New Insights into Chloramphenicol Biosynthesis in Streptomyces venezuelae ATCC 10712

Comparative genome analysis revealed seven uncharacterized genes, sven0909 to sven0915, adjacent to the previously identified chloramphenicol biosynthetic gene cluster (sven0916–sven0928) of Streptomyces venezuelae strain ATCC 10712 that was absent in a closely related Streptomyces strain that does not produce chloramphenicol. Transcriptional analysis suggested that three of these genes might be involved in chloramphenicol production, a prediction confirmed by the construction of deletion mutants. These three genes encode a cluster-associated transcriptional activator (Sven0913), a phosphopantetheinyl transferase (Sven0914), and a Na(+)/H(+) antiporter (Sven0915). Bioinformatic analysis also revealed the presence of a previously undetected gene, sven0925, embedded within the chloramphenicol biosynthetic gene cluster that appears to encode an acyl carrier protein, bringing the number of new genes likely to be involved in chloramphenicol production to four. Microarray experiments and synteny comparisons also suggest that sven0929 is part of the biosynthetic gene cluster. This has allowed us to propose an updated and revised version of the chloramphenicol biosynthetic pathway

Epidemiological characteristics and outcomes of COVID-19 in asymptomatic versus symptomatic patients

Background. The clinical manifestations of COVID-19 are different, which can be attributed to asymptomatic carriers, acute respiratory disease and pneumonia with different severities. The aim of this study was to compare the epidemiological characteristics and outcomes of COVID-19 in patients with clinical symptoms versus asymptomatic patients. Methods. In this retrospective cohort study, the epidemiological characteristics of two groups of patients, with clinical symptoms (n = 38,630) and without clinical symptoms who were definitive cases of COVID-19 (n = 2,327) were investigated in the southwestern of Iran. Chi-square test was used to evaluate the differences between qualitative variables in the two study groups. Results. Of 40,957 patients with COVID-19, 2,327 (5.68) were asymptomatic, of whom 1391 (59.77) were males, 1841 patients (79.11) had a history of contact with definite or suspected cases of COVID-19. Asymptomatic patients were older than symptomatic cases. Patients with clinical symptoms had higher mortality rate than asymptomatic patients (2.68 in symptomatic patients vs 0 in asymptomatic patients). Conclusion. According to the results of our study, the detected viral load in asymptomatic individuals was similar to that of symptomatic patients, indicating that asymptomatic infections can potentially transmit the disease. Therefore, screening and detection of asymptomatic cases is an important and key measure in prevention and early control of COVID-19 worldwide. © 2021 Pacini Editore S.p.A.. All rights reserved

Isolation and identification of three new 5-Alkenyl-3,3(2H)-furanones from two Streptomyces species using a genomic screening approach

Analyses of biosynthetic gene clusters derived from Streptomyces aculeolatus NRRL 18422 and Streptomyces sp. Eco86 indicated that both microorganisms have similar type I polyketide synthase (PKS) gene clusters with relatively few genes encoding post-PKS elaborative enzymes. However both gene clusters included a sequence coding for a relatively uncommon oxidative enzyme related to Baeyer-Villiger, flavin-type monooxygenases. Screening of culture extracts for compounds with the predicted physicochemical properties of the end products from these loci, led to the isolation of three 5-alkenyl-3,3(2H)-furanones, one (E-837, 1) from the former and two (E-492, 2, E-975, 3) from the latter strain. The structures, confirmed by spectral analyses including MS, and 1D and 2D NMR experiments, were in accord with those predicted by genomic analyses. Baeyer-Villiger type oxidation is postulated to be involved in the formation of the furanone moieties in these molecules. All three new compounds were tested for their electron transport inhibitory activities. They had IC50 values of 1approx4 microg/ml against Ascaris suum NADH-fumarate reductase and 1approx12 microg/ml against bovine heart NADH oxidase.Peer reviewed: YesNRC publication: N

Genomic analyses lead to novel secondary metabolites. Part 3 ECO-0501, a novel antibacterial of a new class

Genomic analyses of Amycolatopsis orientalis ATCC 43491 strain, deposited as a vancomycin producer, revealed the presence of genetic loci for the production of at least 10 secondary metabolites other than vancomycin. One of these gene clusters, which contained a type I polyketide synthase, was predicted to direct the synthesis of novel class of compound, a glycosidic polyketide ECO-0501 (1). Screening of culture extracts for a compound with the predicted physicochemical properties of the product from this locus, led to the isolation of the 13-O-glucuronide of 13-hydroxy-2,12,14,16,22-pentamethyl-28-(N-methyl-guanidino)-octacosa-2,4,6,8,10,14,20,24-octaenoic acid (2-hydroxy-5-oxo-cyclopent-1-enyl)-amide (ECO-0501, 1). The structure, confirmed by spectral analyses including MS, and 1D and 2D NMR experiments, were in accord with that predicted by genomic analyses. ECO-0501 possessed strong antibacterial activity against a series of Gram-positive pathogens including several strains of methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE). ECO-0501 was chemically modified by esterification (1a~1c), N-acetylation (1d) and hydrogenation (1e) in order to explore structure activity relationships (SAR).Peer reviewed: YesNRC publication: N

TLN-05220, TLN-05223, new Echinosporamicin-type antibiotics, and proposed revision of the structure of bravomicins

The deposited strain of the hazimicin producer, Micromonospora echinospora ssp. challisensis NRRL 12255 has considerable biosynthetic capabilities as revealed by genome scanning. Among these is a locus containing both type I and type II PKS genes. The presumed products of this locus, TLN-05220 (1) and TLN-05223 (2), bear a core backbone composed of six fused rings starting with a 2-pyridone moiety. The structures were confirmed by conventional spectral analyses including MS, and 1D and 2D NMR experiments. Comparison of both the 1H and 13C NMR data of the newly isolated compound with those of echinosporamicin and bravomicin A led us to propose a revision of the structure of the latter to include a 2-pyridone instead of the pyran originally postulated. Both compounds (1 and 2) possessed strong antibacterial activity against a series of gram-positive pathogens including several strains of methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococci (VRE), and cytotoxic activities against several human tumor cell lines. The TLN compounds are the first of this group with reported anticancer activity.Peer reviewed: YesNRC publication: Ye

Biosynthesis of diazepinomicin/ECO-4601, a Micromonospora secondary metabolite with a novel ring system

The novel microbial metabolite diazepinomicin/ECO-4601 (1) has a unique tricyclic dibenzodiazepinone core, which was unprecedented among microbial metabolites. Labeled feeding experiments indicated that the carbocyclic ring and the ring nitrogen of tryptophan could be incorporated via degradation to the 3-hydroxyanthranilic acid, forming ring A and the nonamide nitrogen of 1. Genomic analysis of the biosynthetic locus indicated that the farnesyl side chain was mevalonate derived, the 3-hydroxyanthranilic acid moiety could be formed directly from chorismate, and the third ring was constructed via 3-amino-5-hydroxybenzoic acid. Successful incorporation of 4,6-D2-3-hydroxyanthranilic acid into ring A of 1 via feeding experiments supports the genetic analysis and the allocation of the locus to this biosynthesis. These studies highlight the enzymatic complexity needed to produce this structural type, which is rare in nature.Peer reviewed: YesNRC publication: N

Touchdown PCR for increased specificity and sensitivity in PCR amplification

Touchdown (TD) PCR offers a simple and rapid means to optimize PCRs, increasing specificity, sensitivity and yield, without the need for lengthy optimizations and/or the redesigning of primers