# Basic Bioelement Contents in Anaerobic Intestinal Sulfate-Reducing Bacteria
## 1 Introduction  
Inflammatory bowel diseases (IBD), which includes Crohn's disease (CD) and ulcerative colitis (UC), occur more often among citizens of European countries, recently [1; 2; 3; 4; 5]. The explanation for many diseases is genetic predisposition, causing the impairment of the immune response [4], but the etiology of these diseases remains uncertain. The intestinal microbiome plays a significant role in the intestinal tract [6; 7; 8; 9; 10; 11; 12; 13; 14]. Due to their production of the toxic hydrogen sulfide (H\({}_{2}\)S), sulfate-reducing bacteria (SRB) can significantly influencethe human gut environment [10; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25]. Therefore, the fact of interaction of microorganisms with a macroorganism--human--is interesting and actual. Our previous research has shown that SRB are involved in the development of IBD [26]. Studies of the intestinal microbiota of patients suffering from UC, especially studies with animal gut inflammation models, demonstrated the connection between SRB and IBD prevalence [15; 16; 20]. Inflammatory processes under the influence of SRB occur in the human intestine due to the functional role of cellular systems of bacteria, as a result of H2S and acetate formation [26]. Previous studies have indicated differences between SRB strains isolated from healthy people and individuals with colitis. The differences were observed in the following factors: biomass accumulation, sulfate consumption, lactate oxidation, H2S, and acetate production [27; 28; 29; 30; 31]. It is well known that the cytoplasm of bacterial cells, in particular SRB, includes micro- and trace elements. The presence of these elements plays an important role in bacteria enzyme systems (i.e., cytoplasmic, periplasmic, and membrane). Different metals act as cofactors in key enzymes. Several superoxide dismutases depending on the type of metal cofactor of the active center of enzymes: Cu, Zn-SOD, and Mn-SOD, as well as the less common Fe-SOD and Ni-SOD [32; 33; 34]. ATP sulfurylase, an enzyme of the process of dissimilatory sulfate reduction, contains Zn [35]. APS (adenosine-phosphulfate) reductases and dissimilatory sulfite reductases preferably contain Fe\({}^{2+}\) or Fe\({}^{3+}\)[36]. Enzymes involved in lactate oxidation, in particular lactate dehydrogenase, function together with cytochrome \(\varOmega\), which contains iron ions. Pyruvate:ferredoxin oxidoreductase contains thiamine diphosphate and [4 Fe-4S] clusters. Acetate kinase, for example, requires Mg\({}^{2+}\) for their activity [9]. Elements such as Na\({}^{+}\), K\({}^{+}\), Ca\({}^{2+}\), and Mg\({}^{2+}\) are non-cofactors and play a substantial role in the sodium potassium pump and transport to the cytoplasm, same as in the synthesis of ATP in SRB. Additionally, antioxidant enzymes (superoxide dismutase (SOD) EC 1.15.1.1, catalase EC 1.11.1.6, and peroxidase EC 1.11.1.7) are important for SRB because they are involved in the stress response of bacterial cells. Catalase has sites for binding to metal ions, iron (Fe) ions, heme, and NADP. Thus, a lot of trace metallic elements are involved in SRB metabolism and are essential for bacterial cells. Despite the essential role in bacterial enzymatic systems of bacteria, some metals (i.e., Pb, Co, Cu) occurring at high concentrations, are often toxic for biological systems, mainly through the following effects [37]: (a) the blockage of enzymes' and transport systems' function in all groups; (b) essential ions can be replaced by the present metals; (c) the active conformation of biomolecules can be modified in the presence of metals. Metal ions bond with proteins, nucleotides, coenzymes, phospholipids, porphyrins, and other metabolites due to their capability to form complexes with hydroxyl, phosphate, carboxyl, amino, and sulfhydryl groups [38]. The toxicity of metals can be overviewed through their adverse effects on cell transport functions; they can have mutagenic effects.