The order Cytophagales, which was initially established by Winogradsky in 1929 and subsequently revised by Skerman in 1980 (Skerman et al., 1980), represents a diverse group of Gram-negative, gliding bacteria that are widely distributed in various environments including soil, freshwater, marine ecosystems, and extreme habitats (Reichenbach, 1992). Members of this order are characterized by their ability to degrade complex polysaccharides, such as cellulose, chitin, and pectin, making them key players in the global carbon cycle (McBride et al., 2014). The ecological significance of Cytophagales is further underscored by their involvement in organic matter decomposition and their interactions with other microorganisms in microbial communities (Thomas et al., 2011). Taxonomically, the order Cytophagales has undergone significant revisions with the advent of molecular phylogenetic techniques. Initially classified based on morphological and physiological traits, the order now includes families such as Cytophagaceae, Flammeovirgaceae, and Bernardetiaceae, among others (García-López et al., 2019; Hahnke et al., 2016). These families encompass a wide range of genera, including Cytophaga, Sporocytophaga, and Flavobacterium, which exhibit considerable metabolic and ecological diversity (Bernardet and Nakagawa, 2006).

Recent advances in genomics and metagenomics have provided deeper insights into the evolutionary relationships and functional potential of Cytophagales. Comparative genomic analyses have revealed adaptations to specific niches, such as the presence of genes encoding carbohydrate-active enzymes (CAZymes) and secondary metabolite biosynthetic pathways (García-López et al., 2019; McBride et al., 2014). These findings highlight the importance of Cytophagales in biotechnology and their potential applications in biofuel production, bioremediation, and the discovery of novel bioactive compounds (Hahnke et al., 2016; Thomas et al., 2011). Despite their ecological and biotechnological relevance, many aspects of Cytophagales biology remain underexplored. This includes their roles in host-associated microbiomes, their responses to environmental stressors, and the mechanisms underlying their gliding motility (McBride et al., 2014; Reichenbach, 1992). Further research is needed to elucidate these aspects and to uncover the full potential of this diverse and ecologically important bacterial order.

Deep-sea polymetallic nodules represent an important but unexploited resource of a wide range of critical metals such as manganese (Mn), copper (Cu), cobalt (Co), and nickel (Ni) (Hein et al., 2020), which indicates huge economic and scientific value (Hein et al., 2020), attracting much attention on mining for substantial metals on the seabed (Margolis and Burns, 1976). Polymetallic nodules are widely found in the surface of the sediments from deep sea, and is most abundant in the Clarion-Clipperton Zone (CCZ) located in the East Pacific Ocean (Hein et al., 2020). Manganese is the second most abundant redox active transition metal in the Earth's crust, where Mn (IV) could be found on up to 30 % of the Pacific Ocean seafloor (Butterfield et al., 2013; Post, 1999). Microorganisms are believed to have major control of the formation of Mn oxide minerals, thus the mechanisms of the formation of manganese nodules in this environment has become a heated discussion.

During an investigation in the bacterial diversity in the CCZ, strain EPR-FJ-38T was isolated and characterized taxonomically to represent novel Cytophagales taxa. Based on the result of blast search against the GenBank (https://blast.ncbi.nlm.nih.gov/Blast.cgi) databases, strain SYC-11 isolated from the seawater sample of South China Sea showed 99.8 % 16S rRNA gene sequence similarity with strain EPR-FJ-38T. Strain SYC-11 was obtained from the Extreme Lab of Zhejiang University and included in this study. Strains' resistance and removal ability to heavy metals (e.g. Mn2+) were evaluated. The elemental composition and crystallographic structure results as well as the 16S rRNA sequences were combined in order to learn more about the mechanics of the strains' heavy metal resistance and biomineralization. According to the identification by polyphasic taxonomy methods, strains EPR-FJ-38T and SYC-11 may be categorized to a new family belonging to the Cytophagales order.