Secondary metabolites produced by Microbacterium sp. LGMB471 with antifungal activity against the phytopathogen Phyllosticta citricarpa

Abstract

The citrus black spot (CBS), caused by Phyllosticta citricarpa, is one of the most important citrus diseases in subtropical regions of Africa, Asia, Oceania, and the Americas, and fruits with CBS lesions are still subject to quarantine regulations in the European Union. Despite the high application of fungicides, the disease remains present in the citrus crops of Central and South America. In order to find alternatives to help control CBS and reduce the use of fungicides, we explored the antifungal potential of endophytic actinomycetes isolated from the Brazilian medicinal plant Vochysia divergens found in the Pantanal biome. Two different culture media and temperatures were selected to identify the most efficient conditions for the production of active secondary metabolites. The metabolites produced by strain Microbacterium sp. LGMB471 cultured in SG medium at 36 °C considerably inhibited the development of P. citricarpa. Three isoflavones and five diketopiperazines were identified, and the compounds 7-O-β-D-glucosylgenistein and 7-O-β-D-glucosyl-daidzein showed high activity against P. citricarpa, with the MIC of 33 μg/mL and inhibited the production of asexual spores of P. citricarpa on leaves and citrus fruits. Compounds that inhibit conidia formation may be a promising alternative to reduce the use of fungicides in the control of CBS lesions, especially in regions where sexual reproduction does not occur, as in the USA. Our data suggest the use of Microbacterium sp. LGMB471 or its metabolites as an ecological alternative to be used in association with the fungicides for the control of CBS disease.

Antimicrobial Biosynthetic Potential and Phylogenetic Analysis of Culturable Bacteria Associated with the Sponge Ophlitaspongia sp. from the Yellow Sea, China

“…Phylogenetic analyses confirmed that all 20 genera of the isolated strains overlapped with previously reported isolates associated with sponges and other marine hosts, such as corals, ascidians, and algae, from different geographical locations obtained using culture-dependent methods [ 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ]. Genera such as Bacillus , Microbacterium , Nocardiopsis , Pseudoalteromonas , Saccharomonospora , and Streptomyces are distributed throughout aquatic environments and are well-known secondary metabolite producers that may protect host sponges from microbial infection and predators [ 47 , 48 , 49 , 50 , 51 , 52 ]. For example, at least 740 bioactive substances have been isolated from the genus Micromonospora , which produces the largest number of natural products among rare actinomycetes [ 53 ].…”

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

“…Microbacterium sp. LGMB471 isolated from the medicinal plant Vochysia divergens inhibited the development of Phyllosticta citricarpa [ 29 ]. Microbacterium sp.…”

“…isolated from tomato plants inhibited the growth of Alternaria alternata , Corynespora cassiicola, and Stemphylium lycopersici [ 30 ]. Among these, antifungal compounds, 5-methyl-2-phenyl-1H-indole produced by strain KU143, 7-O-β-D-glucosyl-genistein and 7-O-β-D-glucosyl-daidzein produced by strain LGMB471, were also discovered [ 28 , 29 ]. Brachybacterium exists in various environments, such as soil (poultry deep litter, contaminated sand), roots, fermented food, and animals [ 31 ].…”

Bio-priming with a consortium of Streptomyces araujoniae strains modulates defense response in chickpea against Fusarium wilt

“…Over the last decade, there is an increased interest in the search for new biocontrol agents with better efficiency, adaptation, and colonization. Due to their diversity and potential to create unique antibiotics, antifungal metabolites, and extracellular enzymes, actinomycetes are the most economically and biotechnologically valuable prokaryotes ( Mohite et al, 2019 ; Savi et al, 2019 ). Actinomycetes inhabiting various rhizosphere soils have also been reported to produce active biomolecules which promote plant growth like phytohormones, siderophores, iron chelators, and organic acids ( Anwar et al, 2016 ).…”