Reactivation of microbial nitrogen cycling conversions after Lower Earth Orbit Space exposure

Abstract

Various processes within the microbial nitrogen cycle are considered as resource efficient alternatives to the physicochemical methods for recovery of both nitrogen and water for long-term manned Space missions. One of the major application challenges is to start up biological reactors with inocula that can be preserved under the conditions of microgravity and radiation conditions prevalent in Space. Furthermore, when a biological treatment system fails, re-inoculation should prevent that it take months to recover steady-state operation. In the current study, a Space flight was performed with (i) three natural microbial communities, containing members of the ammonia oxidizing archaea (AOA) and bacteria (AOB), nitrite oxidizing bacteria (NOB), denitrifiers and anammox bacteria (AnAOB), and with (ii) a synthetic culture of the ureolytic Cupriavidus pinatubonensis, the AOB Nitrosomonas europaea and the NOB Nitrobacter winogradskyi. The cultures were sent on a PHOTON-M4 flight to Lower Earth Orbit (LEO) Space and were exposed to 20 ± 4oC, hyper and μ-gravity and to 30.5 ± 6.9 mGy of radiation over 44 days. Upon return to Earth the cultures were reactivated and volumetric activity in mg N L-1 d-1 was compared to the same cultures that were stored terrestrially at ambient temperature (23 ± 3°C) and in the refrigerator (4oC). It should be noted that the measured background radiation on Earth was only 1.6 ± 0.1 mGy over the same period. Nevertheless the LEO-samples performed either similar or better after reactivation compared to the ambient terrestrial stored cultures. Both the LEO and the ambient terrestrial stored cultures showed a significant decline in activity compared 4oC storage. More in-depth data on specific conversion rates, changes in biomass concentrations, cell viability tests using flow cytometry, Illumina-sequencing of the microbial communities is being processed. In conclusion, this study for the first time reports on the specific Space-flight survival capacity of the key conversions in the microbial nitrogen cycle, a necessary step in advancing toward a bio-regenerative life support system