The adaptation of Escherichia coli cells grown in simulated microgravity for an extended period is both phenotypic and genomic

• Published in: NPJ microgravity Vol. 3; no. 1; pp. 15 - 9
• Main Authors: Tirumalai, Madhan R., Karouia, Fathi, Tran, Quyen, Stepanov, Victor G., Bruce, Rebekah J., Ott, C. Mark, Pierson, Duane L., Fox, George E.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 23.05.2017; Nature Publishing Group; Nature Portfolio
• Subjects: 631/326; 704/158/855; Adaptation; Antibiotic resistance; Applied Microbiology; Bacteria; Biomedical and Life Sciences; Biotechnology; Cell culture; Classical and Continuum Physics; Deoxyribonucleic acid; DNA; E coli; Escherichia coli; Fluid flow; Immunology; Life Sciences; Mechanical stimuli; Microgravity; Mutation; Nucleotide sequence; Space Exploration and Astronautics; Space flight; Space Sciences (including Extraterrestrial Physics
• ISSN: 2373-8065; 2373-8065
• DOI: 10.1038/s41526-017-0020-1

Microorganisms impact spaceflight in a variety of ways. They play a positive role in biological systems, such as waste water treatment but can be problematic through buildups of biofilms that can affect advanced life support. Of special concern is the possibility that during extended missions, the microgravity environment will provide positive selection for undesirable genomic changes. Such changes could affect microbial antibiotic sensitivity and possibly pathogenicity. To evaluate this possibility, Escherichia coli (lac plus) cells were grown for over 1000 generations on Luria Broth medium under low-shear modeled microgravity conditions in a high aspect rotating vessel. This is the first study of its kind to grow bacteria for multiple generations over an extended period under low-shear modeled microgravity. Comparisons were made to a non-adaptive control strain using growth competitions. After 1000 generations, the final low-shear modeled microgravity-adapted strain readily outcompeted the unadapted lac minus strain. A portion of this advantage was maintained when the low-shear modeled microgravity strain was first grown in a shake flask environment for 10, 20, or 30 generations of growth. Genomic sequencing of the 1000 generation strain revealed 16 mutations. Of the five changes affecting codons, none were neutral. It is not clear how significant these mutations are as individual changes or as a group. It is concluded that part of the long-term adaptation to low-shear modeled microgravity is likely genomic. The strain was monitored for acquisition of antibiotic resistance by VITEK analysis throughout the adaptation period. Despite the evidence of genomic adaptation, resistance to a variety of antibiotics was never observed. Evolution: Bacteria gain advantageous mutations under simulated microgravity Bacteria grown for an extended period of time under simulated microgravity adopt growth advantages. George Fox and colleagues from the University of Houston, Texas, USA, cultured Escherichia coli bacteria for 1000 generations in a high aspect rotating vessel to simulate the low fluid shear microgravity environment encountered during spaceflight. They then performed growth competition assays and found that the 1000-generation adapted bacteria outcompeted control bacteria grown without simulated microgravity. Genomic sequencing of the adapted bacteria revealed 16 mutations, five of which altered protein sequences. These DNA changes likely explain the growth advantage of the bacteria grown for multiple generations in simulated microgravity. Similar adaptations during prolonged space missions could result in nastier pathogens that might threaten the health of astronauts. Fortunately, the microbes did not appear to acquire antibiotic resistance over the 1000 generation in the modeled microgravity culture.