Polyhydroxyalkanoic acid compositions and methods for generating same
Embodiments of the invention relate to the microbial production of polyhydroxyalkanoic acids, or polyhydroxyalkanoates (PHA), from substrates which cannot be used as a source of carbon and/or energy for microbial growth or PHA synthesis and which have microbial and environmental toxicity. According to one embodiment of the invention, a process for the production of PHA is provided wherein an enzyme such as methane monooxygenase is used to convert volatile organic compounds into PHA through the use of microorganisms that are unable to use volatile organic compounds as a source of carbon for growth or PHA production.
1. A process for the production of a polyhydroxyalkanoate (PHA) from one or more metabolically toxic and growth-inhibiting volatile organic compounds (VOCS), comprising:
a) providing one or more non-methane VOCs;
b) providing one or more methane-oxidizing microorganisms capable of oxidizing said one or more VOCs to produce an oxidized compound, wherein said one or more methane-oxidizing microorganisms do not use said one or more VOCs as a source of carbon or energy, and wherein said one or more VOCs inhibit the growth of said one or more methane-oxidizing microorganisms, and is thereby metabolically toxic;
c) providing one or more PHA-synthesizing microorganisms capable of incorporating a carbon contained within said oxidized compound into a PHA material;
d) providing a growth-culture medium that regulates the metabolism of said one or more methane-oxidizing microorganisms and said one or more PHA-synthesizing microorganisms;
e) exposing said one or more methane-oxidizing microorganisms to said one or more VOCs in said growth-culture medium, thereby causing or allowing said one or more methane-oxidizing microorganisms to convert said one or more VOCS into said oxidized compound;
f) contacting said oxidized compound with said PHA-synthesizing microorganisms; and
g) increasing or decreasing the concentration of one or more nutrients in said growth-culture medium to cause or allow said one or more PHA-synthesizing microorganisms to use said carbon contained within said oxidized compound for the production of said PHA material, thereby using a metabolically toxic, growth-inhibiting VOC to produce said PHA material.
2. The process of claim 1 , further comprising adding an additional source of carbon to the growth-culture medium to induce said PHA-synthesizing microorganisms to synthesize a PHA having a different molecular structure as compared to said PHA synthesized from said carbon contained within said oxidized compound, wherein said additional source of carbon is valeric acid.
3. The process of claim 1 , further comprising exposing said one or more methane-oxidizing microorganisms and said one or more PHA-synthesizing microorganisms in said growth-culture medium to methane prior to, while, and/or after exposing said one or more methane-oxidizing microorganisms and said one or more PHA-synthesizing microorganisms to said non-methane volatile organic compounds.
4. The process of claim 3 , wherein said exposing to said methane occurs while said one or more methane-oxidizing microorganisms and said one or more PHA-synthesizing microorganisms is exposed to said non-methane organic compounds by exposing said one or more methane-oxidizing microorganisms and said one or more PHA-synthesizing microorganisms to a gaseous mixture comprising said methane and said non-methane volatile organic compounds.
5. The process of claim 1 , wherein said one or more methane-oxidizing microorganisms use an enzymatic catalyst in the form of methane monooxygenase (MMO) to produce extracellular MMO-oxidized VOCs which are simultaneously contacted with said one or more PHA-synthesizing microorganisms to use the carbon contained within said MMO-oxidized VOCs for the production and accumulation of PHA.
6. The process of claim 1 , wherein said PHA-synthesizing microorganisms comprise one or more methane monooxygenases (MMOs), and wherein said volatile organic compounds are capable of inhibiting the metabolic function of said MMOs.
7. The process of claim 1 , wherein said one or more nutrients is selected from the group consisting of as iron, oxygen, nitrogen, magnesium, calcium, sodium, sulphur, potassium, and phosphate, and wherein the concentration of said one or more nutrients is decreased.
8. The process of claim 1 , wherein said one or more non-methane volatile organic compounds are obtained from one or more of the following sources: a landfill, a wastewater treatment system, a coal mine, a natural gas system, an agricultural waste management system, and a ruminant animal operation.
9. The process of claim 1 , wherein the mass of PHA produced is about 5-80% of the mass of said methane-oxidizing microorganisms and/or non-methanotrophic PHA-synthesizing microorganisms.
10. The process of claim 1 , wherein said one or more methane-oxidizing microorganisms and said one or more PHA-synthesizing microorganisms comprise naturally-occurring microorganisms, genetically-engineered microorganisms, or combinations thereof.
11. The process of claim 1 , wherein increasing or decreasing the concentration of one or more nutrients in said growth-culture medium to cause or allow said culture to produce said PHA comprises adjusting the availability of an essential growth nutrient.
12. The process of claim 11 , wherein said nutrient is selected from the group consisting of oxygen, nitrogen, magnesium, calcium, sodium, sulphur, and potassium.
13. The process of claim 1 , wherein said oxidized compound is produced intracellularly and/or extracellularly.