On the bacterial spore is where you will discover robust and novel biochemistry

Bacterial spores can germinate after centuries, perhaps millennia, in stasis. Enzymes that evolve on the spore surface must be equally resilient. Mn(II, III) oxidizing multicopper oxidases (MCOs) from marine Bacillus isolates are no exception. MCOs catalyze single electron transfers from their substrate to four spectroscopically distinct Cu atoms, terminating in the reduction of O₂ to H₂O. These Bacillus MCOs are heat and protease resistant which is beneficial when combatting harsh environments and predators along the spore’s planktonic voyage towards a favorable germination habitat. Also advantageous is the ability to catalyze the formation of one of the strongest known oxidants, Mn(IV) oxides, by oxidizing Mn(II) to Mn(III) and Mn(III) to Mn(IV). These minerals oxidize of a wide variety of substrates and are able to sorb metals in their crystal lattices. We have recently purified Mnx, the Mn(II, III) MCO from Bacillus sp. PL-12, and shown it to by a unique, robust enzyme with a wide substrate activity range including metals  and phenolic compounds, a promising feature for bioprocessing. The two exceptional features of this MCO are that it (1) catalyzes two energetically distinct electron transfers instead of one while (2) bound to two small, hypothetical proteins with no predicted function. Elucidating the oxidation mechanism of Mnx and its subunits through structural and bioinorganic techniques will facilitate its future engineering towards an even broader set of substrates. The key to enzyme discovery for industrial purposes may be exploring the hardy enzymes on bacterial spores that persist through millennia in Earth’s extreme environments.