Table 3.

Strategies for PHA and PHA derivative production using methane as the primary substrate.

Process	Pros	Cons	Unknowns
Direct production of PHB from CH4	Has been achieved	Average to poor mechanical properties	Processes for maximising yields and rates
Methanotroph PHBV production through the co-addition of a fatty acid with odd carbon numbers	Has been achieved	The cost of the Codd feedstock offsets the savings of CH4; may produce blends of polymer product if there is variation in uptake rates amongst the different members of the community	Yields, homogeneity and maximum co-monomer content
Methanotrophs facilitating growth of a co-culture capable of PHBV production (direct or co-substrate addition)	Potentially achievable using Ralstonia sp.	The cost of the Codd feedstock offsets the savings of CH4; may produce blends of polymer product if there is variation in uptake rates amongst the different members of the community	Yields, homogeneity and maximum co-monomer content
Generate alternative copolymers through supply of appropriate feed.	Delivers broader range of mechanical properties	Cost of adding the monomers	Yields, homogeneity and maximum co-monomer content
Use a co-feeding strategy of timed pulses of methane and alternative feeds to tailor copolymer compositional distribution	Tailored, e.g., block copolymers already produced in the literature using alternating feeding strategy	Not proven in methanotrophs. May produce blends	Pulses of gas feed alternating with soluble carbon feed may prove difficult for cells to adapt to
Generate monomers biologically and polymerise ex situ	Can achieve desired copolymer composition	Monomer concentration and purification	Currently being commercialised
Downstream polymer modification/functionalisation/ depolymerisation into oligomers and use as building block	Processes are well established	Costly, intensive additional processes and can be time-consuming	Potential for development of unique material properties for niche applications.