Title : Managing bacterial eradication in disease and survival for life support systems on Earth and space
Bacteria like Escherichia coli cause disease but are also beneficial in resource regeneration. Its UPEC strain causes cystitis, which is treated by gentamicin. The protein ss, encoded by the rpoS gene, controls E. coli resistance to antimicrobial agents. We discovered that rpoS deletion mutation renders UPEC more sensitive to Gm and other bactericidal antibiotics; proteomic analysis suggested a weakened antioxidant defense as the cause. Reactive oxygen species (ROS) detectors (psfiA gene reporter, and appropriate chemicals) indicated greater ROS generation by Gm in the mutant. When administered along with an antioxidant, or under anaerobic conditions (that prevent ROS formation), Gm was less lethal to the mutant. In vivo studies of treating UPEC infection of mice bladder gave similar results. Thus, oxidative stress produced by insufficient quenching of metabolic ROS accounted for greater sensitivity of the mutant. Gm exposure to other E. coli mutants, missing antioxidant proteins, also resulted in greater ROS production and lethality; these lacked the ROS quencher proteins, (e.g., SodA/SodB; KatE/SodA), or the pentose phosphate pathway proteins, which provide NADPH (e.g., Zwf Gnd; TalA) required by the quencher proteins. Use of a microfluidic device indicated that the results applied at a single cell level. Gm’s lethality in bacteria is due to inhibition of protein synthesis, but most current UPEC patient isolates can overcome this (reflecting the larger problem of growing bacterial antibiotic resistance). Therefore, these findings provide a timely means of restoring Gm effectiveness by curbing bacterial antioxidant defense. Using bioinformatics, we have identified several small molecules that inhibit ss and can overcome bacterial Gm resistance. In space flights, astronauts often suffer from cystitis; further, bacterial antibiotic resistance is a greater threat to them as microgravity (MG) impairs human immune response.
Bacterial gene regulation can differ in normal vs. MG. However, the “EcAMSat” Stanford/NASA mission showed that ss controls Gm resistance also in MG. This work employed a free flying “nanosatellite” equipped with a sophisticated microfluidic system, which autonomously analysed UPEC sensitivity to Gm in space flight over several days and transmitted the results by telemetry to Earth in real time. Bacterial multidrug resistance, such as the one regulated by the emrRAB operon and the EmrR protein, is a major public health problem. Its activation is due to alteration in the EmrR protein structure by antibiotics, which too can be prevented by small molecules and bioinformatic approaches. For long-term space flights and space colonization, ecosystems need to be established for resource regeneration and waste recycling, processes in which E. coli is important. Manipulation of ss levels and the resistance proteins it controls hold the key for stabilizing this bacterium under MG conditions. Several scientists have contributed to this work; they will be recognized in the presentation