Adel Hadj Brahim

A significant strategy for sustainable management, by decreasing the use of chemical fertilizers, can consist of technology based on suitable levels of plant growth promoting bacteria (PGPB) seed biopriming. The main goal of this work was to demonstrate the positive effect of PGPB as seed biopriming factor on the growth of durum wheat plantlets under stress. plantlets physiological and biochemical pathways modifications were assessed in controlled growth chamber under salt stress. Seeds bioprimed with bacterial strains, in particular, Bacillus pumilus (MA9), Virgibacillus halodenitrificans (MA14), Bacillus subtilis (MA17), and Bacillus pumilus (MA19), demonstrated the best development of durum wheat seedlings under salt stress. The total length and total dry weight were altogether higher in bioprimed than in unbioprimed plants. The PGPB-bioprimed plants were very sound and hydrated, and the unbioprimed plant leaves were parched within 120 mM NaCl. In contrast to explants without PGPB, all the biochemical variables, for example, auxin, proline, soluble sugars, amino acids, and protein, were essentially improved in bioprimed explants. Biopriming with MA17 fundamentally diminished the reactive oxygen species (ROS) rate, particularly without salt stress. In any case, this impact of the hindrance of “ROS” was more pronounced under stressful conditions. The explant antioxidant prevention agent pathways catalase (CAT) and ascorbate peroxidase (APX) and the chlorophyll content were improved after seed biopriming with PGPB when explants with unbioprimed seeds had low cell reinforcement pathways under the two treatments, particularly under pressure. The bioprimed plants additionally had higher K⁺/Na⁺ proportions and expanded intracellular K⁺ ion activity. Hence, it can be anticipated that seed biopriming with PGPB is a novel technology that can improve healthy plant development under saline conditions. This study shows that PGPB has a significant effect in initiating resistance under stressful conditions in plants and can be utilized to develop new bioinoculants to reduce the use of chemical fertilizers.

Background: A significant strategy for sustainable management, by decreasing the use of chemical fertilizers, can consist of technology based on suitable levels of plant growth promoting bacteria (PGPB) seed biopriming. The main goal of this work was to demonstrate the positive effect of PGPB as seed biopriming factor on the growth of durum wheat plantlets under stress. Methods: plantlets physiological and biochemical pathways modifications were assessed in controlled growth chamber under salt stress. Results: Seeds bioprimed with bacterial strains, in particular, Bacillus pumilus (MA9), Virgibacillus halodenitrificans (MA14), Bacillus subtilis (MA17), and Bacillus pumilus (MA19), demonstrated the best development of durum wheat seedlings under salt stress. The total length and total dry weight were altogether higher in bioprimed than in unbioprimed plants. The PGPB-bioprimed plants were very sound and hydrated, and the unbioprimed plant leaves were parched within 120 mM NaCl. In contrast to explants without PGPB, all the biochemical variables, for example, auxin, proline, soluble sugars, amino acids, and protein, were essentially improved in bioprimed explants. Biopriming with MA17 fundamentally diminished the OR rate, particularly without salt stress. In any case, this impact of the hindrance of "ORs" was more pronounced under pressure. The explant antioxidant prevention agent pathways (CAT, APX) and the chlorophyll content were improved after seed biopriming with PGPB when explants with unbioprimed seeds had low cell reinforcement pathways under the two treatments, particularly under pressure. The bioprimed plants additionally had higher K+/Na+ proportions and expanded intracellular K+ ion activity. Conclusion: Hence, it can be anticipated that seed biopriming with PGPB is a novel technology that can improve healthy plant development under saline conditions. This study shows that PGPB assume a significant effect in initiating resistance under stressful conditions in plants and can be utilized to develop new bioinoculants to reduce the use of chemical fertilizers.

Bacteriophages could be a useful adjunct to antibiotics for the treatment of multidrug-resistant Pseudomonas aeruginosa infections. In this study, lytic P. aeruginosa myoviruses PsCh, PsIn, Ps25, and Ps12on-D were isolated from Tunisian sewage samples. Phage Ps12on-D displayed an adsorption time of ~10 min, a short latency period (~10 min), and a large burst size (~115 PFU per infected cell) under standard growth conditions. All phages were active at broad temperature (4 °C to 50 °C) and pH (3.0 to 11.0) ranges and were able to lyse a wide variety of P. aeruginosa strains isolated from clinical and environmental samples worldwide. Illumina sequencing revealed double-stranded DNA genomes ranging from 87,887 and 92,710 bp with high sequence identity to Pseudomonas phage PAK_P1. All four phages based on sequence analysis were assigned to the Pakpunavirus genus. The presented characterization and preclinical assessment are part of an effort to establish phage therapy treatment as an alternative strategy for the management of multidrug-resistant P. aeruginosa infections in Tunisia.

There is growing interest in the use of bio inoculants based on plant growth-promoting bacteria (PGPB) to promote plant growth under biotic and abiotic stresses. Here, we provided a detailed account of the effectiveness of a number of endophytic PGPB strains, isolated from the roots of the halophyte Salicornia brachiata in promoting durum wheat growth and enhancing its tolerance to salinity and fusarium head blight (FHB) disease. Bacillus spp. strains MA9, MA14, MA17, and MA19 were found to have PGPB characteristics as they produced indole-3-acetic acid, siderophores, and lytic enzymes, fixed free atmospheric nitrogen, and solubilized inorganic phosphate in vitro. Additionally, the in vivo study that involved in planta inoculation assays under control and stress conditions indicated that all PGPB strains significantly (p < 0.05) increased the total plant length, dry weight, root area, seed weight, and nitrogen, protein, and mineral contents. Particularly, the MA17 strain showed a superior performance since it was the most efficient in reducing disease incidence in wheat explants by 64.5%, in addition to having the strongest plant growth promotion activity under salt stress. Both in vitro and in vivo assays showed that MA9, MA14, MA17, and MA19 strains were able to play significant PGPB roles. However, biopriming with Bacillus subtilis MA17 offered the highest plant growth promotion and salinity tolerance, and bioprotection against FHB. Hence, it would be worth testing the MA17 strain under field conditions as a step towards its commercial production. Moreover, the strain could be further assessed for its plausible role in bioprotection and growth promotion in other crop plants. Thus, it was believed that the strain has the potential to significantly contribute to wheat production in arid and semi-arid regions, especially the salt-affected Middle Eastern Region, in addition to its potential role in improving wheat production under biotic and abiotic stresses in other parts of the world.

Newly discovered Erwinia amylovora phages PEar1, PEar2, PEar4 and PEar6 were isolated from three different orchards in North Tunisia to study their potential as biocontrol agents. Illumina sequencing revealed that the PEar viruses carry a single-strand DNA genome between 6608 and 6801 nucleotides and belong to the Inoviridae, making them the first described filamentous phages of E. amylovora. Interestingly, phage-infected cells show a decreased swimming and swarming motility and a cocktail of the four phages can significantly reduce infection of E. amylovora in a pear bioassay, potentially making them suitable candidates for phage biocontrol.

Glucanases are enzymes that hydrolysis glucans which are the major cell wall components in cereals. A newly isolated bacteria, assigned as Bacillus subtilis HB2, produces a monomeric glucanase (GLU HB2) of a molecular mass of 75 kDa. GLU HB2 has an optimal activity at pH 5 and 55°C. It is extremely stable at a broad range of pH and temperature up to 65°C, in presence of 5 mM of CaCl2. In order to overcome the enzymatic inhibition problem observed in wild-type strains, GluHB2 gene was integrated into the genome of B. subtilis HB2 and the recombinant strain was named HB2G. The correlation of glucanase production with bacterial growth shows that the level of expression of HB2G remains low and relatively comparable to the wild-type strain. But in terms of productivity, the HB2G strain is more productive throughout bacterial culture. This low production and growth of the recombinant strain can be attributed to the toxicity of the overexpression of the glucanase gene under a constitutive promoter.

Salicola sp. strain SBJ9 is an extremely halophilic bacterium newly isolated from a hypersaline lake in Sfax (Tunisia). It is an aerobic Gram negative bacterium, bacilli shaped and motile. The strain SBJ9 grows optimally at 150 g/l (2.57 M) NaCl, 35 °C and pH 7 and it is able to hydrolyze proteins and lipids at high salinities. Actually, Salicola genus contains only two species (S. marasensis and S. salis). This research reported the first draft genome of a bacterium belonging to Salicola and the different obtained and annotated sequences and genes. Salicola sp. strain SBJ9 genomic sequence contains 4.643.441 bp with a G+C content of 60.52%. The annotation monitored by the RAST server reveals 65 RNA sequences and 3995 coding genes including 255 and 182 sub-systems of protein metabolism and lipids, respectively. The further analysis of SBJ9 genomic sequence will clarify the ideas regarding the adaptation of the Salicola strains and their proteins to the extremely high salt concentrations and will permit the development of new bio-catalyzers for industrial applications.

A number of newly isolated halophilic microorganisms were screened for protease production. A bacterium designated as strain SBJ9 showed an important enzyme production at high salt concentrations and was then retained. The 16S DNA identification put this strain in the genus of Salicola with two reference species only. Protease production was higher at salinities ranging from 150 to 200 g/l (3.2 M) NaCl, when monitored at 35 °C and pH 7. The protease activity was optimal at 2.5 MNaCl, 40°C and pH 8, with high stability at wide ranges of salinity (1-5 MNaCl), temperatures (20- 70 °C) and pH values (5- 11). It was slightly improved by 5 mM CaCl₂ and totally inhibited by PMSF which indicated the dominance of serine proteases. Besides, it was perfectly stable in the presence of many detergent additives and organic solvents at high concentrations. These important features make Salicola sp. strain SBJ9 protease activity a good candidate for many industrial applications such as detergency and organic synthesis.

The rapid development of aquaculture, its intensification, and the occurrence of fish health problems on farms push to develop alternative methods to antibiotics and chemotherapy for controlling fish diseases. Probiotics may provide a potential alternative method to protect fish from opportunistic and pathologic bacteria and promote a balanced environment. In this work, we have assessed the in vitro probiotic properties of twenty one bacteria from aquatic and fish origin, for their application in aquaculture. Selection was based on their antimicrobial activity (Bacteriocin) against fish pathogens and their in vitro safety assessment. This includes the evaluation of their haemolytic, proteolytic and mucinolytic activities, bile salt deconjugation ability and antibiotic susceptibility. Twelve of the twenty one bacteria isolated from several showed strong antibacterial activity against several pathogenic species such as Lactococcus garvieae, Vibrio anguillarum, Vibrio harveyi, Aeromonas hydrophila and Aeromonas salmonicida, and were taxonomically identified by partial 16S rDNA gene sequencing. The cell-free culture supernatants from cultures of these twelve strains were treated with proteinase K (10 mg/ml; 37ºC, 1h) and submitted to heat treatment (100ºC, 10 min), which showed that eleven strains exert extracellular antimicrobial activity against fish pathogens due to the production and secretion of thermo-stable antimicrobial peptides (i.e., Bacteriocins). The tested strains showed a great heterogeneity respect to their safety and antibiotic susceptibility. Given their antimicrobial (Bacteriocin) activity against fish pathogens and their safety, some of the tested strains may be considered as potential fish probiotics, and their effectiveness will be further tested in vivo.

Attributed to a Gram-negative bacterium, identified as Erwinia amylovora, the fire blight disease, recently detected in Tunisia, has become a real threat to our economy and our arboriculture.There is no effective curative treatment to eliminate the installed bacterium. It is therefore essential to prevent attacks and to limit the spread of the bacteria if it is already present. To do so we have chosen the biocontrol by bacteriophages. In this work we have isolated new strains of Erwinia amylovora (10 strains) from plant tissues where fire blight symptoms are persistent. These strains have been the subject of a molecular study. The isolated phages (30 isolates) were studied for their infectivity on Erwinia amylovora isolates and showed a surprising effect. Our phage isolates formed plaque of different sizes, with a diameter ranging between 0.5 and 2mm on the soft agar layer containing the test bacterium. The phages thermostability showed that all these viruses resist at 80 ° C for 45 min