A Bacillus subtilis strain as probiotic in poultry: selection based on in vitro functional properties and enzymatic potentialities.

We have proposed and validate an in vitro probiotic selection, based on enzymatic potentialities associated to well-established probiotic functional properties. A new Bacillus subtilis HB2 isolate, selected based on its high extracellular enzyme production, was chosen as a probiotic candidate for application as animal feed supplement. The HB2 strain showed an excellent acid and bile salts tolerance, a strong adhesion to chick enterocytes and produced antimicrobials against pathogens. An in vivo trial in poultry farming was conducted to evaluate the HB2 probiotic performance. After 35 days, HB2 achieved the higher growth performance than the control groups. The mortality and the feed conversion ratio were significantly decreased. Finally, the HB2 treated group showed wet litter and less severe ammonia odor in the atmosphere. Our study provides new insights into the importance of enzymatic potentialities, associated with the common functional properties, as a novel approach for probiotic selection.

Characterization of thermo-solvent stable protease from Halobacillus sp. CJ4 isolated from Chott Eldjerid hypersaline lake in Tunisia.

About 110 newly isolated halophilic and halotolerant bacteria were screened for protease production. A moderately halophilic strain (CJ4), isolated from Chott Eldjerid Hypersaline lake in Tunisia, showed the highest activity on agar plate and was then selected. The biochemical and physiological characterization of the isolate along with the 16S rRNA sequence analysis placed it in the genus Halobacillus. Protease production was maximal at 120 g/L NaCl (2 M) and it started from the post-exponential phase reaching a maximum level at the early decline phase of bacterial growth. Protease activity was optimal at 0.4 M NaCl, pH 9 and 45 °C. It showed an excellent stability over wide ranges of temperatures (30-60 °C), NaCl concentrations (0-5 M), and pH values (5-10), which make it a good candidate for industrial applications at harsh conditions. Crude protease was strongly inhibited by PMSF revealing the dominance of serine proteases. Protease activity exhibited high stability in the presence of several organic solvents and detergent additives. These findings make Halobacillus sp. CJ4 protease with a great interest for many biotechnological applications at high salt or low water content such as peptide synthesis and detergent formulation.

Biopriming of Durum Wheat Seeds with Endophytic Diazotrophic Bacteria Enhances Tolerance to Fusarium Head Blight and Salinity.

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.

Toward the smallest active subdomain of a TIM-barrel fold: insights from a truncated α-amylase.

AmyTM is a truncated mutant of the α-amylase of Bacillus stearothermophilus US100. It has been derived from the wild type amylase gene via a reading frame shift, following a tandem duplication of the mutant primer, associated to an Adenine base deletion. AmyTM was composed of 720 nucleotides encoding 240 amino acid residues out of 549 of the wild type. The AmyTM protein was devoided of the three catalytic residues but still retains catalytic activity. It is Ca-independent maltotetraose producing amylase, optimally active at pH 6 and 60°C, under monomeric or multimeric forms. AmyTM is the smallest functional truncated TIM barrel. It contains the ßαßα unit as the minimal subdomain associated to an enzymatic function. The enzymatic activity can, until now, be attributed to the presence of the whole domain B, in the structure of AmyTM. This mutant revealed, for the first time, the regeneration of a catalytic site after its abolition. This fact may be considered as the restoration of a primitive active site, which was lost in the course of evolution toward more stable domains.