Figure 5 Percentage of sequences associated with the metabolism of aromatic compounds in the pygmy loris microbiome. KEGG Pathway Assignment Pathway assignment was performed based on the Kyoto Encyclopedia of Genes and Genomes (KEGG). selleckchem First, the 78,619 reads were compared using BLASTX with the default parameters from the KEGG database. A total of 18,410 reads with corresponding enzyme commission (EC) numbers were assigned to the metabolic pathways. Given that the sequences related to the metabolism of aromatic compounds were more abundant in the pygmy loris fecal metagenomes compared with other animals in terms of subsystem, we focused our attention on xenobiotic biodegradation and metabolism.
A high number of sequences in the benzoate degradation pathway was observed, which is coherent with the fact that benzoate is a central intermediary compound in the anaerobic and aerobic metabolism of various aromatic compounds, such as toluence, xylene, fluorine, carbazole, and biphenyl . The key enzymes involved in benzoate degradation via hydroxylation, such as catechol 1,2-dioxygenase (EC 220.127.116.11), and protocatechuate 3,4-dioxygenase (EC 18.104.22.168) were identified in the pygmy loris fecal metagenomes (Figure 6a). The two usual methods of aerobic benzoate metabolism are dioxygenation to form catechol, utilized by some bacteria such as Pseudomonas putida and Acinetobacter calcoaceticus , and monooxygenation to form protocatechuate, mostly by Aspergillus niger . Almost all the enzymes involved in the two methods of aerobic benzoate metabolism in the KEGG pathway (Figure 6a).
The main organisms, P. putida, A. calcoaceticus, and A. niger, involved in the course of metabolism were all represented in the pygmy loris fecal microbiome (Table S2 and S3). Figure 6 Reference pathway of benzoate degradation. Although several key enzymes such as benzoyl-CoA reductase (EC 22.214.171.124) were missing in the method of anaerobic benzoate metabolism via CoA ligation, partial enzymes were identified (Figure 6b). This particular result may be due to the fact that the pathway of anaerobic benzoate metabolism in the pygmy loris was a little different. These results suggest that the fecal microbiota of the pygmy loris under study have a potential to degrade phenol and derivatives by the aerobic and anaerobic pathway.
Moreover, these pathways may interchange because of the cross-regulation between the anaerobic and aerobic pathways for the catabolism of aromatic compounds, which may reflect a biological strategy to increase cell fitness in organisms Brefeldin_A that survive in environments subject to changing oxygen concentrations . Aromatic compounds comprise one-quarter of the Earth’s biomass and are the second most widely distributed class of organic compounds in nature, next to carbohydrates.