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Polyhydroxyalkanoates (PHAs) are polyesters intracellularly accumulated by various microorganisms as carbon and energy storage materials. The most common representative is poly-β-hydroxybutyrate (PHB). These biopolymers have been considered to be good substitutes for petroleum-derived synthetic plastics because of their similar properties to synthetic polymers and its complete biodegradability after disposal. Nevertheless a major drawback to the commercialisation of PHAs is their much higher production cost compared with petrochemical-based synthetic plastic materials. Optimization of fermentation process is one of the strategies more used to reducing high production costs of PHB. The aims of this work were to determine the optimal initial pH value for PHB production, as well as to optimize the agitation-aeration conditions of the fermentation process for product-biomass yield and for PHB accumulation by Rhizobium tropici strain 3. Optimization of initial pH was carried out in an orbital shaker. The pH values were adjusted between 6 and 8. The relation between pH and PHB concentration (g ⋅ L-1 ) was modelled by using orthogonal polynomials. The optimal pH that assures the biggest PHB production is 6.58 ± 0.2. As statistical tools, a central compose design Box-Wilson was used to search the optimal values of two important variables in fermentation process: agitation-aeration rates, for PHB production and for product-biomass yield. The fermentations were carried out in a bioreactor with 7.5 L capacity with 5 L of optimum culture medium. It was determined that optimal values to obtain a maximum PHB production are 500 r ⋅ min-1 and 1 vvm (volumes of air per minute per volume of batch) for agitation and aeration respectively and for product-biomass yield optimal values are 472 r ⋅ min-1 and 1.55 vvm. [ABSTRACT FROM AUTHOR]

The strain ICA 8001 from Bradyrhizobium elkanii is broadly used in Cuba for soybean inoculant production. One culture medium designed to multiply this microorganism contains molasses and aqueous soybean extract, which are elements of a variable composition and origin providing considerable amounts of carbonated substrates. Therefore, concentrations of total soluble carbohydrates and reducing carbohydrates as well as N, P, K, Ca, Mg and Na contents were determined, to get a partial nutritional characterization of these components. Analyses showed substantial quantities of these bacterium-absorbing elements within cell growth. The influence of molasses and aqueous soybean extract concentrations on the specific strain growth rate μ (h-1) was estimated by varying molasses concentrations in Bradyfact medium from 3 to 20 g.L-1 and aqueous soybean extract from 5 to 20 g.L-1. Growth dynamics were recorded for each variant, besides calculating μ. Results proved that higher than 10 and 12,5 g.L-1 molasses and aqueous soybean extract concentrations, respectively, inhibit Bradyrhizobium elkanii ICA 8001 growth. This phenomenon could be mathematically and physiologically explained through two new kinetic models. This research work contributes to Bradyrhizobium physiological knowledge, since it makes evident the relationship between culture medium composition and microorganism nutritional requirements, also how culture medium design may ensure more effective inoculants containing high cell concentrations. [ABSTRACT FROM AUTHOR]

Nineteen rhizobium strains were isolated from the nodules of the legumes Canavalia ensiformis, Stylosanthes guianensis, Centrosema molle, Pueraria phaseoloides and Macroptilium atropurpureum, with the objective of obtaining effective inoculants for such crops in acid soils. For the characterization of the bacterial isolates, their micromorphological, staining and cultural characteristics were studied, as well as some physiological-biochemical responses, such as the excretion of acid or base to the culture medium and the cetolactase assay. An in vitro nodulation essay was performed with each legume to determine the effectiveness of the isolates. According to the cultural characteristics, the growth rate in YMA method and the production of acid or base, the isolates obtained could belong to the genera Bradyrhizobium and Rhizobium and/or Sinorhizobium. The cetolactase test allowed to learn that none of the studied isolates belongs to the Agrobacterium genus. The trial with inoculated plants showed that all the isolated strains were effective in nodulation, because they nodulated in the tested legumes. It is concluded that from the isolated strains, 11 could belong to the genus Bradyrhizobium, while the other eight share similar characteristics with the genera Rhizobium and/or Sinorhizobium; all the isolates were effective in nodulation and they can be considered promising strains for obtaining inoculants for the studied forage legumes. [ABSTRACT FROM AUTHOR]

Se aislaron 19 cepas de rizobio a partir de los nódulos de las leguminosas Canavalia ensiformis, Stylosanthes guianensis, Centrosema molle, Pueraria phaseoloides y Macroptilium atropurpureum, con el objetivo de obtener inoculantes efectivos para dichos cultivos en suelos ácidos. Para la caracterización de los aislados bacterianos se estudiaron sus características micromorfológicas, tintoriales y culturales, así como algunas respuestas fisiológico-bioquímicas, tales como la excreción de ácido o base al medio de cultivo y el ensayo de la cetolactasa. Se hizo un ensayo de nodulación in vitro con cada una de las leguminosas para determinar la efectividad de los aislados. De acuerdo con las características culturales, la tasa de crecimiento en medio LMA y la producción de ácido o base, los aislados obtenidos pudieran pertenecer a los géneros Bradyrhizobium y Rhizobium y/o Sinorhizobium. La prueba de la cetolactasa permitió conocer que ninguno de los aislados en estudio pertenece al género Agrobacterium. El ensayo con plantas inoculadas mostró que todas las cepas aisladas fueron efectivas en la nodulación, ya que nodularon en las leguminosas probadas. Se concluye que de las cepas aisladas 11 pudieran pertenecer al género Bradyrhizobium, mientras que las ocho restantes comparten características similares con los géneros Rhizobium y/o Sinorhizobium; todos los aislados fueron efectivos en la nodulación y pueden considerarse cepas promisorias para la obtención de inoculantes para las leguminosas forrajeras en estudio. [ABSTRACT FROM AUTHOR]

Lipo-chitooligosaccharides produced by rhizobia are a class of signalling molecules mediating nodule recognition and organogenesis in the Rhizobium--leguminous symbiosis. Their synthesis is determined by rhizobiumnodulating genes; therefore, they are commonly known as Nod factors. This review is a compilation of updated information on some general topics, as Rhizobium-leguminous interaction signals, nod factor structure, as well as their role in symbiosis. Besides, a research view about this subject in Cuba is presented, describing results related to the design and optimization of culture media with nod factor inducers, with quorum sensing, with nod factor anti-stress effect, with the use of nod factor synthesis-induced inoculants and other oligosaccharines, and with the possible beneficial effect of the latter ones on bacterium-leguminous symbiosis. [ABSTRACT FROM AUTHOR]

Culture media constitute the world of microorganisms under laboratory conditions, trying to simulate their natural habitat to satisfy their most vital needs as living beings. The design of a culture medium responds to demands of the microorganism in question and to the objective pursued with its multiplication; therefore, the selection of nutrients and their appropriate concentrations is a greatly important factor. However, the employment of an appropriate methodology makes possible the obtaining of an optimum culture medium, either for growth and/or metabolite production. Numerous methods and designs of optimization exist with dissimilar characteristics, advantages and limitations that determine their use in diverse branches of investigation. The complete and fractional factorial designs, Plackett Burman, Box-Behnken and the uniform designs were approached in the work. The optimization of medium components and environmental conditions guarantees remarkable yield increments of fermentative processes in a quick and economic way. Therefore, this review seeks to approach the principles and methods of optimization, as well as characterize and exemplify the application of most used designs in culture media optimization, with the objective of extending their use to agricultural biotechonology. [ABSTRACT FROM AUTHOR]

Cells need a source of energy carbon and other nutrients to grow in nature or under laboratory conditions. They also require adequate oxygen concentration, temperature and pH conditions. In this work, the behaviour of two Bradyrhizobium elkanii strains in different culture media, was studied. Different cell multiplication dynamics were evident to each strain under those culture media, as a result of its nutrient composition. Modified propagation medium was notable for both strains studied. [ABSTRACT FROM AUTHOR]