation Stress

Many bacteria have developed strategies for metamorphosis into sophisticated survival forms to survive extended periods of environmental stress. As a global causative agent of vibriosis in marine fish farming, Vibrio anguillarum (V. anguillarum) can efficiently grow and proliferate under environmental stress, but the specific mechanism is not clear. In the present study, survival, virulent characteristics, and transcriptomic analysis of the V. anguillarum BH1 were performed under starvation stress. The results demonstrated that V. anguillarum was still culturable and showed rippled surface after 6 months of starvation. Starved cells maintained their infectivity in half-smooth tongue sole (Cynoglossus semilaevi). Detection of virulence factors and virulence-associated genes in starved cells showed that the starved strain still produced β-hemolysis on rabbit blood agar, caseinase, dnase, and gelatinase, and possessed empA, vah1, vah2, vah3, vah4, vah5, rtxA, flaA, flaD, flaE, virC, tonB, mreB, toxR, rpoS, and ftsZ virulence-related genes. In addition, we first reported the RNA-seq study for V. anguillarum with and without starvation treatment for a period of 6 months and emphasized the regulation of gene expression at the whole transcriptional level. It indicated that V. anguillarum expressed 3,089 and 3,072 genes in the control group and starvation stress group, respectively. The differently expressed genes (DEGs) of the starved strain were thereby identified, including 251 up-regulated genes and 272 down-regulated genes in comparison with the non-starved strain. Gene Ontology (GO) analysis and Kyto Encyclopedia Genes and Genomes (KEGG) enrichment analysis of DEGs were also analyzed. GO functional classification revealed that among the significantly regulated genes with known function categories, more genes affiliated with signal transducer activity, molecular transducer activity, and cell communication were significantly up-regulated, and more genes affiliated with cellular macromolecule, cellular component, and structural molecule activity were significantly down-regulated. In addition, the DEGs involved in the pathway of two-component system was significantly up-regulated, and the pathways of ribosome and flagellar assembly were significantly down-regulated. This study provides valuable insight into the survival strategies of V. anguillarum and suggests that a portion of the bacterial populations may remain pathogenic while persisting under starvation stress by up-regulating or down-regulating a series of genes.

Role of the Extremolytes Ectoine and Hydroxyectoine as Stress Protectants and Nutrients: Genetics, Phylogenomics, Biochemistry, and Structural Analysis

Fluctuations in environmental osmolarity are ubiquitous stress factors in many natural habitats of microorganisms, as they inevitably trigger osmotically instigated fluxes of water across the semi-permeable cytoplasmic membrane. Under hyperosmotic conditions, many microorganisms fend off the detrimental effects of water efflux and the ensuing dehydration of the cytoplasm and drop in turgor through the accumulation of a restricted class of organic osmolytes, the compatible solutes. Ectoine and its derivative 5-hydroxyectoine are prominent members of these compounds and are synthesized widely by members of the Bacteria and a few Archaea and Eukarya in response to high salinity/osmolarity and/or growth temperature extremes. Ectoines have excellent function-preserving properties, attributes that have led to their description as chemical chaperones and fostered the development of an industrial-scale biotechnological production process for their exploitation in biotechnology, skin care, and medicine. We review, here, the current knowledge on the biochemistry of the ectoine/hydroxyectoine biosynthetic enzymes and the available crystal structures of some of them, explore the genetics of the underlying biosynthetic genes and their transcriptional regulation, and present an extensive phylogenomic analysis of the ectoine/hydroxyectoine biosynthetic genes. In addition, we address the biochemistry, phylogenomics, and genetic regulation for the alternative use of ectoines as nutrients.

Tinkering with Osmotically Controlled Transcription Allows Enhanced Production and Excretion of Ectoine and Hydroxyectoine from a Microbial Cell Factory

Ectoine and hydroxyectoine are widely synthesized by members of the Bacteria and a few members of the Archaea as potent osmostress protectants. We have studied the salient features of the osmostress-responsive promoter directing the transcription of the ectoine/hydroxyectoine biosynthetic gene cluster from the plant-root-associated bacterium Pseudomonas stutzeri by transferring it into Escherichia coli, an enterobacterium that does not produce ectoines naturally. Using ect-lacZ reporter fusions, we found that the heterologous ect promoter reacted with exquisite sensitivity in its transcriptional profile to graded increases in sustained high salinity, responded to a true osmotic signal, and required the buildup of an osmotically effective gradient across the cytoplasmic membrane for its induction. The involvement of the -10, -35, and spacer regions of the sigma-70-type ect promoter in setting promoter strength and response to osmotic stress was assessed through site-directed mutagenesis. Moderate changes in the ect promoter sequence that increase its resemblance to housekeeping sigma-70-type promoters of E. coli afforded substantially enhanced expression, both in the absence and in the presence of osmotic stress. Building on this set of ect promoter mutants, we engineered an E. coli chassis strain for the heterologous production of ectoines. This synthetic cell factory lacks the genes for the osmostress-responsive synthesis of trehalose and the compatible solute importers ProP and ProU, and it continuously excretes ectoines into the growth medium. By combining appropriate host strains and different plasmid variants, excretion of ectoine, hydroxyectoine, or a mixture of both compounds was achieved under mild osmotic stress conditions.IMPORTANCE Ectoines are compatible solutes, organic osmolytes that are used by microorganisms to fend off the negative consequences of high environmental osmolarity on cellular physiology. An understanding of the salient features of osmostress-responsive promoters directing the expression of the ectoine/hydroxyectoine biosynthetic gene clusters is lacking. We exploited the ect promoter from an ectoine/hydroxyectoine-producing soil bacterium for such a study by transferring it into a surrogate bacterial host. Despite the fact that E. coli does not synthesize ectoines naturally, the ect promoter retained its exquisitely sensitive osmotic control, indicating that osmoregulation of ect transcription is an inherent feature of the promoter and its flanking sequences. These sequences were narrowed to a 116-bp DNA fragment. Ectoines have interesting commercial applications. Building on data from a site-directed mutagenesis study of the ect promoter, we designed a synthetic cell factory that secretes ectoine, hydroxyectoine, or a mixture of both compounds into the growth medium.