No abstract

Algal cell wall polysaccharides constitute a large fraction in the biomass of marine primary producers and are thus important in nutrient transfer between trophic levels in the marine ecosystem. In order for this transfer to take place, polysaccharides must be degraded into smaller mono-and disaccharide units, which are subsequently metabolized, and key components in this degradation are bacterial enzymes. The marine bacterium Colwellia echini A3 T is a potent enzyme producer since it completely hydrolyzes agar and -carrageenan. Here, we report that the genome of C. echini A3 T harbors two large gene clusters for the degradation of carrageenan and agar, respectively. Phylogenetical and functional studies combined with transcriptomics and in silico structural modeling revealed that the carrageenolytic cluster encodes furcellaranases, a new class of glycoside hydrolase family 16 (GH16) enzymes that are key enzymes for hydrolysis of furcellaran, a hybrid carrageenan containing both ␤and -carrageenan motifs. We show that furcellaranases degrade furcellaran into neocarratetraose-43-O-monosulfate [DA-(␣1,3)-G4S-(␤1,4)-DA-(␣1,3)-G], and we propose a molecular model of furcellaranases and compare the active site architectures of furcellaranases, -carrageenases, ␤-agarases, and ␤-porphyranases. Furthermore, C. echini A3 T was shown to encode -carrageenases, -carrageenases, and members of a new class of enzymes, active only on hybrid ␤/-carrageenan tetrasaccharides. On the basis of our genomic, transcriptomic, and functional analyses of the carrageenolytic enzyme repertoire, we propose a new model for how C. echini A3 T degrades complex sulfated marine polysaccharides such as furcellaran, -carrageenan, and -carrageenan. IMPORTANCE Here, we report that a recently described bacterium, Colwellia echini, harbors a large number of enzymes enabling the bacterium to grow on -carrageenan and agar. The genes are organized in two clusters that encode enzymes for the total degradation of -carrageenan and agar, respectively. As the first, we report on the structure/ function relationship of a new class of enzymes that hydrolyze furcellaran, a partially sulfated ␤/-carrageenan. Using an in silico model, we hypothesize a molecular structure of furcellaranases and compare structural features and active site architectures of furcellaranases with those of other GH16 polysaccharide hydrolases, such as -carrageenases, ␤-agarases, and ␤-porphyranases. Furthermore, we describe a new class of enzymes distantly related to GH42 and GH160 ␤-galactosidases and show that this new class of enzymes is active only on hybrid ␤/-carrageenan oligosaccharides. Finally, we propose a new model for how the carrageenolytic enzyme repertoire enables C. echini to metabolize ␤/-, -, and -carrageenan.

Marine microorganisms encode a complex repertoire of carbohydrate-active enzymes (CAZymes) for the catabolism of algal cell wall polysaccharides. While the core enzyme cascade for degrading agar is conserved across agarolytic marine bacteria, gain of novel metabolic functions can lead to the evolutionary expansion of the gene repertoire. Here, we describe how two less abundant GH96 α-agarases harbored in the agar specific polysaccharide utilization locus (PUL) of Colwellia echini A3T facilitate the versatility of the agarolytic pathway. The cellular and molecular functions of the α-agarases examined by genomic, transcriptomic, and biochemical analyses revealed that α-agarases of C. echini A3T create a novel auxiliary pathway. α-Agarases convert even-numbered neoagarooligosaccharides to odd-numbered agaro- and neoagarooligosaccharides, providing an alternative route for the depolymerization process in the agarolytic pathway. Comparative genome analysis of agarolytic bacteria implied that the agarolytic gene repertoire in marine bacteria has been diversified during evolution while the essential core agarolytic gene set was conserved. The expansion of the agarolytic gene repertoire and novel hydrolytic functions, including the elucidated molecular functionality of α-agarase, promote metabolic versatility by channeling agar metabolism through different routes. Importance Colwellia echini A3T is an example of how the gene gain can lead to the evolutionary expansion of agar specific polysaccharide utilization loci (PUL). C. echini A3T encodes two α-agarases in addition to the core β-agarolytic enzymes in its agarolytic PUL. Among the agar-degrading CAZymes identified so far, only a few α-agarases have been biochemically characterized. The molecular and biological functions of two α-agarases revealed that their unique hydrolytic pattern leads to the emergence of auxiliary agarolytic pathways. Through the combination of transcriptomic, genomic, and biochemical evidence, we elucidate the complete α-agarolytic pathway in C. echini A3T. The addition of α-agarases to the agarolytic enzyme repertoire might allow marine agarolytic bacteria to increase competitive abilities through metabolic versatility.

Background Gut is a crucial organ for the host’s defense system due to its filtering action of the intestinal membrane from hazardous foreign substances. One strategy to strengthen the gut epithelial barrier function is to upregulate beneficial microflora populations and their metabolites. Sophorolipid (SPL), which is a glycolipid bio-surfactant, could increase beneficial microflora and decrease pathogenic bacteria in the gastrointestinal tract. Therefore, herein, we conducted an experiment with broiler chickens to investigate the fortifying effects of SPL on the host’s gut defense system by modulating the microbiota population. Methods A total of 540 1-day-old chicks (Ross 308) were used, and they were immediately allotted into three treatment groups (6 replications with 30 chicks/pen) according to their initial body weight. The dietary treatments consisted of CON (basal diet), BAM (10 mg/kg bambermycin), and SPL (10 mg/kg SPL). During the experiment, birds freely accessed feed and water, and body weight and feed intake were measured at the end of each phase. On d 35, birds (one bird/pen) were sacrificed to collect jejunum and cecum samples. Results Dietary SPL and BAM supplementation significantly accelerated birds’ growth and also significantly improved feed efficiency compared to CON. Intestinal microbial community was significantly separated by dietary SPL supplementation from that of CON, and dietary SPL supplementation significantly increased Lactobacillus spp. and Akkermansia muciniphila. Moreover, birds fed with dietary SPL also showed the highest concentration of cecal butyrate among all treatment groups. Gut morphological analysis showed that dietary SPL significantly increased villus height, ratio of villus height to crypt depth, goblet cell numbers, and the gene expression levels of claudin-1 and mucin 2. Additionally, dietary SPL significantly decreased the mRNA expression level of pro-inflammatory cytokine, interleukin-6, and increased that of anti-inflammatory cytokine, interleukin-10, compared to other treatments. Conclusions Dietary SPL increases the beneficial bacterial population and butyrate concentration, which leads to a strengthened gut barrier function. In addition, the intestinal inflammation was also downregulated by dietary SPL supplementation.

Aegilops tauschii (Ae. tauschii) is a diploid (2n = 2x = 14) wild grass species, which has been reported as the progenitor of hexaploid wheat (Triticum aestivum) with D-genome. In this study, 68 Ae. tauschii accessions with diverse geographical backgrounds were investigated for their resistance to infection by the leaf rust fungi Puccinia triticina. Two Ae. tauschii accessions that exhibited hyper-resistance to leaf rust at both seedling and adult stages were identified. Utilizing two susceptible Ae. tauschii ecotypes and keumkang, a common Korean wheat cultivar known to be susceptible to leaf rust, as the negative control, further investigations were conducted for understanding the mechanism underlying immunity to leaf rust disease of these two resistant accessions. Resistant accessions displayed the increased β-1,3-glucanase activity to prevent fungal penetration and the better peroxidase activity to cope with leaf rustinduced oxidative stress. Moreover, transcriptional analyses reveal the important role of the LRR receptor-like serine/ threonine-protein kinase FLS2 (lrr) to the disease resistance of the two ecotypes. Ae. tauschii is a remarkable genetic source, especially for abiotic and biotic stress resistance genes, as the plant is known for its wide-ranging geographical habitat and adaptability to different environments. This, combined with the fact that Ae. tauschii and wheat share a close evolutionary relationship, is indicative of the immense benefit of using Ae. tauschii as a material for improving the quality of synthetic wheat. Our aim was to identify and evaluate the strongest Ae. tauschii contenders for breeding leaf rust-resistant synthetic wheat.