Lessons from Clostridial Genetics: Toward Engineering Acetogenic Bacteria

Acetogens are a group of bacteria that harbor the Wood-Ljungdahl or reductive acetyl-CoA pathway for fixation of CO or CO2 plus H-2. Acetogens have been receiving great attention as biological catalysts for conversion of C1 gases into higher compounds since they are able to efficiently utilize these gases. Despite the industrial potential of these bacteria, however, metabolic engineering of acetogens remains difficult due to their little-known molecular biology in addition to the nature of strict anaerobicity. Fortunately, experimental techniques and genetic tools have been developed for the genus Clostridium, many members of which had been impervious to genetic modifications. Since commonly used acetogens belong to or are closely related to Clostridium, the lessons obtained from studies on other Clostridium spp. will be useful to establish experimental protocols and tools for the genetic manipulation of acetogenic bacteria. To this end, this review focuses on the basic techniques, genetic elements, and tools for metabolic engineering of clostridia, with key examples of their implementation in acetogens.