Marine Actinomycete Genus Salinispora Research Articles

Natural Products from Marine Actinomycete Genus Salinispora Might Inhibit 3CLpro and PLpro Proteins of SARS-CoV-2: An In Silico Evidence

Among the oldest marine species on the planet, the genus Salinispora is often encountered inhabiting sediments and other marine creatures in tropical and subtropical marine settings. This bacterial genus produces a plethora of natural products. The purpose of this study was to examine the potential for salinispora-based natural products (NPs) to combat the SARS-CoV-2 virus. The RCSB PDB was used to obtain the crystal structures of proteins 3CLpro and PLpro. All 125 NPs were obtained from online databases. Using Autodock Vina software v1.2.0 the molecular docking process was carried out after the proteins and ligands were prepared. Assessments of binding affinities and interacting amino acids were rigorously examined prior to MD simulations. The docking experiments revealed 35 NPs in total for both 3CLpro and PLpro, with high docking scores ranging from −8.0 kcal/mol to −9.0 kcal/mol. However, a thorough binding residue analyses of all docked complexes filtered nine NPs showing strong interactions with HIS: 41 and CYS: 145 of 3CLpro. Whereas, for PLpro, merely six NPs presented good interactions with residues CYS: 111, HIS: 272, and ASP: 286. Further research was conducted on residue–residue and ligand–residue interactions in both the filtered docked complexes and the Apo-protein structures using the Protein Contacts Atlas website. All complexes were found to be stable in CABS-flex 2.0 MD simulations conducted at various time frames (50, 125, 500, and 1000 cycles). In conclusion, salinaphthoquinone B appears to be the most promising metabolite, based on favorable amino acid interactions forming stable confirmations towards 3CLpro and PLpro enzymes, acting as a dual inhibitor.

Phylogenetic analysis of the salinipostin γ-butyrolactone gene cluster uncovers new potential for bacterial signalling-molecule diversity.

Bacteria communicate by small-molecule chemicals that facilitate intra- and inter-species interactions. These extracellular signalling molecules mediate diverse processes including virulence, bioluminescence, biofilm formation, motility and specialized metabolism. The signalling molecules produced by members of the phylum Actinobacteria generally comprise γ-butyrolactones, γ-butenolides and furans. The best-known actinomycete γ-butyrolactone is A-factor, which triggers specialized metabolism and morphological differentiation in the genus Streptomyces . Salinipostins A–K are unique γ-butyrolactone molecules with rare phosphotriester moieties that were recently characterized from the marine actinomycete genus Salinispora . The production of these compounds has been linked to the nine-gene biosynthetic gene cluster (BGC) spt. Critical to salinipostin assembly is the γ-butyrolactone synthase encoded by spt9. Here, we report the surprising distribution of spt9 homologues across 12 bacterial phyla, the majority of which are not known to produce γ-butyrolactones. Further analyses uncovered a large group of spt-like gene clusters outside of the genus Salinispora , suggesting the production of new salinipostin-like diversity. These gene clusters show evidence of horizontal transfer and location-specific recombination among Salinispora strains. The results suggest that γ-butyrolactone production may be more widespread than previously recognized. The identification of new γ-butyrolactone BGCs is the first step towards understanding the regulatory roles of the encoded small molecules in Actinobacteria.

Expansion of Gamma-Butyrolactone Signaling Molecule Biosynthesis to Phosphotriester Natural Products.

Bacterial hormones, such as the iconic gamma-butyrolactone A-factor, are essential signaling molecules that regulate diverse physiological processes, including specialized metabolism. These low molecular weight compounds are common in Streptomyces species and display species-specific structural differences. Recently, unusual gamma-butyrolactone natural products called salinipostins were isolated from the marine actinomycete genus Salinispora based on their antimalarial properties. As the salinipostins possess a rare phosphotriester motif of unknown biosynthetic origin, we set out to explore its construction by the widely conserved 9-gene spt operon in Salinispora species. We show through a series of in vivo and in vitro studies that the spt gene cluster dually encodes the salinipostins and newly identified natural A-factor-like gamma-butyrolactones (Sal-GBLs). Remarkably, homologous biosynthetic gene clusters are widely distributed among many actinomycete genera, including Streptomyces, suggesting the significance of this operon in bacteria.

Genome and metabolome mining of marine obligate Salinisporsatrains to discover new natural products.

Marine microorganisms are receiving more attention as a promising potential source of new natural products. In the present study, we performed genomic and metabolomic analyses to explore the metabolic potential of the obligate marine actinomycete genus Salinispora. The genomes of thirty Salinispora strains were prospected in search of biosynthetic gene clusters including polyketide synthase (PKS), nonribosomal peptide synthetase (NPRS), terpene, indole, lantibiotics, and siderophores. We determined considerable diversity of natural product biosynthetic gene clusters in their genome. There were a total of 1428 putative gene clusters involved in the biosynthesis of various bioactive natural products. Furthermore, 1509 ketosynthase (KS) and condensation (C) domains were detected by using NapDoS belonging to PKS and NRPS genes, respectively. Metabolic profiling was performed by a nontargeted LC-MS/MS approach combined with spectral networking using Global Natural Product Social Molecular Networking (GNPS). Dereplication and tentative identification of natural products were evaluated for common chemical properties and their associated pathways. Significant bioactive natural products such as lomaiviticin C, 7-OH-staurosporine, staurosporine, and cyanosporaside B were determined. More importantly, an unknown glycosylated compound associated with an NRPS/PKS-I hybrid gene cluster in Salinispora pacifica CNY703 was established through chemical and genomic analyses.

Use of genome-scale models to get new insights into the marine actinomycete genus Salinispora

BackgroundThere is little published regarding metabolism of Salinispora species. In continuation with efforts performed towards this goal, this study is focused on new insights into the metabolism of the three-identified species of Salinispora using constraints-based modeling. At present, only one manually curated genome-scale metabolic model (GSM) for Salinispora tropica strain CNB-440T has been built despite the role of Salinispora strains in drug discovery.ResultsHere, we updated, and expanded the scope of the model of Salinispora tropica CNB-440T, and GSMs were constructed for two sequenced type strains covering the three-identified species. We also constructed a Salinispora core model that contains the genes shared by 93 sequenced strains and a few non-conserved genes associated with essential reactions. The models predicted no auxotrophies for essential amino acids, which was corroborated experimentally using a defined minimal medium (DMM). Experimental observations suggest possible sulfur accumulation. The Core metabolic content shows that the biosynthesis of specialised metabolites is the less conserved subsystem. Sets of reactions were analyzed to explore the differences between the reconstructions. Unique reactions associated to each GSM were mainly due to genome sequence data except for the ST-CNB440 reconstruction. In this case, additional reactions were added from experimental evidence. This reveals that by reaction content the ST-CNB440 model is different from the other species models. The differences identified in reaction content between models gave rise to different functional predictions of essential nutrient usage by each species in DMM. Furthermore, models were used to evaluate in silico single gene knockouts under DMM and complex medium. Cluster analysis of these results shows that ST-CNB440, and SP-CNR114 models are more similar when considering predicted essential genes.ConclusionsModels were built for each of the three currently identified Salinispora species, and a core model representing the conserved metabolic capabilities of Salinispora was constructed. Models will allow in silico metabolism studies of Salinispora strains, and help researchers to guide and increase the production of specialised metabolites. Also, models can be used as templates to build GSMs models of closely related organisms with high biotechnology potential.

Engineering Salinispora tropica for heterologous expression of natural product biosynthetic gene clusters.

The marine actinomycete genus Salinispora is a remarkably prolific source of structurally diverse and biologically active secondary metabolites. Herein, we select the model organism Salinispora tropica CNB-440 for development as a heterologous host for the expression of biosynthetic gene clusters (BGCs) to complement well-established Streptomyces host strains. In order to create an integratable host with a clean background of secondary metabolism, we replaced three genes (salA-C) essential for salinosporamide biosynthesis with a cassette containing the Streptomyces coelicolor ΦC31 phage attachment site attB to generate the mutant S. tropica CNB-4401 via double-crossover recombination. This mutagenesis not only knocks-in the attachment site attB in the genome of S. tropica CNB-440 but also abolishes production of the salinosporamides, thereby simplifying the strain's chemical background. We validated this new heterologous host with the successful integration and expression of the thiolactomycin BGC that we recently identified in several S. pacifica strains. When compared to the extensively engineered superhost S. coelicolor M1152, the production of thiolactomycins from S. tropica CNB-4401 was approximately 3-fold higher. To the best of our knowledge, this is the first example of using a marine actinomycete as a heterologous host for natural product BGC expression. The established heterologous host may provide a useful platform to accelerate the discovery of novel natural products and engineer biosynthetic pathways.

Genomic insights into specialized metabolism in the marine actinomycete Salinispora.

Comparative genomics is providing new opportunities to address the diversity and distributions of genes encoding the biosynthesis of specialized metabolites. An analysis of 119 genome sequences representing three closely related species of the marine actinomycete genus Salinispora reveals extraordinary biosynthetic diversity in the form of 176 distinct biosynthetic gene clusters (BGCs) of which only 24 have been linked to their products. Remarkably, more than half of the BGCs were observed in only one or two strains, suggesting they were acquired relatively recently in the evolutionary history of the genus. These acquired gene clusters are concentrated in specific genomic islands, which represent hot spots for BGC acquisition. While most BGCs are stable in terms of their chromosomal position, others migrated to different locations or were exchanged with unrelated gene clusters suggesting a plug and play type model of evolution that provides a mechanism to test the relative fitness effects of specialized metabolites. Transcriptome analyses were used to address the relationships between BGC abundance, chromosomal position and product discovery. The results indicate that recently acquired BGCs can be functional and that complex evolutionary processes shape the micro-diversity of specialized metabolism observed in closely related environmental bacteria.

The marine actinomycete genus Salinispora: a model organism for secondary metabolite discovery.

This review covers the initial discovery of the marine actinomycete genus Salinispora through its development as a model for natural product research. A focus is placed on the novel chemical structures reported with reference to their biological activities and the synthetic and biosynthetic studies they have inspired. The time line of discoveries progresses from more traditional bioassay-guided approaches through the application of genome mining and genetic engineering techniques that target the products of specific biosynthetic gene clusters. This overview exemplifies the extraordinary biosynthetic diversity that can emanate from a narrowly defined genus and supports future efforts to explore marine taxa in the search for novel natural products.

Sioxanthin, a novel glycosylated carotenoid, reveals an unusual subclustered biosynthetic pathway.

Members of the marine actinomycete genus Salinispora constitutively produce a characteristic orange pigment during vegetative growth. Contrary to the understanding of widespread carotenoid biosynthesis pathways in bacteria, Salinispora carotenoid biosynthesis genes are not confined to a single cluster. Instead, bioinformatic and genetic investigations confirm that four regions of the Salinispora tropica CNB-440 genome, consisting of two gene clusters and two independent genes, contribute to the in vivo production of a single carotenoid. This compound, namely (2'S)-1'-(β-D-glucopyranosyloxy)-3',4'-didehydro-1',2'-dihydro-φ,ψ-caroten-2'-ol, is novel and has been given the trivial name 'sioxanthin'. Sioxanthin is a C40 -carotenoid, glycosylated on one end of the molecule and containing an aryl moiety on the opposite end. Glycosylation is unusual among actinomycete carotenoids, and sioxanthin joins a rare group of carotenoids with polar and non-polar head groups. Gene sequence homology predicts that the sioxanthin biosynthetic pathway is present in all of the Salinispora as well as other members of the family Micromonosporaceae. Additionally, this study's investigations of clustering of carotenoid biosynthetic genes in heterotrophic bacteria show that a non-clustered genome arrangement is more common than previously suggested, with nearly half of the investigated genomes showing a non-clustered architecture.

Direct capture and heterologous expression of Salinispora natural product genes for the biosynthesis of enterocin.

Heterologous expression of secondary metabolic pathways is a promising approach for the discovery and characterization of bioactive natural products. Herein we report the first heterologous expression of a natural product from the model marine actinomycete genus Salinispora. Using the recently developed method of yeast-mediated transformation-associated recombination for natural product gene clusters, we captured a type II polyketide synthase pathway from Salinispora pacifica with high homology to the enterocin pathway from Streptomyces maritimus and successfully produced enterocin in two different Streptomyces host strains. This result paves the way for the systematic interrogation of Salinispora’s promising secondary metabolome.

Targeted search for actinomycetes from nearshore and deep-sea marine sediments

Sediment samples collected off the coast of San Diego were analyzed for actinomycete diversity using culture-independent techniques. Eight new operational taxonomic units (OTUs) in the Streptomycetaceae were identified as well as new diversity within previously cultured marine OTUs. Sequences belonging to the marine actinomycete genus Salinispora were also detected, despite the fact that this genus has only been reported from more tropical environments. Independent analyses of marine sediments from the Canary Basin (3814m) and the South Pacific Gyre (5126 and 5699m) also revealed Salinispora sequences providing further support for the occurrence of this genus in deep-sea sediments. Efforts to culture Salinispora spp. from these samples have yet to be successful. This is the first report of Salinispora spp. from marine sediments >1100m and suggests that the distribution of this genus is broader than previously believed.

Comparative genomics reveals evidence of marine adaptation in Salinispora species

BackgroundActinobacteria represent a consistent component of most marine bacterial communities yet little is known about the mechanisms by which these Gram-positive bacteria adapt to life in the marine environment. Here we employed a phylogenomic approach to identify marine adaptation genes in marine Actinobacteria. The focus was on the obligate marine actinomycete genus Salinispora and the identification of marine adaptation genes that have been acquired from other marine bacteria.ResultsFunctional annotation, comparative genomics, and evidence of a shared evolutionary history with bacteria from hyperosmotic environments were used to identify a pool of more than 50 marine adaptation genes. An Actinobacterial species tree was used to infer the likelihood of gene gain or loss in accounting for the distribution of each gene. Acquired marine adaptation genes were associated with electron transport, sodium and ABC transporters, and channels and pores. In addition, the loss of a mechanosensitive channel gene appears to have played a major role in the inability of Salinispora strains to grow following transfer to low osmotic strength media.ConclusionsThe marine Actinobacteria for which genome sequences are available are broadly distributed throughout the Actinobacterial phylogenetic tree and closely related to non-marine forms suggesting they have been independently introduced relatively recently into the marine environment. It appears that the acquisition of transporters in Salinispora spp. represents a major marine adaptation while gene loss is proposed to play a role in the inability of this genus to survive outside of the marine environment. This study reveals fundamental differences between marine adaptations in Gram-positive and Gram-negative bacteria and no common genetic basis for marine adaptation among the Actinobacteria analyzed.

Exploration and engineering of biosynthetic pathways in the marine actinomycete Salinispora tropica

Abstract In recent years, members of the marine actinomycete genus Salinispora have proven to be a precious source of structurally diverse secondary metabolites, including the potent anticancer agent salinosporamide A and the enediyne-derived sporolides. The tremendous potential of these marine-dwelling microbes for natural products biosynthesis, however, was not fully realized until sequencing of the Salinispora tropica genome revealed the presence of numerous orphan biosynthetic loci besides a plethora of rare metabolic pathways. This contribution summarizes the biochemical exploration of this prolific organism, highlighting studies in which genome-based information was exploited for the discovery of new enzymatic processes and the engineering of unnatural natural products. Inactivation of key genes within the salinosporamide pathway has expanded its inherent metabolic plasticity and enabled access to various salinosporamide derivatives by mutasynthesis. New insights into the biosynthesis of the sporolides allowed us to increase production titers of these structurally complex molecules, thereby providing the means to search for the DNA cleaving presporolide enediyne.

Cyanosporasides A and B, Chloro- and Cyano-cyclopenta[a]indene Glycosides from the Marine Actinomycete “Salinispora pacifica”

[structure: see text] Two structurally novel cyclopenta[a]indene glycosides, cyanosporasides A and B (1 and 2) have been isolated from the culture broth of a new species of the obligate marine actinomycete genus Salinispora. The structures and absolute stereochemistries of these compounds were determined by spectral and chemical methods. The cyanosporasides possess a new 3-keto-pyranohexose sugar as well as a cyano- and chloro-substituted cyclopenta[a]indene ring system. The cyanosporasides are proposed to be cyclization products of an enediyne precursor.