Table 1.
Main classes of microbial metabolites in the Exposome-Explorer database and type of evidence supporting their microbial origin.
| Metabolite class | Number of metabolites | Examples of metabolites1 | |||
|---|---|---|---|---|---|
| Total | Produced by human faecal bacteria | Reduced by antibiotic treatment | Reduced in germ-free animals | ||
| Amino acids, peptides, and analogues | 62 | 25 | 36 | 28 | Phenylacetylglycine; Alanine; Tyrosine |
| Phenylpropanoids and polyketides | 46 | 44 | 11 | 16 | 3-Hydroxyphenylpropionic acid; 3-Phenylpropionic acid; 4-Hydroxyphenylpropionic acid |
| Fatty acyls | 45 | 30 | 25 | 6 | Butyric acid (4:0); Valeric acid (5:0); Isovaleric acid (5:0) |
| Bile acids, alcohols and derivatives | 45 | 33 | 11 | 12 | Deoxycholic acid; 7-Ketolithocholic acid; Isochenodeoxycholic acid |
| Phenols | 31 | 18 | 15 | 15 | 4-Hydroxyphenylacetic acid; 3,4-Dihydroxyphenylacetic acid; 3-Hydroxyphenylacetic acid |
| Indoles and derivatives | 23 | 13 | 10 | 12 | Indolepropionic acid; Indoleacetic acid; Indolelactic acid |
| Carbohydrates and carbohydrate conjugates | 22 | 0 | 16 | 9 | Glucose; N-Acetylglucosamine; Glycerol |
| Organic nitrogen compounds | 22 | 15 | 10 | 10 | Spermidine; Spermine; Trimethylamine N-oxide |
| Benzoic acids and derivatives | 21 | 16 | 7 | 7 | Protocatechuic acid; Hippuric acid; Gallic acid |
| Carboxylic acids and derivatives | 14 | 11 | 7 | 9 | Propionic acid (3:0); Acetic acid (2:0); Isobutyric acid (4:0) |
| Benzene and substituted derivatives | 12 | 10 | 3 | 4 | Phenylacetic acid; Tyramine; Phenethylamine |
| Hydroxy acids and derivatives | 10 | 4 | 5 | 2 | Lactic acid; D-Lactic acid; 3-Hydroxypropionic acid |
| Steroids and steroid derivatives | 10 | 9 | 2 | 1 | Estradiol; Estrone; 5beta-Coprostanol |
| Alcohols and polyols | 9 | 6 | 2 | 1 | Quinic acid; Ethanol; Pantothenic acid |
| Nucleosides, nucleotides, and analogues | 9 | 0 | 5 | 5 | Cytidine; Deoxycytidine; Adenosine 5'-monophosphate |
| Organic acids and derivatives | 8 | 1 | 6 | 4 | Indoxyl sulfate; N1-Acetylspermidine; Taurine |
| Pyridines and derivatives | 7 | 0 | 4 | 5 | 4-Pyridoxic acid; Pyridoxal; Nicotinic acid |
| Prenol lipids | 7 | 0 | 3 | 4 | Menaquinone-6; Menaquinone-10; Menaquinone-11 |
| Keto acids and derivatives | 7 | 1 | 5 | 4 | 4-Methyl-2-oxovaleric acid; 2-Oxoglutaric acid; 3-Methyl-2-oxobutyric acid |
| Purines and purine derivatives | 7 | 1 | 4 | 6 | Hypoxanthine; Adenine; Xanthine |
| Carbonyl compounds | 6 | 4 | 2 | 0 | 3-Hydroxypropanal; 4-Hydroxybenzaldehyde; 3,4-Dihydroxybenzaldehyde |
| Lipids and lipid-like molecules | 6 | 1 | 5 | 0 | Isocholic acid; Sphingomyelin (d18:2/18:0); 1-Decanoyl-rac-glycerol |
| Tetrapyrroles and derivatives | 5 | 4 | 4 | 1 | Vitamin B12; Urobilinogen; Urobilin |
| Pyrimidines and pyrimidine derivatives | 5 | 1 | 4 | 2 | Uracil; Thiamin; Cytosine |
| Organoheterocyclic compounds | 4 | 3 | 1 | 1 | Pyrrolidine; Piperidine; Biotin |
| Imidazoles | 4 | 0 | 2 | 3 | Nt-Methylimidazoleacetic acid; Allantoin; Urocanic acid |
| Pteridines and derivatives | 3 | 2 | 2 | 1 | Folates; Riboflavin; 7,8-Dihydropteroic acid |
| Lignans, neolignans and related compounds | 2 | 2 | 0 | 1 | Enterolactone; Enterodiol |
| Alkaloids and derivatives | 1 | 1 | 1 | 0 | Trigonelline |
| Organosulfur compounds | 1 | 0 | 0 | 1 | Dimethylsulfone |
| Hybrid peptides | 1 | 0 | 1 | 0 | 4'-Phosphopantothenoylcysteine |
| Phenol ethers | 1 | 1 | 0 | 0 | 5-(3'-Methoxyphenyl)valeric acid |
| Phenol esters | 1 | 1 | 0 | 0 | 2'',3''-Dihydroxyphenoxyl-3-(3',4'-dihydroxyphenyl)propionic acid |
| Total | 457 | 257 | 209 | 170 | |
1The first three metabolites with larger number of records on experimental evidence.