Quorum sensing in life support systems: The MELiSSA loop

Currently space exploration is possible thanks to the advanced technology that allow humans to survive on Space. However, for future long space mission it is necessary to investigate new technologies to ensure human life. Nowadays humans can survive at Space in the International Space Station (ISS) for a limited period of time i.e. almost 6 months at ISS whereas 40 days is foreseen for the Chinese Space Laboratory to be ready by 2020. Longer times of space exploration can be achieved if food oxygen and water (among other products) could be produced continuously without resupplying products from Earth. Several research groups have investigated about this possibility using Controlled Ecological Life-Support Systems (CELSS). Among those systems is the MELiSSA project that uses microorganism such as bacteria, cyanobacteria and higher plants to use human waste and convert it into water, oxygen and food. The use of microorganism in these recycling systems needs special attention at different levels e.g. technical, environmental and biological parameters. In the frame work of the MELiSSA project some of the technical challenges include bioreactors design, the monitoring and control systems. Microorganisms behavior at space can be affected by environmental conditions such microgravity, space ionizing radiation as well as intrinsic biological behavior such genetic instability, metabolism and cell-to-cell communication also termed as quorum sensing. The aim of this chapter is to focus on that microbiological behavior and its possible effects on the MELiSSA loop.