Transcriptional co-regulation of five chitinase genes scattered on the Streptomyces coelicolor A3(2) chromosome

Proteomic and Transcriptomic Analyses to Decipher the Chitinolytic Response of Jeongeupia spp

In nature, chitin, the most abundant marine biopolymer, does not accumulate due to the action of chitinolytic organisms, whose saccharification systems provide instructional blueprints for effective chitin conversion. Therefore, discovery and deconstruction of chitinolytic machineries and associated enzyme systems are essential for the advancement of biotechnological chitin valorization. Through combined investigation of the chitin-induced secretome with differential proteomic and transcriptomic analyses, a holistic system biology approach has been applied to unravel the chitin response mechanisms in the Gram-negative Jeongeupia wiesaeckerbachi. Hereby, the majority of the genome-encoded chitinolytic machinery, consisting of various glycoside hydrolases and a lytic polysaccharide monooxygenase, could be detected extracellularly. Intracellular proteomics revealed a distinct translation pattern with significant upregulation of glucosamine transport, metabolism, and chemotaxis-associated proteins. While the differential transcriptomic results suggested the overall recruitment of more genes during chitin metabolism compared to that of glucose, the detected protein-mRNA correlation was low. As one of the first studies of its kind, the involvement of over 350 unique enzymes and 570 unique genes in the catabolic chitin response of a Gram-negative bacterium could be identified through a three-way systems biology approach. Based on the cumulative data, a holistic model for the chitinolytic machinery of Jeongeupia spp. is proposed.

Isolation, biochemical characterization, and genome sequencing of two high-quality genomes of a novel chitinolytic Jeongeupia species

Chitin is the second most abundant polysaccharide worldwide as part of arthropods' exoskeletons and fungal cell walls. Low concentrations in soils and sediments indicate rapid decomposition through chitinolytic organisms in terrestrial and aquatic ecosystems. The enacting enzymes, so-called chitinases, and their products, chitooligosaccharides, exhibit promising characteristics with applications ranging from crop protection to cosmetics, medical, textile, and wastewater industries. Exploring novel chitinolytic organisms is crucial to expand the enzymatical toolkit for biotechnological chitin utilization and to deepen our understanding of diverse catalytic mechanisms. In this study, we present two long-read sequencing-based genomes of highly similar Jeongeupia species, which have been screened, isolated, and biochemically characterized from chitin-amended soil samples. Through metabolic characterization, whole-genome alignments, and phylogenetic analysis, we could demonstrate how the investigated strains differ from the taxonomically closest strain Jeongeupia naejangsanensis BIO-TAS4-2T (DSM 24253). In silico analysis and sequence alignment revealed a multitude of highly conserved chitinolytic enzymes in the investigated Jeongeupia genomes. Based on these results, we suggest that the two strains represent a novel species within the genus of Jeongeupia, which may be useful for environmentally friendly N-acetylglucosamine production from crustacean shell or fungal biomass waste or as a crop protection agent.

Chitin Biodegradation by Lytic Polysaccharide Monooxygenases from Streptomyces coelicolor In Vitro and In Vivo

Lytic polysaccharide monooxygenases (LPMOs) have the potential to improve recalcitrant polysaccharide hydrolysis by the oxidizing cleavage of glycosidic bond. Streptomyces species are major chitin decomposers in soil ecological environments and encode multiple lpmo genes. In this study, we demonstrated that transcription of the lpmo gene, Sclpmo10G, in the Streptomyces coelicolor A3(2) (ScA3(2)) strain is strongly induced by chitin. The ScLPMO10G protein was further expressed in Escherichia coli and characterized in vitro. The ScLPMO10G protein showed oxidation activity towards chitin. Chitinase synergy experiments demonstrated that the addition of ScLPMO10G resulted in a substantial in vitro increase in the reducing sugar levels. Moreover, in vivo the LPMO-overexpressing strain ScΔLPMO10G(+) showed stronger chitin-degrading ability than the wild-type, leading to a 2.97-fold increase in reducing sugar level following chitin degradation. The total chitinase activity of ScΔLPMO10G(+) was 1.5-fold higher than that of ScA3(2). In summary, ScLPMO10G may play a role in chitin biodegradation in S. coelicolor, which could have potential applications in biorefineries.

Carbon catabolite regulation in Streptomyces: new insights and lessons learned

One of the most significant control mechanisms of the physiological processes in the genus Streptomyces is carbon catabolite repression (CCR). This mechanism controls the expression of genes involved in the uptake and utilization of alternative carbon sources in Streptomyces and is mostly independent of the phosphoenolpyruvate phosphotransferase system (PTS). CCR also affects morphological differentiation and the synthesis of secondary metabolites, although not all secondary metabolite genes are equally sensitive to the control by the carbon source. Even when the outcome effect of CCR in bacteria is the same, their essential mechanisms can be rather different. Although usually, glucose elicits this phenomenon, other rapidly metabolized carbon sources can also cause CCR. Multiple efforts have been put through to the understanding of the mechanism of CCR in this genus. However, a reasonable mechanism to explain the nature of this process in Streptomyces does not yet exist. Several examples of primary and secondary metabolites subject to CCR will be examined in this review. Additionally, recent advances in the metabolites and protein factors involved in the Streptomyces CCR, as well as their mechanisms will be described and discussed in this review.

Microbial Degradation of Lobster Shells to Extract Chitin Derivatives for Plant Disease Management

Biodegradation of lobster shells by chitinolytic microorganisms are an environment safe approach to utilize lobster processing wastes for chitin derivation. In this study, we report degradation activities of two microbes, "S223" and "S224" isolated from soil samples that had the highest rate of deproteinization, demineralization and chitinolysis among ten microorganisms screened. Isolates S223 and S224 had 27.3 and 103.8 protease units mg-1 protein and 12.3 and 11.2 μg ml-1 of calcium in their samples, respectively, after 1 week of incubation with raw lobster shells. Further, S223 contained 23.8 μg ml-1 of N-Acetylglucosamine on day 3, while S224 had 27.3 μg ml-1 on day 7 of incubation with chitin. Morphological observations and 16S rDNA sequencing suggested both the isolates were Streptomyces. The culture conditions were optimized for efficient degradation of lobster shells and chitinase (∼30 kDa) was purified from crude extract by affinity chromatography. The digested lobster shell extracts induced disease resistance in Arabidopsis by induction of defense related genes (PR1 > 500-fold, PDF1.2 > 40-fold) upon Pseudomonas syringae and Botrytis cinerea infection. The study suggests that soil microbes aid in sustainable bioconversion of lobster shells and extraction of chitin derivatives that could be applied in plant protection.

Psychrotolerant antifungal Streptomyces isolated from Tawang, India and the shift in chitinase gene family

A total of 210 Streptomyces were isolated from the soil samples of Tawang, India where temperature varied from 5 °C during daytime to -2 °C during the night. Based on antifungal activity, a total of 33 strains, putatively Streptomyces spp., were selected. Optimal growth temperature for the 33 strains was 16 °C, with growth occurring down to 6 °C but not above 30 °C. Phylogenetic analysis based on 16S rDNA sequences revealed the taxonomic affiliation of the 33 strains as species of Streptomyces. To examine the relatedness of the chitinase genes from six strong antifungal Streptomyces strains, a phylogenetic tree was constructed using the catalytic domain nucleotide sequences and resulted in seven distinct monophyletic groups. A quantitative PCR study for chitinase expressing ability revealed that of the six antifungal strains tested, the strain Streptomyces roseochromogenus TSR12 was the most active producer of family 18 chitinase genes. Streptomyces strains with enhanced inhibitory potential usually encode a family 19 chitinase gene; however, our present study did not show expression of this family in the six strains tested.

Novel biological activities of allosamidins

Allosamidins, which are secondary metabolites of the Streptomyces species, have chitin-mimic pseudotrisaccharide structures. They bind to catalytic centers of all family 18 chitinases and inhibit their enzymatic activity. Allosamidins have been used as chitinase inhibitors to investigate the physiological roles of chitinases in a variety of organisms. Two prominent biological activities of allosamidins were discovered, where one has anti-asthmatic activity in mammals, while the other has the chitinase-production- promoting activity in allosamidin-producing Streptomyces. In this article, recent studies on the novel biological activities of allosamidins are reviewed.

Bacterial and fungal chitinase chiJ orthologs evolve under different selective constraints following horizontal gene transfer

Background

Certain bacteria from the genus Streptomyces are currently used as biological control agents against plant pathogenic fungi. Hydrolytic enzymes that degrade fungal cell wall components, such as chitinases, are suggested as one possible mechanism in biocontrol interactions. Adaptive evolution of chitinases are previously reported for plant chitinases involved in defence against fungal pathogens, and in fungal chitinases involved in fungal-fungal interactions. In this study we investigated the molecular evolution of chitinase chiJ in the bacterial genus Streptomyces. In addition, as chiJ orthologs are previously reported in certain fungal species as a result from horizontal gene transfer, we conducted a comparative study of differences in evolutionary patterns between bacterial and fungal taxa.

Findings

ChiJ contained three sites evolving under strong positive selection and four groups of co-evolving sites. Regions of high amino acid diversity were predicted to be surface-exposed and associated with coil regions that connect certain α-helices and β-strands in the family 18 chitinase TIM barrel structure, but not associated with the catalytic cleft. The comparative study with fungal ChiJ orthologs identified three regions that display signs of type 1 functional divergence, where unique adaptations in the bacterial and fungal taxa are driven by positive selection.

Conclusions

The identified surface-exposed regions of chitinase ChiJ where sequence diversification is driven by positive selection may putatively be related to functional divergence between bacterial and fungal orthologs. These results show that ChiJ orthologs have evolved under different selective constraints following the horizontal gene transfer event.

High expression levels of chitinase genes in Streptomyces coelicolor A3(2) grown in soil

Although Streptomyces species are major chitin-degraders in soil ecosystems, the expression of the diverse chitinase genes within Streptomyces coelicolor grown in soil has not been assessed. As a first step, the induction pattern of nine chitinase genes in S. coelicolor growing in autoclaved soil was compared with those in liquid cultures. The relative expression levels of nine chitinase genes were measured using real-time reverse transcription PCR. The expression of all chitinase genes was induced by chitin in both autoclaved soil and liquid cultures, but to different levels. The expression levels of five chitinase genes in autoclaved soil were significantly higher than those in the liquid cultures. In particular, a putative chitinase gene, chitinase H, showed the highest induction in autoclaved soil. The same induction pattern was confirmed in nonautoclaved soil, indicating that soil contains some factors affecting the expression of chitinase genes. The chiH gene product, ChiH, cloned in Streptomycetes lividans was secreted and exhibited chitin degradation activity that was stable within a wide range of acidic pHs. The disruption of dasR, a transcriptional regulator for the uptake of N-acetylglucosamine, abolished the expression of chiH, demonstrating that DasR is required for the regulation of ChiH expression.

Degradation of chitosans with chitinase G from Streptomyces coelicolor A3(2): production of chito-oligosaccharides and insight into subsite specificities

We have studied the degradation of soluble heteropolymeric chitosans with a bacterial family 19 chitinase, ChiG from Streptomyces coelicolor A3(2), to obtain insight into the mode of action of ChiG, to determine subsite preferences for acetylated and deacetylated sugar units, and to evaluate the potential of ChiG for production of chito-oligosaccharides. Degradation of chitosans with varying degrees of acetylation was followed using NMR for the identity (acetylated/deacetylated) of new reducing and nonreducing ends as well as their nearest neighbors and using gel filtration to analyze the size distribution of the oligomeric products. Degradation of a 64% acetylated chitosan yielded a continuum of oligomers, showing that ChiG operates according to a nonprocessive, endo mode of action. The kinetics of the degradation showed an initial rapid phase dominated by cleavage of three consecutive acetylated units (A; occupying subsites -2, -1, and +1), and a slower kinetic phase reflecting the cleavage of the glycosidic linkage between a deacetylated unit (D, occupying subsite -1) and an A (occupying subsite +1). Characterization of isolated oligomer fractions obtained at the end of the initial rapid phase and at the end of the slower kinetic phase confirmed the preference for A binding in subsites -2, -1, and +1 and showed that oligomers with a deacetylated reducing end appeared only during the second kinetic phase. After maximum conversion of the chitosan, the dimers AD/AA and the trimer AAD were the dominating products. Degradation of chitosans with varying degrees of acetylation to maximum degree of scission produced a wide variety of oligomer mixtures, differing in chain length and composition of acetylated/deacetylated units. These results provide insight into the properties of bacterial family 19 chitinases and show how these enzymes may be used to convert chitosans to several types of chito-oligosaccharide mixtures.

Heterodisaccharide 4-O-(N-acetyl-beta-D-glucosaminyl)-D-glucosamine is a specific inducer of chitinolytic enzyme production in Vibrios harboring chitin oligosaccharide deacetylase genes

Vibrio parahaemolyticus KN1699 produces 4-O-(N-acetyl-beta-d-glucosaminyl)-d-glucosamine (GlcNAc-GlcN) as a major end product from chitin using two extracellular hydrolases: glycoside hydrolase family 18 chitinase, which produces (GlcNAc)(2) from chitin, and carbohydrate esterase (CE) family 4 chitin oligosaccharide deacetylase (COD), which hydrolyzes the N-acetyl group at the reducing-end GlcNAc residue of (GlcNAc)(2). In this study, we clarified that this heterodisaccharide functions as an inducer of the production of the two above-mentioned chitinolytic enzymes, particularly chitinase. Similar results for chitinase production were obtained with other chitin-decomposing Vibrio strains harboring the CE family 4 COD gene; however, such an increase in chitinase production was not observed in chitinolytic Vibrio strains that did not harbor the COD gene. These results suggest that GlcNAc-GlcN is a unique inducer of chitinase production in Vibrio bacteria that have the COD-producing ability and that the COD involved in the synthesis of this signal compound is one of the key enzymes in the chitin catabolic cascade of these bacteria.

The msiK gene, encoding the ATP-hydrolysing component of N,N'-diacetylchitobiose ABC transporters, is essential for induction of chitinase production in Streptomyces coelicolor A3(2)

The dasABC genes encode an ATP-binding cassette (ABC) transporter, which is one of the uptake systems for N,N'-diacetylchitobiose [(GlcNAc)(2)] in Streptomyces coelicolor A3(2), although the gene encoding the ABC subunit that provides ATP hydrolysis for DasABC has not been identified. In this study, we disrupted the sequence that is highly homologous to the msiK gene, the product of which is an ABC subunit assisting several ABC permeases in other Streptomyces species. Disruption of msiK severely affected the ability of S. coelicolor A3(2) to utilize maltose, cellobiose, starch, cellulose, chitin and chitosan, but not glucose. The msiK null mutant lacked (GlcNAc)(2)-uptake activity, but GlcNAc transport activity was unaffected. The data indicated that msiK is essential for (GlcNAc)(2) uptake, which in S. coelicolor A3(2) is governed by ABC transporters including the DasABC-MsiK system, in contrast to Escherichia coli and Serratia marcescens, in which (GlcNAc)(2) uptake is mediated by the phosphotransferase system. Interestingly, the induction of chitinase production by (GlcNAc)(2) or chitin was absent in the msiK null mutant, unlike in the parent strain M145. The defect in chitinase gene induction was rescued by expressing the His-tagged MsiK protein under the control of the putative native promoter on a multicopy plasmid. The data suggest that uptake of (GlcNAc)(2) is necessary for induction of chitinase production. The msiK gene was constitutively transcribed, whereas the transcription of dasA [(GlcNAc)(2)-binding protein gene], malE (putative maltose-binding protein gene), cebE1 (putative cellobiose-binding protein gene) and bxlE1 (putative xylobiose-binding protein gene) was induced by their corresponding sugar ligands. This is believed to be the first report to indicate that (GlcNAc)(2) uptake mediated by ABC transporters is essential for chitinase production in streptomycetes, which are known to be the main degraders of chitin in soil.

A novel goose-type lysozyme gene with chitinolytic activity from the moderately thermophilic bacterium Ralstonia sp. A-471: cloning, sequencing, and expression

In this study, we cloned the gene encoding goose-type (G-type) lysozyme with chitinase (Ra-ChiC) activity from Ralstonia sp. A-471 genomic DNA library. This is the first report of another type of chitinase after the previously reported chitinases ChiA (Ra-ChiA) and ChiB (Ra-ChiB) in the chitinase system of the moderately thermophilic bacterium, Ralstonia sp. A-471 and also the first such data in Ralstonia sp. G-type lysozyme gene. It consisted of 753 bp nucleotides, which encodes 251 amino acids including a putative signal peptide. This ORF was modular enzyme composed of a signal sequence, chitin-binding domain, linker, and catalytic domain. The catalytic domain of Ra-ChiC showed homologies to those of G-type lysozyme (glycoside hydrolases (GH) family 23, 16.8%) and lysozyme-like enzyme from Clostridium beijerincki (76.1%). Ra-ChiC had activities against ethylene glycol chitin, carboxyl methyl chitin, and soluble chitin but not against the cell wall of Micrococcus lysodeikticus. The enzyme produced alpha-anomer by hydrolyzing beta-1,4-glycosidic linkage of the substrate, indicating that the enzyme catalyzes the hydrolysis through an inverting mechanism. When N-acetylglucosamine hexasaccharide [(GlcNAc)6] was hydrolyzed by the enzyme, the second and third glycosidic linkage from the non-reducing end were split producing (GlcNAc)2 + (GlcNAc)4 and (GlcNAc)3 + (GlcNAc)3 of almost the same concentration in the early stage of the reaction. The G-type lysozyme hydrolyzed (GlcNAc)6 in an endo-splitting manner, which produced (GlcNAc)3 + (GlcNAc)3 predominating over that to (GlcNAc)2 + (GlcNAc)4. Thus, Ra-ChiC was found to be a novel enzyme in its structural and functional properties.

SIGffRid: a tool to search for sigma factor binding sites in bacterial genomes using comparative approach and biologically driven statistics

Background

Many programs have been developed to identify transcription factor binding sites. However, most of them are not able to infer two-word motifs with variable spacer lengths. This case is encountered for RNA polymerase Sigma (σ) Factor Binding Sites (SFBSs) usually composed of two boxes, called -35 and -10 in reference to the transcription initiation point. Our goal is to design an algorithm detecting SFBS by using combinational and statistical constraints deduced from biological observations.

Results

We describe a new approach to identify SFBSs by comparing two related bacterial genomes. The method, named SIGffRid (SIGma Factor binding sites Finder using R'MES to select Input Data), performs a simultaneous analysis of pairs of promoter regions of orthologous genes. SIGffRid uses a prior identification of over-represented patterns in whole genomes as selection criteria for potential -35 and -10 boxes. These patterns are then grouped using pairs of short seeds (of which one is possibly gapped), allowing a variable-length spacer between them. Next, the motifs are extended guided by statistical considerations, a feature that ensures a selection of motifs with statistically relevant properties. We applied our method to the pair of related bacterial genomes of Streptomyces coelicolor and Streptomyces avermitilis. Cross-check with the well-defined SFBSs of the SigR regulon in S. coelicolor is detailed, validating the algorithm. SFBSs for HrdB and BldN were also found; and the results suggested some new targets for these σ factors. In addition, consensus motifs for BldD and new SFBSs binding sites were defined, overlapping previously proposed consensuses. Relevant tests were carried out also on bacteria with moderate GC content (i.e. Escherichia coli/Salmonella typhimurium and Bacillus subtilis/Bacillus licheniformis pairs). Motifs of house-keeping σ factors were found as well as other SFBSs such as that of SigW in Bacillus strains.

Conclusion

We demonstrate that our approach combining statistical and biological criteria was successful to predict SFBSs. The method versatility autorizes the recognition of other kinds of two-box regulatory sites.

The dasABC gene cluster, adjacent to dasR, encodes a novel ABC transporter for the uptake of N,N'-diacetylchitobiose in Streptomyces coelicolor A3(2)

N,N'-Diacetylchitobiose [(GlcNAc)(2)] induces the transcription of chitinase (chi) genes in Streptomyces coelicolor A3(2). Physiological studies showed that (GlcNAc)(2) addition triggered chi expression and increased the rate of (GlcNAc)(2) concentration decline in culture supernatants of mycelia already cultivated with (GlcNAc)(2), suggesting that (GlcNAc)(2) induced the synthesis of its own uptake system. Four open reading frames (SCO0531, SCO0914, SCO2946, and SCO5232) encoding putative sugar-binding proteins of ABC transporters were found in the genome by probing the 12-bp repeat sequence required for regulation of chi transcription. SCO5232, named dasA, showed transcriptional induction by (GlcNAc)(2) and N,N',N'''-triacetylchitotriose [(GlcNAc)(3)]. Surface plasmon resonance analysis showed that recombinant DasA protein exhibited the highest affinity for (GlcNAc)(2) (equilibrium dissociation constant [K(D)] = 3.22 x 10(-8)). In the dasA-null mutant, the rate of decline of the (GlcNAc)(2) concentration in the culture supernatant was about 25% of that in strain M145. The in vitro and in vivo data clearly demonstrated that dasA is involved in (GlcNAc)(2) uptake. Upstream and downstream of dasA, the transcriptional regulator gene (dasR) and two putative integral membrane protein genes (dasBC) are located in the opposite and same orientations, respectively. The expression of dasR and dasB, which seemed independent of dasA transcription, was also induced by (GlcNAc)(2) and (GlcNAc)(3).

Conserved cis-Acting Elements Upstream of Genes Composing the Chitinolytic System of Streptomycetes Are DasR-Responsive Elements

For soil-dwelling bacteria that usually live in a carbon-rich and nitrogen-poor environment, the ability to utilize chitin - the second most abundant polysaccharide on earth - is a decisive evolving advantage as it is a source for both elements. Streptomycetes are high-GC Gram-positive soil bacteria that are equipped with a broad arsenal of chitinase-degrading genes. These genes are induced when the streptomycetes sense the presence of chitooligosaccharides. Their expression is repressed as soon as more readily assimilated carbon sources become available. This includes for example glucose or N-acetylglucosamine, the monomer subunit of chitin. Historically, the first cis-acting elements involved in carbon regulation in streptomycetes were found more than a decade ago upstream of chitinase genes, but the transcriptional regulator had so far remained undiscovered. In this work, we show that these cis-acting elements consist of inverted repeats with multiple occurrences and are bound by the HutC/GntR type regulator DasR. We have therefore designated these sites as DasR-responsive elements (dre). DasR, which is also the repressor of the genes for the N-acetylglucosamine-specific phosphotransferase transport system, should therefore play a critical role in sensing the balance between the monomeric and polymeric forms of N-acetylglucosamine.

Cloning and expression of a Bacillus circulans KA-304 gene encoding chitinase I, which participates in protoplast formation of Schizophyllum commune

KA-prep, a culture filtrate of Bacillus circulans KA-304 grown on a cell-wall preparation of Schizophyllum commune, has an activity to form protoplasts from S. commune mycelia, and a combination of alpha-1,3-glucanase and chitinase I, isolated from KA-prep, brings about the protoplast-forming activity. The gene of chitinase I was cloned from B. circulans KA-304 into pGEM-T Easy vector. The gene consists of 1,239 nucleotides, which encodes 413 amino acids including a putative signal peptide (24 amino acid residues). The molecular weight of 40,510, calculated depending on the open reading frame without the putative signal peptide, coincided with the apparent molecular weight of 41,000 of purified chitinase I estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The C-terminal domain of the deduced amino acid sequence showed high similarity to that of family 19 chitinases of actinomycetes and other organisms, indicating that chitinase I is the first example of family 19 chitinase in Bacillus species. Recombinant chitinase I without the putative signal peptide was expressed in Escherichia coli Rosetta-gami B (DE 3). The properties of the purified recombinant enzyme were almost the same as those of chitinase I purified from KA-prep, and showed the protoplast-forming activity when it was combined with alpha-1,3-glucanase from KA-prep. Recombinant chitinase I as well as the native enzyme inhibited hyphal extension of Trichoderma reesei.

Identification of the sequences involved in the glucose-repressed transcription of the Streptomyces halstedii JM8 xysA promoter

The expression of xysA, a gene encoding for an endoxylanase from Streptomyces halstedii JM8, is repressed by glucose. In order to define the regions involved in its regulation, several deletions were made in the 475 bp xysA promoter and were studied using the melC operon from S. glaucescens as a reporter. Four of the deleted versions obtained were seen to be derepressed when driving melC or its own xysA gene expression in Streptomyces lividans. Quantitative assays revealed that the activity of xylanase produced under the control of these four deleted promoters was higher than the original one in the presence of glucose. Three regions - RI, R16 and R21 - involved in glucose repression were defined in this analysis: RI is a palindromic sequence that is highly conserved among xylanase gene promoters from Actinomycetes (-213 GAAAxxTTTCxGAAA -197) and, R16 and R21 define two new seven-pair conserved motifs, respectively (-113 5'-CCTTCCC-3' -106 in R16 and -76 5'-CGAACGG-3' -69 in R21) located in the untranslated mRNA. Gel shift assays demonstrated the existence of proteins that bind specifically to these regions.

Bioinformatic identification of novel regulatory DNA sequence motifs in Streptomyces coelicolor

BACKGROUND

Streptomyces coelicolor is a bacterium with a vast repertoire of metabolic functions and complex systems of cellular development. Its genome sequence is rich in genes that encode regulatory proteins to control these processes in response to its changing environment. We wished to apply a recently published bioinformatic method for identifying novel regulatory sequence signals to gain new insights into regulation in S. coelicolor.

RESULTS

The method involved production of position-specific weight matrices from alignments of over-represented words of DNA sequence. We generated 2497 weight matrices, each representing a candidate regulatory DNA sequence motif. We scanned the genome sequence of S. coelicolor against each of these matrices. A DNA sequence motif represented by one of the matrices was found preferentially in non-coding sequences immediately upstream of genes involved in polysaccharide degradation, including several that encode chitinases. This motif (TGGTCTAGACCA) was also found upstream of genes encoding components of the phosphoenolpyruvate phosphotransfer system (PTS). We hypothesise that this DNA sequence motif represents a regulatory element that is responsive to availability of carbon-sources. Other motifs of potential biological significance were found upstream of genes implicated in secondary metabolism (TTAGGTtAGgCTaACCTAA), sigma factors (TGACN19TGAC), DNA replication and repair (ttgtCAGTGN13TGGA), nucleotide conversions (CTACgcNCGTAG), and ArsR (TCAGN12TCAG). A motif found upstream of genes involved in chromosome replication (TGTCagtgcN7Tagg) was similar to a previously described motif found in UV-responsive promoters.

CONCLUSIONS

We successfully applied a recently published in silico method to identify conserved sequence motifs in S. coelicolor that may be biologically significant as regulatory elements. Our data are broadly consistent with and further extend data from previously published studies. We invite experimental testing of our hypotheses in vitro and in vivo.

Molecular analysis of a bacterial chitinolytic community in an upland pasture

The effects of agricultural-improvement treatments on the chitinolytic activity and diversity of a microbial community were investigated within an upland pasture. The treatments of interest were lime and treated sewage sludge, both commonly applied to pasture land to improve fertility. Burial of chitin-containing litter bags at the field site resulted in enrichment of bacteria according to 16S rRNA fingerprinting. Chitinolytic-activity measurements showed that the highest activity occurred in those bags recovered from sludge-amended plots, which correlated well with increased counts of actinobacteria in samples from these chitin bags. Our findings suggest that sewage sludge increases the fertility of the soil in terms of chitinase activity. Ten clone libraries were constructed from family 18 subgroup A chitinases, PCR amplified from litter bags buried in soil in July 2000 or in September 2000, in a separate study. Analysis of these libraries by restriction fragment length polymorphism and sequencing showed that they were dominated by actinobacterium-like chitinase sequences. This suggests that actinobacteria have an important chitinolytic function in this soil ecosystem. Our findings showed that sludge application increased chitinolytic activity but decreased the diversity of chitinases present.

Response regulator ChiR regulates expression of chitinase gene, chiC, in Streptomyces coelicolor

Transcription from the chiC promoter, directing expression of the chitinase gene, chiC, in Streptomyces coelicolor, was analyzed using xylE reporter gene and high-resolution S1-nuclease mapping. The transcription from the chiC promoter was induced by chitin, and this induction was dramatically reduced in the S. coelicolor chiR-disrupted strain. This indicated a dependence of chiC expression upon the chiR gene encoding a response regulator protein. To investigate this relationship, the S. coelicolor ChiR was overproduced using Escherichia coli T7 RNA polymerase expression system. However, gel mobility shift-assay with such a purified ChiR showed no binding in the chiC promoter region, which indicates a lack of specific phosphorylation of E. coli overproduced ChiR that is necessary for DNA-binding activity of response regulators.

Characteristics of a Streptomyces coelicolor A3(2) extracellular protein targeting chitin and chitosan

Upstream of the Streptomyces coelicolor A3(2) chitinase G gene, a small gene (named chb3) is located whose deduced product shares 37% identical amino acids with the previously described CHB1 protein from Streptomyces olivaceoviridis. The chb3 gene and its upstream region were cloned in a multicopy vector and transformed into the plasmid-free Streptomyces lividans TK21 strain. The CHB3 protein (14.9 kDa) was secreted by the S. lividans TK21 transformant during growth in the presence of glucose, N-acetylglucosamine, yeast extract, and chitin. The protein was purified to homogeneity using anionic exchange, hydrophobic interaction chromatographies, and gel filtration. In contrast to CHB1, CHB3 targets alpha-chitin, beta-chitin, and chitosan at pH 6.0 but does so relatively loosely. The ecological implications of the divergence of substrate specificity of various types of chitin-binding proteins are described.