Search

Actinomycetota in the phylum of bacteria has been explored extensively as a source of antibiotics and secondary metabolites. In addition to acting as plant growth-promoting agents, they also possess the potential to control various plant pathogens; however, there are limited studies that report the facultative predatory ability of Actinomycetota spp. Furthermore, the mechanisms that underline predation are poorly understood. We assessed the diversity of strategies employed by predatory bacteria to attack and subsequently induce the cell lysing of their prey. We revisited the diversity and abundance of secondary metabolite molecules linked to the different predation strategies by bacteria species. We analyzed the pros and cons of the distinctive predation mechanisms and explored their potential for the development of new biocontrol agents. The facultative predatory behaviors diverge from group attack “wolfpack,” cell-to-cell proximity “epibiotic,” periplasmic penetration, and endobiotic invasion to degrade host-cellular content. The epibiotic represents the dominant facultative mode of predation, irrespective of the habitat origins. The wolfpack is the second-used approach among the Actinomycetota harboring predatory traits. The secondary molecules as chemical weapons engaged in the respective attacks were reviewed. We finally explored the use of predatory Actinomycetota as a new cost-effective and sustainable biocontrol agent against plant pathogens.

Number: 1 Publisher: Multidisciplinary Digital Publishing Institute; International audience; Some soil-borne microorganisms are known to have the ability to solubilize insoluble rock phosphate and this process often involves the excretion of organic acids. In this issue, we describe the characterization of a novel solubilizing mechanism used by a Streptomyces strain related to Streptomyces griseus isolated from Moroccan phosphate mines. This process involves the excretion of a compound belonging to the viridomycin family that was shown to play a major role in the rock phosphate bio weathering process. We propose that the chelation of the positively charged counter ions of phosphate constitutive of rock phosphate by this molecule leads to the destabilization of the structure of rock phosphate. This would result in the solubilization of the negatively charged phosphates, making them available for plant nutrition. Furthermore, this compound was shown to inhibit growth of fungi and Gram positive bacteria, and this antibiotic activity might be due to its strong ability to chelate iron, a metallic ion indispensable for microbial growth. Considering its interesting properties, this metabolite or strains producing it could contribute to the development of sustainable agriculture acting as a novel type of slow release bio-phosphate fertilizer that has also the interesting ability to limit the growth of some common plant pathogens.

Fungal diseases are currently a serious public health problem, due to the limited number of fact-based effective principles, and the emergence of resistant strains to the polyenic antifungals. The aim of this study was to screen, for non-polyenic antifungals production by Actinobacteria, and to validate the screening program by characterizingthe produced compounds.Actinobacteria isolates were tested against four clinic human-pathogenic fungi isolated from Hospital Mohammed V Rabat, Morocco. The production of non-polyenic antifungal metabolites by active isolates was investigated based on the yeast cell specificity as challenging targets, antibacterial activity, activity against resistant Candida tropicalis R2 and Pythium irregular (resistant to polyenes), inhibition of antifungal activity by the addition of exogenous ergosterol, and the UV-visible light spectrophotometric analysis of the active crude extracts.The antifungal compound produced was purified using various chromatographic techniques and the selected producing strain was identified using the polyphasic approach.Among 480 Actinobacteria isolates, 55 showed antifungal activity against all tested clinically derived fungi. After performing the screening program, 4 Actinobacteria that hadall the desired criteriawere selected. Using the polyphasic approach, the taxonomic position of the selected Streptomyces AS25, isolated from rhizospheric soil of Alyssum spinosum, showed that it belongs to Streptomyces genus with 100% partial 16S similarity with Streptomyces albidoflavus NBRC13010. On the basis of HPLC and mass spectrometry, the purified compound produced by Streptomyces AS25 was identified as a non-polyenic lactone, antimycin A19, which has been found for the first time to be produced by Streptomyces albidoflavus strain. Following the obtained results, it is important to note that our screening criteria for non-polyenic antifungals have been validated and the rhizospheric soil represents an interesting source to isolate Actinobacteria.