Hadda-Imene Ouzari

Thuricin 7: a novel bacteriocin produced by Bacillus thuringiensis BMG1.7, a new strain isolated from soil

Aims: Detection and identification of new antagonistic activities towards Bacillus cereus and relatives.

Characterization of a repetitive element polymorphism- polymerase chain reaction chromosomal marker that discriminates Bacillus anthracis from related species

Aims: To identify a chromosomal marker with signature nucleotides specific for Bacillus anthracis. 
Methods and Results: Repetitive element polymorphism‐polymerase chain reaction with BOX‐A1R primer was used to discriminate 52 strains of all six species of the ‘B. cereus group’. A B. anthracis signature fragment, named AC‐390, was cloned and sequenced. The deduced amino acid sequence was homologous to that of YwfK of B. subtilis. Using two internal primers, the AC‐390 fragment was sequenced from two other B. anthracis strains as well as from strains of B. cereus and B.thuringiensis which have an AC‐390 fragment homologous to that of B. anthracis as shown by Southern hybridization experiments. 
Conclusions: Two new signature sequences specific for B. anthracis were identified on a chromosomal fragment homologous to YwfK, a transcriptional regulator of B. subtilis. 
Significance and Impact of the Study: These results show a new chromosomal DNA trait useful for distinguishing B. anthracis from the related species of the B. cereus group, regardless of the presence of the virulence plasmids pXO1 and pXO2.

The autolytic phenotype of Bacillus thuringiensis.

Aims:  To evaluate the autolytic phenotype of Bacillus thuringiensis.

The Date Palm Tree Rhizosphere Is a Niche for Plant Growth Promoting Bacteria in the Oasis Ecosystem

In arid ecosystems environmental factors such as geoclimatic conditions and agricultural practices are of major importance in shaping the diversity and functionality of plant-associated bacterial communities. Assessing the influence of such factors is a key to understand (i) the driving forces determining the shape of root-associated bacterial communities and (ii) the plant growth promoting (PGP) services they provide. Desert oasis environment was chosen as model ecosystem where agriculture is possible by the microclimate determined by the date palm cultivation. The bacterial communities in the soil fractions associated with the root system of date palms cultivated in seven oases in Tunisia were assessed by culture-independent and dependent approaches. According to 16S rRNA gene PCR-DGGE fingerprinting, the shapes of the date palm rhizosphere bacterial communities correlate with geoclimatic features along a north-south aridity transect. Despite the fact that the date palm root bacterial community structure was strongly influenced by macroecological factors, the potential rhizosphere services reflected in the PGP traits of isolates screened in vitro were conserved among the different oases. Such services were exerted by the 83% of the screened isolates. The comparable numbers and types of PGP traits indicate their importance in maintaining the plant functional homeostasis despite the different environmental selection pressures.

A novel phenotype based on esterase electrophoretic polymorphism for the differentiation of Lactococcus lactis ssp. lactis and cremoris

Aims:  To evaluate the esterase phenotype in Lactococcus lactis strains isolated from traditional Tunisian dairy products.

Increased plasmatic soluble HLA-G levels in endometrial cancer

HIGHLIGHTSsHLA‐G is significantly increased in patients with EC.sHLA‐G is highly increased in early stages and in high grade EC.HLA‐G5 are more represented than sHLA‐G1 molecules in patients with EC.sHLA‐G are represented majorly in monomeric forms.sHLA‐G dimeric forms are specifically associated to early stages of EC. ABSTRACT Human Leukocyte Antigen‐G (HLA‐G) is known as an immune suppressive molecule; it interacts with several immune cells and inhibits their functions. HLA‐G molecule is highly represented in pathological conditions including malignant transformation. To the best of our knowledge this is the first study that focuses on the expression of soluble HLA‐G (sHLA‐G) in endometrial cancer (EC). We aimed at exploring sHLA‐G plasma levels and its prognostic value in EC. We examined total sHLA‐G expression as well as the sHLA‐G1 and HLA‐G5 isoforms expression in plasma samples from 40 patients with EC and 45 healthy controls by a specific sandwich ELISA. Immunoprecipitation and Coomassie blue staining were performed to explore the presence of plasmatic sHLA‐G monomers and dimers. sHLA‐G plasma level was significantly enhanced in patients with EC compared to healthy controls (p=0.028). Additionally, HLA‐G5 molecules were highly represented than sHLA‐G1 molecules in EC, at the borderline of significance (p=0.061). Interestingly, sHLA‐G has been shown to be increased in early stages (Stages I and II) as well as in high grade EC (Grade 3) that is associated with rapid spread of the disease (p=0.057). sHLA‐G positive EC plasma were majorly in monomeric form (75%). Clinically, all the HLA‐G dimers were detected in early stages and in high grade of EC. Our data strengthen the implication of HLA‐G molecules in EC etiology and especially in progression.

Two New Secreted Proteases Generate a Casein-Derived Antimicrobial Peptide in Bacillus cereus Food Born Isolate Leading to Bacterial Competition in Milk

Milk and dairy products harbor a wide variety of bacterial species that compete for both limited resources and space. Under these competitive conditions, bacteria develop specialized mechanisms to protect themselves during niche colonization and nutrient acquisition processes. The bacterial antagonism mechanisms include the production of antimicrobial agents or molecules that facilitate competitor dispersal. In the present work, a bacterial strain designated RC6 was isolated from Ricotta and identified as Bacillus cereus. It generates antimicrobial peptide (AMP) when grown in the presence of casein. The AMP was active against several species of Bacillus and Listeria monocytogenes. MALDI-TOF analysis of the RP-HPLC purified fractions and amino acid sequencing revealed a molecular mass of 751 Da comprised of a 6-residue sequence, YPVEPF. BLAST analysis showed that the AMP corresponds to the fractions 114–119 of bovine β-casein and represents the product of a specific proteolysis. Analysis of the purified proteolytic fractions from the B. cereus RC6 culture supernatant indicated that the presence of at least two different endoproteases is crucial for the generation of the AMP. Indeed, we were able to identify two new candidate endoproteases by means of genome sequencing and functional assignment using a 3D structural model and molecular docking of misannotated hypothetical proteins. In this light, the capacity of B. cereus RC6 to generate antimicrobial peptides from casein, through the production of extracellular enzymes, presents a new model of antagonistic competition leading to niche colonization. Hence, as a dairy product contaminant, this strategy may enable proteolytic B. cereus RC6 niche specialization in milk matrices.

Plant growth-promoting Rhizopseudomonas: expanded biotechnological purposes and antimicrobial resistance concern

The present study was conducted to characterize a collection of plant growth-promoting (PGP) Rhizopseudomonas isolated from date palm roots for their biosurfactant production ability, heavy metal tolerance, and antimicrobial susceptibility. A collection of 36 bacterial strains was evaluated for several plant growth-promoting abilities including indole acetic acid (IAA) production, mineral phosphate solubilization, siderophores and ammonia release, and protease and cellulase activity. Biosurfactant production was screened throughout hemolytic activity, bleu agar test, and drop collapse method. Strains exhibiting tolerance to heavy metals at high concentration were subjected to PCR for the detection of heavy metal gene tolerance. Moreover, antimicrobial susceptibility patterns were determined using the disk-diffusion method. High rates of plant growth promotion activities were registered among the isolated rhizopseudomonads, mainly, the indole acetic acid production (88.8%), phosphate solubilization (63.8%), siderophore release (83.3%), and ammonia synthesis (52.7%). Furthermore, biosurfactant production was recorded, using three distinct methods, on 77.7% of the tested strains. Particularly, two strains affiliated to Pseudomonas vancouverensis and Pseudomonas brassicacearum harboring copA-arsR and arsB genes, respectively, and producing biosurfactants, were selected. The evaluation of antibiotic resistance dissemination risk analysis in the environment revealed a low rate of resistance among the analyzed strains and the absence of known antibiotic resistance genes. This investigation could provide the basis for the development of microbial inoculums showing multifarious properties for biotechnological application while caring human health.