Heterotrophic bacteria associated with the green alga <Emphasis Type="Italic">Ulva rigida</Emphasis>: identification and antimicrobial potential

Heterotrophic bacteria associated with the green alga Ulva rigida, collected from the coast of Tunisia, were isolated and subsequently identified by their 16S rRNA gene sequences and by phylogenetic analysis. The 71 isolates belong to four phyla: Proteobacteria (Alpha-and Gamma- subclasses), Bacteroidetes, Firmicutes, and Actinobacteria. Most of the isolates belong to Proteobacteria. The Gram-positive Firmicutes and especially the genus Bacillus were well-represented at the surface of U. rigida, collected from the coast as well as from the lagoon, while Actinobacteria were represented only at the surface of algae collected from the coast of Cap Zebib. Bacteroidetes were more represented at the surface of algae collected from the Ghar El Melh lagoon. The bacterial community of the water surrounding the algae was different from that associated with the surface of the algae. Moreover, the abundance of bacteria in the surrounding water was much lower compared to the density of bacteria associated with the surface of the algae. Bacteria isolated from the algal surface were tested for their antimicrobial potential. The results show that ~?36% of the algae-associated bacterial isolates possess antibacterial activity whereas free-living bacteria, isolated from the surrounding water, did not show such activity. The surface of U. rigida was colonized by a high diversity of culturable and possibly novel epiphytic bacteria that may be an important source of antimicrobial compounds and are therefore of biotechnological interest.     

Starvation survival of Pseudomonas aeruginosa in sea water before and after adaptation to salinity

The survival of Pseudomonas aeruginosa ATCC 27853 in sea water was minimally influenced by light, temperature and the presence of an associated marine microflora. Pre-adaptation of cells to a salted medium attenuated the initial stress and even permitted their growth but did not modify their long-term survival. The majority of stressed cells were resuscitated in a nutritive medium prepared with sea water. The morphology of the resulting colonies varied considerably depending on the contact time with sea water and the medium used for enumeration of culturable cells.     

Jania rubens-associated bacteria: molecular identification and antimicrobial activity

Marine macroalgae surfaces constitute suitable substrata for bacterial colonization which are known to produce bioactive compounds. Thus, hereby we focused on heterotrophic aerobic bacteria species associated with coralline red alga Jania rubens (northern coast of Tunisia, southern Mediterranean Sea) and their inhibition against several microbial marine and terrestrial species. The whole collection (19 isolates, J1 to J19) was identified, based on their 16S ribosomal RNA gene sequences as Proteobacteria (14 strains), Bacteroidetes (4 strains) and Firmicutes (1 strain). Thirty-six percent of the isolates (J2, J9, J11, J13, J16, J17 and J18) were antibiotic-like producers with in vitro inhibition against Gram + and Gram ? bacteria and the yeast Candida albicans. Highest level of inhibition was revealed for the isolates J2, J9 and J13 identified respectively as Bacillus, Aquimarina and Pseudomonas, with strong activity against Staphylococcus aureus, Micrococcus and C. albicans, with inhibition diameters of 25 to 35 mm shown by drop test assay on T soy agar plates. Furthermore, we tested inhibition of J. rubens crude organic extracts against human and marine bacteria as well as against all J. rubens isolates, in order to determine the degree of affinity of the epibionts to their proper host. The recovery of strains with antimicrobial activity suggests that J. rubens represent an ecological niche which harbors a specific microbial diversity worthy of further secondary metabolites investigation.     

A novel neutral,halophile <Emphasis Type="Italic">Stachybotrys microspora</Emphasis>-based endoglucanase active impact on β-glucan

The production of cellulases from Stachybotrys microspora strain (A19) has been improved by fed-batch fermentation on Avicel cellulose 10 mg/ml. An endoglucanase EG2 was purified to homogeneity. This cellulase has a molecular mass estimated to 50 kDa when analyzed by a denaturant gel electrophoresis. It exhibited an optimal activity at 50 °C, pH 7.0 and 0.85 M NaCl. Specifically, these results show the thermo-active, alkali-tolerant and halo-tolerant properties of EG2. In addition, this endoglucanase showed its highest activity on barley-β-glucan, compared to the CMC. Moreover, it was less active on Avicel cellulose. Furthermore, the EG2 activity was stimulated in the presence of EDTA, urea and β-mercaptoethanol whereas it was reduced in the presence of SDS. This cellulase was highly stable in the presence of organic solvents such as acetone and n-hexane. TLC showed that the main hydrolysis products from EG2 were cellobiose and glucose. This fungal endoglucanase could be potentially important in the conversion of grass-derived biomass into fermentable sugars.     

Physiological and biochemical parameters: new tools to screen barley root exudate allelopathic potential (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L. subsp. <Emphasis Type="Italic">vulgare</Emphasis>)

Morphological markers/traits are often used in the detection of allelopathic stress, but optical signals including chlorophyll a fluorescence emission could be useful in developing new screening techniques. In this context, the allelopathic effect of barley (Hordeum vulgare subsp. vulgare) root exudates (three modern varieties and three landraces) were assessed on the morphological (root and shoot length, biomass accumulation), physiological (F_v/F_m and F₀), and biochemical (chlorophyll and protein contents) variables of great brome (Bromus diandrus Roth., syn. Bromus rigidus Roth. subsp. gussonii Parl.). All the measured traits were affected when great brome was grown in a soil substrate in which barley plants had previously developed for 30 days before being removed. The response of receiver plants was affected by treatment with activated charcoal, dependent on barley genotype and on the nature of the growing substrate. The inhibitory effect was lower with the addition of the activated charcoal suggesting the release of putative allelochemicals from barley roots into the soil. The barley landraces were more toxic than modern varieties and their effect was more pronounced in sandy substrate than in silty clay sand substrate. In our investigation, the chlorophyll content and F_v/F_m were the most correlated variables with barley allelopathic potential. These two parameters might be considered as effective tools to quantify susceptibility to allelochemical inhibitors in higher plants.     

Trans-glycosylation capacity of a highly glycosylated multi-specific β-glucosidase from Fusarium solani

An extracellular β-glucosidase from Fusaruim solani cultivated on wheat bran was purified by only two chromatographic steps. The purified enzyme exhibited optimal temperature and pH at 60 °C and pH 5, respectively. The purified β-glucosidase behaves as a very large protein due to its high degree of glycosylation. More interestingly, the endoglycosidase H (Endo H) treatment led to 97.55% loss of its initial activity after 24 h of treatment. Besides, the addition of Tunicamycin (nucleoside antibiotic blocking the N-glycosylation first step) during the culture of the fungus affected seriously the glycosylation of the enzyme. Both treatments (endo H and Tunicamycin) strengthened the idea that the hyperglycosylation is involved in the β-glucosidase activity and thermostability. This enzyme was also shown to belong to class III of β-glucosidases (multi-specific) since it was able to act on either cellobiose, gentiobiose or sophorose which are disaccharide composed of two units of d-glucose connected by β1–4, β1–6 and β1–2 linkage, respectively. The β-glucosidase activity was strongly enhanced by ferrous ion (Fe²⁺) and high ionic strength (1 M KCl). The purified enzyme exhibited an efficient transglycosylation capacity allowing the synthesis of cellotriose and cellotetraose using cellobiose as donor.

     

Fast activated charcoal prepurification of Fusarium solani β-glucosidase for an efficient oleuropein bioconversion

Fungal β-glucosidases were extensively studied regarding their various potential biotechnology applications. Here, we report the selection of Fusarium solani strain producing high yield of β-glucosidase activity. The effect of some factors on β-glucosidase production was studied including: Initial pH, medium composition, concentration of carbon and nitrogen sources, and particle size of raw substrates. The optimal enzyme production was obtained with 4?units of pH. The highest β-glucosidase activity was produced on 4% wheat bran (WB) as raw carbon sources, reaching 5?U/mL. A positive correlation between WB particle size and the β-glucosidase production level was settled. The last one was enhanced to 13.60?U/mL in the presence of 0.5% (w/v) of ammonium sulfate. Interestingly, the activated charcoal was used as an inexpensive reagent enabling a rapid and efficient purification prior step that improved the enzyme-specific activity. Eventually, F. solani β-glucosidase acts efficiently during the bioconversion process of oleuropein. Indeed, 82.5% of oleuropein was deglycosylated after 1?hr at 40°C. Altogether, our data showed that the β-glucosidase of F. solani has a potential application to convert oleuropein to ameliorate food quality.     

Chloroplast Implication in the Tolerance to Salinity of the Halophyte Cakile maritima

Russian Journal of Plant Physiology - In this study, the response of the chloroplastic antioxidant system of the halophyte Cakile maritima Scop. and its tolerance to NaCl stress have been studied...