Genome sequence of the Spinosyns-producing bacterium Saccharopolyspora spinosa NRRL 18395

Flaviolin-Like Gene Cluster Deletion Optimized the Butenyl-Spinosyn Biosynthesis Route in Saccharopolyspora pogona

Reduction and optimization of the microbial genome is an important strategy for constructing synthetic biological chassis cells and overcoming obstacles in natural product discovery and production. However, it is of great challenge to discover target genes that can be deleted and optimized due to the complicated genome of actinomycetes. Saccharopolyspora pogona can produce butenyl-spinosyn during aerobic fermentation, and its genome contains 32 different gene clusters. This suggests that there is a large amount of potential competitive metabolism in S. pogona, which affects the biosynthesis of butenyl-spinosyn. By analyzing the genome of S. pogona, six polyketide gene clusters were identified. From those, the complete deletion of clu13, a flaviolin-like gene cluster, generated a high butenyl-spinosyn-producing strain. Production of this strain was 4.06-fold higher than that of the wildtype strain. Transcriptome profiling revealed that butenyl-spinosyn biosynthesis was not primarily induced by the polyketide synthase RppA-like but was related to hypothetical protein Sp1764. However, the repression of sp1764 was not enough to explain the enormous enhancement of butenyl-spinosyn yields in S. pogona-Δclu13. After the comparative proteomic analysis of S. pogona-Δclu13 and S. pogona, two proteins, biotin carboxyl carrier protein (BccA) and response regulator (Reg), were investigated, whose overexpression led to great advantages of butenyl-spinosyn biosynthesis. In this way, we successfully discovered three key genes that obviously optimize the biosynthesis of butenyl-spinosyn. Gene cluster simplification performed in conjunction with multiomics analysis is of great practical significance for screening dominant chassis strains and optimizing secondary metabolism. This work provided an idea about screening key factors and efficient construction of production strains.

Comparative transcriptomic analysis of two Saccharopolyspora spinosa strains reveals the relationships between primary metabolism and spinosad production

Saccharopolyspora spinosa is a well-known actinomycete for producing the secondary metabolites, spinosad, which is a potent insecticides possessing both efficiency and safety. In the previous researches, great efforts, including physical mutagenesis, fermentation optimization, genetic manipulation and other methods, have been employed to increase the yield of spinosad to hundreds of folds from the low-yield strain. However, the metabolic network in S. spinosa still remained un-revealed. In this study, two S. spinosa strains with different spinosad production capability were fermented and sampled at three fermentation periods. Then the total RNA of these samples was isolated and sequenced to construct the transcriptome libraries. Through transcriptomic analysis, large numbers of differentially expressed genes were identified and classified according to their different functions. According to the results, spnI and spnP were suggested as the bottleneck during spinosad biosynthesis. Primary metabolic pathways such as carbon metabolic pathways exhibited close relationship with spinosad formation, as pyruvate and phosphoenolpyruvic acid were suggested to accumulate in spinosad high-yield strain during fermentation. The addition of soybean oil in the fermentation medium activated the lipid metabolism pathway, enhancing spinosad production. Glutamic acid and aspartic acid were suggested to be the most important amino acids and might participate in spinosad biosynthesis.

Synthetic biology, genome mining, and combinatorial biosynthesis of NRPS-derived antibiotics: a perspective

Combinatorial biosynthesis of novel secondary metabolites derived from nonribosomal peptide synthetases (NRPSs) has been in slow development for about a quarter of a century. Progress has been hampered by the complexity of the giant multimodular multienzymes. More recently, advances have been made on understanding the chemical and structural biology of these complex megaenzymes, and on learning the design rules for engineering functional hybrid enzymes. In this perspective, I address what has been learned about successful engineering of complex lipopeptides related to daptomycin, and discuss how synthetic biology and microbial genome mining can converge to broaden the scope and enhance the speed and robustness of combinatorial biosynthesis of NRPS-derived natural products for drug discovery.

Analysis of nucleotide diphosphate sugar dehydrogenases reveals family and group-specific relationships

UDP‐glucose dehydrogenase (UDPGDH), UDP‐N‐acetyl‐mannosamine dehydrogenase (UDPNAMDH) and GDP‐mannose dehydrogenase (GDPMDH) belong to a family of NAD⁺‐linked 4‐electron‐transfering oxidoreductases called nucleotide diphosphate sugar dehydrogenases (NDP‐SDHs). UDPGDH is an enzyme responsible for converting UDP‐d‐glucose to UDP‐d‐glucuronic acid, a product that has different roles depending on the organism in which it is found. UDPNAMDH and GDPMDH convert UDP‐N‐acetyl‐mannosamine to UDP‐N‐acetyl‐mannosaminuronic acid and GDP‐mannose to GDP‐mannuronic acid, respectively, by a similar mechanism to UDPGDH. Their products are used as essential building blocks for the exopolysaccharides found in organisms like Pseudomonas aeruginosa and Staphylococcus aureus. Few studies have investigated the relationships between these enzymes. This study reveals the relationships between the three enzymes by analysing 229 amino acid sequences. Eighteen invariant and several other highly conserved residues were identified, each serving critical roles in maintaining enzyme structure, coenzyme binding or catalytic function. Also, 10 conserved motifs that included most of the conserved residues were identified and their roles proposed. A phylogenetic tree demonstrated relationships between each group and verified group assignment. Finally, group entropy analysis identified novel conservations unique to each NDP‐SDH group, including residue positions critical to NDP‐sugar substrate interaction, enzyme structure and intersubunit contact. These positions may serve as targets for future research.

Enzymes

UDP‐glucose dehydrogenase (UDPGDH, EC 1.1.1.22).

Genetic manipulation of secondary metabolite biosynthesis for improved production in Streptomyces and other actinomycetes

Actinomycetes continue to be important sources for the discovery of secondary metabolites for applications in human medicine, animal health, and crop protection. With the maturation of actinomycete genome mining as a robust approach to identify new and novel cryptic secondary metabolite gene clusters, it is critical to continue developing methods to activate and enhance secondary metabolite biosynthesis for discovery, development, and large-scale manufacturing. This review covers recent reports on promising new approaches and further validations or technical improvements of existing approaches to strain improvement applicable to a wide range of Streptomyces species and other actinomycetes.

Mangrove rare actinobacteria: taxonomy, natural compound, and discovery of bioactivity

Actinobacteria are one of the most important and efficient groups of natural metabolite producers. The genus Streptomyces have been recognized as prolific producers of useful natural compounds as they produced more than half of the naturally-occurring antibiotics isolated to-date and continue as the primary source of new bioactive compounds. Lately, Streptomyces groups isolated from different environments produced the same types of compound, possibly due to frequent genetic exchanges between species. As a result, there is a dramatic increase in demand to look for new compounds which have pharmacological properties from another group of Actinobacteria, known as rare actinobacteria; which is isolated from special environments such as mangrove. Recently, mangrove ecosystem is becoming a hot spot for studies of bioactivities and the discovery of natural products. Many novel compounds discovered from the novel rare actinobacteria have been proven as potential new drugs in medical and pharmaceutical industries such as antibiotics, antimicrobials, antibacterials, anticancer, and antifungals. This review article highlights the latest studies on the discovery of natural compounds from the novel mangrove rare actinobacteria and provides insight on the impact of these findings.

Phylogenetic relatedness determined between antibiotic resistance and 16S rRNA genes in actinobacteria

BACKGROUND

Distribution and evolutionary history of resistance genes in environmental actinobacteria provide information on intensity of antibiosis and evolution of specific secondary metabolic pathways at a given site. To this day, actinobacteria producing biologically active compounds were isolated mostly from soil but only a limited range of soil environments were commonly sampled. Consequently, soil remains an unexplored environment in search for novel producers and related evolutionary questions.

RESULTS

Ninety actinobacteria strains isolated at contrasting soil sites were characterized phylogenetically by 16S rRNA gene, for presence of erm and ABC transporter resistance genes and antibiotic production. An analogous analysis was performed in silico with 246 and 31 strains from Integrated Microbial Genomes (JGI_IMG) database selected by the presence of ABC transporter genes and erm genes, respectively. In the isolates, distances of erm gene sequences were significantly correlated to phylogenetic distances based on 16S rRNA genes, while ABC transporter gene distances were not. The phylogenetic distance of isolates was significantly correlated to soil pH and organic matter content of isolation sites. In the analysis of JGI_IMG datasets the correlation between phylogeny of resistance genes and the strain phylogeny based on 16S rRNA genes or five housekeeping genes was observed for both the erm genes and ABC transporter genes in both actinobacteria and streptomycetes. However, in the analysis of sequences from genomes where both resistance genes occurred together the correlation was observed for both ABC transporter and erm genes in actinobacteria but in streptomycetes only in the erm gene.

CONCLUSIONS

The type of erm resistance gene sequences was influenced by linkage to 16S rRNA gene sequences and site characteristics. The phylogeny of ABC transporter gene was correlated to 16S rRNA genes mainly above the genus level. The results support the concept of new specific secondary metabolite scaffolds occurring more likely in taxonomically distant producers but suggest that the antibiotic selection of gene pools is also influenced by site conditions.

Draft Genome Sequence of Insecticidal Streptomyces sp. Strain PCS3-D2, Isolated from Mangrove Soil in Philippines

A draft genome sequence of a Streptomyces sp. isolated from mangrove soil in Cebu, Philippines, is described here. This isolate produced compounds with contact insecticidal activity against important corn pests. The genome contains 7,479,793 bp (in 27 scaffolds), 6,297 predicted genes, and 29 secondary metabolite biosynthetic gene clusters.

Genome-scale metabolic network reconstruction of Saccharopolyspora spinosa for spinosad production improvement

BACKGROUND

Spinosad is a macrolide antibiotic produced by Saccharopolyspora spinosa with aerobic fermentation. However, the wild strain has a low productivity. In this article, a computational guided engineering approach was adopted in order to improve the yield of spinosad in S. spinosa.

RESULTS

Firstly, a genome-scale metabolic network reconstruction (GSMR) for S.spinosa based on its genome information, literature data and experimental data was established. The model was consists of 1,577 reactions, 1,726 metabolites, and 733 enzymes after manually refined. Then, amino acids supplying experiments were performed in order to test the capabilities of the model, and the results showed a high consistency. Subsequently, transhydrogenase (PntAB, EC 1.6.1.2) was chosen as the potential target for spinosad yield improvement based on the in silico metabolic network models. Furthermore, the target gene was manipulated in the parent strain in order to validate the model predictions. At last, shake flask fermentation was carried out which led to spinosad production of 75.32 mg/L, 86.5% higher than the parent strain (40.39 mg/L).

CONCLUSIONS

Results confirmed the model had a high potential in engineering S. spinosa for spinosad production. It is the first GSMM for S.spinosa, it has significance for a better understanding of the comprehensive metabolism and guiding strain designing of Saccharopolyspora spinosa in the future.

Differential proteomic profiling reveals regulatory proteins and novel links between primary metabolism and spinosad production in Saccharopolyspora spinosa

Background

Saccharopolyspora spinosa is an important producer of antibiotic spinosad with clarified biosynthesis pathway but its complex regulation networks associated with primary metabolism and secondary metabolites production almost have never been concerned or studied before. The proteomic analysis of a novel Saccharopolyspora spinosa CCTCC M206084 was performed and aimed to provide a global profile of regulatory proteins.

Results

Two-dimensional-liquid chromatography-tandem mass spectrometry (LC-MS/MS) identified 1090, 1166, 701, and 509 proteins from four phases respectively, i.e., the logarithmic growth phase (T1), early stationary phase (T2), late stationary phase (T3), and decline phase (T4). Among the identified proteins, 1579 were unique to the S. spinosa proteome, including almost all the enzymes for spinosad biosynthesis. Trends in protein expression over the various time phases were deduced from using the modified protein abundance index (PAI), revealed the importance of stress pathway proteins and other global regulatory network proteins during spinosad biosynthesis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis followed by one-dimensional LC-MS/MS identification revealed similar trend of protein expression from four phases with the results of semi-quantification by PAI. qRT-PCR analysis revealed that 6 different expressed genes showed a positive correlation between changes at translational and transcriptional expression level. Expression of three proteins that likely promote spinosad biosynthesis, namely, 5-methyltetrahydropteroyltriglutamate-homocysteine S-methyltransferase (MHSM), glutamine synthetase (GS) and cyclic nucleotide-binding domain-containing protein (CNDP) was validated by western blot, which confirmed the results of proteomic analysis.

Conclusions

This study is the first systematic analysis of the S. spinosa proteome during fermentation and its valuable proteomic data of regulatory proteins may be used to enhance the production yield of spinosad in future studies.

Draft Genome Sequence of Saccharopolyspora rectivirgula

We have sequenced the genome of Saccharopolyspora rectivirgula, the causative agent of farmer’s lung disease. The draft genome consists of 182 contigs totaling 3,977,051 bp, with a GC content of 68.9%.