Chitinases of the GH18 family perform hydrolysis while retaining the C1 configuration, the enzymes of GH19 and 48 utilize an inverting mechanism, while for one GH23 chitinase, a tunnel-like catalytic cavity relying on two acidic residues has been described [12]. GH18 chitinases utilize a conserved glutamic acid residue in the catalytic center and produce single GlcNAc units, disaccharides or higher oligosaccharides. To date, the structure, function, and biotechnological application of primarily bacterial and fungal GH18 chitinases have been the focus of further studies [13]. However, research on the role of chitinases in human health has grown after the publication of the human genome. Humans express an acidic mammalian chitinase connected with asthma in addition to other chitinases or chitinase-like proteins of the family GH18 [14; 15]. Recent studies have focused on proteins of human commensal organisms, such as intestinal bacteria [4; 16], which can serve either as markers of health state, potential active substances against candidoses or triggers for colon-specific drug delivery [17]. _Clostridium paraputrificum_ J4 is one of the bacterial species in the gastrointestinal tract of a healthy human. The strain _C. paraputrificum_ J4 was discovered by [PERSON] et al. [4] as a strictly anaerobic bacterium, which can survive on chitin as the sole source of carbon. We have identified at least five different chitinases in the extracellular extracts of this bacterium [16] and have characterized the main components with endo-, exochitinase and \(N\)-acetylglucosamineidase activity. Complete genomes of thirty-two other Clostridia, excluding _C. paraputrificum_ J4, have been annotated (NCBI, [[http://www.ncbi.nlm.nih.gov/genome/](http://www.ncbi.nlm.nih.gov/genome/)]([http://www.ncbi.nlm.nih.gov/genome/](http://www.ncbi.nlm.nih.gov/genome/)), accessed on 25 April 2021), twenty of which do not contain any chitinase and only one that has at least two predicted chitinases. Within Clostridia, only _C. paraputrificum_ J4 harbors genes for such a high number of chitinolytic enzymes. _C. paraputrificum_ J4 secretes enzymes in support of its nutrition in the human intestine, where chitin or ethicoligosaccharides cannot be normally processed by human enzymes, which raises questions about the source of chitin in humans. Chitin, chitosan, and derived substances have been used in the food industry as antimicrobial agents, for beverage clarification, and in pharmaceutical and therapeutic applications, etc. [18; 19]. These applications, apart from food contamination by fungi, explain the occurrence of a commensal bacterium well equipped for chitin degradation. Fungal infections can become a major issue in human health and more effective means of treatment are sought [20]. Chitinases, capable of degradation of chitin-containing fungal cell walls and originating from human symbionts, may be used in applications against candidoses or in targeted drug release [21]. The research efforts directed at the understanding of the interactions of the SARS-CoV-2 virus within humans, indicated, among other effects, infection-related changes in microbiome composition [22] as an important direction for diagnostic development and understanding the fitness of the human immune system. Better understanding of the molecular details behind microbiome development and interdependencies between a healthy human and commensal species should provide a solid base for further developments in diagnostics and treatment of pathogen-borne diseases. In this work, we characterized an isolated form and two recombinant forms of the most abundant chitinase of the human commensal bacterium _Clostridium paraputritcium_ J4. We bring functional analysis and insights into the domain structure of the major chitinase of this bacterium and evidence of gene/enzyme adjustment to the typical conditions of the human colon environment.