Members of Ensifer and Rhizobium genera are new bacterial endosymbionts nodulating Pisum sativum (L.)

A total of 84 Pisum sativum legume nodulating bacteria (LNB) were isolated from seven geographical sites from southern Tunisia. Phylogenetic analyses based on partial sequences of 16S rRNA gene and the housekeeping genes glnII, and recA grouped strains into six clusters, four of which belonged to the genus Rhizobium and two to the Ensifer genus. Among Rhizobium clusters, 41 strains were affiliated to Rhizobium leguminosarum, two strains to R. pisi, two strains to R. etli, and interestingly two strains belonged to previously undescribed Rhizobium species. The remaining two strains were closely related to Ensifer medicae (two strains) and Ensifer meliloti (two strains). A symbiotic nodC gene-based phylogeny and host specificity test showed that all Rhizobium strains nodulating pea belonged to the symbiovar viciae, whereas the Ensifer strains were associated with the symbiovar meliloti never described to date. All strains under investigation differed in the number of induced root nodules and the effectiveness of atmospheric nitrogen fixation. The R. leguminosarum PsZA23, R. leguminosarum PsGBL42, and E. medicae PsTA22a, forming the most effective symbiosis with the plant host, are potential candidates for inoculation programs.

Quality and antioxidant response of gilthead seabream (Sparus aurata L.) to dietary supplements of fenugreek (Trigonella foenum graecum) alone or combined with probiotic strains

The present study was conducted to determine the potential effect of the dietary intake of fenugreek (Trigonella foenum graecum) seeds alone or in combination with Bacillus licheniformis, Lactobacillus plantarum or B. subtilis on gilthead seabream quality and antioxidant response after 2 and 3 weeks of experimental feeding. The results showed that the supplements did not affect the percentage of the fatty acid profiles of muscle, demonstrating that all the additives tested can be administrated without any negative effect on biochemical composition and quality of gilthead seabream. The quantification of thiobarbituric acid reactive substances in muscle demonstrated the significant beneficial effect of the experimental diets compared with the control one. Besides, an increase in superoxide dismutase and catalase in liver was recorded after 3 weeks of administration of experimental diets. Furthermore, real time qPCR revealed that dietary supplementation with FEBS significantly enhances the expression of scavenging enzymes, such as cat and gr genes in the liver after 3 weeks. The findings suggest that the administration of fenugreek supplement alone or combined with probiotic strains could be considered as a good source of natural antioxidants and as a functional aquafeed ingredient for gilthead seabream.

Effects of dietary administration of fenugreek seeds, alone or in combination with probiotics, on growth performance parameters, humoral immune response and gene expression of gilthead seabream (Sparus aurata L.)

The use of immunostimulants is considered a promising preventive practice that may help to maintain animal welfare and a healthy environment, while increasing production and providing higher profits. The purpose of this study was to evaluate the effects on gilthead seabream (Sparus aurata L.) of the dietary administration of fenugreek (Trigonella foenum graecum) seeds, alone or combined with one of the following probiotic strains: Bacillus licheniformis (TSB27), Lactobacillus plantarum or Bacillus subtilis (B46). Gilthead seabream were fed a control or one of the supplemented diets for 3 weeks. The effects of these supplemented diets on growth performance parameters and the humoral immune response (natural haemolytic complement, peroxidase, total IgM levels, proteases and antiproteases activities) were evaluated after 2 and 3 weeks of feeding. Simultaneously, the expression levels of some immune-relevant genes (igm, tcr-β, csfr1 and bd) were measured in the head-kidney. Interestingly, all probiotic supplemented diets increased seabream growth rates, especially the B. licheniformis supplemented diet. Generally, humoral immune parameters were enhanced by the dietary supplementation at the different time points measured. The results showed a significant increases in the immune parameters, principally in fish fed only fenugreek or fenugreek combined with B. subtilis. Furthermore, real time qPCR revealed that dietary supplementation significantly enhances the expression of immune-associated genes in the head-kidney, particularly igm gene expression. These results suggest that fenugreek alone or combined with one of the probiotic strains mentioned enhances the immune response of gilthead seabream, a species with one of the highest rates of production in marine aquaculture.

Interactions between candidate probiotics and the immune and antioxidative responses of European sea bass (Dicentrarchus labrax) larvae

The use of lactic acid bacteria (LAB) as probiotics in aquaculture may improve the quality of seed production and limit the use of antibiotics in fish hatcheries. This study attempted to further characterize the candidate probiotic Lactobacillus casei X2, and the immune and physiological responses of the sea bass larvae. L. casei X2 was confirmed as a good candidate, due to its wide antibacterial spectrum against both Gram-positive and Gram-negative bacteria, and its free radical scavenging activity. In addition, if the strain did not seem able to form biofilm on abiotic surfaces, it adhered strongly to Hep-2 cells. However, these characteristics did not seem efficient in vivo. At 20 days post-hatch (dph), the expression level of CAT gene was significantly different between group fed without probiotic and the two groups treated with either Pediococcus acidilactici or L. casei. This gene was upregulated in the group treated with strain X2 and downregulated in the group with a commercial probiotic strain P. acidilactici, suggesting a better antioxidant activity with the later strain. At the same sampling date, the IL-1β gene was upregulated in the group treated with P. acidilactici, and the HSP70 gene was overexpressed at 41 dph. As the stimulation of these two last genes, such transcriptomic indicators must be cautiously interpreted.

Effect of dietary supplementation of probiotics and palm fruits extracts on the antioxidant enzyme gene expression in the mucosae of gilthead seabream (Sparus aurata L.)

Antioxidant activity is particularly important, since oxidation is an unavoidable reaction in all living bodies. At present, natural antioxidants to be used on food as an alternative to synthetic ones are being sought. Gilthead seabream (Sparus aurata L.) specimens were fed for 4 weeks with diets enriched with bacterial probiotics (Shewanella putrefaciens Pdp11 and Bacillus sp), single or in combination with Tunisian dates palm fruit extracts. The expression of the main antioxidant enzyme genes (superoxide dismutase, catalase and glutathione reductase) in the mucosae (gut, skin and gill) was evaluated after 2 and 4 weeks. Previously, free radical scavenging and several antioxidant assays were developed to know the antioxidant properties present on the palm fruits extracts. The results demonstrated that experimental diets alter the expression of the studied antioxidant genes, primarily in the gill and skin. Furthermore, the tested probiotics and mainly, the aqueous date palm fruits extracts had significant antioxidant properties based on their protective effect against the levels of intracellular reactive oxygen species, especially when administering during 4 weeks. For this reason, probiotics and date palm fruit extracts may serve as good natural antioxidants and could potentially be considered as a functional food ingredient for fish in farms.

Preliminary characterization of the probiotic properties of Candida famata and Geobacillus thermoleovorans

BACKGROUND AND OBJECTIVE

Probiotics are live microbial feed supplements which beneficially affect the host animal by improving its intestinal microbial balance, producing metabolites which inhibit the colonization or growth of other microorganisms or by competing with them for resources such as nutrients or space. The aim of this study was to investigate the probiotic properties of Candida famata and Geobacillus thermoleovorans.

MATERIAL AND METHODS

In this study, yeast and bacterial strains isolated from pure oil waste were identified using Api 50 CHB and Api Candida Systems and their probiotic properties were studied through antimicrobial activity, biofilm production, adherence assay and enzymatic characterization.

RESULTS AND CONCLUSION

According to biochemical analyses, these strains corresponded to Geobacillus thermoleovorans and Candida famata. Antagonism assay results showed that the tested strains have an inhibitory effect against tested pathogenic bacteria. The yeast Candida famata was unable to produce biofilm on Congo Red Agar (CRA), while the bacterial strain was a slime producer. Adherence assays to abiotic surfaces revealed that the investigated strains were fairly adhesive to polystyrene with values ranging from 0.18 to 0.34 at 595 nm. The enzymatic characterization revealed that the tested strains expressed enzymes such as phosphatase alkaline, esterase lipase (C8), amylase, lipase, lecitenase and caseinase. The obtained results may allow the isolated strains to be considered as having the potential to be candidate probiotics.