Another Brick in the Wall: the role of the actinobacterial cell wall in antibiotic resistance, phylogeny and development

Streptomyces are multicellular, Gram-positive bacteria in the phylum of actinobacteria which produce a high amount of bioactive natural products of which the expression is tightly coordinated with the life cycle. This thesis shows the identification of S. roseifaciens, a novel species with an uncommon, verticillate spore morphology and a unique household of SsgA-like proteins. Analyses of the peptidoglycan composition show that S. coelicolor show a pattern of 3-3 cross-linking befitting a tip-growing organism and change in composition between vegetative mycelium and spores. Kitasatosporae carry meso-DAP in the peptidoglycan of vegetative mycelium and LL-DAP in the peptidoglycan of spores. In line with this difference, the peptidoglycan architecture of these two growth stages undergoes such radical changes that they would seem to be from different species. S. coelicolor is naturally vancomycin resistant, but the addition of D-alanine and disruption in a single gene increases vancomycin sensitivity by a thousandfold. A knockout mutant of the alanine racemase, alr, requires exogenous addition of D-alanine. The Alr crystal structure of S. coelicolor and the D-cycloserine producer S. lavendulae were compared as to look for possible mechanisms for D-cycloserine resistance. Microbial Biotechnolog

Structural and functional characterization of the alanine racemase from Streptomyces coelicolor A3(2)

The conversion of l-alanine (L-Ala) into d-alanine (D-Ala) in bacteria is performed by pyridoxal phosphate-dependent enzymes called alanine racemases. D-Ala is an essential component of the bacterial peptidoglycan and hence required for survival. The Gram-positive bacterium Streptomyces coelicolor has at least one alanine racemase encoded by alr. Here, we describe an alr deletion mutant of S. coelicolor which depends on D-Ala for growth and shows increased sensitivity to the antibiotic d-cycloserine (DCS). The crystal structure of the alanine racemase (Alr) was solved with and without the inhibitors DCS or propionate, at 1.64 Å and 1.51 Å resolution, respectively. The crystal structures revealed that Alr is a homodimer with residues from both monomers contributing to the active site. The dimeric state of the enzyme in solution was confirmed by gel filtration chromatography, with and without L-Ala or d-cycloserine. The activity of the enzyme was 66 ± 3 U mg−1 for the racemization of L- to D-Ala, and 104 ± 7 U mg−1 for the opposite direction. Comparison of Alr from S. coelicolor with orthologous enzymes from other bacteria, including the closely related d-cycloserine-resistant Alr from S. lavendulae, strongly suggests that structural features such as the hinge angle or the surface area between the monomers do not contribute to d-cycloserine resistance, and the molecular basis for resistance therefore remains elusive.Macromolecular Biochemistr

An alternative and conserved cell wall enzyme that can substitute for the lipid II synthase MurG

Microbial Biotechnolog

Teichoic acids anchor distinct cell wall lamellae in an apically growing bacterium

The bacterial cell wall is a multicomponent structure that provides structural support and protection. In monoderm species, the cell wall is made up predominantly of peptidoglycan, teichoic acids and capsular glycans. Filamentous monoderm Actinobacteria incorporate new cell-wall material at their tips. Here we use cryo-electron tomography to reveal the architecture of the actinobacterial cell wall ofStreptomyces coelicolor. Our data shows a density difference between the apex and subapical regions. Removal of teichoic acids results in a patchy cell wall and distinct lamellae. Knock-down oftagOexpression using CRISPR-dCas9 interference leads to growth retardation, presumably because build-in of teichoic acids had become rate-limiting. Absence of extracellular glycans produced by MatAB and CslA proteins results in a thinner wall lacking lamellae and patches. We propose that theStreptomycescell wall is composed of layers of peptidoglycan and extracellular polymers that are structurally supported by teichoic acids.Eveline Ultee et al. reveal the architecture of the actinobacterial cell wall of a polar growing bacteriumStreptomyces coelicolor, using cryo-electron tomography. This study suggests that theStreptomycescell wall is composed of layers of peptidoglycan and extracellular polymers that are structurally supported by teichoic acids.Microbial Biotechnolog

Teichoic acids anchor distinct cell wall lamellae in an apically growing bacterium

Microbial Biotechnolog

Another Brick in the Wall: the role of the actinobacterial cell wall in antibiotic resistance, phylogeny and development

Streptomyces are multicellular, Gram-positive bacteria in the phylum of actinobacteria which produce a high amount of bioactive natural products of which the expression is tightly coordinated with the life cycle. This thesis shows the identification of S. roseifaciens, a novel species with an uncommon, verticillate spore morphology and a unique household of SsgA-like proteins. Analyses of the peptidoglycan composition show that S. coelicolor show a pattern of 3-3 cross-linking befitting a tip-growing organism and change in composition between vegetative mycelium and spores. Kitasatosporae carry meso-DAP in the peptidoglycan of vegetative mycelium and LL-DAP in the peptidoglycan of spores. In line with this difference, the peptidoglycan architecture of these two growth stages undergoes such radical changes that they would seem to be from different species. S. coelicolor is naturally vancomycin resistant, but the addition of D-alanine and disruption in a single gene increases vancomycin sensitivity by a thousandfold. A knockout mutant of the alanine racemase, alr, requires exogenous addition of D-alanine. The Alr crystal structure of S. coelicolor and the D-cycloserine producer S. lavendulae were compared as to look for possible mechanisms for D-cycloserine resistance. </p

Polyphasic classification of the gifted natural product producer Streptomyces roseifaciens sp. nov.

A polyphasic study was designed to establish the taxonomic status of a Streptomyces strain isolated from soil from the QinLing Mountains, Shaanxi Province, China, and found to be the source of known and new specialized metabolites. Strain MBT76T was found to have chemotaxonomic, cultural and morphological properties consistent with its classification in the genus Streptomyces . The strain formed a distinct branch in the Streptomyces16S rRNA gene tree and was closely related to the type strains of Streptomyces hiroshimensis and Streptomyces mobaraerensis. Multi-locus sequence analyses based on five conserved house-keeping gene alleles showed that strain MBT76T is closely related to the type strain of S. hiroshimensis, as was the case in analysis of a family of conserved proteins. The organism was also distinguished from S. hiroshimensis using cultural and phenotypic features. Average nucleotide identity and digital DNA–DNA hybridization values between the genomes of strain MBT76T and S. hiroshimensis DSM 40037T were 88.96 and 28.4±2.3%, respectively, which is in line with their assignment to different species. On the basis of this wealth of data it is proposed that strain MBT76T (=DSM 106196T=NCCB 100637T), be classified as a new species, Streptomyces roseifaciens sp. nov.Microbial Biotechnolog

A novel and conserved cell wall enzyme that can substitute for the Lipid II synthase MurG

Microbial Biotechnolog

Systematic evaluation of corticosteroid use in obese and non-obese individuals: A multi-cohort study

Background: Although the use of corticosteroids has been linked to high incidence of weight gain, no data are available concerning the differences in corticosteroid use between a diverse obese population and non-obese individuals. The main purpose of this study was to systematically explore the use of corticosteroids in obese subjects compared to non-obese controls. In addition, we also explored self-reported marked weight gain within obese subjects. Methods: Two hundred seventy-four obese outpatients (median [range] BMI: 40.1 kg/m2 [30.5-67.0]), and 526 non-obese controls (BMI: 24.1 kg/m2 [18.6-29.9]) from two different Dutch cohort studies were included. Corticosteroid use at the time of clinic or research site visit for up to the preceding three months was recorded in detail. Medical records and clinical data were evaluated with regard to age and body mass index in relation to corticosteroid use, single or multiple type use, and administration forms. Results: Recent corticosteroid use was nearly twice as high for obese subjects than for non-obese controls (27.0% vs. 11.9% and 14.8%, both P<.001). Largest differences were found for use of local corticosteroids, in particular inhaled forms, and simultaneous use of multiple types. Marked weight gain was self-reported during corticosteroid use in 10.5% of the obese users. Conclusion: Corticosteroid use, especially the inhaled agents, is higher in obese than in non-obese individuals. Considering the potential systemic effects of also local corticosteroids, caution is warranted on the increasing use in the general population and on its associations with weight gain