Process for the selection of PHB-producing methanotrophic cultures
A method of selection for type II methanotrophs is provided that includes enriching a microbial feedstock using a non-sterile bioreactor with a methane source and a nitrogen source, where the microbial feedstock includes a mixture of Type I and Type II methanotrophic cells, where an inhibited growth of the Type I methanotrophic cells and an enhanced growth of the Type II methanotrophic cells forms. The method further includes exposing intermittently the enriched microbial feedstock to i) nitrate, ii) urea, or i) and ii), where enhanced growth of the Type II methanotrophs is established, and exposing the Type II methanotrophs to an unbalanced growth condition where production of polyhydroxybutyrate is induced.
1. A method of selecting for type II methanotrophs and producing polyhydroxybutyrate, comprising:
a. adding an effective amount of an ammonium source to a microbial feedstock within a bioreactor, wherein said microbial feedstock comprises a mixture of Type I and Type II methanotrophic cells, under conditions to enhance the growth of said Type II methanotrophic cells and inhibit the growth of said Type I methanotrophic cells;
b. adding an effective amount of a nitrogen growth source selected from the group consisting of nitrate, urea, and a mixture thereof to the microbial feedstock, under conditions to allow uninhibited replication of said Type II methanotrophic cell to occur: and
c. growing the replicated Type II methanotrophic cells in a cultural environment that is absent of nitrogen for a suitable period of time to produce the polyhydroxybutyrate.
2. The method according to claim 1 , further comprising providing limited nutrients to the microbial feedstock during the uninhibited replication of said Type II methanotrophic cells.
3. The method according to claim 2 , wherein said limited nutrients are selected from the group consisting of nitrogen, phosphorus, calcium, copper, potassium, iron, magnesium, and sulfur.
4. The method according to claim 1 , wherein i) methane, ii) biogas, iii) methane and oxygen, or iv) biogas and oxygen is provided continuously during steps a through c.
5. The method according to claim 1 , wherein methane or oxygen is reduced or eliminated in said bioreactor during step b.
6. The method according to claim 1 , comprising varying concentrations of said nitrogen growth source are varied to promote growth of said Type II methanotrophic cells and inhibit growth of said type I methanotrophic cells.
7. The method of claim 1 , wherein in step b, said adding comprises intermittently adding an effective amount of said nitrogen growth source.