With the aim to explore the possible role of mineral phosphate-solubilizing bacteria (PSB) in phosphorus (P) cycling in iron-rich, acidic soils, we conducted a survey of PSB naturally colonizing a limonitic crust in the south-east region of Venezuela (Bolı´var State). A total of 130 heterotrophic bacterial isolates showing different degrees of mineral tri-calcium phosphate (Ca 3 (PO 4 ) 2 )-solubilizing activities were isolated from NBRIP plates. In contrast, no isolates showing iron phosphate (FePO 4 )-or aluminum phosphate (AlPO 4 )-solubilizing activities were detected by this experimental approach. The 10 best Ca 3 (PO 4 ) 2 -solubilizers were selected for further characterization. These isolates were shown to belong to the genera Burkholderia, Serratia, Ralstonia and Pantoea by partial sequencing analysis of their respective 16S rRNA genes. All the PSB isolates were able to mediate almost complete solubilization of Ca 3 (PO 4 ) 2 in liquid cultures; in contrast, the PSB isolates were less effective when solubilizing FePO 4 . Two groups of PSB isolates were clearly differentiated on the basis of their Ca 3 (PO 4 ) 2 solubilization kinetics. Acidification of culture supernatants seemed to be the main mechanism for P solubilization. Indeed, gluconic acid was shown to be present in the supernatant of five isolates. Furthermore, detection of genes involved in the production of this organic acid was possible in three isolates by means of a PCR protocol. r

The mineral phosphate-solubilizing (MPS) activity of a Pantoea agglomerans strain, namely MMB051, isolated from an iron-rich, acidic soil near Ciudad Piar (Bolívar State, Venezuela), was characterized on a chemically defined medium (NBRIP). Various insoluble inorganic phosphates, including tri-calcium phosphate [Ca 3 (PO 4 ) 2 ], iron phosphate (FePO 4 ), aluminum phosphate (AlPO 4 ), and Rock Phosphate (RP) were tested as sole sources of P for bacterial growth. Solubilization of Ca 3 (PO 4 ) 2 was very efficient and depended on acidification of the external milieu when MMB051 cells were grown in the presence of glucose. This was also the case when RP was used as the sole P source. On the other hand, the solubilization efficiency toward more insoluble mineral phosphates (FePO 4 and AlPO 4 ) was shown to be very low. Even though gluconic acid (GA) was detected on culture supernatants of strain MMB051, a consequence of the direct oxidation pathway of glucose, inorganic-P solubilization seemed also to be related to other processes dependent on active cell growth. Among these, proton release by ammonium (NH 4 ? ) fixation appeared to be of paramount importance to explain inorganic-P solubilization mediated by strain MMB051. On the contrary, the presence of nitrate (NO 3 -) salts as the sole N source affected negatively the ability of MMB051 cells to solubilize inorganic P.

Morphological studies of bacterial strains Micromorphological study: Consisted in evaluation of cell motility and shape by observation under the optical microscope and determination of the biochemical nature of the bacterial wall (Gram staining). 12 Macromorphological study: The macroscopic characteristics of the colonies such as color, shape, texture and appearance, as well as the production of pigments, were observed after 24 hours of incubation of isolates cultured on brain heart infusion (BHI) agar at 30°C. 13 Biochemical characterization A preliminary taxonomic location at the group or family level was performed using the following biochemical tests: Hugh and Leifson medium, nitrate reduction, MIO (Motility, Indol, Ornithine), oxidase test, MacConkey Agar, and urea hydrolysis, according to procedures previously described. 12-14

La miel es uno de los productos más comercializados y falsificados, por lo que es importante establecer estándares de calidad y autenticidad. En el presente estudio se evaluó la calidad nutracéutica y autenticidad de la miel con base a parámetros bioquímicos (polifenoles, flavonoides y proteínas) y capacidad antioxidante. Se seleccionaron 8 mieles comercializadas en el Mercado Periférico de Mérida (Venezuela) (muestras C), así como 8 muestras auténticas (A) y una miel artificial (AR). A todas las muestras se les midió la concentración de proteínas, polifenoles y flavonoides; y se determinó la capacidad antioxidante de las mieles empleando los métodos capacidad antioxidante total (CAT), % de inhibición del radical hidroxilo (RH) y actividad antioxidante (AOA). Se encontró una importante correlación entre la concentración de fenoles y flavonoides y la capacidad antioxidante para cada uno de los métodos usados. Se elaboró un dendograma utilizando el método clúster, lo que permitió agrupar a las mieles por propiedades comunes. El análisis de clúster permitió determinar que la concentración de flavonoides y polifenoles, así como la capacidad antioxidante determinada a través de los métodos CAT y AOA son parámetros útiles para determinar la calidad nutracéutica y autenticidad de las muestras de miel. No son útiles en este sentido la concentración de proteínas y la actividad antioxidante medida por el método de inhibición del radical hidroxilo. En resumen, estos parámetros podrían ser incluidos en los estándares de calidad de las muestras de miel, valorizando este tipo de productos como alimentos nutracéuticos.