Antonino Baez

Fungal diseases significantly affect crop yield and product quality. The use of chemical fungicides to control fungal infestations can disturb the plant-associated microbiome and raise concerns about food security. Therefore, the use of biological antifungals, such as Bacillus species, is encouraged as they offer a sustainable alternative to chemical fungicides. However, the success of such biocontrol agents in the field depends on their ability to withstand environmental stressors like solar UV light and dryness. Here, we present a targeted strategy for selecting resilient biocontrol agents by first isolating endophytic microorganisms that are already adapted to extreme conditions, followed by screening them for antifungal activity. Using this approach, we investigated the chromium-tolerant, root nodule-associated strain Bacillus velezensis VM54 for its ability to antagonize fungal pathogens. B. velezensis VM54 exhibited strong in vitro and in vivo antagonism against Fusarium fujikuroi, F. oxysporum, and Alternaria alternata. Notably, the VM54 strain tolerated UV-C radiation up to 1824 J/m², a level comparable to that of the extremophile Deinococcus radiodurans, highlighting its robustness for potential field application. PCR-based genome analysis revealed the presence of biosynthetic gene clusters for several antimicrobial compounds, including surfactin, bacillaene, difficidin, and macrolactins. Mass spectrometry of cell-free culture extracts confirmed the production of putative fengycin A C16 and C17 lipopeptides. These bioactive metabolites, along with volatile compounds produced by VM54, are likely responsible for its antifungal activity. This study supports the use of environmentally adapted endophytes as a promising source of resilient biocontrol agents for sustainable agriculture. Resumen. Las enfermedades causadas por hongos afectan significativamente el rendimiento de los cultivos y la calidad del producto. El uso de fungicidas químicos para controlar las infestaciones fúngicas puede alterar el microbioma asociado a las plantas y generar riesgos para la seguridad alimentaria. Por lo tanto, el uso de antifúngicos biológicos es altamente recomendable, ya que ofrece una alternativa sostenible a los fungicidas químicos. Sin embargo, el éxito de estos agentes de biocontrol en el campo depende de su capacidad para resistir estresores ambientales como la luz solar UV y la sequía. En este trabajo, presentamos una estrategia para seleccionar agentes de biocontrol resilientes mediante el aislamiento de microorganismos endófitos ya adaptados a condiciones extremas, seguida de un escrutinio de la actividad antifúngica. Con este enfoque, investigamos la cepa Bacillus velezensis VM54, tolerante al cromo y asociada a nódulos radiculares, debido a su capacidad de antagonizar patógenos fúngicos. B. velezensis VM54 exhibió un fuerte antagonismo in vitro e in vivo frente a Fusarium fujikuroi, F. oxysporum y Alternaria alternata. Cabe destacar que la cepa VM54 toleró la radiación UV-C hasta 1824 J/m², un nivel comparable al de extremófilo Deinococcus radiodurans, lo que evidencia su robustez para su posible aplicación en el campo. El análisis genómico basado en ensayos de PCR reveló la presencia de grupos de genes biosintéticos para varios compuestos antimicrobianos, incluidos surfactina, bacillaeno, difficidina y macrolactinas. La espectrometría de masas de los extractos de cultivos confirmó la producción de los supuestos lipopéptidos C16 y C17 de fengicina A. Estos metabolitos bioactivos, junto con los compuestos volátiles producidos por VM54, probablemente son los responsables de la actividad antifúngica. Este estudio respalda el uso de endófitos adaptados al medio ambiente como una fuente prometedora de agentes de biocontrol resilientes para la agricultura sostenible.

Prosopis laevigata (mesquite) plants can tolerate drought, thermal stress, alkalinity, salinity, and toxicity of heavy metals, making them attractive for phytoremediation. Nonetheless, most of these features have been studied under controlled laboratory conditions. In this work, the bioaccumulation of heavy metals in a free-living population of P. laevigata trees growing in a heavily metal-contaminated site (aluminum, chromium, iron, titanium, copper, and zinc) was analyzed. Furthermore, crystal phases of mineral nutrients and trace elements found in P. laevigata tissues were determined by X-ray diffraction. P. laevigata trees accumulated 705 (± 17), 47,064 (± 1459), 14,800 (± 401) and 30,000 (± 1719) mg/kg of Cu, Zn, Fe and Al, confirming the potential of these plants to hyper-accumulate metals. The X-ray diffraction analysis showed that P. laevigata trees can chelate Al³⁺ with phosphates to form orthorhombic crystals of aluminum phosphate (AlPO₄) in the tissues. This aluminum chelation was probably a mechanism of tolerance used by the plant. The inoculation of seedlings with the endophytic Bacillus cereus MH778713 did not prevent Cr-accumulation in the plant but increased metal tolerance and seedling development. These results highlight the use of P. laevigata and B. cereus MH778713 together as tools for heavy metal bioremediation, particularly on arid and semiarid soils.

Aeromonas es un género bacteriano reportado como patógeno emergente; debido a su capacidad de generar enfermedades infecciosas que afectan el sistema gastrointestinal, el circulatorio y algunos tejidos blandos de individuos inmunocomprometidos, adultos mayores e infantes. También, Aeromonas se comporta como un patógeno oportunista de mamíferos y peces, y posee diversos factores de virulencia. Este género prolifera en diversos ambientes como el suelo, agua y diferentes hospederos. La presente revisión bibliográfica tiene como objetivo describir los procesos metabólicos y genéticos que le confieren al género Aeromonas la resistencia a antibióticos, la capacidad de formar biopelícula, los genes regulados por el Quorum Sensing (QS) y la transferencia horizontal de genes. Además, de discutir algunas características que posicionan a la infección por Aeromonas como un problema potencial de salud pública. La revisión exhaustiva se realizó en las bases de datos del Centro Nacional de Información Biotecnológica (NCBI) y del Instituto Multidisciplinario de Publicaciones Digitales (MDPI), del 2017 a la fecha y se consideraron los siguientes criterios de búsqueda: factores de virulencia, resistencia a antibióticos formación de biopelícula y transferencia horizontal de genes. La investigación indicó que Aeromonas presenta varios factores de virulencia extracelulares, enzimáticos y estructurales; es resistente a antibióticos como betalactámicos, tetraciclinas y macrólidos y presenta varios genes que le confieren esta resistencia; asimismo, el género tiene la capacidad de formar biopelícula y posee tres sistemas de QS.

Las actividades antropogénicas y la disposición inadecuada de sus desechos ha provocado la acumulación de metales pesados en el suelo. El Cromo VI es uno de los metales pesados más tóxicos para el medio ambiente, que causa cambios en la expresión génica de diferentes especies vegetales, algunas de ellas han sido capaces de adaptarse a este ambiente contaminado usando estrategias cómo algunos sistemas enzimáticos que las protegen del estrés oxidativo generado por la presencia de Cromo VI en el medio.

Los antibióticos son un grupo de medicamentos que son utilizados para el control de infecciones causadas por bacterias y parásitos. La resistencia a los antibióticos es originada por un mal uso en el tratamiento de las infecciones, y se produce cuando los microorganismos logran adaptarse y crecer en presencia de medicamentos que alguna vez los impactaron. El débil control en la utilización de estos agentes ha propiciado que en la naturaleza se distribuyan organismos resistentes a los antimicrobianos prescritos popularmente, lo cual se ha convertido en un problema de salud pública. La infección por microorganismos resistentes a diferentes compuestos antimicrobianos conduce a enfermedades graves, ingresos hospitalarios prolongados, aumento en los costos de atención médica y en medicamentos de segunda línea, y fracasos en los tratamientos. Uno de los patógenos del cual se ha descrito una alta incidencia en infecciones nosocomiales, identificado como multidrogorresistentes, de mal pronóstico en pacientes inmunosuprimidos, es Staphylococcus aureus, el cual se caracteriza por ser la principal causa de bacteriemia nosocomial. Otro de los principales patógenos responsables de muchos de los casos de neumonía reportados en niños y adultos es Streptococcus pneumoniae. La información sobre los diferentes mecanismos de resistencia permite recalcar la urgencia e importancia de encontrar nuevas alternativas terapéuticas para combatir las infecciones nosocomiales. La generación y propagación de cepas multidrogorresistentes debe prevenirse mediante restricciones severas en el uso de los antibióticos, respetando la prescripción, incluyendo el número de dosis y el periodo de tiempo de su ingesta, así como evitando la automedicación. Palabras clave Staphylococcus aureus, Streptococcus pneumoniae, multidrogorresistencia, bacteria, antibiótico

Aim The genus Fusarium comprises plant pathogenic species with agricultural relevance. Fusarium oxysporum causes tomato wilt disease with significant production losses. The use of agrochemicals to control the Fusarium wilt of tomato is not environmentally friendly. Bacillus species, as biocontrol agents, provide a safe and sustainable means to control Fusarium-induced plant diseases. In this study, the ability of Bacillus cereus MH778713, a strain isolated from root nodules of Prosopis laevigata, to protect tomato plants against Fusarium wilt was evaluated. Methods and results Bacillus cereus MH778713 and its volatiles inhibited the radial growth of F. oxysporum and stimulated tomato seedling growth in in vitro and in vivo tests. When tomato plants growing in the greenhouse were inoculated with B. cereus MH778713, the percentage of wilted plants decreased from 96% to 12%, indicating an effective crop protection against Fusarium wilt. Among the metabolites produced by B. cereus MH778713, hentriacontane and 2,4-di-tert-butylphenol promoted tomato seedling growth and showed antifungal activity against the target pathogen. Conclusion The inoculation of B. cereus MH778713 on tomato seedlings helped plants to manage Fusarium wilt, suggesting the potential of B. cereus MH778713 as a biocontrol agent. Significance and Impact of the Study These results complement our previous studies on chromium tolerance and bioremediation traits of B. cereus MH778713 by highlighting the potential of this metal-resistant micro-organism to boost crop growth and disease resistance.

The use of bacteriocins holds great promise in different areas such as health, food, nutrition, veterinary, nanotechnology, among others. Many research groups worldwide continue to advance the knowledge to unravel a novel range of therapeutic agents and food preservatives. This review addresses the advances of bacteriocins and their producer organisms as biocontrol agents for applications in the medical industry and agriculture. Furthermore, the bacteriocin mechanism of action and structural characteristics will be reviewed. Finally, the potential role of bacteriocins to modulate the signaling in host-associated microbial communities will be discussed.

Purpose: Pseudomonas putida KT2440 is a desiccation-sensitive bacterium that loses culturability after 15 days of air desiccation. We have previously shown that P. putida KT2440 can develop a viable but nonculturable (VBNC) state after being exposed to desiccation stress and eventually recover when desiccated cells are rehydrated for at least 24 h. Methods: To determine which genes of transport, oxidation-reduction, and transcription processes could be involved in the return of P. putida KT2440 to the culturable state, a transcriptome analysis was carried out comparing the gene expression of non-desiccated samples with samples subjected to desiccation followed by 20 min of rehydration or desiccation followed by 24 h of rehydration. Results: Desiccation stress triggered a VBNC state of P. putida. The major response was detected after 24 h of rehydration with 148 upregulated and 42 downregulated genes. During the VBNC state, P. putida activated transmembrane transport processes like that of siderophores through a TonB-dependent transporter and putative polyhydric alcohol transport systems. Prolonged rehydration with distilled water resuscitated P. putida KT2440 cells activating the catabolism of phenylalanine/tyrosine to provide energy and carbon for ubiquinone biosynthesis while maintaining a reduced protein synthesis. On the other hand, the interruption of the TonB-dependent receptor gene (PP_1446) increased desiccation survival of the mutant strain. Conclusion: The activation of the iron transport system (TonB-dependent siderophore receptor) and alcohol transport can be helping the VBNC state of P. putida. Activation of catabolism of phenylalanine/tyrosine and reduced protein synthesis was needed for resuscitation from the VBNC state.

Volatile organic compounds (VOCs) produced by rhizobacteria have been proven to stimulate plant growth during germination and seedling stages. However, the modulating effect of bacterial volatiles on the germination of seeds subjected to heavy metal stress is scarcely studied. In this work, the ability of volatiles released by Bacillus sp. MH778713 to induce seed dormancy breakage in Prosopis laevigata and Arabidopsis thaliana seeds were examined. The minimal inhibitory concentration of chromium (Cr) VI that prevents seed germination of P. laevigata and A. thaliana on water-Cr-agar plates was 2500 and 100 mg L^–1, respectively. Remarkably, partitioned Petri-dish co-cultivation of Bacillus sp. MH778713 and plant seeds under Cr-stress showed the beneficial effect of volatiles emitted by Bacillus sp. MH778713, helping plant seeds to overcome Cr-stress. Among the metabolites emitted by Bacillus sp. MH778713, octadecane, heneicosane, 2,4-di-tert-butylphenol, hexadecane, eicosane, octacosane, and tetratriacontane were the most abundant. To confirm that these long-chain compounds produced by Bacillus sp. MH778713 could be responsible for the seed dormancy breakage, high pure organic compounds (2,4-di-tert-butylphenol, heneicosane, hentriacontane, and tetracosane) were used directly in germination assays of P. laevigata and A. thaliana seeds instead of volatiles emitted by Bacillus sp. MH778713. All organic compounds allowed Prosopis and Arabidopsis seeds to overcome Cr-toxicity and germinate. The results of this study provide new insight into the role of long-chain bacterial compounds produced by Bacillus sp. MH778713 as triggers of seed abiotic stress tolerance, surmounting chromium stress and stimulating seedling development.

Bacteria produce antimicrobial compounds to compete for nutrients and space in a particular habitat. Antagonistic interactions can be evaluated by several methodologies including the double-layer agar and simultaneous inhibition assays. Among the well-known inhibitory substances produced by bacteria are the broad-spectrum antibiotics, organic acids, siderophores, antifungal, and bacteriocins. The most studied bacterial genera able to produce these inhibitory substances are Enterococcus, Lactococcus, Streptomyces, Bacillus, Pseudomonas, Klebsiella, Escherichia, and Burkholderia. Some beneficial bacteria can promote plant growth and degrade toxic compounds in the environment representing an attractive solution to diverse issues in agriculture and soil pollution, particularly in fields with damaged soils where pesticides and fertilizers have been indiscriminately used. Beneficial bacteria may increase plant health by inhibiting pathogenic microorganisms; some examples include Gluconacetobacter diazotrophicus, Azospirullum brasilense, Pseudomonas fluorescens, Pseudomonas protegens, and Burkholderia tropica. However, most studies showing the antagonistic potential of these bacteria have been performed in vitro, and just a few of them have been evaluated in association with plants. Several inhibitory substances involved in pathogen antagonism have not been elucidated yet; in fact, we know only 1 % of the bacterial diversity in a natural environment leading us to assume that many other inhibitory substances remain unexplored. In this review, we will describe the characteristics of some antimicrobial compounds produced by beneficial bacteria, the principal methodologies performed to evaluate their production, modes of action, and their importance for biotechnological purposes.