Commercially-supplied potato galactan (PG) is widely used as a model polysaccharide in various bioactivity studies. However, results using this galactan are not always consistent with the stated composition. Here, we assessed its composition by fractionating this commercial PG and purified its primary components: PG-A, PG-B and PG-Cp with weight-averaged molecular weights of 430, 93, and 11.3 kDa, respectively. PG-Cp consists of free β-1,4-galactan chains, whereas PG-A and PG-B are type I rhamnogalacturonans with long β-1,4-galactan side chains of up to 80 Gal residues and short β-1,4-galactan side chains of 0 to 3 Gal residues that display a \"trees in lawn\" pattern. Structures of these polysaccharides correlate well with their activities in terms of galectin-3 binding and gut bacterial growth assays. Our study clarifies the confusion related to commercial PG, with purified fractions serving as better model polysaccharides in bioactivity investigations.

Although the strategies used by bacteria to adapt to specific environmental conditions are widely reported, fewer studies have addressed how microbes with a cosmopolitan distribution can survive in diverse ecosystems. Exiguobacterium is a versatile genus whose members are commonly found in various habitats. To better understand the mechanisms underlying the universality of Exiguobacterium, we collected 105 strains from diverse environments and performed large-scale metabolic and adaptive ability tests. We found that most Exiguobacterium members have the capacity to survive under wide ranges of temperature, salinity, and pH. According to phylogenetic and average nucleotide identity analyses, we identified 27 putative species and classified two genetic groups: groups I and II. Comparative genomic analysis revealed that the Exiguobacterium members utilize a variety of complex polysaccharides and proteins to support survival in diverse environments and also employ a number of chaperonins and transporters for this purpose. We observed that the group I species can be found in more diverse terrestrial environments and have a larger genome size than the group II species. Our analyses revealed that the expansion of transporter families drove genomic expansion in group I strains, and we identified 25 transporter families, many of which are involved in the transport of important substrates and resistance to environmental stresses and are enriched in group I strains. This study provides important insights into both the overall general genetic basis for the cosmopolitan distribution of a bacterial genus and the evolutionary and adaptive strategies of Exiguobacterium. IMPORTANCE The wide distribution characteristics of Exiguobacterium make it a valuable model for studying the adaptive strategies of bacteria that can survive in multiple habitats. In this study, we reveal that members of the Exiguobacterium genus have a cosmopolitan distribution and share an extensive adaptability that enables them to survive in various environments. The capacities shared by Exiguobacterium members, such as their diverse means of polysaccharide utilization and environmental-stress resistance, provide an important basis for their cosmopolitan distribution. Furthermore, the selective expansion of transporter families has been a main driving force for genomic evolution in Exiguobacterium. Our findings improve our understanding of the adaptive and evolutionary mechanisms of cosmopolitan bacteria and the vital genomic traits that can facilitate niche adaptation.