In the myrmecophytic mutualistic relationship between Azteca ants and Cecropia plants both species receive protection and exchange nutrients. The presence of microorganisms in this symbiotic system has been reported, and the symbiotic role of some fungi involved in the myrmecophytic interactions has been described. In this work we focus on bacteria within this mutualism, conducting isolations and screening for antimicrobial activities, genome sequencing, and biochemical characterization. We show that Pantoea, Rhizobium, Methylobacterium, Streptomyces and Pseudomonas are the most common cultivable genera of bacteria. Interestingly, Pseudomonas spp. isolates showed potent activity against 83% of the pathogens tested in our antimicrobial activity assays, including a phytopathogenic fungus isolated from Cecropia samples. Given the predicted nitrogen limitations associated with the fungal patches within this myrmecophyte, we performed nitrogen fixation analyses on the bacterial isolates within the Proteobacteria and show the potential for nitrogen fixation in Pseudomonas strains. The genome of one Pseudomonas strain was sequenced and analyzed. The gene cluster involved in the biosynthesis of cyclic lipodepsipeptides (CLPs) was identified, and we found mutations that may be related to the loss of function in the dual epimerization/condensation domains. The compound was isolated, and its structure was determined, corresponding to the antifungal viscosinamide. Our findings of diazotrophy and production of viscosinamide in multiple Pseudomonas isolates suggests that this bacterial genus may play an important role in the Cecropia-Azteca symbiosis.

No abstract

In this study, we report the isolation and identification of an endophytic strain of Burkholderia cepacia (COPS strain) associated with Polygala paniculata roots. Polygala plants are rich sources of promising microbiomes, of which the literature reports several pharmacological effects, such as trypanocidal, antinociceptive, anesthetic, anxiolytics, and anticonvulsant activities. B. cepacia COPS belongs to a new sequence type (ST 1870) and harbors a genome estimated in 8.3 Mbp which exhibits the aminoglycosides and beta-lactams resistance genes aph(3′)-IIa and blaTEM-116, respectively. Analysis performed using MLST, average nucleotide identity, and digital DNA-DNA hybridization support its species-level identification and reveals its novel housekeeping genes alleles gyrB, lepA, and phaC. The root endophyte B. cepacia COPS drew our attention from a group of 14 bacterial isolates during the primary screening for being potentially active against Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212, Micrococcus luteus ATCC 9341, Escherichia coli ATCC 25922, and Candida albicans ATCC 10231 and exhibited the broad-spectrum activity against phytopathogenic fungi. In addition, COPS strain showed production of protease, lipase, and esterase in solid media, and its natural product extract showed potent inhibition against fungal plant pathogens, such as Moniliophthora perniciosa, whose antagonism index (89.32%) exceeded the positive control (74.17%), whereas Sclerotinia sclerotiorum and Ceratocystis paradoxa showed high percentages of inhibition (85.53% and 82.69%, respectively). COPS crude extract also significantly inhibited S. epidermidis ATCC 35984, E. faecium ATCC 700221 (MIC values of 32 μg/mL for both), E. faecalis ATCC 29212 (64 μg/mL), and S. aureus ATCC 25923 (128 μg/mL). We observed moderate antagonistic activity against A. baumannii ATCC 19606 and E. coli ATCC 25922 (both at 512 μg/mL), as well as potent cytotoxic effects on Leishmania infantum and Leishmania major promastigote forms with 78.25% and 57.30% inhibition. In conclusion, this study presents for the first time the isolation of an endophytic B. cepacia strain associated with P. paniculata and enough evidence that these plants may be considered a rich source of microbes for the fight against neglected diseases.

Os microrganismos endofíticos são fungos ou bactérias que colonizam o interior dos tecidos vegetais sem causar dano à planta hospedeira. Os fungos endofíticos têm interessado a comunidade científica devido à produção de metabolitos secundários com aplicação nas indústrias biotecnológicas e farmacêuticas. Desta forma, o presente estudo objetivou isolar, purificar, identificar genotipicamente e avaliar a atividade antagônica, o potencial biotecnológico para solubilização fosfato e produção de enzimas de 66 fungos endofíticos de folhas e ramos isolados de S. adstringens e S. lycocarpum St. Hill. Para isso, folhas e caules saudáveis de S. adstringens e S. lycocarpum foram coletadas e submetidas à assepsia superficial. Após a incubação do material botânico procedeu-se o isolamento, identificação molecular dos fungos endofíticos. Posteriormente, os isolados endofíticos foram avaliados in vitro quanto ao potencial antagônico contra os fitopatógenos Colletotrichum sp., Fusarium oxysporum e Lasiodiplodia subglobosa, quanto a solubilização de fosfato inorgânico e a produção de enzimas (amilase, celulase, pectinase, protease, lipase e esterase). Os resultados mostraram que a comunidade endofítica fúngica associada à S. adstringens é composta por: Diaporthe sp., Neopestalotiopsis sp., Nigrospora sp., Paraconiothrium sp., Phomopsis sp., Pseudofusicoccum sp., Schizophyllum sp. e Xenoacremonium sp. e os gêneros da comunidade fúngica de S. lycocarpum St. Hill. é composta por: Colletotrichum sp., Curvalaria sp., Diaporthe sp., Neurospora sp., Phlebiopsis sp., Phomopsis sp. e Schizophyllum sp.. Os fungos endofíticos se mostraram promissores contra Colletotrichum sp., Fusarium oxysporum e Lasiodiplodia subglobosa sendo observados elevados índices de inibição e a maioria das interações do tipo A, onde há um bloqueio de crescimento do fitopatógeno com contato micelial do fungo endofítico. Além disso, os fungos endofíticos apresentaram potencial de solubilizar fosfato inorgânico com índice de solubilização de fosfato médio. Quanto à produção de enzimas, os isolados fúngicos de ambas as espécies vegetais apresentaram maior atividade pectinolítica com produção de pectato liase e a poligalactorose. Com base nos resultados o estudo evidencia a importância dos fungos endofíticos na produção de compostos de interesse para biotecnologia e para a conservação das espécies vegetais do Cerrado, as quais abrigam esses micro-organismos promissores.

Solanum lycocarpumSt. Hil. is an endemic plant of the Brazilian tropical savannah (cerrado) that is capable of growing on acidic and nutrient-poor land, an ability which attracts attention to its rhizospheric microbiota, including plant growth-promoting rhizobacteria (PGPR). In this work, 131 bacterial strains were isolated from rhizosphere samples of S. lycocarpum and were tested in vitro for direct mechanisms of plant growth promotion (biological nitrogen fixation, phosphate solubilization and indolic compounds production) and enzyme activities. The 26 most promising isolates selected from the previous tests were used to continue the screening. Ten of these isolates showed antifungal activity against fourteen phytopathogenic fungi and twelve isolates showed antimicrobial activity against at least one of the three clinical pathogens evaluated. Seven of the 26 isolates were identified at random as belonging to the genera Bacillus, Burkholderia and Microbacterium, are PGPR and have potential to participate in more in-depth research aimed at the development of bio-inputs, especially the Bacillus strains.