Obscure quorum sensing-mediated modulations facilitating enhanced biogas production

Abstract

A stable functioning of microbial metabolism is critical for AD; however, due to the physiological limitations of the microbes involved, it encounters frequent system failures. Strengthening of the elaborate nexus between fermentative bacteria and methanogenic archaea is pivotal for AD. This will enable robust interspecies exchange and communication involving quorum sensing (QS) in syntrophic interactions, enhancing viability of the microbes. Over the years, several QS-mediated regulations of AD for enhanced methanogenesis have been apparent, such as, improvement in microbial community structure and substrate degradation, increased secretion of EPS, etc. However, there are some atypical, obscure QS influences that need attention. For example, increased microbial competition, secretion of public goods for optimal resource partitioning and conservation of energy, modulation of downstream signal transduction, and alleviation of various kinds of stresses. In this vein, we review the less-known QS modulations of AD and methanogenesis comprehensively. It is evident that tweaking the molecular mechanisms and signaling pathways, and underexplored themes such as role of secondary messengers, management of oxidative stress, and optimization of endogenous stimulation versus exogenous addition would aid optimal regulation of QS in AD via a robust microbial community structure, ensuring consistent biogas production with high methane content. A critical assessment on current challenges and future research directives suggests the need for determining the QS molecules functional in methanogens, role of inter-domain communication, activation of genetic circuits, etc., via gene knockout studies and heterologous expression combined with metabolomics in realizing the full potential of QS in AD for enhanced biogas production.