Characterization of two truncated forms of xylanase recombinantly expressed by Lactobacillus reuteri with an introduced rumen fungal xylanase gene

Anaerobic Fungi: Past, Present, and Future

Anaerobic fungi (AF) play an essential role in feed conversion due to their potent fiber degrading enzymes and invasive growth. Much has been learned about this unusual fungal phylum since the paradigm shifting work of Colin Orpin in the 1970s, when he characterized the first AF. Molecular approaches targeting specific phylogenetic marker genes have facilitated taxonomic classification of AF, which had been previously been complicated by the complex life cycles and associated morphologies. Although we now have a much better understanding of their diversity, it is believed that there are still numerous genera of AF that remain to be described in gut ecosystems. Recent marker-gene based studies have shown that fungal diversity in the herbivore gut is much like the bacterial population, driven by host phylogeny, host genetics and diet. Since AF are major contributors to the degradation of plant material ingested by the host animal, it is understandable that there has been great interest in exploring the enzymatic repertoire of these microorganisms in order to establish a better understanding of how AF, and their enzymes, can be used to improve host health and performance, while simultaneously reducing the ecological footprint of the livestock industry. A detailed understanding of AF and their interaction with other gut microbes as well as the host animal is essential, especially when production of affordable high-quality protein and other animal-based products needs to meet the demands of an increasing human population. Such a mechanistic understanding, leading to more sustainable livestock practices, will be possible with recently developed -omics technologies that have already provided first insights into the different contributions of the fungal and bacterial population in the rumen during plant cell wall hydrolysis.

Dietary administration of Bacillus amyloliquefaciens R8 reduces hepatic oxidative stress and enhances nutrient metabolism and immunity against Aeromonas hydrophila and Streptococcus agalactiae in zebrafish (Danio rerio)

Zebrafish (Danio rerio) are an excellent model for assessing the beneficial effects of probiotics before applying them in aquaculture. This study evaluated the effects on zebrafish of dietary supplementation with the probiotic Bacillus amyloliquefaciens R8, which heterologously expresses xylanase from rumen fungi. Nutrient metabolism, hepatic oxidative stress, and innate immunity against pathogen infections were investigated. Treated zebrafish received feed supplemented with B. amyloliquefaciens R8 for 30 days and then were compared to zebrafish that were fed a control diet. The treated fish showed significant increases in xylanase activity in the intestines. The livers of the treated fish showed increased mRNA expressions of glycolysis-related genes of hexokinase, glucokinase, glucose-6-phosphatase, and pyruvate kinase; and higher enzyme activities of 3-hydroxyacyl-coenzyme A dehydrogenase and citrate synthase which are associated with fatty acid β-oxidation and mitochondrial integrity. The livers of treated fish also showed decreased mRNA expressions of oxidative stress-related genes (SOD, Gpx, NOS2, and Hsp70) and an apoptotic gene (tp53), as well as increased expression of an anti-apoptotic gene (bcl-2). The probiotics-treated fish had increased expression of innate immune-related genes (IL-1β, IL-6, IL-21, TNF-α, and TLR-1, -3, and -4). Following challenge with Aeromonas hydrophila and Streptococcus agalactiae, treated fish showed increased a higher survival rate than control fish. Overall, results showed that the administration of xylanase-expressing B. amyloliquefaciens R8 can potentially improve nutrient metabolism and hepatic stress tolerance, and enhance immunity and disease resistance against A. hydrophila and S. agalactiae in zebrafish.

Dietary supplementation with xylanase-expressing B. amyloliquefaciens R8 improves growth performance and enhances immunity against Aeromonas hydrophila in Nile tilapia (Oreochromis niloticus)

Bacillus amyloliquefaciens has attracted attention as a probiotic in aquaculture due to its immunostimulatory activity against pathogenic infection. Xylanases are extensively used in animal feed to degrade plant ingredients, enhancing nutrient utilization and increasing the growth rate of various animals. In the present study, the effects of dietary supplementation with B. amyloliquefaciens and xylanase-expressing B. amyloliquefaciens R8 on the growth of Nile tilapia (Oreochromis niloticus) and immunity against Aeromonas hydrophila were evaluated. The results showed that the xylanase activity in the intestine, weight gain (WG), feed efficiency (FE) and condition factor (CF) of Nile tilapia fed B. amyloliquefaciens R8 for 2 months were significantly increased compared with those of the fish fed the control diet and B. amyloliquefaciens. Moreover, the mRNA expression of growth- and metabolism-related genes, such as insulin-like growth factor-1 (igf-1), glucokinase (GK), glucose-6-phosphate 1-dehydrogenase (G6PD), and glucose-6-phosphatase (G6Pase), was significantly induced in Nile tilapia fed administered B. amyloliquefaciens R8, and this group also exhibited a higher survival rate than the control fish following a challenge with A. hydrophila. The phagocytic activity and respiratory burst activity of head kidney leukocytes as well as the serum lysozyme activity of B. amyloliquefaciens R8-fed Nile tilapia were significantly higher than those of fish fed the control diet for 2 months. Superoxide dismutase (SOD) levels in the head kidney leukocytes of Nile tilapia fed B. amyloliquefaciens R8 differed from those of fish fed the control diet, but this was not significant. These results indicate that dietary supplementation with xylanase-expressing B. amyloliquefaciens R8 improves growth performance and enhances immunity and disease resistance against A. hydrophila in Nile tilapia.