Gloeosporiocide, a new antifungal cyclic peptide from Streptomyces morookaense AM25 isolated from the Amazon bulk soil.

Actinobacteria are known by their ability to produce several antimicrobial compounds of biotechnological interest. Thus, in this study, we isolated and identified by partial 16S RNA sequencing ∼100 actinobacteria isolates from guarana (Paullinia cupana) bulk soil. Besides, we isolated from the actinobacteria Streptomyces morookaense AM25 a novel cyclic peptide, named gloeosporiocide, molecular formula C44H48N11O7S3 (calculated 938.2901), and characterized by the presence of cyclized cysteins to form three thiazols. The novel compound had activity against the plant pathogen Colletotrichum gloeosporioides, assayed by the paper disk diffusion method (42.7% inhibition, 0.1 mg disk-1) and by the microdilution assay (1.25 g L-1). Our results reveal the potential of the actinobacteria from the Amazon rhizospheric soils as biocontrol agents as well as producers of new compounds with antifungal activity. Thus, this work constitutes a step forward in the development of the biotechnology of actinobacteria in the production of compounds of agronomic interest.

Bacterial communities associated with anthracnose symptomatic and asymptomatic leaves of guarana, an endogenous tropical crop, and their pathogen antagonistic effects.

Plants are colonized by diverse microorganisms that can substantially impact their health and growth. Understanding bacterial diversity and the relationships between bacteria and phytopathogens may be key to finding effective biocontrol agents. We evaluated the bacterial community associated with anthracnose symptomatic and asymptomatic leaves of guarana, a typical tropical crop. Bacterial communities were assessed through culture-independent techniques based on extensive 16S rRNA sequencing, and cultured bacterial strains were evaluated for their ability to inhibit the growth of Colletotrichum sp. as well as for enzyme and siderophore production. The culture-independent method revealed that Proteobacteria was the most abundant phylum, but many sequences were unclassified. The emergence of anthracnose disease did not significantly affect the bacterial community, but the abundance of the genera Acinetobacter, Pseudomonas and Klebsiella were significantly higher in the symptomatic leaves. In vitro growth of Colletotrichum sp. was inhibited by 11.38% of the cultured bacterial strains, and bacteria with the highest inhibition rates were isolated from symptomatic leaves, while asymptomatic leaves hosted significantly more bacteria that produced amylase and polygalacturonase. The bacterial isolate Bacillus sp. EpD2-5 demonstrated the highest inhibition rate against Colletotrichum sp., whereas the isolates EpD2-12 and FD5-12 from the same genus also had high inhibition rates. These isolates were also able to produce several hydrolytic enzymes and siderophores, indicating that they may be good candidates for the biocontrol of anthracnose. Our work demonstrated the importance of using a polyphasic approach to study microbial communities from plant diseases, and future work should focus on elucidating the roles of culture-independent bacterial communities in guarana anthracnose disease.