Typhimurium) in response to
spaceflight culture. As a follow-up
experiment, the MDRV experiment was
performed in March 2008 during the
STS-123/1JA mission to the
International Space Station to
reproduce and confirm the Microbe
findings (Wilson 2008). MDRV
expanded the scope of Microbe by
culturing S. Typhimurium in 3 different
growth conditions, which included a
rich medium, a minimal, high inorganic
salt medium, and the rich media
supplemented with key inorganic salts.
This experiment confirmed the
Microbe findings, as S. Typhimurium grown in a rich medium exhibited increased virulence
compared to identically grown bacteria on Earth. Interestingly, the S. Typhimurium grown in
either the minimal, high inorganic salt medium or the rich media supplemented with key
inorganic salts did not display this increased virulence. Subsequent ground-based testing using
the NASA designed spaceflight analogue Rotating Wall Vessel (RWV) bioreactor supported this
finding and indicated that the key inorganic salt which was influencing the changes in S.
Typhimurium was inorganic phosphate.
Both Microbe and MDRV have prompted new studies using spaceflight analogues and true
spaceflight. One example includes the study of bacterial genes that were identified as a part of
the spaceflight response but have not had their function previously identified. These genes are
of particular importance to determine if they play a role in mediating bacterial responses to low
fluid shear and/or have additional functions that influence bacterial physiology in general. The
study in collaboration with the Microbe/MDRV team (Jennings 2011) investigated the gene
ydcI, which was found to be differentially regulated when cultures grown in the RWV were
compared to controls. The ydcI gene is a highly conserved DNA binding protein found in
multiple Gram-negative bacteria, including S. Typhimurium; however, the function was previous
not well understood. From this study, ydcI was found to be a part of the rpoS regulon, which is
responsible for a variety of stress responses in S. Typhimurium. Future experiments will be
aimed to identify the genes that are members of a potential "ydcI regulon" and how they are
linked to stress resistance, host cell interactions, biofilm formation, and other bacterial
characteristics. The results of MDRV and future follow-up studies should continue to provide
newfound knowledge to keep crew members safe during space exploration and to identify
novel targets for vaccines and therapeutic development.
PUBLICATION(S)
Jennings ME, Quick L, Soni A, et al. Characterization of the Salmonella enterica serovar
Typhimurium ydcI gene which encodes a conserved DNA binding protein required for full acid
stress resistance. Journal of Bacteriology. 2011;193(9):2208-2217. doi: 10.1128/?JB.01335-10.
Lead investigator Cheryl Nickerson with colleagues Jennifer
Barrila and Aurélie Crabbé.