Chemical Ecology of Streptomyces albidoflavus Strain A10 Associated with Carpenter Ant Camponotus vagus

The insect microbiome is a vast source of bioactive small molecules

Covering: September 1964 to June 2023Bacteria and fungi living in symbiosis with insects have been studied over the last sixty years and found to be important sources of bioactive natural products. Not only classic producers of secondary metabolites such as Streptomyces and other members of the phylum Actinobacteria but also numerous bacteria from the phyla Proteobacteria and Firmicutes and an impressive array of fungi (usually pathogenic) serve as the source of a structurally diverse number of small molecules with important biological activities including antimicrobial, cytotoxic, antiparasitic and specific enzyme inhibitors. The insect niche is often the exclusive provider of microbes producing unique types of biologically active compounds such as gerumycins, pederin, dinactin, and formicamycins. However, numerous insects still have not been described taxonomically, and in most cases, the study of their microbiota is completely unexplored. In this review, we present a comprehensive survey of 553 natural products produced by microorganisms isolated from insects by collating and classifying all the data according to the type of compound (rather than the insect or microbial source). The analysis of the correlations among the metadata related to insects, microbial partners, and their produced compounds provides valuable insights into the intricate dynamics between insects and their symbionts as well as the impact of their metabolites on these relationships. Herein, we focus on the chemical structure, biosynthesis, and biological activities of the most relevant compounds.

Streptomyces phaeochromogenes BV-204, K-1115A Anthraquinone-Producing Strain: A New Protein Biosynthesis Inhibitor

In the search for new antibiotics, it is a common occurrence that already known molecules are "rediscovered" while new promising ones remain unnoticed. A possible solution to this problem may be the so-called "target-oriented" search, using special reporter microorganisms that combine increased antibiotic sensitivity with the ability to identify a molecule's damaging effect. The use of such test organisms makes it possible to discover new promising properties even in known metabolites. In this study, we used a high-throughput screening method based on the pDualrep2 dual reporter system, which combines high sensitivity through the use of modified strains of test organisms and makes it possible to easily and accurately identify the interaction mechanisms of a substance and a bacterial cell at the initial stages of screening. This reporter system is unknown in Russia and is significantly superior to its global analogues. In the system, translation inhibition induces the expression of the fluorescent protein Katushka2s, while DNA damage is induced by TurboRFP. Using pDualrep2, we have isolated and described BV-204, an S. phaeochromogenes strain producing K-1115A, the biologically active substance that we have previously described. In our study, K-1115A for the first time has demonstrated antibiotic activity and an ability to inhibit bacterial translation, which was confirmed in vitro in a cell-free translation system for FLuc mRNA. K-1115A's antibacterial activity was tested and confirmed for S. aureus (MRSA) and B. subtilis, its cytotoxicity measured against that for the HEK293 cell line. Its therapeutic index amounted to 2 and 8, respectively. The obtained results open up prospects for further study of K-1115A; so, this can be regarded as the basis for the production of semi-synthetic derivatives with improved therapeutic properties to be manufactured in dosage forms.

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.

Observation of the Antimicrobial Activities of Two Actinomycetes in the Harvester Ant Messor orientalis

Simple Summary

Observations in the animal room have shown that the seeds stored by harvester ants, although in a damp environment, are less likely to mold. It was hypothesized that harvester ants may use actinomycetes to protect their seed stores, given that leafcutter ants use actinomycetes as producers of defensive substances. Two actinomycetes were isolated from the harvester ant Messor orientalis. The fermentation broth of the actinomycetes showed significant inhibitory effects on the three indicator fungi. Coculture experiments supported the observed inhibitory effects. The antifungal activities of actinomycetes in harvester ants were revealed. This research provides a significant theoretical reference for the abovementioned hypothesis and for the potential agricultural applications of these actinomycetes for multiple crops.

Abstract

Observations have shown that seeds collected by harvester ants are less likely to mold. Based on evolutionary analysis and other research, it was hypothesized that harvester ants could apply actinomycetes to protect seeds, similar to the protection of mutualistic fungi by leafcutter ants. Two actinomycetes were successfully isolated from the harvester ant Messor orientalis. The taxonomic status of the actinomycetes was determined by 16S rRNA sequence analysis and biochemical experimental observations. Their inhibitory effects on plant pathogens were measured. One of the bacteria was identified as Brachybacterium phenoliresistens and denoted as B. phenoliresistens MO. The other belonged to the genus Microbacterium. It was named Microbacterium sp. Growth rate determination and coculture experiments were performed to explore the inhibitory effect of actinomycetes on indicator plant pathogens. The inhibition rates of the actinomycetes toward Peronophythora litchii and Rhizoctonia solani were 100% in media containing 30% or more fermentation broth, and they also showed an inhibitory effect on Colletotrichum siamense. The coculture experiment supported this result by showing that the growth of P. litchii and R. solani was inhibited in the presence of actinomycetes. Therefore, the results of this study show the agricultural application potential of these bacteria and may provide a reference for research on the symbiosis of harvester ants with actinomycetes.