A Novel Peptide Antibiotic Produced by Streptomyces roseoflavus Strain INA-Ac-5812 With Directed Activity Against Gram-Positive Bacteria

Anti-Staphylococcus aureus effects of natural antimicrobial peptides and the underlying mechanisms

Staphylococcus aureus can cause localized infections such as abscesses and pneumonia, as well as systemic infections such as bacteremia and sepsis. Especially, methicillin-resistant S. aureus often presents multidrug resistance, which becomes a major clinical challenge. One of the most common reasons for methicillin-resistant S. aureus antibiotic resistance is the presence of biofilms. Natural antimicrobial peptides derived from different species have shown effectiveness in combating S. aureus biofilms. In this review, we summarize the inhibitory activity of antimicrobial peptides against S. aureus planktonic cells and biofilms. We also summarize the possible inhibitory mechanisms, involving cell adhesion inhibition, membrane fracture, biofilm disruption and DNA disruption. We believe this can provide the basis for further research against S. aureus biofilm-associated infections.

Natural products acting against S. aureus through membrane and cell wall disruption

Covering: 2015 to 2022Staphylococcus aureus (S. aureus) is responsible for several community and hospital-acquired infections with life-threatening complications such as bacteraemia, endocarditis, meningitis, liver abscess, and spinal cord epidural abscess. In recent decades, the abuse and misuse of antibiotics in humans, animals, plants, and fungi and the treatment of nonmicrobial diseases have led to the rapid emergence of multidrug-resistant pathogens. The bacterial wall is a complex structure consisting of the cell membrane, peptidoglycan cell wall, and various associated polymers. The enzymes involved in bacterial cell wall synthesis are established antibiotic targets and continue to be a central focus for antibiotic development. Natural products play a vital role in drug discovery and development. Importantly, natural products provide a starting point for active/lead compounds that sometimes need modification based on structural and biological properties to meet the drug criteria. Notably, microorganisms and plant metabolites have contributed as antibiotics for noninfectious diseases. In this study, we have summarized the recent advances in understanding the activity of the drugs or agents of natural origin that directly inhibit the bacterial membrane, membrane components, and membrane biosynthetic enzymes by targeting membrane-embedded proteins. We also discussed the unique aspects of the active mechanisms of established antibiotics or new agents.

A peptide encoded by a highly conserved gene belonging to the genus Streptomyces shows antimicrobial activity against plant pathogens

The genus Streptomyces has been unceasingly highlighted for the versatility and diversity of the antimicrobial agents they produce. Moreover, it is a heavily sequenced taxon in the phylum Actinobacteria. In this study, 47 sequence profiles were identified as proteins highly conserved within the genus Streptomyces. Significant hits to the 38 profiles were found in more than 2000 Streptomyces genomes, 11 of which were further conserved in more than 90% of Actinobacterial genomes analyzed. Only a few genes corresponding to these sequence profiles were functionally characterized, which play regulatory roles in the morphology and biosynthesis of antibiotics. Here a highly conserved sequence, namely, SHC-AMP (Streptomyces highly conserved antimicrobial peptide), which exhibited antimicrobial activity against bacterial and fungal plant pathogens, was reported. In particular, Arabidopsis thaliana was effectively protected against infection with Pseudomonas syringae pv. tomato DC3000 by treatment with this peptide. Results indicated the potential application of this peptide as an antimicrobial agent for control of plant diseases. Our results suggest putative target genes for controlling Streptomyces spp., including the one exhibiting antimicrobial activity against a wide range of phytopathogens.

Gausemycin A-Resistant Staphylococcus aureus Demonstrates Affected Cell Membrane and Cell Wall Homeostasis

Antibiotic resistance is a significant and pressing issue in the medical field, as numerous strains of infectious bacteria have become resistant to commonly prescribed antibiotics. Staphylococcus aureus is a bacterium that poses a grave threat, as it is responsible for a large number of nosocomial infections and has high mortality rates worldwide. Gausemycin A is a new lipoglycopeptide antibiotic that has considerable efficacy against multidrug-resistant S. aureus strains. Although the cellular targets of gausemycin A have been previously identified, detailing the molecular processes of action is still needed. We performed gene expression analysis to identify molecular mechanisms that may be involved in bacterial resistance to gausemycin A. In the present study, we observed that gausemycin A-resistant S. aureus in the late-exponential phase showed an increased expression of genes involved in cell wall turnover (sceD), membrane charge (dltA), phospholipid metabolism (pgsA), the two-component stress-response system (vraS), and the Clp proteolytic system (clpX). The increased expression of these genes implies that changes in the cell wall and cell membrane are essential for the bacterial resistance to gausemycin A. In the stationary phase, we observed a decrease in the expression of genes involved in the phospholipid metabolism (mprF) and Clp proteolytic system (clpX).

Occurrence of Streptomyces tauricus in mangrove soil of Mangalore region in Dakshina Kannada as a source for antimicrobial peptide

Microbial resistance and deprivation of the effective drugs have become the foremost problem that propels to seek out for advanced approach. This concept initiated a need to search for more effective antimicrobial compounds from reliable sources. The Streptomyces is grouped under phylum Actinobacteria and are considered prolific producers of antibiotics, around 70% of presently available antibiotics are contributed by Streptomyces alone. In this study, Mangroves of the Mangalore Coast offered a unique source for screening Actinomyces group of microorganisms. We investigated on the four soil samples collected from Mangrove swamps of Mangalore, Karnataka, India. Based on their culture traits, the 18 distinct Actinomyces isolates were analyzed through a series of morphological and biochemical tests on starch casein nitrate (SCN) media. Culture biomasses were subjected for intracellular protein extraction through acetone precipitation method; the extracted proteins from each Actinomyces isolate were examined for antimicrobial activity against test organisms. The isolate ANTB-YKMU4 showed potential antimicrobial activity against significant number of test organisms; Bacillus cereus, Proteus vulgaris, Staphylococcus aureus, Salmonella typhimurium, and Pseudomonas aeruginosa. The isolate ANTB-YKMU4 through 16 s rRNA gene sequence analysis was identified as Streptomyces tauricus strain with GenBank accession no. MW785875.1. The S. tauricus further cultivated for efficient biomass growth on SCN media for subsequent protein extraction and purification by a series of Electrophoretic and chromatographic techniques. Thus, by intracellular extractions from S. tauricus resulted in the identification of peptide with a molecular weight of 266 Da that was characterized by LC-MS.

Investigation of diverse biosynthetic secondary metabolites gene clusters using genome mining of indigenous Streptomyces strains isolated from saline soils in Iran

Background and Objectives

Bioactive secondary metabolites are the products of microbial communities adapting to environmental challenges, which have yet remained anonymous. As a result of demands in the pharmaceutical, agricultural, and food industries, microbial metabolites should be investigated. The most substantial sources of secondary metabolites are Streptomyces strains and are potential candidates for bioactive compound production. So, we used genome mining and bioinformatics to predict the isolates secondary metabolites, biosynthesis, and potential pharmaceuticals.

Materials and Methods

This is a bioinformatics part of our previous experimental research. Here, we aimed to inspect the underlying secondary metabolite properties of 20 phylogenetically diverse Streptomyces species of saline soil by a rationalized computational workflow by several software tools. We examined the Metabolites' cytotoxicity and antibacterial effects using the MTT assay and plate count technique, respectively.

Results

Among Streptomyces species, three were selected for genome mining and predicted novel secondary metabolites and potential drug abilities. All 11 metabolites were cytotoxic to A549, but ectoine (p≤0.5) and geosmin (p≤0.001) significantly operated as an anti-cancer drug. Metabolites of oxytetracycline and phosphinothricin (p≤0.001), 4Z-annimycin and geosmin (p≤0.01), and ectoine (p≤0.5) revealed significant antibacterial activity.

Conclusion

Of all the 11 compounds investigated, annimycin, geosmin, phosphinothricin, and ectoine had antimicrobial properties, but geosmin also showed very significant anti-cancer properties.

Staphylococcus aureus is able to generate resistance to novel lipoglycopeptide antibiotic gausemycin A

Gausemycin A is the first member of the novel lipoglycopeptides family produced by Streptomyces roseoflavus INA-Ac-5812. Gausemycin A has a pronounced bactericidal activity against methicillin-resistant Staphylococcus aureus. However, the ability of S. aureus to be resistant to gausemycin A has not been investigated yet. Using serial passaging, we have obtained the resistant variant S. aureus 5812R, which is 80 times more resistant compared to the parent strain. Susceptibility testing of S. aureus 5812R revealed the acquisition of cross-resistance to daptomycin, cefazolin, tetracycline, and gentamicin, while the resistance to vancomycin, nisin, and ramoplanin was absent. Whole genome sequencing revealed single nucleotide polymorphism (SNP) and deletions in S. aureus 5812R, among which are genes encoding efflux pump (sepA), the two-component Kdp system (kdpE), and the component of isoprenoid biosynthesis pathway (hepT). Phenotypically, S. aureus 5812R resembles a small-colony variant, as it is slow-growing, forms small colonies, and is deficient in pigments. Profiling of fatty acids (FA) composition constituting the cytoplasmic membrane of S. aureus 5812R revealed the prevalence of anteiso-branched FA, while straight FA was slightly less present. The evidence also showed that the gausemycin A-resistant strain has increased expression of the cls2 gene of the cardiolipin synthase. The performed checkerboard assay pointed out that the combination of gausemycin A and ciprofloxacin showed a synergistic effect against S. aureus 5812R.

Streptomyces: The biofactory of secondary metabolites

Natural products derived from microorganisms serve as a vital resource of valuable pharmaceuticals and therapeutic agents. Streptomyces is the most ubiquitous bacterial genus in the environments with prolific capability to produce diverse and valuable natural products with significant biological activities in medicine, environments, food industries, and agronomy sectors. However, many natural products remain unexplored among Streptomyces. It is exigent to develop novel antibiotics, agrochemicals, anticancer medicines, etc., due to the fast growth in resistance to antibiotics, cancer chemotherapeutics, and pesticides. This review article focused the natural products secreted by Streptomyces and their function and importance in curing diseases and agriculture. Moreover, it discussed genomic-driven drug discovery strategies and also gave a future perspective for drug development from the Streptomyces.

Recently Discovered Secondary Metabolites from Streptomyces Species

The Streptomyces genus has been a rich source of bioactive natural products, medicinal chemicals, and novel drug leads for three-quarters of a century. Yet studies suggest that the genus is capable of making some 150,000 more bioactive compounds than all Streptomyces secondary metabolites reported to date. Researchers around the world continue to explore this enormous potential using a range of strategies including modification of culture conditions, bioinformatics and genome mining, heterologous expression, and other approaches to cryptic biosynthetic gene cluster activation. Our survey of the recent literature, with a particular focus on the year 2020, brings together more than 70 novel secondary metabolites from Streptomyces species, which are discussed in this review. This diverse array includes cyclic and linear peptides, peptide derivatives, polyketides, terpenoids, polyaromatics, macrocycles, and furans, the isolation, chemical structures, and bioactivity of which are appraised. The discovery of these many different compounds demonstrates the continued potential of Streptomyces as a source of new and interesting natural products and contributes further important pieces to the mostly unfinished puzzle of Earth’s myriad microbes and their multifaceted chemical output.

Streptomyces sp.-A Treasure Trove of Weapons to Combat Methicillin-Resistant Staphylococcus aureus Biofilm Associated with Biomedical Devices

Biofilms formed by methicillin-resistant S. aureus (MRSA) are among the most frequent causes of biomedical device-related infection, which are difficult to treat and are often persistent and recurrent. Thus, new and effective antibiofilm agents are urgently needed. In this article, we review the most relevant literature of the recent years reporting on promising anti-MRSA biofilm agents derived from the genus Streptomyces bacteria, and discuss the potential contribution of these newly reported antibiofilm compounds to the current strategies in preventing biofilm formation and eradicating pre-existing biofilms of the clinically important pathogen MRSA. Many efforts are evidenced to address biofilm-related infections, and some novel strategies have been developed and demonstrated encouraging results in preclinical studies. Nevertheless, more in vivo studies with appropriate biofilm models and well-designed multicenter clinical trials are needed to assess the prospects of these strategies.

Gausemycins A,B: Cyclic Lipoglycopeptides from Streptomyces sp.*

We report a novel family of natural lipoglycopeptides produced by Streptomyces sp. INA-Ac-5812. Two major components of the mixture, named gausemycins A and B, were isolated, and their structures were elucidated. The compounds are cyclic peptides with a unique peptide core and several remarkable structural features, including unusual positions of d-amino acids, lack of the Ca²⁺ -binding Asp-X-Asp-Gly (DXDG) motif, tyrosine glycosylation with arabinose, presence of 2-amino-4-hydroxy-4-phenylbutyric acid (Ahpb) and chlorinated kynurenine (ClKyn), and N-acylation of the ornithine side chain. Gausemycins have pronounced activity against Gram-positive bacteria. Mechanistic studies highlight significant differences compared to known glyco- and lipopeptides. Gausemycins exhibit only slight Ca²⁺ -dependence of activity and induce no pore formation at low concentrations. Moreover, there is no detectable accumulation of cell wall biosynthesis precursors under treatment with gausemycins.

Antimicrobial and Amyloidogenic Activity of Peptides. Can Antimicrobial Peptides Be Used against SARS-CoV-2?

At present, much attention is paid to the use of antimicrobial peptides (AMPs) of natural and artificial origin to combat pathogens. AMPs have several points that determine their biological activity. We analyzed the structural properties of AMPs, as well as described their mechanism of action and impact on pathogenic bacteria and viruses. Recently published data on the development of new AMP drugs based on a combination of molecular design and genetic engineering approaches are presented. In this article, we have focused on information on the amyloidogenic properties of AMP. This review examines AMP development strategies from the perspective of the current high prevalence of antibiotic-resistant bacteria, and the potential prospects and challenges of using AMPs against infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

MFAP9: Characterization of an extracellular thermostable antibacterial peptide from marine fungus with biofilm eradication potential

An extracellular thermostable antibacterial peptide designated as MFAP9 was purified from marine Aspergillus fumigatus BTMF9 by ammonium sulfate precipitation followed by ion exchange chromatography on a DEAE-sepharose column. The molecular weight of MFAP9 was found to be∼3 kDa in SDS-PAGE gel corresponding a single intensity peak in MALDI-TOF. The distinct peak with a retention time of 32.5 min appeared in high performance liquid chromatography (HPLC), further confirming the purity. Isoelectric focusing, two-dimensional gel electrophoresis and peptide mass fingerprinting were performed for the characterization of MFAP9. Functional analysis of purified MFAP9 exhibited strong antibacterial activity against Bacillus circulans (NCIM 2107) with MIC and MBC values of 0.525 μg/mL and 4.2 μg/mL, respectively. The in vitro antibiofilm effect of MFAP9 was analyzed against bacteria which have strong biofilm forming potential. The antibiofilm effect of MFAP9 treatment on Bacillus pumilus was examined using scanning electron microscopy. MFAP9 was found to be active at high temperatures and a wide range of pH (28). In addition, it showed varied sensitivity towards proteolytic enzymes. The peptide was nontoxic to human RBCs at higher concentrations. These results indicate that MFAP9 is an antibacterial peptide, suitable for the development of novel anti-infective agent with strong antibiofilm potential.