Methanogenic Archaea Disruption: Anaerobic Digestion of Waste Sewage Sludge Affected by Indole- and Its Analogs-interlinked Microbial Interactions

As an interspecies signalling molecule, indole that is also regulating the microbial community quorum sensing (QS) can be an indispensable factor to influence the performance of an anaerobic digestion process. Mainly released by Gram-negative bacteria, the impact of indole regulation towards methane production in such system is hardly exposed. This research intends to analyse the methane production affected by the microbial community fluctuations in the waste sewage sludge (WSS) in response to QS repression by indole and its analogs: 4-fluoroindole (4-FI), 5-fluoroindole (5-FI), 6-fluoroindole (6-FI), 3- indoleacetic acid (3-IAA), and 3- indoleacrylic acid (3-IARA). Illumina MiSeq platform was utilized to delve into the active microbes, with ribonucleic acid (RNA) used as the template to generate the 16S metagenomic library. As results, all of them inhibit methane generation even with substrates (acetic acid) availability, and this phenomenon can be led by the slight imbalance of Gram-positive/negative bacterial composition and the inactivation of the viable core fermenters: Firmicutes, Proteobacteria and Chloroflexi. Plus, the following compounds, indole, 3-IAA, and 6-FI directly disrupted methane productions by both acetoclastic and hydrogenotropic methanogenic archaea. Methanosarcina acetivorans C2A as a prominent methane synthesizer was also characterised in terms of its viability and methane synthesis activity against them. Notably, Methanosarcina acetivorans C2A was non-viable in the presence of indole and 6-FI thus lowering methane production. From here, the affirmation on the direct and indirect inhibitions of methanogenic archaea by indole and its derivatives will pave the way for a valuable future exploration of QS mechanism mapping in archaea during methanogenesis.