Structure and elemental distribution of (Ga,Mn)N nanowires

(Ga,Mn)N nanowires were grown by plasma-assisted molecular beam epitaxy on p-type Si(111) substrates. Chemical composition and elemental distribution of single nanowires were analyzed by energy dispersive X-ray spectroscopy revealing an inhomogeneous Mn distribution decreasing from the surface of the nanowires toward the inner core region. The average Mn concentration within the nanowires is found to be below 1%. High-resolution transmission electron microscopy shows the presence of planar defects perpendicular to the growth direction in undoped and Mn-doped GaN nanowires. The density of planar defects dramatically increases under Mn supply.     

Rapid selection of phage-resistant mutants in Streptococcus thermophilus by immunoselection and cell sorting

Immunoselection and flow cytometry allowed the isolation from Streptococcus thermophilus strain Str31 of double mutants displaying resistance to the phage phi31 and good acid production. Strain Str31 is very sensitive to phage phi31. This phage-host system seemed therefore particularly suitable to test the validity of the selection method adopted in this study. Mutants were stable with respect to both characters. The isolation of the double mutants required 4 to 5 days. The approach does not involve genetic manipulations and can therefore be an alternative to genetic engineering when this technology cannot be applied.     

Lactobacillus pentosus dominates spontaneous fermentation of Italian table olives

Culture-dependent and -independent approaches were applied to identify the bacterial species involved in Italian table olive fermentation. Bacterial identification showed that Lactobacillus pentosus was the dominant species although the presence of Lactobacillus plantarum, Lactobacillus casei, Enterococcus durans, Lactobacillus fermentum and Lactobacillus helveticus was observed. Rep-PCR allowed to obtain strain-specific profiles and to establish a correlation with table olive environment. PCR-DGGE (Denaturing Gradient Gel Electrophoresis) confirmed the heterogeneity of bacterial community structure in fermented table olives as well as the prevalence of L. pentosus. The strains were characterized on the basis of technological properties (NaCl tolerance, β-glucosidase activity and the ability to grow in synthetic brine and in presence of 1 g/100 mL oleuropein). L. pentosus showed a high capacity of adaptation to the different conditions characterizing the olive ecosystem. This species showed the highest percentage of strains able to grow in presence of 10 g/100 mL NaCl, oleuropein and in the synthetic brine. Moreover, all the strains belonging to L. pentosus and L. plantarum species showed a β-glucosidase activity. This study allowed both to identify the main species and strains associated to Italian table olives and to obtain a lactic acid bacteria collection to apply as starter culture in the process of olive fermentation.     

Alginate-based coatings charged with hydroxyapatite and quercetin for fresh-cut papaya shelf life

In this study, the effect of alginate-based coatings charged with quercetin glycoside compounds and hydroxyapatite/quercetin glycoside compounds (HA/QUE) on the microbiological quality, and on bioactive compounds of fresh-cut papaya, was evaluated for 14 days at 6 °C. Alginate coatings with hydroxyapatite/quercetin showed a high capability to slow down the growth of all microbiological parameters investigated. At the end of cold storage, the total bacteria count in papaya samples covered with HA/QUE alginate coating was 4.8 log CFU g⁻¹ which is significantly lower (P < 0.05) than 8.3 log CFU g⁻¹ for uncoated samples. Total carotenoids’ percentage decrease, at the end of storage, was about 20% in papaya with active coatings, with respect to the losses of 39 and 35%, registered in uncoated and alginate-coated samples respectively. Vitamin C content and the antioxidant activity measured in papaya coated with HA/QUE alginate showed significantly higher values (P < 0.05) for each storage day than those detected for control- and alginate-coated samples. Based on the sensory evaluation, active-coated fresh-cut papaya reached, at the end of the storage period, suitable values for commercial purposes.     

Fine Mapping and Candidate Gene Analysis of Pm36, a Wild Emmer-Derived Powdery Mildew Resistance Locus in Durum Wheat

Powdery mildew (PM) is an economically important foliar disease of cultivated cereals worldwide. The cultivation of disease-resistant varieties is considered the most efficient, sustainable and economical strategy for disease management. The objectives of the current study were to fine map the chromosomal region harboring the wild emmer PM resistance locus Pm36 and to identify candidate genes by exploiting the improved tetraploid wheat genomic resources. A set of backcross inbred lines (BILs) of durum wheat were genotyped with the SNP 25K chip array and comparison of the PM-resistant and susceptible lines defined a 1.5 cM region (physical interval of 1.08 Mb) harboring Pm36. The genetic map constructed with F_2:3 progenies derived by crossing the PM resistant line 5BIL-42 and the durum parent Latino, restricted to 0.3 cM the genetic distance between Pm36 and the SNP marker IWB22904 (physical distance 0.515 Mb). The distribution of the marker interval including Pm36 in a tetraploid wheat collection indicated that the positive allele was largely present in the domesticated and wild emmer Triticum turgidum spp. dicoccum and ssp. dicoccoides. Ten high-confidence protein coding genes were identified in the Pm36 region of the emmer, durum and bread wheat reference genomes, while three added genes showed no homologous in the emmer genome. The tightly linked markers can be used for marker-assisted selection in wheat breeding programs, and as starting point for the Pm36 map-based cloning.     

Anti-Virulence Potential of a Chionodracine-Derived Peptide against Multidrug-Resistant Pseudomonas aeruginosa Clinical Isolates from Cystic Fibrosis Patients

Pseudomonas aeruginosa is an opportunistic pathogen causing several chronic infections resistant to currently available antibiotics. Its pathogenicity is related to the production of different virulence factors such as biofilm and protease secretion. Pseudomonas communities can persist in biofilms that protect bacterial cells from antibiotics. Hence, there is a need for innovative approaches that are able to counteract these virulence factors, which play a pivotal role, especially in chronic infections. In this context, antimicrobial peptides are emerging drugs showing a broad spectrum of antibacterial activity. Here, we tested the anti-virulence activity of a chionodracine-derived peptide (KHS-Cnd) on five P. aeruginosa clinical isolates from cystic fibrosis patients. We demonstrated that KHS-Cnd impaired biofilm development and caused biofilm disaggregation without affecting bacterial viability in nearly all of the tested strains. Ultrastructural morphological analysis showed that the effect of KHS-Cnd on biofilm could be related to a different compactness of the matrix. KHS-Cnd was also able to reduce adhesion to pulmonary cell lines and to impair the invasion of host cells by P. aeruginosa. A cytotoxic effect of KHS-Cnd was observed only at the highest tested concentration. This study highlights the potential of KHS-Cnd as an anti-biofilm and anti-virulence molecule against P. aeruginosa clinical strains.     

Programming robots by example

This article presents a prototypical machine learning system (ETAR) that acquir programs for robot tasks. the long-term goal of this project is to discover how to make computer technology, in particular robots, more useful to (and controllable by) people in general. Rather than require programming expertise, the idea is to build a system that learns robot programs from users' examples. Thus the ETAR learning algorithm begins by sampling the robot path while a user physically leads it through the task. A general procedure, possibly containing loops, branches, and variables, is induced from these examples. the ETAR algorithm is novel because an implicit focus mechaism is used to control the entire generalization process. the focus forces ETAR to concentrate on the important domain objects, thus eliminating useless steps and translat the sampled sequence into a series of robot primitive motions. Loops and branches are introduced as the focus objects repeat or differ. Finally, robot positional variables are introduced as functions of the common characteristics of the objects in the focus. the programs that ETAR generates for three tasks-block stacking, obtaining an object with a certain characteristic, and sorting-are shown to provide an intuitive feel for the types of tasks that ETAR can learn. the article concludes with a general discussion of the current issues in programming by example and describes how this new learner is related to previous systems in this area. ETAR has been implemented on an Excalibur robot © 1993 John Wiley & Sons, Inc.