Lyme disease: antibodies against <i>Borrelia burgdorferi</i> in farm workers in Argentina

Lyme Disease is a tick-borne (specially by Ixodes ticks) immune-mediated inflammatory disorder caused by a newly recognize spirochete, Borrelia burgdorferi. Indirect fluorescent antibody (IF) staining methods and enzyme-linked immunosorbent assay are frequently relied upon to confirm Lyme borreliosis infections. Although serologic testing for antibodies has limitations, it is still the only practical means of confirming B. burgdorferi infections. Because we have no previous report of Lyme disease in human inhabitants in Argentina, a study was designed as a seroepidemiologic investigation of the immune response to B. burgdorferi in farm workers of Argentina with arthritis symptoms. Three out of 28 sera were positive (#1, 5 and 9). Serum #1 was positive for Immunoglobulin G at dilution 1:320, serum #5 and #9 both to dilution 1:160; while for Immunoglobulin M all (#1, 5 and 9) were positive at low dilution (1:40) using IF. The results showed that antibodies against B. burgdorferi are present in an Argentinian population. Thus caution should be exercised in the clinical interpretation of arthritis until the presence of B. burgdorferi be confirmed by culture in specific media.Facultad de Ciencias Veterinaria

Lyme disease: antibodies against <i>Borrelia burgdorferi</i> in farm workers in Argentina

Lyme Disease is a tick-borne (specially by Ixodes ticks) immune-mediated inflammatory disorder caused by a newly recognize spirochete, Borrelia burgdorferi. Indirect fluorescent antibody (IF) staining methods and enzyme-linked immunosorbent assay are frequently relied upon to confirm Lyme borreliosis infections. Although serologic testing for antibodies has limitations, it is still the only practical means of confirming B. burgdorferi infections. Because we have no previous report of Lyme disease in human inhabitants in Argentina, a study was designed as a seroepidemiologic investigation of the immune response to B. burgdorferi in farm workers of Argentina with arthritis symptoms. Three out of 28 sera were positive (#1, 5 and 9). Serum #1 was positive for Immunoglobulin G at dilution 1:320, serum #5 and #9 both to dilution 1:160; while for Immunoglobulin M all (#1, 5 and 9) were positive at low dilution (1:40) using IF. The results showed that antibodies against B. burgdorferi are present in an Argentinian population. Thus caution should be exercised in the clinical interpretation of arthritis until the presence of B. burgdorferi be confirmed by culture in specific media.Facultad de Ciencias Veterinaria

Identification of a transmissible plasmid from an Argentine Sinorhizobium meliloti strain which can be mobilised by conjugative helper functions of the European strain S. meliloti GR4

We describe in this work the identification and the conjugal properties of two cryptic plasmids present in the strain Sinorhizobium meliloti LPU88 isolated from an Argentine soil. One of the plasmids, pSmeLPU88b (22 kb), could be mobilised from different S. meliloti strains to other bacteria by conjugation only if the other plasmid, pSmeLPU88a (139 kb), was present. This latter plasmid, however, could not be transferred via conjugation (frequency -9 transconjugants per recipient) contrasting with the conjugal system from the previously described strain GR4, where one plasmid is mobilisable and a second one (helper) is self-transmissible. Despite the differences between the two systems, the conjugative helper functions present in the cryptic plasmids of strain GR4 were active in the mobilisation of plasmid pSmeLPU88b from strain LPU88. Contrasting with this, plasmid pSmeLPU88b was not mobilised by the helper functions of the broad-host-range plasmid RP4. Eckhardt gel analysis showed that none of the plasmids from strain GR4 were excluded in the presence of plasmid pSmeLPU88b suggesting that they all belong to different incompatibility groups for replication. The small plasmid from strain LPU88, pSmeLPU88b, was only able to replicate in members of the Rhizobiaceae family such as Rhizobium leguminosarum, Rhizobium tropici and Agrobacterium tumefaciens, but not in Escherichia coli or Pseudomonas fluorescens. The observation suggests that most likely plasmid pSmeLPU88b was not received from a phylogenetically distant bacterium.Facultad de Ciencias ExactasInstituto de Biotecnologia y Biologia Molecula

Identification of a transmissible plasmid from an Argentine Sinorhizobium meliloti strain which can be mobilised by conjugative helper functions of the European strain S. meliloti GR4

We describe in this work the identification and the conjugal properties of two cryptic plasmids present in the strain Sinorhizobium meliloti LPU88 isolated from an Argentine soil. One of the plasmids, pSmeLPU88b (22 kb), could be mobilised from different S. meliloti strains to other bacteria by conjugation only if the other plasmid, pSmeLPU88a (139 kb), was present. This latter plasmid, however, could not be transferred via conjugation (frequency -9 transconjugants per recipient) contrasting with the conjugal system from the previously described strain GR4, where one plasmid is mobilisable and a second one (helper) is self-transmissible. Despite the differences between the two systems, the conjugative helper functions present in the cryptic plasmids of strain GR4 were active in the mobilisation of plasmid pSmeLPU88b from strain LPU88. Contrasting with this, plasmid pSmeLPU88b was not mobilised by the helper functions of the broad-host-range plasmid RP4. Eckhardt gel analysis showed that none of the plasmids from strain GR4 were excluded in the presence of plasmid pSmeLPU88b suggesting that they all belong to different incompatibility groups for replication. The small plasmid from strain LPU88, pSmeLPU88b, was only able to replicate in members of the Rhizobiaceae family such as Rhizobium leguminosarum, Rhizobium tropici and Agrobacterium tumefaciens, but not in Escherichia coli or Pseudomonas fluorescens. The observation suggests that most likely plasmid pSmeLPU88b was not received from a phylogenetically distant bacterium.Facultad de Ciencias ExactasInstituto de Biotecnologia y Biologia Molecula

Construction of a Sinorhizobium meliloti strain carrying a stable and non-transmissible chromosomal single copy of the green fluorescent protein GFP-P64L/S65T

A single copy of the green fluorescent protein (GFP)-encoding gene gfp-P64L/S65T under the control of the constitutive nptII promoter was introduced in a neutral region of the Sinorhizobium meliloti chromosome, between the genes recA and alaS. Within the same chromosomal region downstream of gfp-P64L/S65T a tetracycline (Tc) resistant cassette was also inserted. Both markers were very stable during at least 40 bacterial generations without any selective pressure. Similarly, the gfp-Tc cassette was stable and functional in all rhizobia that were recovered from alfalfa nodules. The GFP-associated fluorescence derived from the (single copy) chromosomal gfp-P64L/S65T allowed detection of rhizobia during the colonisation of the root, infection thread formation, and nodule development. The gfp-Tc rhizobia showed indistinguishable phenotypes for nodulation, competitiveness, and nitrogen-fixation from the parental strain. The labelling system described here can be used for the stable fluorescent tagging of S. meliloti strains allowing their detection in biologically complex soil environments.Facultad de Ciencias ExactasInstituto de Biotecnologia y Biologia Molecula

Construction of a Sinorhizobium meliloti strain carrying a stable and non-transmissible chromosomal single copy of the green fluorescent protein GFP-P64L/S65T

A single copy of the green fluorescent protein (GFP)-encoding gene gfp-P64L/S65T under the control of the constitutive nptII promoter was introduced in a neutral region of the Sinorhizobium meliloti chromosome, between the genes recA and alaS. Within the same chromosomal region downstream of gfp-P64L/S65T a tetracycline (Tc) resistant cassette was also inserted. Both markers were very stable during at least 40 bacterial generations without any selective pressure. Similarly, the gfp-Tc cassette was stable and functional in all rhizobia that were recovered from alfalfa nodules. The GFP-associated fluorescence derived from the (single copy) chromosomal gfp-P64L/S65T allowed detection of rhizobia during the colonisation of the root, infection thread formation, and nodule development. The gfp-Tc rhizobia showed indistinguishable phenotypes for nodulation, competitiveness, and nitrogen-fixation from the parental strain. The labelling system described here can be used for the stable fluorescent tagging of S. meliloti strains allowing their detection in biologically complex soil environments.Facultad de Ciencias ExactasInstituto de Biotecnologia y Biologia Molecula

Caracterización simbiótica de rizobios noduladores de alfalfa aislados en suelos ácidos de Argentina

En comunicaciones anteriores hemos descripto la estrategia utilizada para el aislamiento de rizobios noduladores de alfalfa de suelos ácidos locales, su caracterización genética preliminar, y el estudio de propiedades de tolerancia a la acidez en medios artificiales en condiciones de laboratorio (SAIB 1996). Dicho análisis permitió diferenciar claramente dos grupos de rizobios noduladores de alfalfa distintas respecto al rango de hospedadores, capacidad fijadora de nitrógeno, y tolerancia a la acidez. Las cepas de S. meliloíi (Sme) resultaron levemente ácido tolerantes (pH 6,0) pero eficientes fijadoras de nitrógeno. Contrariamente, aislamientos de R. spp. genéticamente relacionados a la cepa previamente descripta Orí 91 resultaron muy ácido tolerantes (pH 5,0) pero ineficientes. En el presente trabajo hemos analizado en detalle las propiedades de nodulación y competitividad a diferentes pHs, de cepas representativas de cada uno de los grupos de rizobios previamente caracterizados.Facultad de Ingenierí

A microcosm study on the influence of pH and the host-plant on the soil persistence of two alfalfa-nodulating rhizobia with different saprophytic and symbiotic characteristics

The acid tolerance of Sinorhizobium meliloti in culture media and in soils is considered a useful criteria to select for strains with improved survival in agricultural acidic soils. Using a glass tube system with gamma-irradiated soil at different pH values, we analysed the survival of two different alfalfa-nodulating rhizobia: S. meliloti (pHlimit for growth 5.6–6.0) and the acid-tolerant Rhizobium sp. LPU83, closely related to the strain Rhizobium sp. Or191 (pHlimit for growth below 5.0). Although the acid-tolerant rhizobia showed a slightly better survival during the first months in acid soil (pH=5.6), none of the strains could be detected 2 months after inoculation (bacterial counts were below 10³ colony-forming units (cfu)/30 g of soil). The inclusion of two alfalfa plants/glass tube with soil, however, supported the persistence of both types of rhizobia at pH 5.6 for over 2 months with counts higher than 9×10⁶ cfu/30 g of soil. Remarkably, in the presence of alfalfa the cell densities reached by S. meliloti were higher than those reached by strain LPU83, which started to decline 1 week after inoculation. Although more acid-sensitive in the culture medium than the Or191-like rhizobia, in the presence of the host plant the S. meliloti strains showed to be better adapted to the free-living condition, irrespective of the pH of the soil.Facultad de Ciencias ExactasInstituto de Biotecnología y Biología Molecula

Diferentes estrategias de barbecho en cultivos extensivos: actividad respiratoria y de la enzima ureasa en el suelo

La alta frecuencia del cultivo de soja en las secuencias agrícolas y la tendencia a su monocultivo, acarrea problemas que han sido ampliamente documentados. Podemos mencionar el deterioro en las propiedades químicas, físicas y biológicas de los suelos, bajas eficiencias de uso del agua, problemas de malezas, plagas y enfermedades, entre otras. El área de influencia de la FCAyF de la UNLP es amplia, abarcando varios partidos entre ellos Magdalena, donde la superficie sembrada con soja aumento de 350 a 6.520 ha en el período 2002-2016 (Ministerio de Agricultura de la Provincia de Buenos Aires). Para que las consecuencias que se han registrado en otras zonas no se produzcan en el partido, se requieren resultados experimentales locales, sobre suelos que comparten características, que ofrezcan alternativas más sustentables de incorporar la soja. La rotación de cultivos, la siembra directa y la fertilización son tres pilares fundamentales para mejorar estos problemas. Además, puede plantearse como alternativa promisoria incorporar compost o incluir cultivos de cobertura durante el barbecho, lo que permitiría mejorar las propiedades de suelo mencionadas. La actividad biológica es la responsable de los procesos de mineralización y humificación de la materia orgánica del suelo, los cuales inciden en el ciclo de los nutrientes. Estos parámetros biológicos resultan ser más sensibles que los físico-químicos pudiendo detectarse tempranamente los cambios producidos por el uso al que están sometidos los suelos. El objetivo general del proyecto en el que se enmarca este trabajo es contribuir con opciones de manejo que puedan mejorar la sustentabilidad ecológica de los sistemas netamente agrícolas. En el presente resumen se presentan los primeros resultados de uno de los objetivos del trabajo, donde se plantea monitorear parámetros biológicos del suelo en el tiempo, entre ellos, la actividad respiratoria (AR) y de la enzima ureasa (AEU).Facultad de Ciencias Agrarias y Forestale

Propuesta para la valoración del rol de los microorganismos del suelo en sistemas agrícolas sustentables: aplicación en el ámbito de la Escuela Agropecuaria Nº 1 de Berisso

La transferencia del conocimiento científico hacia el sector productivo es clave para incrementar la producción sustentable. Un caso modelo es el uso adecuado de los recursos, en particular, valorar el rol de los microorganismos del suelo y concientizar a los actores de la producción. Con este fin docentes del Curso de Microbiología Agrícola de la Fac. de Cs. Agrarias y Forestales de la UNLP generaron una actividad que estuvo dirigida a estudiantes secundarios de escuelas agropecuarias y se aplicó en la Escuela Agropecuaria Nº 1 de Berisso. Los participantes tomaron conciencia sobre la importancia de los microorganismos en el suelo y el rol que juegan en la conservación de este recurso, lo que en definitiva conduce a un manejo sustentable. Estos resultados sugieren que la actividad se debe extender a otros centros educativos agrotécnicos y también a los productores de la región productiva del Gran La Plata, de manera de fortalecer el concepto que cumplen los microorganismos en la producción y sostenibilidad de los sistemas agrícolas.Eje: B5 Sistemas de conocimiento (Relatos de experiencias)Facultad de Ciencias Agrarias y Forestale