Apis andreniformis associated Actinomycetes show antimicrobial activity against black rot pathogen (Xanthomonas campestris pv. campestris)

Nontargeted Metabolomics of Streptomyces Sourced from Thailand Reveals the Presence of Bioactive Metabolites

Actinobacteria are widely recognized as prolific producers of bioactive metabolites with diverse biological properties, yet they remain largely unexplored. In this study, we investigated the antimicrobial potential and chemical diversity of crude extracts from actinobacterial strains isolated from mangrove sediments collected in Chonburi and Chachoengsao provinces of Thailand. Taxonomic identification confirmed that these isolates belong to the genus Streptomyces. Notably, ten isolates, identified as Streptomyces iranensis, Streptomyces yogyakartensis, Streptomyces cacaoi, Streptomyces ardesiacus, Streptomyces phaeoluteichromatogenes, and Streptomyces albiaxialis, exhibited potent inhibitory activity against chloroquine-resistant Plasmodium falciparum K1 at concentrations <10 μg/mL. Among these, only S. albiaxialis displayed anti-human immunodeficiency virus-1 viral protein R (HIV-1 Vpr) activity in HeLa cells harboring the TREx plasmid encoding full-length Vpr (TREx-HeLa-Vpr cells). MS/MS-guided molecular networking analysis highlighted the metabolic complexity of the isolates, revealing a diverse array of distinct compounds. These included chymostatin B, geldanamycin, dehydroxynocardamine, ikarugamycin epoxide, kanchanamycin C, glochidone, bisucaberin, coproporphyrin III, futalosine, and various siderophores such as ferrioxamine B, desferrioxamine D2, desferrioxamine G, desferrioxamine E, desferrioxamine, desferrioxamine H, and ferrioxamine E. Moreover, guided by the potent antimalarial activity of strain S2-SC19, the compound elaiophylin was detected, isolated, and identified using analytical techniques. Remarkably, the compound exhibited potent antimalarial activity with an IC50 value of 0.002 ± 0.002 μg/mL against P. falciparum K1. Furthermore, genomic analysis revealed that strain S2-SC19 is most closely related to Streptomyces asiaticus DSM no. 41761. This study highlights Thai mangrove soil as a valuable source of bioactive compounds, including elaiophylin, and underscores the bioactive potential and chemical diversity of mangrove ecosystems as a rich, untapped reservoir of natural products.

Diversity and antibacterial potential of the Actinobacteria associated with Apis mellifera ligustica

Insect-associated Actinobacteria are a potentially rich source of novel natural products with antibacterial activity. Here, the community composition of Actinobacteria associated with Apis mellifera ligustica was investigated by integrated culture-dependent and independent methods. A total of 61 strains of Streptomyces genera were isolated from the honeycomb, larva, and different anatomical parts of the honeybee's body using the culture-dependent method. Amplicon sequencing analyses revealed that the actinobacterial communities were dominated by the family of Bifidobacteriaceae and Microbacteriaceae in the honeybee gut, and Nocardiaceae and Pseudonocardiaceae in the honeycomb, whereas only Streptomyces genera were isolated by the culture-dependent method. Culture-independent analyses showed more diverse actinobacterial communities than those of culture-dependent methods. The antibacterial bioassay showed that most crude extracts of representative isolates exhibited antibacterial activities. Among them, the crude extract of Streptomyces sp. FCF01 showed the best antibacterial activities against Staphylococcus aureus, Micrococcus tetragenus, and Pseudomonas syringae pv. actinidiae (Psa) with the disc diameter of inhibition zone diameter (IZD) of 23.00, 15.00, and 13.33 mm, respectively. Chemical analysis of Streptomyces sp. FCF01 led to the isolation of three secondary metabolites, including mayamycin (1), mayamycin B (2), and N-(2-Hydroxyphenyl) acetamide (3). Among them, compound 1 displayed strong antibacterial activity against S. aureus, M. tetragenus, and Psa with minimum inhibitory concentrations (MIC) values of 6.25, 12.5, and 6.25 μg/ml, respectively. In addition, two novel derivative compounds 1a and 1b were synthesized by acetylation of compound 1. Both compounds 1a and 1b displayed similar antibacterial activities with those of metabolite 1. These results indicated that Streptomyces species associated with honeybees had great potential in finding antibiotics.

Antibiotics from Insect-Associated Actinobacteria

Actinobacteria are involved into multilateral relationships between insects, their food sources, infectious agents, etc. Antibiotics and related natural products play an essential role in such systems. The literature from the January 2016-August 2022 period devoted to insect-associated actinomycetes with antagonistic and/or enzyme-inhibiting activity was selected. Recent progress in multidisciplinary studies of insect-actinobacterial interactions mediated by antibiotics is summarized and discussed.

Identification of Antimicrobial Compounds in Two Streptomyces sp. Strains Isolated From Beehives

The World Health Organization warns that the alarming increase in antibiotic resistant bacteria will lead to 2.7 million deaths annually due to the lack of effective antibiotic therapies. Clearly, there is an urgent need for short-term alternatives that help to alleviate these alarming figures. In this respect, the scientific community is exploring neglected ecological niches from which the prototypical antibiotic-producing bacteria Streptomycetes are expected to be present. Recent studies have reported that honeybees and their products carry Streptomyces species that possess strong antibacterial activity. In this study, we have investigated the antibiotic profile of two Streptomycetes strains that were isolated from beehives. One of the isolates is the strain Streptomyces albus AN1, which derives from pollen, and shows potent antimicrobial activity against Candida albicans. The other isolate is the strain Streptomyces griseoaurantiacus AD2, which was isolated from honey, and displays a broad range of antimicrobial activity against different Gram-positive bacteria, including pathogens such as Staphylococcus aureus and Enterococus faecalis. Cultures of S. griseoaurantiacus AD2 have the capacity to produce the antibacterial compounds undecylprodigiosin and manumycin, while those of S. albus AN1 accumulate antifungal compounds such as candicidins and antimycins. Furthermore, genome and dereplication analyses suggest that the number of putative bioactive metabolites produced by AD2 and AN1 is considerably high, including compounds with anti-microbial and anti-cancer properties. Our results postulate that beehives are a promising source for the discovery of novel bioactive compounds that might be of interest to the agri-food sector and healthcare pharmaceuticals.