Mixotrophic bacteria for environmental detoxification of contaminated waste and wastewater

Mixotrophic bacteria provide a desirable alternative to the use of classical heterotrophic or chemolithoautotrophic bacteria in environmental technology, particularly under limiting nutrients conditions. Their bi-modal ability of adapting to inorganic or organic carbon feed and sulfur, nitrogen, or even heavy metal stress conditions are attractive features to achieve efficient bacterial activity and favorable operation conditions for the environmental detoxification or remediation of contaminated waste and wastewater. This review provides an overview on the state of the art and summarizes the metabolic traits of the most promising and emerging non-model mixotrophic bacteria for the environmental detoxification of contaminated wastewater and waste containing excess amounts of limiting nutrients. Although mixotrophic bacteria usually function with low organic carbon sources, the unusual capabilities of mixotrophic electroactive exoelectrogens and electrotrophs in bioelectrochemical systems and in microbial electrosynthesis for accelerating simultaneous metabolism of inorganic or organic C and N, S or heavy metals are reviewed. The identification of the mixotrophic properties of electroactive bacteria and their capability to drive mono- or bidirectional electron transfer processes are highly exciting and promising aspects. These aspects provide an appealing potential for unearthing new mixotrophic exoelectrogens and electrotrophs, and thus inspire the next generation of microbial electrochemical technology and mixotrophic bacterial metabolic engineering. KEY POINTS: • Mixotrophic bacteria efficiently and simultaneously remove C and N, S or heavy metals. • Exoelectrogens and electrotrophs accelerate metabolism of C and N, S or heavy metals. • New mixotrophic exoelectrogens and electrotrophs should be discovered and exploited.