Laboratory course on Streptomyces genetics and secondary metabolism

The "Streptomyces genetics and secondary metabolism" laboratory course gives an introduction to the versatile soil dwelling Gram-positive bacteria Streptomyces and their secondary metabolism. The course combines genetic modification of Streptomyces; growing of the strain and protoplast preparation, plasmid isolation by alkaline lysis and phenol precipitation, digestions, and ligations prior to protoplast transformation, as well as investigating the secondary metabolites produced by the strains. Thus, the course is a combination of microbiology, molecular biology, and chemistry. After the course the students should understand the relationship between genes, proteins, and the produced metabolites. © 2016 by The International Union of Biochemistry and Molecular Biology, 44(5):492-499, 2016.

Studies on a second and third ring cyclization in anthracycline biosynthesis

This paper focuses on study of second and third ring cyclization in anthracycline biosynthesis by a heterologous gene expression. Firstly, anthracycline non-producing Streptomyces peucetius mutant, D2 was heterologously complemented to produce daunomycins with plasmids pSgs44 and pSYE66, which contain putative cyclase genes of S. galilaeus and S. nogalater, respectively. A point mutation in the cyclase gene dpsY of D2 has changed glycine to serine resulting inactivation of the enzyme. Secondly, the putative cyclase gene snoaM from S. nogalater, was expressed in a gene cassette in S. lividans TK24 and S. coelicolor CH999 to study the influence of the cyclase gene on auramycinone production and the impact of endogenous genes on production profiles. The results obtained confirms that a cyclase closing the second and third ring of a polyketide is essential in anthracycline biosynthesis.

Characterization of mutations in aclacinomycin A-non-producing Streptomyces galilaeus strains with altered glycosylation patterns

In this study a set of Streptomyces galilaeus ATCC 31615 mutants was characterized, which are incapable of synthesizing some or all of the deoxyhexose sugars of aclacinomycin A. Complementation experiments with the the mutant strains H026, H038, H039, H054, H063, H065 and H075 were carried out with glycosylation genes previously derived from the wild-type S. galilaeus. Mutations in strains H038, H063 and H075 were complemented with single PCR-amplified genes. Furthermore, amplification and sequencing of the corresponding genes from the mutant strains revealed single point mutations in the sequences. First, in H038 a transition mutation in aknQ, encoding a putative dTDP-hexose 3-ketoreductase, causes an amino acid substitution from glycine to aspartate, suppressing the biosynthesis of both 2-deoxyfucose and rhodinose and thus leading to the accumulation of aclacinomycin T with rhodosamine as its only sugar. Second, in H063, which accumulates aklavinone without a sugar moiety, amino acid substitution occurs, with threonine being substituted by isoleucine in dTDP-glucose synthase, the first enzyme participating in deoxyhexose biosynthesis, encoded by aknY. Third, a nonsense mutation in aknP leads to truncated dTDP-hexose 3-dehydratase in H075, which is incapable of synthesizing rhodinose. In addition, mutants H054 and H065, which accumulate aclacinomycins without aminosugars, were complemented by a gene for an aminotransferase, aknZ. Characterization of the nature of the mutations adds to the usefulness and value of the mutants in the analysis of gene function and in the creation of novel compounds by combinatorial biosynthesis. Furthermore, these results strengthen the assignments of akn gene products and enlighten the biosynthetic pathway for deoxyhexoses.

Cloning and characterization of Streptomyces galilaeus aclacinomycins polyketide synthase (PKS) cluster

We have cloned and sequenced polyketide synthase (PKS) genes from the aclacinomycin producer Streptomyces galilaeus ATCC 31,615. The sequenced 13.5-kb region contained 13 complete genes. Their organization as well as their protein sequences showed high similarity to those of other type II PKS genes. The continuous region included the genes for the minimal PKS, consisting of ketosynthase I (aknB), ketosynthase II (aknC), and acyl carrier protein (aknD). These were followed by the daunomycin dpsC and dpsD homologues (aknE2 and F, respectively), which are rare in type II PKS clusters. They are associated with the unusual starter unit, propionate, used in the biosynthesis of aklavinone, a common precursor of aclacinomycin and daunomycin. Accordingly, when aclacinomycins minimal PKS genes were substituted for those of nogalamycin in the plasmid carrying genes for auramycinone biosynthesis, aklavinone was produced in the heterologous hosts. In addition to the minimal PKS, the cloned region included the PKS genes for polyketide ketoreductase (aknA), aromatase (aknE1) and oxygenase (aknX), as well as genes putatively encoding an aklanonic acid methyl transferase (aknG) and an aklanonic acid methyl ester cyclase (aknH) for post-polyketide steps were found. Moreover, the region carried genes for an activator (aknI), a glycosyl transferase (aknK) and an epimerase (aknL) taking part in deoxysugar biosynthesis.

Physiology and taxonomy of thiobacillus strain TJ330, which oxidizes carbon disulphide (CS2)

A bacterium (strain TJ330) capable of using carbon disulphide (CS2) as its sole energy source in an acidic environment was isolated from a peat biofilter used in experiments to remove CS2 and hydrogen sulphide (H2S) from air. Its physiology and taxonomy are described here. The strain oxidized CS2, H2S and elemental sulphur to sulphate chemolithotrophically. The rate of sulphate production was highest at pH 2. The maximum growth rate constant (micromax) using CS2 as a substrate was 3.9 x 10(-2) h(-1) (generation time 18 h) and the Monod constant (Ks) was 0.97-2.6 micromol l(-1) CS2 (74-198 microg l(-1)), corresponding to an equilibrium with 15-40 ppm CS2 in the headspace. The optimum growth temperature using elemental sulphur as a substrate was 28 degrees C. The strain bears morphological and physiological similarities to Thiobacillus thiooxidans, but the latter is incapable of oxidizing CS2. The strain TJ330 (DSM 8985) showed only 44.2 + 11.8% DNA homology with the type strain T. thiooxidans ATCC 19377, while its homology with T. ferrooxidans ATCC 23270 was 17.1 + 3.4%. The strain TJ 330 represents a high-affinity bacterium which can effectively remove low CS2 concentrations in an acid environment. These properties can be utilized in biotechnological purification applications.

A gene cluster from Streptomyces galilaeus involved in glycosylation of aclarubicin

We have cloned and characterized a gene cluster for anthracycline biosynthesis from Streptomyces galilaeus. This cluster, 15-kb long, includes eight genes involved in the deoxyhexose biosynthesis pathway, a gene for a glycosyltransferase and one for an activator, as well as two genes involved in aglycone biosynthesis. Gene disruption targeted to the activator gene blocked production of aclacinomycins in S. galilaeus. Plasmid pSgs4, containing genes for a glycosyltransferase (aknS), an aminomethylase (aknX), a glucose-1-phosphate thymidylyltransferase (akn Y) and two genes for unidentified glycosylation functions (aknT and aknV), restored the production of aclacinomycins in the S. galilaeus mutants H063, which accumulates aklavinone, and H054, which produces aklavinone with rhodinose and deoxyfucose residues. Furthermore, pSgs4 directed the production of L-rhamnosyl-epsilon-rhodomycinone and L-daunosaminyl-epsilon-rhodomycinone in S. peucetius strains that produce epsilon-rhodomycinone endogenously. Subcloning of the gene cluster was carried out in order to further define the genes that are responsible for complementation and hybrid anthracycline generation.

The nucleotide sequence for the replication region of pVS40, a lactococcal food grade cloning vector

The replication region of a limited host range lactococcal vector, pVS40, was located within a 2359 bp EcoRI--ClaI fragment. Within this fragment a sequence for a 1197 bp reading frame coding for a 46,826 Da protein together with a putative ribosomal binding site and the -10 and -35 promoter regions could be detected. Immediately upstream from the promoter were three complete and one nearly complete successive direct repeats (TATAGCGTATGAAAAAACTGTG), suggesting an origin of replication. The protein has considerable homologies to certain lactococcal plasmid replication proteins.