The GacS/A-Rsm Pathway Positively Regulates Motility and Flagella Synthesis in Azotobacter vinelandii.

Azotobacter vinelandii is a motile bacterium that possesses an unusual pattern of peritrichous flagellation for members of the Pseudomonadaceae family. Unlike what has been reported for Pseudomonas spp. FleQ is not the master regulator of motility in A. vinelandii, this role is performed by FlhDC. Other factors involved in the regulation of motility are AlgU (σE) and CydR which act as negative regulators. In some members of the Enterobacteriaceae and Pseudomonadaceae families, the GacS/A-Rsm pathway is another important factor regulating motility. In the present study, the involvement of the GacS/A-Rsm pathway in regulating the motility of A. vinelandii was explored; we found that contrary to what has been reported for most of the strains studied of Pseudomonas species, GacS/A, through the Rsm system, positively controlled swimming motility. We show that the target of this regulation is the synthesis of flagella, which most likely occurs in an FlhDC-independent manner.

The decrease in the population of Gluconacetobacter diazotrophicus in sugarcane after nitrogen fertilization is related to plant physiology in split root experiments.

It has been established that a decrease in the population of Gluconacetobacter diazotrophicus associated with sugarcane occurs after nitrogen fertilization. This fact could be due to a direct influence of NH(4)NO(3) on bacterial cells or to changes in plant physiology after fertilizer addition, affecting bacterial establishment. In this work, we observed that survival of G. diazotrophicus was directly influenced when 44.8mM of NH(4)NO(3) (640mgN/plant) was used for in vitro experiments. Furthermore, micropropagated sugarcane plantlets were inoculated with G. diazotrophicus and used for split root experiments, in which both ends of the system were fertilized with a basal level of NH(4)NO(3) (0.35mM; 10mgN/plant). Twenty days post inoculation (dpi) one half of the plants were fertilized with a high dose of NH(4)NO(3) (6.3mM; 180 mgN/plant) on one end of the system. This nitrogen level was lower than that directly affecting G. diazotrophicus cells; however, it caused a decrease in the bacterial population in comparison with control plants fertilized with basal nitrogen levels. The decrease in the population of G. diazotrophicus was higher in pots fertilized with a basal nitrogen level when compared with the corresponding end supplied with high levels of NH4NO3 (100dpi; 80 days post fertilization) of the same plant system. These observations suggest that the high nitrogen level added to the plants induce systemic physiological changes that affect the establishment of G. diazotrophicus.

Calidad microbiológica: detección de Aeromonas sp y Pseudomonas sp en garrafones provenientes de pequeñas plantas purificadoras de agua / Microbiological quality: detection of Aeromonas sp and Pseudomonas sp in jugs from small water purification establishments

RESUMEN Las plantas purificadoras de agua que carecen de un adecuado sistema de control de calidad pueden generar problemas de salud pública. El objetivo de este estudio fue examinar la calidad microbiológica del agua proveniente de pequeñas plantas purificadoras de la ciudad de Puebla, así como, determinar la existencia de bacterias Aeromonas sp y Pseudomonas sp, y caracterizar si presentan un fenotipo patógeno oportunista. Se recolectaron 70 muestras de garrafones de agua de 25 establecimientos. La cuantificación bacteriana se realizó mediante el método de goteo en placa. Se comprobaron los géneros microbianos mediante análisis bioquímico. En las cepas que mostraron discrepancia se utilizó la identificación molecular con base a secuencias parciales del gen 16S rRNA para confirmar su especie y se les evaluaron sus características de patogenicidad: multirresistencia a antibióticos, producción de biopelícula y actividad hemolítica. El 40 % de las plantas purificadoras no cumplieron con la calidad microbiológica del agua para consumo humano. El 41.4 % de los garrafones de agua muestreados incumplió la normativa, presentando coliformes totales 35.7 %, Pseudomonas 30 %, Enterococcus faecalis 8.6 % y bacterias coliformes fecales el 5.7 %. Se obtuvieron 56 aislados, provenientes de los 29 garrafones contaminados; 10 de ellos se caracterizaron molecularmente, resultando 7 aislados relacionados con especies diferentes de P. aeruginosa y 3 con especies de Aeromonas. De los aislados de Pseudomonas, 5 presentaron resistencia a 2 familias de antibióticos y 2 mostraron multirresistencia. El 36 % de los 10 aislados produjeron hemólisis y biopelícula. Dos cepas de Aeromonas mostraron resistencia a Cefalosporina 3a generación pero no produjeron hemólisis. Los 10 aislados analizados fueron clasificados como no patógenos. Es necesario un seguimiento sanitario más estricto para lograr el cumplimiento de las normas nacionales e internacionales relacionadas con el consumo de agua purificada, para evitar dañar la salud de los consumidores.

ABSTRACT Water purification establishments that lack an adequate quality control system can cause public health problems. The objective of this study was to examine the microbiological quality of water from small purification establishments in the city of Puebla, as well as to determine the existence of Aeromonas sp and Pseudomonas sp bacteria, and to characterize whether they present an opportunistic pathogenic phenotype. 70 water jug samples were collected from 25 establishments. Bacterial quantification was performed using the drop plate method. Microbial genera were determined by biochemical analysis using the standard methodology. In the strains that showed discrepancy, molecular identification based on partial sequences of the 16S rRNA gene was used to confirm their species, and their pathogenic characteristics were evaluated: multiresistance to antibiotics, biofilm production, and hemolytic activity. The results showed that 40 % of the purification establishments did not comply with the microbiological quality of water for human consumption. Similarly, 41.4 % of the jugs of water sampled failed to comply with the regulations, presenting total coliforms 35.7 %, Pseudomonas 30 %, Enterococcus faecalis 8.6 % and fecal coliform bacteria 5.7 %. Likewise, 56 isolates were obtained from the 29 contaminated jugs, of which 10 were molecularly characterized, resulting in 4 different species for P. aeruginosa and 3 for Aeromonas. Of the 7 Pseudomonas isolates, 5 presented resistance to 2 families of antibiotics and 2 showed multiresistance. In total, 36 % of the 10 isolates produced hemolysis and biofilm. Two Aeromonas strains showed resistance to 3rd generation Cephalosporin but did not produce hemolysis. The 10 isolates analyzed were classified as non-pathogenic. A stricter sanitary monitoring is necessary to achieve compliance with national and international standards related to the consumption of purified water, to avoid harming the health of consumers.

Compatible bacterial mixture, tolerant to desiccation, improves maize plant growth.

Plant growth-promoting rhizobacteria (PGPR) increase plant growth and crop productivity. The inoculation of plants with a bacterial mixture (consortium) apparently provides greater benefits to plant growth than inoculation with a single bacterial strain. In the present work, a bacterial consortium was formulated containing four compatible and desiccation-tolerant strains with potential as PGPR. The formulation had one moderately (Pseudomonas putida KT2440) and three highly desiccation-tolerant (Sphingomonas sp. OF178, Azospirillum brasilense Sp7 and Acinetobacter sp. EMM02) strains. The four bacterial strains were able to adhere to seeds and colonize the rhizosphere of plants when applied in both mono-inoculation and multi-inoculation treatments, showing that they can also coexist without antagonistic effects in association with plants. The effects of the bacterial consortium on the growth of blue maize were evaluated. Seeds inoculated with either individual bacterial strains or the bacterial consortium were subjected to two experimental conditions before sowing: normal hydration or desiccation. In general, inoculation with the bacterial consortium increased the shoot and root dry weight, plant height and plant diameter compared to the non-inoculated control or mono-inoculation treatments. The bacterial consortium formulated in this work had greater benefits for blue maize plants even when the inoculated seeds underwent desiccation stress before germination, making this formulation attractive for future field applications.

La disminución de la población de Gluconacetobacter diazotrophicus en caña de azúcar, después de la fertilización nitrogenada, está relacionada con la fisiología de las plantas en experimentos de raíz dividida / The decrease in the population of Gluconacetobacter diazotrophicus in sugarcane after nitrogen fertilization is related to plant physiology in split root experiments

It has been established that a decrease in the population of Gluconacetobacter diazotrophicus associated with sugarcane occurs after nitrogen fertilization. This fact could be due to a direct influence of NH4NO3 on bacterial cells or to changes in plant physiology after fertilizer addition, affecting bacterial establishment. In this work, we observed that survival of G. diazotrophicus was directly influenced when 44.8 mM of NH4NO3 (640 mg N/plant) was used for in vitro experiments. Furthermore, micropropagated sugarcane plantlets were inoculated with G. diazotrophicus and used for split root experiments, in which both ends of the system were fertilized with a basal level of NH4NO3 (0.35 mM; 10 mg N/plant). Twenty days post inoculation (dpi) one half of the plants were fertilized with a high dose of NH4NO3 (6.3 mM; 180 mg N/plant) on one end of the system. This nitrogen level was lower than that directly affecting G. diazotrophicus cells; however, it caused a decrease in the bacterial population in comparison with control plants fertilized with basal nitrogen levels. The decrease in the population of G. diazotrophicus was higher in pots fertilized with a basal nitrogen level when compared with the corresponding end supplied with high levels of NH4NO3 (100 dpi; 80 days post fertilization) of the same plant system. These observations suggest that the high nitrogen level added to the plants induce systemic physiological changes that affect the establishment of G. diazotrophicus.

La población de Gluconacetobacter diazotrophicus asociada a la caña de azúcar disminuye después de la fertilización nitrogenada, lo cual podría ocurrir por la influencia directa del NH4NO3 sobre la supervivencia bacteriana, o por cambios en la fisiología de las plantas, que impiden el establecimiento bacteriano. En el presente trabajo se observó que en experimentos in vitro la supervivencia de G. diazotrophicus fue influenciada por 44,8 mM de NH4NO3 (640 mg N/plant). Además, G. diazotrophicus fue inoculado en plántulas micropropagadas de caña de azúcar, que fueron usadas para realizar experimentos de raíz dividida, en las que ambos extremos de los sistemas se fertilizaron con un nivel basal de NH4NO3 (0,35 mM; 10 mg N/planta). A los 20 días posteriores a la inoculación (dpi), la mitad de plantas fueron fertilizadas en uno de sus extremos con una dosis elevada de NH4NO3 (6,3 mM; 180 mg of N/plant). Este nivel fue menor al que afectó directamente a las células de G. diazotrophicus; sin embargo, provocó una disminución de la población bacteriana en comparación con plantas testigo fertilizadas con niveles basales de nitrógeno. La disminución de la población fue mayor para raíces fertilizadas con un nivel basal de nitrógeno en comparación con las raíces fertilizadas con altos niveles del mismo sistema de plantas (100 dpi; 80 días posfertilización). Estas observaciones indican que el alto nivel de nitrógeno añadido a las plantas inducen cambios fisiológicos sistémicos que afectan el establecimiento de G. diazotrophicus.