Inactivation of the uptake hydrogenase in the purple non-sulfur photosynthetic bacterium Rubrivivax gelatinosus CBS enables a biological water–gas shift platform for H2 production

Recent Advances in Biotechnologies for the Treatment of Environmental Pollutants Based on Reactive Sulfur Species

The definition of reactive sulfur species (RSS) is inspired by the reactivity and variable chemical valence of sulfur. Sulfur is an essential element for life and is a part of global geochemical cycles. Wastewater treatment bioreactors can be divided into two major categories: sulfur reduction and sulfur oxidation. We review the origins of the definition of RSS and related biotechnological processes in environmental management. Sulfate reduction, sulfide oxidation, and sulfur-based redox reactions are key to driving the coupled global carbon, nitrogen, and sulfur co-cycles. This shows the coupling of the sulfur cycle with the carbon and nitrogen cycles and provides insights into the global material-chemical cycle. We also review the biological classification and RSS metabolic mechanisms of functional microorganisms involved in the biological processes, such as sulfate-reducing and sulfur-oxidizing bacteria. Developments in molecular biology and genomic technologies have allowed us to obtain detailed information on these bacteria. The importance of RSS in environmental technologies requires further consideration.

Anaerobic and hydrogenogenic carbon monoxide-oxidizing prokaryotes: Versatile microbial conversion of a toxic gas into an available energy

Carbon monoxide (CO) is a gas that is toxic to various organisms including humans and even microbes; however, it has low redox potential, which can fuel certain microbes, namely, CO oxidizers. Hydrogenogenic CO oxidizers utilize an energy conservation system via a CO dehydrogenase/energy-converting hydrogenase complex to produce hydrogen gas, a zero emission fuel, by CO oxidation coupled with proton reduction. Biochemical and molecular biological studies using a few model organisms have revealed their enzymatic reactions and transcriptional response mechanisms using CO. Biotechnological studies for CO-dependent hydrogen production have also been carried out with these model organisms. In this chapter, we review recent advances in the studies of these microbes, which reveal their unique and versatile metabolic profiles and provides future perspectives on ecological roles and biotechnological applications. Over the past decade, the number of isolates has doubled (37 isolates in 5 phyla, 20 genera, and 32 species). Some of the recently isolated ones show broad specificity to electron acceptors. Moreover, accumulating genomic information predicts their unique physiologies and reveals their phylogenomic relationships with novel potential hydrogenogenic CO oxidizers. Combined with genomic database surveys, a molecular ecological study has unveiled the wide distribution and low abundance of these microbes. Finally, recent biotechnological applications of hydrogenogenic CO oxidizers have been achieved via diverse approaches (e.g., metabolic engineering and co-cultivation), and the identification of thermophilic facultative anaerobic CO oxidizers will promote industrial applications as oxygen-tolerant biocatalysts for efficient hydrogen production by genomic engineering.