UC San Diego

In response to the accumulation of plastic waste in the environment, the development of degradable bioplastics as an alternative has been highly sought after, yet should certain bioplastics succeed the non-biodegradable plastics, there may be implications of how the accumulation of this more bioavailable form of plastic impact the carbon cycle, particularly in the marine environment, where nutrient conditions are diverse and play an important biological role in carbon utilization. This Thesis examines the model marine bacterium Alteromonas macleodii ATCC 27126’s ability to utilize 3-Hydroxybutyrate (3HB), a monomer of the bioplastic Polyhydroxybutyrate (PHB) among glucose, galactose, and maltose, components of natural polysaccharides and certain bioplastics, depending on the provision of reduced nitrogen (NH4) or oxidized (NO3). According to Optical Density (OD600) growth curves, cell counts, and respiration determined by the INT Reduction method, 3HB resulted in peak biomass levels comparable to the sugars, but led to slower growth and was less efficiently incorporated into biomass; this may imply that at a metabolic level, PHB, or organic acid-based bioplastics, is more recalcitrant and may sink as Particulate Organic Carbon (POC), but when degraded, less PHB-derived biomass would sink as POC. With the more bioavailable NH4 as the sole nitrogen source, 3HB resulted in higher peak levels of biomass and a marginally higher growth efficiency when compared to NO3, yet the nitrogen-source preference was flipped towards NO3 with the sugars. These results add nuance to designing replete conditions in laboratory studies, as more bioavailable substrates do not innately result in better growth.