(485c) Life in the Balance: Energy Fluxes and Classic/Reverse Diauxie in Chronic Wound Consortia

Staphylococcus aureus and Pseudomonas aeruginosa consortia are notorious for producing robust and recalcitrant infections, such as those found in diabetic chronic wounds. It is hypothesized that the two bacteria commonly co-occur based on complementary metabolic strategies. S. aureus utilizes a textbook example of diauxie to prioritize available substrates such as glucose. By contrast, P. aeruginosa employs a metabolism termed reverse diauxie, prioritizing a near-opposite order of substrates for catabolism. In this context, oxygen availability modulates common substrate bioavailability and potential species competition, playing a critical role in shaping the dynamics of these bacterial interactions. Oxygen gradients in chronic wounds are, accordingly, well-documented barriers to effective treatment. Yet oxygen gradient influence on microbial consortia behavior is not fully understood.

In this study, we measure consortia energy fluxes along an electron donor-to-acceptor gradient for cocultures of S. aureus and P. aeruginosa clinical isolates. The cocultures were grown in hermetically sealed batch reactors, which permitted control of the donor:acceptor ratio. Isothermal microcalorimetry analysis of the growing cultures demonstrated that the total heat accumulation varies along the donor:acceptor gradient and between monocultures and cocultures. The availability of electron acceptor was a major control parameter for coculture strain abundance, imposing over two-fold strain ratio variation across the donor:acceptor gradient. Furthermore, under oxygen-rich conditions, the coculture demonstrated the emergent property of higher conversion of electron donor into heat than either S. aureus or P. aeruginosa monocultures. Under anoxic conditions, however, the coculture produced less heat than S. aureus monocultures. Taken into consideration with biomass and metabolite flux analysis, we hypothesize that these energy flux trends depict a shift in consortia symbiosis as a function of oxygen availability. The presence of oxygen spurs competition, leading to greater stress-induced heat production. In the absence of oxygen, however, the consortium opts for a cooperative approach which lowers stress-induced heat flux and improves total community yields.