Metabolites Of Actinobacteria Research Articles

Bioprospecting of Metabolites from Actinomycetes and their Applications.

Actinomycetes are present in various terrestrial and aquatic habitats, predominantly in the soil rhizosphere, encompassing marine and freshwater ecosystems. These microorganisms exhibit characteristics that resemble both bacteria and fungi. Numerous actinomycetes exhibit a mycelial existence and undergo significant morphological transformations. These bacteria are widely recognized as biotechnologically significant microorganisms utilized for the production of secondary metabolites. In all, over 45% of all bioactive microbial metabolites are produced by actinomycetes, which are responsible for producing around 10,000 of them. The majority of actinomycetes exhibit substantial saprophytic characteristics in their natural environment, enabling them to effectively decompose a diverse range of plant and animal waste materials during the process of decomposition. Additionally, these organisms possess a sophisticated secondary metabolic system, which enables them to synthesize almost two-thirds of all naturally occurring antibiotics. Moreover, they can create a diverse array of chemical compounds with medical or agricultural applications, including anticancer, antiparasitic, and antibacterial agents. This review aims to provide an overview of the prominent biotechnological domains in which actinobacteria and their metabolites demonstrate noteworthy applicability. The graphical abstract provides a preview of the primary sections covered in this review. This paper presents a comprehensive examination of the biotechnological applications and metabolites of actinobacteria, highlighting their potential for patent innovations.

Engineering the TetR-family transcriptional regulator XNR_0706 to enhance heterologous spinosad production in Streptomyces albus B4 chassis

The TetR family of regulators are an important group of transcription regulators that regulate diverse cellular processes in prokaryotes. In this study, we found that XNR_0706, a TetR family regulator, controlled the expression of XNR_0345, XNR_0454, XNR_0513 and XNR_1438 putatively involved in fatty acid β-oxidation by interacting with the promoter regions in Streptomyces albus B4. The transcription level of these four genes was downregulated in XNR_0706 deletion strain (ΔXNR_0706) and restored by XNR_0706 complementation in Δ0706/pIB-0706, demonstrating that XNR_0706 was a positive transcriptional regulator of the genes. With toxic long-chain fatty acids addition in TSB media, deletion of XNR_0706 caused significantly poor growth, whereas XNR_0706 complementation increased the utilization of additional fatty acids, resulting in restored growth. Fatty acid β-oxidation is one source of acetyl- and malonyl-CoA precursors for polyketides biosynthesis in actinobacteria. Overexpression of XNR_0706 in B4/spnNEW, a spinosad heterologous expression strain derived from S. albus B4, increased spinosad yield by 20.6 %. Additionally, supplement of 0.3 g/L fatty acids resulted in a further 42.4 % increase in spinosad yield. Our study reveals a regulatory mechanism in long-chain fatty acids metabolism in S. albus and these insights into the molecular regulation of β-oxidation by XNR_0706 are instrumental for increasing secondary metabolites in actinobacteria.

Roles of LuxR-family regulators in the biosynthesis of secondary metabolites in Actinobacteria.

Actinobacteria are well-known Gram-positive bacteria that produce approximately two-thirds of microbial bioactive natural products (NPs) through secondary metabolism. Usually, genes involved in the biosynthesis of NPs in actinobacteria are clustered, and their expression is regulated by an elaborate and stringent regulatory network formed by diverse regulators. These regulators can be classified into more than 50 superfamilies/families according to conserved amino acid sequences and biological functions. Among them, LuxR family regulators, which are widely distributed in microorganisms and feature an HTH_LUXR domain (PFAM00196, SMART00421), play key roles in quorum sensing (QS), bioluminescence, virulence and secondary metabolism. In this mini-review, we focus on their roles in regulating NP production in actinobacteria. First, the domain architecture and classification of LuxR proteins are summarized on the basis of their size and biological function diversity. Second, the landscape of the roles and action mechanism of LuxR regulators involved in NP production in actinobacteria is presented in detail. Finally, the application of LuxR is described from two perspectives: enhancement of NP production and discovery of novel NPs by engineering LuxR. This mini-review will help us comprehensively understand the role of LuxR in actinobacteria and promote the future application of LuxR family regulators in synthetic biology.

Study on a two-component signal transduction system RimA1A2 that negatively regulates oxytetracycline biosynthesis in Streptomyces rimosus M4018

Biosynthesis of secondary metabolites in actinobacteria is regulated by complex regulatory mechanisms on responding environmental changes. In this study, we have identified a two-component system (TCS) designated as RimA1A2 in the genome of Streptomyces rimosus M4018, with high homology to the TCS RapA1A2 from Streptomyces coelicolor, known for its positive regulatory function towards actinorhodin (ACT) biosynthesis. Using RT-PCR analysis, we demonstrate that rimA1 encodes response regulator (RR) and rimA2 encoding histidine kinase (HK) from S. rimosus that are co-transcribed as a single-polycistronic mRNA. When S. rimosus was cultivated on standard media, no significant difference in culture growth or morphological properties was observed between the rimA1-disrupted mutant and parent strain M4018. However, the rimA1-disrupted strain displayed significant increase in oxytetracycline (OTC) titer when cultivated in minimal medium (MM) containing glycine as sole nitrogen source, and the transcription of selected genes involved in OTC biosynthesis was increased, supporting the hypothesis that RimA1A2 has a negative regulatory role in OTC biosynthesis via global regulation. We observed an increased resistance of the rimA1-disrupted mutant strain to selected antibiotics. Interestingly, in the rimA1-disrupted strain, OTC biosynthesis was affected under different environmental stress conditions such as osmotic and oxidative stress. Accordingly, this phenotype was observed in a medium-dependent manner. Considering complexity of regulatory networks in antibiotic-producing organisms, this study demonstrates the importance of cultivation conditions, which is often neglected.

Secondary metabolites overproduction through transcriptional gene cluster refactoring

We present a random rational approach enabling the construction of overproducing strains in two steps. The approach first involves creating a library of clusters of interest, in which native promoters are substituted with randomly generated constitutive synthetic promoters, and then expressing this library in an appropriate host strain. This strategy is fast, easy to use, accounts for the architecture of a cluster and completely decouples the expression of a gene cluster from complex native regulatory networks. The strategy was applied to improve the production of a macrocyclic peptide, bottromycin, which possesses antibacterial activity against multidrug-resistant bacteria and is a blueprint for a new class of antibacterials. We successfully optimized the expression of genes in operons and created several variants of the bottromycin gene cluster that provide 5–50 fold higher titres of bottromycin than the natural one, thus resulting in the identification of several new bottromycin derivatives not previously described. Moreover, due to the higher bottromycin yield, bottromycin derivatization was performed via the biosynthetic engineering of the gene cluster. The abovementioned features make this generic strategy a promising tool for the overproduction of known secondary metabolites and the activation of silent secondary metabolites in Actinobacteria.

Regulation of specialised metabolites in Actinobacteria- expanding the paradigms.

SummaryThe increase in availability of actinobacterial whole genome sequences has revealed huge numbers of specialised metabolite biosynthetic gene clusters, encoding a range of bioactive molecules such as antibiotics, antifungals, immunosuppressives and anticancer agents. Yet the majority of these clusters are not expressed under standard laboratory conditions in rich media. Emerging data from studies of specialised metabolite biosynthesis suggest that the diversity of regulatory mechanisms is greater than previously thought and these act at multiple levels, through a range of signals such as nutrient limitation, intercellular signalling and competition with other organisms. Understanding the regulation and environmental cues that lead to the production of these compounds allows us to identify the role that these compounds play in their natural habitat as well as provide tools to exploit this untapped source of specialised metabolites for therapeutic uses. Here, we provide an overview of novel regulatory mechanisms that act in physiological, global and cluster‐specific regulatory manners on biosynthetic pathways in Actinobacteria and consider these alongside their ecological and evolutionary implications.