Impact of Carbon Source Supplementations on Pseudomonas aeruginosa Physiology.

Pseudomonas aeruginosa is an opportunistic pathogen highly resistant to a wide range of antimicrobial agents, making its infections very difficult to treat. Since microorganisms need to perpetually adapt to their surrounding environment, understanding the effect of carbon sources on P. aeruginosa physiology is therefore essential to avoid increasing drug-resistance and better fight this pathogen. By a global proteomic approach and phenotypic assays, we investigated the impact of various carbon source supplementations (glucose, glutamate, succinate, and citrate) on the physiology of the P. aeruginosa PA14 strain. A total of 581 proteins were identified as differentially expressed in the 4 conditions. Most of them were more abundant in citrate supplementation and were involved in virulence, motility, biofilm development, and antibiotic resistance. Phenotypic assays were performed to check these hypotheses. By coupling all this data, we highlight the importance of the environment in which the bacterium evolves on its metabolism, and thus the necessity to better understand the metabolic pathways implied in its adaptative response according to the nutrient availability.

Global Dynamic Proteome Study of a Pellicle-forming Acinetobacter baumannii Strain.

For several decades, many bacteria, among which A. baumannii, have shown their ability to colonize the upper surface of static liquids, forming a biofilm at the air-liquid interface named pellicle. Despite the ubiquity of these pellicles in both natural and artificial environments, few studies have investigated this biofilm type. The present data set provides the first description of the whole proteome of A. baumannii cells grown as pellicle, using a label-free mass spectrometry approach. Results are in accord with the general findings reporting that sessile bacteria are far more resistant to detrimental conditions than their planktonic counterparts, by the accumulation of stress proteins. The present investigation also confirmed previous studies suggesting a correlation between the pellicle forming ability and the bacterial virulence. Indeed, we showed the up-regulation of numerous virulence factors during the pellicle growth, e.g. phospholipases, adhesion factors, as well as those of the GacAS Two-Component System (TCS) and Type 6 Secretion System (T6SS). We also highlighted that Bam and Tam systems, both related to the OM insertion machinery, play a critical role during pellicle biogenesis. Moreover, sessile bacteria activate several pathways, e.g. iron, magnesium, phosphate pathways, which allows for increasing the panel of nutrient sources.

SSR marker-assisted screening of commercial tomato genotypes under salt stress.

Salt stress was applied to tomato commercial genotypes to study adverse effects on their phenotypic traits. Three were saline tolerant (San Miguel, Romelia and Llanero), two were mildly tolerant (Perfect peel HF1 and Heinz 1350) whereas the remaining were sensitive. Genotyping cultivars using 19 polymorphic SSRs out of 25 tested produced a total of 70 alleles with an average of 3.68 alleles per locus and PIC values ranging from 0.22 (SSR 26, 92, 66 and TG35) to 0.82 (SSR 356). Principal component analysis (PCA) showed two contrasting panels discriminating tolerant and sensitive groups and one panel with scattered genotypes. STRUCTURE analysis clustered genotypes within three groups in accordance with their salt stress behavior. The success of tomato salt-tolerance breeding programs can be enhanced through molecular characterization of diversity within commercial cultivars that adapt differently to stress conditions. To this end, we combined phenotypes and SSR marker-genotypes to seek sources of salt tolerance that might be tomato species-specific. We integrated and represented genotype-phenotype associations from multiple loci into a multi-layer network representation. It is a systemic view linking discriminating genotypes to salt stress phenotypes, which may guide strategies for the introgression of valuable traits in target tomato varieties to overcome salinity.

Development of molecular tools for characterization and genetic diversity analysis in Tunisian fig (Ficus carica) cultivars.

Fig, Ficus carica L., is a useful genetic resource for commercial cultivation. In this study, RAPD (60), ISSR (48), RAMPO (63), and SSR (34) markers were compared to detect polymorphism and to establish genetic relationships among Tunisian fig tree cultivars. The statistical procedures conducted on the combined data show considerable genetic diversity, and the tested markers discriminated all fig genotypes studied. The identification key established on the basis of SSR permitted the unambiguous discrimination of cultivars and confirmed the reliability of SSR for fingerprinting fig genotypes. The study findings are discussed in relation to the establishment of a national reference collection that will aid in the conservation of Tunisian fig resources.

A landscape genetic analysis of important agricultural pest species in Tunisia: The whitefly Bemisia tabaci.

Combining landscape ecology and genetics provides an excellent framework to appreciate pest population dynamics and dispersal. The genetic architectures of many species are always shaped by environmental constraints. Because little is known about the ecological and genetic traits of Tunisian whitefly populations, the main objective of this work is to highlight patterns of biodiversity, genetic structure and migration routes of this pest. We used nuclear microsatellite loci to analyze B. tabaci populations collected from various agricultural areas across the country and we determine their biotype status. Molecular data were subsequently interpreted in an ecological context supplied from a species distribution model to infer habitat suitability and hereafter the potential connection paths between sampling localities. An analysis of landscape resistance to B. tabaci genetic flow was thus applied to take into account habitat suitability, genetic relatedness and functional connectivity of habitats within a varied landscape matrix. We shed light on the occurrence of three geographically delineated genetic groups with high levels of genetic differentiation within each of them. Potential migration corridors of this pest were then established providing significant advances toward the understanding of genetic features and the dynamic dispersal of this pest. This study supports the hypothesis of a long-distance dispersal of B. tabaci followed by infrequent long-term isolations. The Inference of population sources and colonization routes is critical for the design and implementation of accurate management strategies against this pest.