Transaminases are a class of enzymes that catalyze the transfer of amino between amino acids and keto acids, playing an important role in the biosynthesis of organic amines and the corresponding derivatives. However, natural enzymes often have low catalytic efficiency against non-natural substrates, which limits their widespread applications. Enzyme engineering serves as an effective approach to improve the catalytic properties and thereby expand the application scope of transaminases. In this study, a high-throughput screening method for transaminases was established based on the fluorescent color reaction between methoxy-2-aminobenzoxime (PMA) and ketones. According to the changes in fluorescence intensity, the concentration changes of ketones could be easily monitored. The efficiency, sensitivity, and accuracy of the screening method were improved by optimization of the system. With 4-hydroxy-2-butanone as the substrate, the mutant library of the transaminase from Actinobacteria sp. was established and a mutant with increased activity was successfully obtained, which improved the production efficiency of (R)-3-aminobutanol by enzyme-catalyzed synthesis. This study laid an important foundation for efficient screening, modification, and application of transaminase.
Transaminases/metabolism* ; Fluorescent Dyes/chemistry* ; High-Throughput Screening Assays/methods* ; Ketones/metabolism* ; Actinobacteria/enzymology*

Actinomycetes are important producers of high-value natural products, and the engineering of actinomycetes to enhance the biosynthesis of target natural products has long been a hot research topic in the scientific community. However, non-rational engineering methods suffer from low beneficial mutation rates, which limit the efficiency of mutant screening. The integration of high-throughput screening (HTS) technologies can effectively enhance the screening efficiency of elite mutants and significantly shorten the cycle of actinomycete strain engineering. This review comprehensively discusses various HTS technologies suitable for the engineering of actinomycete strains and compares them in terms of application scenarios, advantages, and disadvantages. HTS technologies include microplate-based screening, antimicrobial activity screening, antibiotic resistance screening, fluorescence-activated cell sorting (FACS), and fluorescence-activated droplet sorting (FADS). Additionally, this review summarizes the applications of these technologies in assisting actinomycete strain engineering and enhancing the yields of target compounds. The development and application of HTS technologies have not only facilitated the exploration of natural product resources in actinomycetes but also provided strong support for the rapid and efficient construction of high-performance engineered actinomycete strains.
Actinobacteria/metabolism* ; High-Throughput Screening Assays/methods* ; Genetic Engineering/methods* ; Biological Products/metabolism* ; Flow Cytometry ; Metabolic Engineering/methods*

Cyclodipeptide (CDP) composed of two amino acids is the simplest cyclic peptide. These two amino acids form a typical diketopiperazine (DKP) ring by linking each other with peptide bonds. This characteristic stable ring skeleton is the foundation of CDP to display extensive and excellent bioactivities, which is beneficial for CDPs' pharmaceutical research and development. The natural CDP products are well isolated from actinomycetes. These bacteria can synthesize DKP backbones with nonribosomal peptide synthetase (NRPS) or cyclodipeptide synthase (CDPS). Moreover, actinomycetes could produce a variety of CDPs through different enzymatic modification. The presence of these abundant and diversified catalysis indicates that actinomycetes are promising microbial resource for exploring CDPs. This review summarized the pathways for DKP backbones biosynthesis and their post-modification mechanism in actinomycetes. The aim of this review was to accelerate the genome mining of CDPs and their isolation, purification and structure identification, and to facilitate revealing the biosynthesis mechanism of novel CDPs as well as their synthetic biology design.
Actinobacteria/metabolism* ; Actinomyces/metabolism* ; Biological Products/metabolism* ; Bacteria/metabolism* ; Diketopiperazines/metabolism* ; Amino Acids

Ribosomal engineering is a technique that can improve the biosynthesis of secondary metabolites in the antibiotics-resistant mutants by attacking the bacterial RNA polymerase or ribosome units using the corresponding antibiotics. Ribosomal engineering can be used to discover and increase the production of valuable bioactive secondary metabolites from almost all actinomycetes strains regardless of their genetic accessibility. As a consequence, ribosomal engineering has been widely applied to genome mining and production optimization of secondary metabolites in actinomycetes. To date, more than a dozen of new molecules were discovered and production of approximately 30 secondary metabolites were enhanced using actinomycetes mutant strains generated by ribosomal engineering. This review summarized the mechanism, development, and protocol of ribosomal engineering, highlighting the application of ribosomal engineering in actinomycetes, with the aim to facilitate future development of ribosomal engineering and discovery of actinomycetes secondary metabolites.
Actinobacteria/metabolism* ; Actinomyces/genetics* ; Anti-Bacterial Agents/metabolism* ; Multigene Family ; Ribosomes/genetics*

Aims: The objective of this study was to analyze the genome of endophytic actinomycete associated with orchids and evaluate its plant hormone activities, including phytohormone, siderophore, ammonia production, zinc and phosphate solubilization. Methodology and results: Strain DR1-2 isolated from the roots of the Thai orchid, Dendrobium christyanum Rchb.f., was closely related to Pseudonocardia alni DSM 44104T, P. antarctica DSM 44749T and P. carboxydivorans Y8T (99.93-100% similarity) based 16S rRNA gene sequence. This strain exhibited IAA production (294.10 ± 12.17 μg/mL), phosphate solubilization (2.20 ± 0.08 solubilization Index, SI), positive for siderophore production and ammonia production (36.99 ± 2.24 μg/mL). It showed a maximum IAA of 489.73 ± 8.90 μg/mL, when optimized using 0.5% Ltryptophan, pH 6 and incubated at 30 °C for 7 days. The IAA of strain enhanced the root length, shoot length, number of roots and fresh weight of rice seedlings (Oryza sativa L. cv. RD49). The draft genome of strain DR1-2 was 6,077,423 bp in 23 contigs with G+C content of 74.6%. The average nucleotide identity-Blast (ANIb) and average nucleotide identity-MUMmer (ANIm) values of strain DR1-2 and related type strains were 95.81 to 97.25% and the digital DNA-DNA hybridization (dDDH) values were 72.60 to 74.00%, respectively. Genomic analysis of strain DR1-2 revealed that the gene encodes the enzyme involved in the phytohormones biosynthesis and gene clusters involved in the biosynthesis of bioactive metabolites. Conclusion, significance and impact of study Endophytic actinomycete, Pseudonocardia strain DR1-2 from Thai orchid, D. christyanum Rchb.f., exhibited significant IAA production and affected the growth of the plant, which was the potential source of plant hormones for agricultural applications.
Endophytes ; Actinobacteria ; Pseudonocardia

Aims: The marine actinomycetes are a rich source of novel bioactive molecules. Especially the exotic tropical marine habitat of the Kerala coastal region favours the actinomycete diversity. The present study focuses on the isolation, purification and morphological characterization of marine actinomycetes for the discovery of new bioactive compounds. Methodology and results: A total of 280 morphologically distinct actinomycetes were isolated from marine soil and sediments of 10 different isolation sites located along the coastal region of Thiruvananthapuram district, Kerala, India using standard microbiological techniques. The physicochemical analysis of the soil samples collected from different stations was also done. Conclusion, significance and impact of study Even though the soil/sediment samples were collected from geographically nearby places, the physicochemical parameters showed a significant variation. This may be one of the factors which may trigger the actinomycete diversity in these regions. The diversity of actinomycetes prevalent in this region could serve as a potential source for the discovery of novel biomolecules.
Actinobacteria ; Soil ; Chemical Phenomena

To investigate the effect of Polygonum multiflorum-Andrographis paniculata intercropping system on rhizosphere soil actinomycetes of P. multiflorum, the community structure and diversity of soil actinomycetes were studied by using the original soil as the control group and the rhizosphere soil actinomycetes communities of P. multiflorum under monoculture and intercropping systems as the experimental group. In this study 655 221 effective sequences were obtained with an average length of 408 bp. OTU coverage and rarefaction curve showed that the sequencing could represent the real situation of soil actinomycetes. According to the results of alpha diversity analysis, the diversity soil actinomycetes varied as follows: original soil>intercropping soil>monoculture soil. The soil actinomycetes community structure and the relative abundance of dominant genera were significantly changed by both monoculture and intercropping, especially monoculture. OTU clustering and PCA analysis of soil samples showed that all the soil samples were divided into three distinct groups and the original soil was more similar to intercropping soil. In addition, intercropping increased the relative abundance of some beneficial actinomyces, such as Kitasatospora and Mycobacterium, which was beneficial to maintain soil health and reduce the occurrence of soil-borne diseases. The results show that, P. multiflorum-A. paniculata intercropping reduced the change of community structure and the decrease of diversity of soil actinomycetes caused by P. multiflorum monoculture, and made the actinomycete community in rhizosphere soil of P. multiflorum close to the original soil.
Actinobacteria ; Actinomyces ; Agriculture ; Andrographis ; Fallopia multiflora ; Rhizosphere ; Soil ; Soil Microbiology

Two-hundred and fifty-five strains of actinomycetes isolated from soil samples were screened for their antagonistic activities against four well-known wood decay fungi (WDF), including a brown rot fungus, Gloeophyllum trabeum and three white rot fungi Donkioporia expansa, Trametes versicolor, and Schizophyllum commune. A dual culture assay using culture media supplemented with heated or unheated culture filtrates of selected bacterial strains was used for the detection of their antimicrobial activity against four WDF. It was shown that Streptomyces atratus, S. tsukiyonensis, and Streptomyces sp. greatly inhibited the mycelial growth of the WDF tested compared with the control. To evaluate the biocontrol efficacy of S. atratus, S. tsukiyonensis, and Streptomyces sp., wood blocks of Pinus densiflora inoculated with three selected Streptomyces isolates were tested for weight loss, compression strength (perpendicular or parallel to the grain), bending strength, and chemical component changes. Of these three isolates used, Streptomyces sp. exhibited higher inhibitory activity against WDF, especially G. trabeum, as observed in mechanical and chemical change analyses. Scanning electron microscopy showed that cell walls of the wood block treated with Streptomyces strains were thicker and collapsed to a lesser extent than those of the non-treated control. Taken together, our findings indicate that Streptomyces sp. exhibits the potential to be used as a biocontrol agent for wood decay brown rot fungus that causes severe damage to coniferous woods.
Actinobacteria ; Cell Wall ; Coniferophyta ; Culture Media ; Fungi* ; Hot Temperature ; Mass Screening* ; Microscopy, Electron, Scanning ; Pinus ; Schizophyllum ; Soil ; Streptomyces* ; Trametes ; Weight Loss ; Wood*

In this study, Paeonia suffruticosa roots and rhizospheric soil in five geographic regions which were harvested in October were utilized as experimental materials, then the diversity of endophytic and rhizospheric actinomycetes were investigated by High-throughput sequencing technique. The 1 754 operational taxonomic units (OTUs) were obtained from 129 954 high quality sequences, 1 311 OTUs were detected in rhizospheric actinomycetes and belonged to four classes, four orders, twenty-seven families and ninety-seven genera, thirty-three genera such as Ilumatobacter were found in the five regions rhizospheric soil while three genera such as Longispora were only detected in the Dao-di regions, the dominant genera were Mycobacterium, Nocardioides, Streptomyces. 443 OTUs were obtained in roots and distributed in three classes, three orders, twenty-four families and fifty genera, thirteen genera such as Cryptosporangium were found in the five regions roots while Planosporangium, Luteococcus were only detected in the Dao-di regions, the dominant genera were Nocardioides. Alpha diversity analysis showed that the Shannon and Chao1 index in rhizospheric actinomycetes in Bozhou, Tongling and Nanling region were higher than Heze and Luoyang. Based on principal co-ordinates analysis (PCoA) analysis, the rhizospheric actinomycetes formations were similar in Tongling and Nanling region, at the same in Tongling and Luoyang endophytic actinomycetes. According to heatmap analysis, Bozhou, Tongling and Nanling region rhizospheric actinomycetes showed a close similarity in actinomycetes community structures on phylogenetic analysis, while Tongling, Luoyang and Nanling endophytic actinomycetes showed the same. Our results not only suggested that the rich and diverse actinomycetes resources in P. suffruticosa roots and rhizospheric soil but also revealed rhizospheric actinomycetes in the Dao-di regions had high similarity.
Actinobacteria ; Paeonia ; Phylogeny ; Plant Roots ; Soil Microbiology

BACKGROUND/AIMS: Probiotics are expected to modify the composition of gut microbiota. We aimed to investigate the changes in the composition and diversity of gut microbiota by the administration of probiotics in healthy individuals. METHODS: Twelve healthy volunteers with age range of 30–42 years provided baseline fecal samples. Subsequently, they took commercially available probiotic capsules (a mixture for Bifidobacterium, Lactobacillus, and Enterococcus) for 4 weeks. Fecal samples were collected at 4 weeks of administration and 2 weeks after the stop of administration. Fecal microbiota was analyzed via 16S ribosomal RNA gene sequencing. RESULTS: The mean Shannon index was not significantly altered by the 4-week administration of probiotics (4.365 vs 4.556, P > 0.05). The proportion of Bacteroidetes, Actinobacteria, Firmicutes, and Proteobacteria was not significantly changed by the 4-week administration of probiotics. At the genus level, the proportions of Lactobacillus (2.138% vs 2.773%, P = 0.028) and Enterococcus (0.022% vs 2.758%, P = 0.004) significantly increased 4 weeks after the administration of probiotics, but reduced 2 weeks after the stop of administration (2.773% vs 3.292%, P = 0.064 and 2.758% vs 0.001%, P = 0.001). CONCLUSIONS: The diversity of fecal microbiota is not significantly affected by 4 weeks of probiotics administration. The proportion of fecal microbiota at the genus level is significantly altered by the administration of probiotics. However, this effect does not seem to last long, probably because of homeostasis or dietary influence.
Actinobacteria ; Bacteroidetes ; Bifidobacterium ; Capsules ; Enterococcus ; Firmicutes ; Gastrointestinal Microbiome ; Healthy Volunteers ; Homeostasis ; Lactobacillus ; Microbiota ; Probiotics ; Proteobacteria ; RNA, Ribosomal, 16S