Cyclic, alternating methane and nitrogen limitation increases PHB production in a methanotrophic community

To identify feast-famine strategies that favor PHB accumulation in Type II methanotrophic proteobacteria, three sequencing batch reactors seeded with a defined inoculum of Type II methanotrophs were subjected to 24-h cycles consisting of (1) repeated nitrogen limitation, (2) repeated nitrogen and oxygen limitation, and (3) repeated nitrogen and methane limitation. PHB levels within each reactor and capacity to produce PHB in offline batch incubations were monitored over 11 cycles. PHB content increased only in the reactor limited by both nitrogen and methane. This reactor became dominated by Methylocystis parvus OBBP with no detectable minority populations. It was concluded that repeated nitrogen and methane limitations favored PHB accumulation in strain OBBP and provided it with a competitive advantage under the conditions imposed.