Expanding the current knowledge and biotechnological applications of the oxygen-independent ortho-phthalate degradation pathway

Abstract

ortho-Phthalate derives from industrially produced phthalate esters, which are massively used as plasticizers and constitute major emerging environmental pollutants. The pht pathway for the anaerobic bacterial biodegradation of o-phthalate involves its activation to phthaloyl-CoA followed by decarboxylation to benzoyl-CoA. Here, we have explored further the pht peripheral pathway in denitrifying bacteria and shown that it requires also an active transport system for o-phthalate uptake that belongs to the poorly characterized class of TAXI-TRAP transporters. The construction of a fully functional pht cassette combining both catabolic and transport genes allowed to expand the o-phthalate degradation ecological trait to heterologous hosts. Unexpectedly, the pht cassette also allowed the aerobic conversion of o-phthalate to benzoyl-CoA when coupled to a functional box central pathway. Hence, the pht pathway may constitute an evolutionary acquisition for o-phthalate degradation by bacteria that thrive either in anoxic environments or in environments that face oxygen limitations and that rely on benzoyl-CoA, rather than on catecholic central intermediates, for the aerobic catabolism of aromatic compounds. Finally, the recombinant pht cassette was used both to screen for functional aerobic box pathways in bacteria and to engineer recombinant biocatalysts for o-phthalate bioconversion into sustainable bioplastics, e.g., polyhydroxybutyrate, in plastic recycling industrial processes.