Antagonic and plant growth-promoting effects of bacteria isolated from mine tailings at El Fraile, Mexico / Efecto antagónico y promotor del crecimiento vegetal de bacterias aisladas de losjales mineros de El Fraile, México

Abstract Mine tailings contain high concentrations of heavy metals such as As, Pb, Cu, Mn, andFe, which are detrimental to the health of humans and the environment. In tailings at the ElFraile mine in Guerrero, Mexico, some plant species are apparently tolerant of heavy metals andcan be found growing in the tailings. These plants could be associating with heavy metal-tolerantbacteria that promote plant growth and improve biomass production, and these bacteria couldbe a useful alternative for bacteria-assisted phytoremediation. The objective of this study wasto isolate bacteria detected in the mine tailings at El Fraile-Taxco, focusing on those in the soilfrom the rhizosphere, the inner tissue of the root, leachate, and water, which have the poten-tial to promote plant growth. The ability of the isolated bacteria to promote plant growth wasevaluated in vitro. Of the 151 morphotypes isolated, 51% fix nitrogen, 12% dissolve phosphates,and 12%, 39.7%, and 48.3% produce indole acetic acid, gibberellins, and siderophores, respec-tively. In addition, 66.7% were observed to produce lytic enzymes, such as proteases, celluloses,lipases, esterases, and amylases, which exhibited activity against Fusarium, Aspergillus, andColletotrichum. The use of 16S rRNA analysis led to the identification of the bacterial generaChryseobacterium, Bacillus, Pseudomonas, Mycobacterium, Staphylococcus, Curtobacterium,Enterobacter, Agrobacterium, Ochrobactrum, Serratia, Stenotrophomonas, and Acinetobac-ter. The bacteria isolated from the rhizosphere exhibited the greatest ability to fix nitrogenand produced indole acetic acid, gibberellins, siderophore, and lytic enzymes. In addition, theisolates collected from the soil samples demonstrated ability to solubilize phosphate.

Resumen Los jales mineros contienen una alta concentración de metales pesados como As, Pb, Cu, Mn y Fe. Estas altas concentraciones de metales son perjudiciales para la salud humana y el medio ambiente. En los jales mineros de El Fraile, México, es posible detectar especies de plantas tolerantes a los metales pesados; estas plantas podrían estar asociadas con bacterias capaces de promover su crecimiento, además de poseer actividad antagonista contra hongos. El objetivo de este estudio fue aislar de diferentes microambientes (suelo rizosférico, tejido de raíz, lixiviado y agua) del área del jale El Fraile bacterias con potencial de promover el crecimiento vegetal y actividad antagonista contra hongos fitopatógenos. Estudios in vitro demostraron que el 51% de los morfotipos aislados (151 en total) fijan nitrógeno y el 12% disuelven fosfatos. Asimismo, el 12, 39,7 y 48,3% producen ácido indolacético, giberelinas y sideróforos, respectivamente. Por otro lado, se observó que el 66,7% producía enzimas líticas como proteasas, celulasas, lipasas, esterasas y amilasas, además de exhibir actividad antagonista contra Fusarium, Aspergillus y Colletotrichum. Mediante análisis del gen 16S ARNr, se identificó a estas bacterias como pertenecientes a los géneros Chryseobacterium, Bacillus, Pseudomonas, Mycobacterium, Staphylococcus, Curtobacterium, Enterobacter, Agrobacterium, Ochrobac-trum, Serratia, Stenotrophomonas y Acinetobacter. Las bacterias de la rizosfera exhibieron la mayor capacidad para fijar nitrógeno y produjeron ácido indolacético, giberelinas, sideróforos y enzimas líticas. Además, se detectó que las cepas aisladas de suelo rizosférico eran las que tenían la capacidad de solubilizar fosfatos.

Antagonic and plant growth-promoting effects of bacteria isolated from mine tailings at El Fraile, Mexico.

Mine tailings contain high concentrations of heavy metals such as As, Pb, Cu, Mn, and Fe, which are detrimental to the health of humans and the environment. In tailings at the El Fraile mine in Guerrero, Mexico, some plant species are apparently tolerant of heavy metals and can be found growing in the tailings. These plants could be associating with heavy metal-tolerant bacteria that promote plant growth and improve biomass production, and these bacteria could be a useful alternative for bacteria-assisted phytoremediation. The objective of this study was to isolate bacteria detected in the mine tailings at El Fraile-Taxco, focusing on those in the soil from the rhizosphere, the inner tissue of the root, leachate, and water, which have the potential to promote plant growth. The ability of the isolated bacteria to promote plant growth was evaluated in vitro. Of the 151 morphotypes isolated, 51% fix nitrogen, 12% dissolve phosphates, and 12%, 39.7%, and 48.3% produce indole acetic acid, gibberellins, and siderophores, respectively. In addition, 66.7% were observed to produce lytic enzymes, such as proteases, celluloses, lipases, esterases, and amylases, which exhibited activity against Fusarium, Aspergillus, and Colletotrichum. The use of 16S rRNA analysis led to the identification of the bacterial genera Chryseobacterium, Bacillus, Pseudomonas, Mycobacterium, Staphylococcus, Curtobacterium, Enterobacter, Agrobacterium, Ochrobactrum, Serratia, Stenotrophomonas, and Acinetobacter. The bacteria isolated from the rhizosphere exhibited the greatest ability to fix nitrogen and produced indole acetic acid, gibberellins, siderophore, and lytic enzymes. In addition, the isolates collected from the soil samples demonstrated ability to solubilize phosphate.

Desarrollo de un sistema de fermentación líquida y de enquistamiento para una bacteria fijadora de nitrógeno con potencial como biofertilizante / Development of a liquid fermentation system and encystment for a nitrogen-fixing bacterium strain having biofertilizer potential

El uso indiscriminado de fertilizantes químicos ha contribuido al deterioro de las propiedades biológicas, físicas y químicas del suelo, lo que derivó en la pérdida de su capacidad productiva. Por esta razón, se ha planteado como alternativa tecnológica el uso de biofertilizantes. El objetivo de esta investigación fue desarrollar un sistema de fermentación líquida y de enquistamiento adecuado para la multiplicación de Azotobacter chroococcum cepa AC1, una bacteria utilizada en la formulación de un biofertilizante actualmente producido por CORPOICA, Colombia. Se emplearon diseños estadísticos secuenciales para determinar las condiciones del sistema de fermentación. Se evaluaron la interacción entre la agitación, la aireación y el pH sobre la biomasa viable obtenida de AC1 (UFC/ml), que se tomó como variable de respuesta. Además, se evaluó la capacidad de enquistamiento de esta bacteria empleando 2 agentes de enquistamiento, AE01 y AE02. La actividad potencial promotora del crecimiento vegetal fue evaluada por medio del ensayo de ARA (fijación biológica de nitrógeno), la técnica de azul de fosfomolibdeno (solubilización de fosfato) y la reacción colorimétrica empleando el reactivo de Salkowski (producción de compuestos indólicos). Se evidenciaron efectos significativos (p <0,05) sobre la producción de biomasa de los 3 factores evaluados (pH, aireación y agitación) individualmente, de una interacción dual y en la interacción tripartita, teniendo un efecto positivo sobre la variable de respuesta la aireación y agitación. La adición de los inductores de enquistamiento AE01 y AE02 demostró la capacidad de la cepa AC1 para formar quistes en condiciones de estrés. Asimismo, las condiciones de fermentación y el enquistamiento no afectaron las actividades biológicas evaluadas.

The indiscriminate use of chemical fertilizers has contributed to the deterioration of the biological, physical and chemical properties of the soil, resulting in the loss of its productive capacity. For this reason, the use of biofertilizers has emerged as a technological alternative. The objective of this research was to develop a suitable liquid fermentation system and encystment for the multiplication of Azotobacter chroococcum AC1 strain, a bacterium employed in a biofertilizer formulation produced at present by CARPOICA, Colombia. Sequential statistical designs were used to determine the conditions in the fermentation system. The interaction between agitation, aeration and pH was evaluated on the viable biomass (CFU/ml) of AC1. In addition, the encystment ability of the strain was evaluated using two encystment agents and the potential plant growth-promoting rhizobacteria (PGPR) activity was assessed by different techniques, such as nitrogen fixation by ARA, phosphate solubilization by the phospho-molybdenum-blue reaction and indolic compound production by colorimetric reaction using the Salkowski reagent. Results showed significant effects (p <0.05) on the viable biomass in the three conditions (pH, aeration and agitation) tested individually, in one dual interaction and one tripartite interaction, were demonstrated to have a positive effect on the response variable aeration and agitation. The addition of the two encystment agents evaluated, AE01 and AE02, demonstrated the ability of AC1 to form cysts under stress conditions. Likewise, fermentation and encystment conditions did not affect the biological activities tested.

[Development of a liquid fermentation system and encystment for a nitrogen-fixing bacterium strain having biofertilizer potential]. / Desarrollo de un sistema de fermentación líquida y de enquistamiento para una bacteria fijadora de nitrógeno con potencial como biofertilizante.

The indiscriminate use of chemical fertilizers has contributed to the deterioration of the biological, physical and chemical properties of the soil, resulting in the loss of its productive capacity. For this reason, the use of biofertilizers has emerged as a technological alternative. The objective of this research was to develop a suitable liquid fermentation system and encystment for the multiplication of Azotobacter chroococcum AC1 strain, a bacterium employed in a biofertilizer formulation produced at present by CARPOICA, Colombia. Sequential statistical designs were used to determine the conditions in the fermentation system. The interaction between agitation, aeration and pH was evaluated on the viable biomass (CFU/ml) of AC1. In addition, the encystment ability of the strain was evaluated using two encystment agents and the potential plant growth-promoting rhizobacteria (PGPR) activity was assessed by different techniques, such as nitrogen fixation by ARA, phosphate solubilization by the phospho-molybdenum-blue reaction and indolic compound production by colorimetric reaction using the Salkowski reagent. Results showed significant effects (p<0.05) on the viable biomass in the three conditions (pH, aeration and agitation) tested individually, in one dual interaction and one tripartite interaction, were demonstrated to have a positive effect on the response variable aeration and agitation. The addition of the two encystment agents evaluated, AE01 and AE02, demonstrated the ability of AC1 to form cysts under stress conditions. Likewise, fermentation and encystment conditions did not affect the biological activities tested.

Solubilización de fosfatos: una función microbiana importante en el desarrollo vegetal / Solubilization of phosphates: an important microbial function in plant development

La agricultura es la base fundamental para la sostenibilidad de la seguridad alimentaria en el planeta, ya que representa la principal fuente de alimento y hace parte de la economía de los países en desarrollo. Sin embargo en la actualidad la demanda de alimento es mayor y existe la necesidad de agilizar el crecimiento vegetal para suplir las necesidades de la población y disminuir los índices de desnutrición y hambre, pero para ello se utilizan prácticas agrícolas como la aplicación de fertilizantes químicos que afectan significativamente el medio ambiente y los ecosistemas del suelo. En busca de encontrar soluciones, en los últimos años se han desarrollado estrategias alternativas para reemplazar los fertilizantes. Los microorganismos han demostrado cumplir funciones que mantienen el equilibrio del suelo y apoyan el crecimiento vegetal mediante diversos mecanismos, entre ellos la solubilización de fosfatos, por el cual se logra liberar el ion fosfato accesible para la planta. Este elemento se encuentra limitado en el suelo y es un nutriente vital después del nitrógeno para el desarrollo de la planta. El género Bacillus se ha destacado como un potencial solubilizador de fosfato y puede ser utilizado como biofertilizante que va a permitir obtener un producto agrícola de calidad y sin generar consecuencias al ambiente.

Agriculture is the fundamental basis for the sustainability of food security on the planet, since it represents the main source of food and is part of the economy of developing countries. At the present time, however, the demand for food is greater and there is the need to speed up plant growth to meet the needs of the population and to reduce rates of malnutrition and hunger, but this is used for agricultural practices as the application of chemical fertilizers which significantly affect the environment and the ecosystems of the soil. In hopes of finding solutions, alternative strategies to replace fertilizers have been developed in recent years. The microorganisms have demonstrated compliance functions that keep the balance of the soil and support plant growth through a variety of mechanisms, including the solubilization of phosphates, which can succeed in freeing the phosphate ion accessible for the plant. This item is limited in the soil and is a vital nutrient after the nitrogen for the growth of the plant. The genus Bacillus has been highlighted as a potential solubilizer phosphate and can be used as biofertilizer that will enable them to obtain a quality agricultural product, without generating consequences to the environment.