Sugar metabolism of the first thermophilic Planctomycetes Thermogutta terrifontis: comparative genomic and transcriptomic approache

Abstract

Xanthan gum, a complex polysaccharide comprising glucose, mannose and glucuronic acid residues, is involved in numerous biotechnological applications in cosmetics, agriculture, pharmaceuticals, food and petroleum industries. Additionally, its oligosaccharides were shown to possess antimicrobial, antioxidant and few other properties. Yet, despite its extensive usage, little is known about xanthan gum degradation pathways and mechanisms.\n\nThermogutta terrifontis R1 was described as the first thermophilic representative of the Planctomycetes phylum. As other cultivated planctomycetes, it grows well on various carbohydrates including oligo- and polysaccharides, however, its capability of anaerobic growth with or without electron acceptors was a novel finding among the representatives of this phylum.\n\nThe aim of this work is to examine T. terrifontis catabolic pathways with a special focus on the xanthan gum degradation pathway using genomic and transriptomic sequencing. Genomic analysis revealed more than a hundred glycosidases, polysaccharide lyases and other CAZymes, involved in oligo- and polysaccharide degradation by T. terrifontis, proteins of central carbohydrate metabolism and aerobic and anaerobic respiration. Furthermore, the combination of genomic and transcriptomic approaches revealed a putative novel xanthan gum degradation pathway involving unusual catalytic steps and enzymes: novel glycosidase(s) of DUF1080 family, hydrolyzing xanthan gum beta-glucosidic backbone linkages and beta-mannosidases instead of xanthan lyases for degradation of terminal beta-mannosidic linkages. Surprisingly, the genes coding DUF1080 proteins were found in high number in T. terrifontis and in many other Planctomycetes genomes, which, together with our observation that xanthan gum being a selective substrate for many planctomycetes, supports the important role of DUF1080 in xanthan gum degradation. Our findings shed light on the metabolism of the first thermophilic planctomycete, capable to degrade a number of polysaccharides, either aerobically or anaerobically, including the biotechnologically important bacterial polysaccharide xanthan gum. The results serve as good foundation for future exploration of T. terrifontis and its enzymes in biotechnological applications.