An Up­date on: Space Odyssey, Sal­mo­nella Style

by Elio

A pre­vi­ous post re­gard­ing the ex­per­i­ments per­formed with Sal­mo­nella dur­ing a Space Shut­tle flight elicited some in­ter­est­ing com­ments. We com­mu­ni­cated them to the se­nior au­thor of the pa­per, Dr. Cheryl Nick­er­son of Ari­zona State Uni­ver­sity. She sent us the fol­low­ing though­tful and in­for­ma­tive re­sponse. We look for­ward to a flurry of fu­ture stud­ies on the ef­fects of space travel on our fa­vorite mi­cro-as­tro­nauts.

Zero grav­ity. Cour­tesy of Fab­u­lous Ad­ven­t­ures.

Cheryl Nickerson's re­sponse:

Thank you for your mes­sage. My lab was very ex­cited to see that our work is posted on your blog! I ap­pre­ci­ate your in­ter­est in our work and the op­por­tu­nity to dis­cuss our space­flight stud­ies with Sal­mo­nella. While NASA and other space agen­cies have been per­form­ing mi­cro­bi­o­log­i­cal flight ex­per­i­ments since the 1960's, the way mi­croor­gan­isms re­spond to the space­flight en­vi­ron­ment is still un­clear. Per­haps the great­est hur­dle of do­ing bi­o­log­i­cal re­search in space is the tremen­dous con­straints of re­sources dur­ing flight. Lim­i­ta­tions of up mass, down mass, power, and crew time cre­ate many unique chal­lenges in ex­per­i­men­tal de­sign and of­ten sim­plify work that could have mul­ti­ple pos­si­bil­i­ties. NASA has been very gen­er­ous in ac­com­mo­dat­ing our ex­per­i­men­tal re­quests, but their re­sources are con­strained as they fin­ish the In­ter­na­tional Space Sta­tion.

The Mi­crobe ex­per­i­ment was de­signed to take an ini­tial look at the ef­fect of space­flight on changes in gene ex­pres­sion and vir­u­lence, as these pa­ra­me­ters had not been pre­vi­ously in­ves­ti­gated. Your sug­ges­tion of a cen­trifuge is an ex­cel­lent con­trol, but this equip­ment was not avail­able for us on the Shut­tle. Even had a cen­trifuge been avail­able for our work, it would not have been com­pat­i­ble for use with our in-flight hard­ware. How­ever, the good news is that a cen­trifuge will be avail­able on the In­ter­na­tional Space Sta­tion and is planned for use in a fu­ture mi­cro­bial flight ex­per­i­ment headed by Dr. Max Mergeay from the Eu­ro­pean Space Agency.

An ad­di­tional point that I would like to make is that while the Mi­crobe ex­per­i­ment in­ves­ti­gated the re­sponse of mi­croor­gan­isms to the space­flight en­vi­ron­ment, we saw sim­i­lar re­sponses in the same strain of Sal­mo­nella in our lab us­ing a space­flight ana­logue cul­ture sys­tem. These sys­tems are spe­cial biore­ac­tors de­signed by NASA to sim­u­late the low fluid shear cul­ture con­di­tions en­coun­tered in the mi­cro­grav­ity en­vi­ron­ment of space­flight. Us­ing these low fluid shear biore­ac­tors, we were able to re­pro­duce many Sal­mo­nella phe­no­types that we ob­served in space­flight here on the ground — in­clud­ing an in­crease in vir­u­lence, as well as dif­fer­en­tial ex­pres­sion of many of the same classes of genes, in­clud­ing the global reg­u­la­tor Hfq. Since the ground-based biore­ac­tors were able to sim­u­late many of the Sal­mo­nella re­sponses that we ob­served dur­ing space­flight, those spe­cific changes could not be due to mi­cro­grav­ity or ion­iz­ing ra­di­a­tion, since those en­vi­ron­ments are not en­coun­tered in the biore­ac­tor. How­ever, it is im­por­tant to add that there were also dif­fer­ences ob­served in Sal­mo­nella 's re­sponses be­tween cul­ture in the biore­ac­tor and space­flight, and we do not know the un­der­ly­ing mech­a­nisms re­spon­si­ble for these changes. Thus, a great deal more work needs to be done in fu­ture ex­per­i­ments to ad­dress this, in­clud­ing the use of a cen­trifuge con­trol, and whole genome se­quenc­ing would also be rea­son­able.

Our col­lec­tive pub­lished data (from both space­flight and space­flight ana­logue cul­ture sys­tems) in­di­cate that it is the low fluid shear growth en­vi­ron­ment as­so­ci­ated with mi­cro­grav­ity, where tur­bu­lence and fluid ac­tion is min­i­mal, that plays a ma­jor role in the re­sponse of Sal­mo­nella to space­flight. Since there are also low fluid shear ar­eas in the body that are en­coun­tered by pathogens dur­ing the nat­ural course of their in­fec­tion (in­clud­ing in the gas­troin­testi­nal tract which is the pri­mary site of Sal­mo­nella in­fec­tion) it is pos­si­ble that the use of low fluid shear plat­forms may hold promise for in­no­va­tions in in­fec­tious dis­ease con­trol here on Earth. If true, that would be ex­cit­ing.