Diversity of Flavobacterium psychrophilum and the potential use of its phages for protection against bacterial cold water disease in salmonids

Flavobacterium psychrophilum causes rainbow trout fry syndrome (RTFS) and cold water disease (CWD) in salmonid aquaculture. We report characterization of F. psychrophilum strains and their bacteriophages isolated in Chilean salmonid aquaculture. Results suggest that under laboratory conditions phages can decrease mortality of salmonids from infection by their F. psychrophilum host strain. Twelve F. psychrophilum isolates were characterized, with DNA restriction patterns showing low diversity between strains despite their being obtained from different salmonid production sites and from different tissues. We isolated 15 bacteriophages able to infect some of the F. psychrophilum isolates and characterized six of them in detail. DNA genome sizes were close to 50 Kbp and corresponded to the Siphoviridae and Podoviridae families. One isolate, 6H, probably contains lipids as an essential virion component, based on its chloroform sensitivity and low buoyant density in CsCl. Each phage isolate rarely infected F. psychrophilum strains other than the strain used for its enrichment and isolation. Some bacteriophages could decrease mortality from intraperitoneal injection of its host strain when added together with the bacteria in a ratio of 10 plaque-forming units per colony-forming unit. While we recognize the artificial laboratory conditions used for these protection assays, this work is the first to demonstrate that phages might be able protect salmonids from RTFS or CWD.     

Antioxidant activity of ethanolic extracts from several asparagus cultivars

Three different methods (antiradical activity, inhibition of primary oxidation, and ferric reducing power) have been used to evaluate the antioxidant activity of eight different asparagus cultivars and byproducts: white and green asparagus from Alcalá del Río (Guadalquivir Valley, Seville) and American hybrids, native spears, and their byproducts from Huétor-Tájar (Vega de Granada). The correlation between antioxidant activity and total phenol content was studied. Six standards were also tested to validate the modified methods for antioxidant activity determination. Results obtained for antiradical capacity and reducing power were very similar, and a high correlation with phenols was found (R > or = 0.9 for both tests). Sample origin was an important factor, spears from Huétor-Tájar having higher values (ARC between 7 and 10 and P(R) of 0.25-0.33) than those from Alcalá del Río (ARC 0.6-2 and P(R) of 0.05-0.07). Significant differences were found between spears with the same origin, suggesting that genetics are another factor to take into account. Asparagus inhibits lipid primary oxidation, but no correlation between the inhibition percentage and phenols was observed. Asparagus origin was the only factor that led to significant differences: samples from Huétor-Tájar had higher values (POIC between 18 and 32) than those from Alcalá del Río (POIC of 5-9). Byproducts from the canning industry at Huétor-Tájar were also assayed for antioxidant activity; the results obtained suggested that byproducts could be considered as an excellent source of natural antioxidants.     

Oxytetracycline treatment reduces bacterial diversity of intestinal microbiota of Atlantic salmon

The effect of oxytetracycline (OTC) treatment on intestinal bacterial populations in juvenile Atlantic salmon Salmo salar was evaluated. Oxytetracycline was administered by way of medicated feed to fish held in experimental tanks. Restriction fragment length polymorphism and sequencing of 16S rDNA from isolates were used to analyze the intestinal microbiota before, during, and after OTC administration. The microbiota from untreated fish was more diverse, consisting mainly of Pseudomonas, Acinetobacter, Bacillus, Flavobacterium, Psycrobacter, and Brevundimonas spp. In contrast, the microbiota of the OTC-treated group was characterized by lower diversity and consisted only of Aeromonas, clustering with A. sobria and A. salmonicida. Antibiotic-resistant isolates were identified as Aeromonas spp.; sequencing the resistance determinant showed it to be the tetE gene. Overall, OTC treatment changed the composition of the intestinal microbiota of Atlantic salmon, as evidenced by a reduction in bacterial diversity. These results support the current concern that antibiotic treatment can facilitate the proliferation of opportunistic bacteria by eradicating competing microorganisms.     

Development of triploid hybrids in asparagus breeding employing a tetraploid landrace

The development of triploid cultivars from crosses between the tetraploid landrace ‘Morado de Huetor’ and diploid commercial cultivars was studied in this work. Fertility of both 4x × 2x and 2x × 4x crosses, as measured by fruit set and number of seeds per fruit, and germination rate of triploid seeds, were studied in order to assess the viability of producing commercial seeds. Seven triploid hybrid progenies were included in a progeny test together with thirteen experimental tetraploid hybrids and four cultivars (‘Grande’, ‘UC157-F2’, ‘Purple Passion’ and ‘Morado de Huetor’). Marketable spear production and mean diameter of spears were evaluated in both 2007 and 2008. Crosses 4x × 2x were more successful than 2x × 4x, and a wide variation from high to very low fertility within tetraploid females was found. Germination rate of triploid seeds was similar to diploid ones. After 2 years of evaluation experimental hybrid triploids were more productive than tetraploids with values similar to the highest yielding diploid cultivar (‘Grande’). Spear diameter of triploid hybrids was in general thicker than the tetraploid hybrids and significantly thinner than the standard cultivars ‘Grande’ and ‘Purple Passion’ (tertraploid). These results suggest that the development of new triploid cultivars (4x × 2x) employing a tetraploid landrace from a different genetic background of current diplods could be interesting in asparagus breeding, broadening the spectrum of cultivated asparagus cultivars.     

Study of Ammonium Contamination in Leachates from an Ultisol Following Application of Various Types of Amendment

The composition of leachates from an Ultisol reconstructed inlysimeters and amended with limestone, sugar foam waste and gypsum rock was studied. The typical rainfall of the area fromwhich the soil was collected was simulated under laboratory conditions over a five-month period. The soil samples treated with gypsum behaved markedly differently from the rest. Thus, the samples amended with gypsum gave leachates with substantially increased ammonium contents that might result in contamination of aquifers. The gypsum-treated samples alsoexhibited marked differences in pH, EC and the Ca, Mg, Na andK contents from the rest.     

Estimation of phosphate adsorption by Acrisols of western Spain from electrical conductivity of potassium dihydrogen phosphate extracts of soil

Estimation of the phosphate adsorption capacity in highly weathered acid soils is crucial for adopting appropriate phosphate fertilization practices. In this work, the salt sorption effect was used to develop a method for estimating phosphate adsorption capacity from the decrease in electrical conductivity of a potassium dihydrogen phosphate solution brought in contact with acidic soil samples from surface and subsurface horizons of Acrisols. The method is fast and simple and requires only the use of a conductimeter.     

Changes in pH and the organic matter and phosphorus contents of asparagus cultivated soils produced by phosphorus fertilization

We tested phosphorus (P) supplementation of green asparagus cultivated in a calcareous soil of alkaline pH and a low available P content in order to obtain preliminary information for adjusting the P dose. For this purpose we monitored changes in pH and available P and organic matter contents over a two‐year period. Available P levels were found to increase with increasing P dose applied. Also, the soil pH was found to decrease, as was the organic matter content of the upper horizon.     

Flavonoid profile of green asparagus genotypes

The determination of flavonoid profiles from different genotypes of triguero asparagus and their comparison to those from green asparagus commercial hybrids was the main goal of this study. The samples consisted of 32 commercial hybrids and 65 genotypes from the Huetor-Tajar population variety (triguero). The analysis of individual flavonoids by HPLC-DAD-MS has allowed the determination of eight naturally occurring flavonol derivatives in several genotypes of triguero asparagus. Those compounds included mono-, di-, and triglycosides of three flavonols, that is, quercetin, isorhamnetin, and kaempferol. The detailed analysis of the flavonoid profiles revealed significant differences among the distinct genotypes. These have been classified in three distinct groups as the result of a k-means clustering analysis, two of them containing both commercial hybrids and triguero asparagus and another cluster constituted by 21 genotypes of triguero asparagus, which contain several key flavonol derivatives able to differentiate them. Hence, the triglycosides tentatively identified as quercetin-3-rhamnosyl-rutinoside, isorhamnetin-3-rhamnosyl-rutinoside, and isorhamnetin-3-O-glucoside have been detected only in the genotypes grouped in the above-mentioned cluster. On the other hand, the compound tentatively identified as isorhamnetin-3-glucosyl-rutinoside was present in most genotypes of triguero asparagus, whereas it has not been detected in any of the commercial hybrids.