Accumulation of streptomycin-phosphate in cultures of streptomycin producers grown on a high-phosphate medium

Degradation of streptomycin in aquatic environment: kinetics, pathway, and antibacterial activity analysis

Streptomycin used in human and veterinary medicine is released into the environment mainly through excretions. As such, its elimination in water should be investigated to control pollution. In this study, the degradation of streptomycin in water was studied, and the influence of variables, including light exposure, solution pH, temperature, ionic strength, dissolved organic matter (DOM), and coexisting surfactants, on degradation was investigated. Streptomycin degradation was consistent with the first-order model in aquatic environments. Its degradation rate under light exposure was 2.6-fold faster than that in the dark. Streptomycin was stable under neutral conditions, but it was easily decomposed in acidic and basic environments. Streptomycin degradation was enhanced by high temperature, and its half-life decreased from 103.4 days at 15 °C to 30.9 days at 40 °C. This process was also accelerated by the presence of Ca²⁺ and slightly improved by the addition of HA. Streptomycin degradation was suppressed by high levels of the cationic surfactant cetyltri- methylammonium bromide (CTAB), but was promoted by the anionic surfactant sodium dodecyl benzene sulfonate (SDBS). The main degradation intermediates/products were identified through liquid chromatography-mass spectrometry, and the possible degradation pathway was proposed. The antibacterial activity of streptomycin solution was also determined during degradation. Results showed that STR degradation generated intermediates/products with weaker antibacterial activity than the parent compound.

An O-phosphotransferase catalyzes phosphorylation of hygromycin A in the antibiotic-producing organism Streptomyces hygroscopicus

The antibiotic hygromycin A (HA) binds to the 50S ribosomal subunit and inhibits protein synthesis in gram-positive and gram-negative bacteria. The HA biosynthetic gene cluster in Streptomyces hygroscopicus NRRL 2388 contains 29 open reading frames, which have been assigned putative roles in biosynthesis, pathway regulation, and self-resistance. The hyg21 gene encodes an O-phosphotransferase with a proposed role in self-resistance. We observed that insertional inactivation of hyg21 in S. hygroscopicus leads to a greater than 90% decrease in HA production. The wild type and the hyg21 mutant were comparably resistant to HA. Using Escherichia coli as a heterologous host, we expressed and purified Hyg21. Kinetic analyses revealed that the recombinant protein catalyzes phosphorylation of HA (K(m) = 30 +/- 4 microM) at the C-2''' position of the fucofuranose ring in the presence of ATP (K(m) = 200 +/- 20 microM) or GTP (K(m) = 350 +/- 60 microM) with a k(cat) of 2.2 +/- 0.1 min(-1). The phosphorylated HA is inactive against HA-sensitive Delta tolC E. coli and Streptomyces lividans. Hyg21 also phosphorylates methoxyhygromycin A and desmethylenehygromycin A with k(cat) and K(m) values similar to those observed with HA. Phosphorylation of the naturally occurring isomers of 5'''-dihydrohygromycin A and 5'''-dihydromethoxyhygromycin A was about 12 times slower than for the corresponding non-natural isomers. These studies demonstrate that Hyg21 is an O-phosphotransferase with broad substrate specificity, tolerating changes in the aminocyclitol moiety more than in the fucofuranose moiety, and that phosphorylation by Hyg21 is one of several possible mechanisms of self-resistance in S. hygroscopicus NRRL 2388.

Two glycosyltransferases and a glycosidase are involved in oleandomycin modification during its biosynthesis by Streptomyces antibioticus

A 5.2 kb region from the oleandomycin gene cluster in Streptomyces antibioticus located between the oleandomycin polyketide synthase gene and sugar biosynthetic genes was cloned. Sequence analysis revealed the presence of three open reading frames (designated oleI, oleN2 and oleR). The oleI gene product resembled glycosyltransferases involved in macrolide inactivation including the oleD product, a previously described glycosyltransferase from S. antibioticus. The oleN2 gene product showed similarities with different aminotransferases involved in the biosynthesis of 6-deoxyhexoses. The oleR gene product was similar to several glucosidases from different origins. The oleI, oleR and oleD genes were expressed in Streptomyces lividans. OleI and OleD intracellular proteins were partially purified by affinity chromatography in an UDP-glucuronic acid agarose column and OleR was detected as a major band from the culture supernatant. OleI and OleD showed oleandomycin glycosylating activity but they differ in the pattern of substrate specificity: OleI being much more specific for oleandomycin. OleR showed glycosidase activity converting glycosylated oleandomycin into active oleandomycin. A model is proposed integrating these and previously reported results for intracellular inactivation, secretion and extracellular reactivation of oleandomycin.

Purification and characterization of an extracellular enzyme from Streptomyces antibioticus that converts inactive glycosylated oleandomycin into the active antibiotic

Cell-free extracts from the oleandomycin producer, Streptomyces antibioticus, possess an intracellular glycosyltransferase capable of inactivating oleandomycin by glycosylation of the 2'-hydroxyl group in the desosamine moiety of the molecule [Vilches, C., Hernández, C., Méndez, C. & Salas, J. A. (1992) J. Bacteriol. 174, 161-165]. Using a four-step purification procedure, we have purified an enzyme activity from the culture supernatants from this organism which is able to release glucose from the inactive glycosylated molecule thus reactivating the antibiotic activity. This enzyme activity appeared in the culture supernatants immediately before oleandomycin is detected. The enzyme (molecular mass 87 kDa) showed a high degree of substrate specificity, not acting on other glycosylated macrolides such as methymycin, lankamycin and rosaramicin which are substrates for the glycosyltransferase. A second activity was detected corresponding to a 34-kDa polypeptide which probably originates from proteolytic cleavage of the larger polypeptide. The 87-kDa polypeptide possibly catalyses the last biosynthetic step in oleandomycin biosynthesis by S. antibioticus.

Identification of the gene encoding an N-acetylpuromycin N-acetylhydrolase in the puromycin biosynthetic gene cluster from Streptomyces alboniger

The biologically inactive compound N-acetylpuromycin is the last intermediate of the puromycin antibiotic biosynthetic pathway in Streptomyces alboniger. Culture filtrates from either this organism or Streptomyces lividans transformants harboring the puromycin biosynthetic gene cluster cloned in low-copy-number cosmids contained an enzymic activity which hydrolyzes N-acetylpuromycin to produce the active antibiotic. A gene encoding the deacetylase enzyme was located at one end of this cluster, subcloned in a 2.5-kb DNA fragment, and expressed from a high-copy-number plasmid in S. lividans.

Role of glycosylation and deglycosylation in biosynthesis of and resistance to oleandomycin in the producer organism, Streptomyces antibioticus

Cell extracts of Streptomyces antibioticus, an oleandomycin producer, can inactivate oleandomycin in the presence of UDP-glucose. The inactivation can be detected through the loss of biological activity or by alteration in the chromatographic mobility of the antibiotic. This enzyme activity also inactivates other macrolides (rosaramicin, methymycin, and lankamycin) which contain a free 2'-OH group in a monosaccharide linked to the lactone ring (with the exception of erythromycin), but not those which contain a disaccharide (tylosin, spiramycin, carbomycin, josamycin, niddamycin, and relomycin). Interestingly, the culture supernatant contains another enzyme activity capable of reactivating the glycosylated oleandomycin and regenerating the biological activity through the release of a glucose molecule. It is proposed that these two enzyme activities could be an integral part of the oleandomycin biosynthetic pathway.

Regulation of hydrolase formation and phosphate release in turimycin fermentations

During the turimycin fermentation hydrolytic enzymes are excreted responsible for orthophosphate release from phosphate-containing dissolved and undissolved complex medium constituents. Following a phosphate-limited growth period the phosphate release leads to a second growth period (diauxic growth). Depending on the rate of phosphate release the length of the lag phase of diauxic growth changes in different fermentations. The resulting second growth period is correlated with a transient delay in the formation of turimycin, of phosphatases and of nucleases. The amylolytic activities are formed already within the first hours after the beginning of fermentations. Phosphatases, nucleases and protease are excreted parallel to turimycin formation after extracellular phosphate limitation in presence of ammonia and glucose. A special role of phosphate limitation initiating enzyme synthesis is proposed.

Sequential processes of phosphate limitation and of phosphate release in streptomycin fermentations

The significance of the sequential processes of phosphate limitation and of phosphate release from medium constituents is demonstrated in technical streptomycin fermentations. The phosphate limitation initiated the streptomycin synthesis as well as the formation of phosphatases and protease. In later periods of the process the phosphate release influences especially the enzyme formation.

Role of phosphatases in the biosynthesis of chlortetracycline in Streptomyces aureofaciens

ATP diphosphohydrolase activity and inorganic pyrophosphatase reached two maxima during cultivation of the low- and high-producing variant of Streptomyces aureofaciens under conditions of phosphate limitation, i.e. after 30 and 70 h of cultivation. Increased levels of inorganic phosphate in a medium inhibitory to biosynthesis of chlortetracycline markedly decreased the levels of both enzymes. The ATP diphosphohydrolase activity was detected both in the supernatant and membrane fractions of the cell-free preparation of the mycelium.

Biosynthesis of streptomycin. Enzymic oxidation of dihydrostreptomycin (6-phosphate) to streptomycin (6-phosphate) with a particulate fraction of Streptomyces griseus

Resting cells and to a greater extent permeabilized cells of Streptomyces griseus can oxidize dihydrostreptomycin to streptomycin. The dihydrostreptomycin oxidoreductase activity was localized in the 100,000 X g particulate fraction. Sucrose density gradient centrifugation of the particulate suspension gave a band at a density of 1.09 which consisted mainly of membrane vesicles. This fraction had high dihydrostreptomycin oxidoreductase activity. S. griseus protoplasts also contain high oxidoreductase activity. These data are consistent with localization of the enzyme in the cell membrane. Dihydrostreptomycin and dihydrostreptomycin 6-phosphate can both serve as substrates for the oxidoreducatase, but the phosphate was the better substrate in the cell free system. Addition of cofactors was not required for the bound dihydrostreptomycin oxidoreductase. The electron acceptor for the oxidation is unknown. Oxidation of dihydrostreptomycin 6-phosphate to streptomycin 6-phosphate very probably represents the penultimate step in the biosynthesis of streptomycin.

The effect of inorganic phosphate on cyanogenesis by Pseudomonas aeruginosa

The biosynthesis of hydrogen cyanide (HCN) by a strain of Pseudomonas aeruginosa is found to be significantly influenced by inorganic phosphate. Optimum HCN production occurs when the phosphate concentration is between 1 and 10 mM. Above and below this concentration the amount of HCN produced decreases sharply and at 0.1 and 100 mM phosphate low HCN production occurs. If a culture growing at 0.1 mM phosphate and producing low HCN is shifted to 10 mM phosphate, HCN biosynthesis resumes. Experiments with chloramphenicol indicate that de novo-protein synthesis is required for the process.

Formation of methylated and phosphorylated metabolites during the fermentation process of verdamicin

In an attempt to understand the biosynthetic processes leading to the formation of verdamicin (end product), we have examined the patterns of the formation of methylated and phosphorylated metabolites, which resulted from either the addition of l-[methyl-(14)C]methionine or [(32)P]KH(2)PO(4) to the fermentation. Incorporation of label from l-[methyl-(14)C]methionine into the bioactive sisomicin, verdamicin, and the chromatographically polar components increased with the progression of time. Two methylated bioinactive metabolites were found in the culture broth after removal of the methylated bioactive metabolites. In contrast to the bioactive metabolites, incorporation of the methyl-(14)C label into the two methylated bioinactive metabolites decreased with the progression of time. A phosphorylated bioinactive metabolite (nonmethylated) was also found in the culture broth, fermented in the presence of [(32)P]KH(2)PO(4). The role of the phosphorylated metabolite in the biosynthesis of the bioactive metabolites cannot yet be explained.

Factors affecting the production of candicidin

Factors affecting candicidin synthesis and mycelial growth of Streptomyces griseus IMRU 3570 were studied. Inorganic phosphate was found to inhibit candicidin synthesis but to stimulate mycelial growth. Zinc, iron, and magnesium ions stimulated candicidin synthesis at relatively high concentrations in a complex medium but not in a synthetic medium. No other factors studied, such as temperature, oxygen absorption rate, and sugar concentration, were found to differentially affect antibiotic synthesis and mycelial growth. Optimum concentration of inorganic phosphate for candicidin synthesis in a chemically defined medium was found to be between 5 x 10(-5) and 5 x 10(-4) M. The culture in idiophase stage can be reverted to typical trophophase growth by the addition of inorganic phosphate, suggesting the controlling role of inorganic phosphate in repression and derepression of secondary metabolic and primary metabolic activity of the culture. With a soya peptone-glucose medium, the maximum rate of candicidin production could be maintained and extended for a considerable length of time by controlling the culture pH at 8.0, using glucose to adjust the pH during the later stages of a batch fermentation. Carrying out fermentations in this way has given candicidin yields up to 4 g/liter.

High aflatoxin production on a chemically defined medium

Aspergillus parasiticus ATCC 15517 produced 28 to 30 mg of aflatoxin per 100 ml of a medium containing sucrose, asparagine, and salts in stationary and shaken cultures. In the absence of asparagine in the medium, the toxin yields fell drastically, and the thin-layer chromatograms of the chloroform extracts of the cultures indicated the total absence of aflatoxin G(1) and the presence of new intense blue and green fluorescent bands having R(F) values lower than aflatoxins. Initial pH was critical and had to be around 4.5 for good growth and high toxin production on this medium. Optimum concentrations of KH(2)PO(4) and MgSO(4).7H(2)O in the medium were much lower than those normally used in fungal growth media.