Shelf Life and Simulated Gastrointestinal Tract Survival of Selected Commercial Probiotics During a Simulated Round-Trip Journey to Mars

Abstract

To enhance the gastrointestinal health of astronauts, probiotic microorganisms are being considered for inclusion on long-duration human missions to the Moon and Mars. Here we tested three commercial probiotics—Bifidobacterium longum strain BB536, Lactobacillus acidophilus strain DDS-1, and spores of Bacillus subtilis strain HU58—for their survival to some of the conditions expected to be encountered during a 3-year, round trip voyage to Mars. All probiotics were supplied as freeze-dried cells in capsules at a titer of >109 colony forming units per capsule. Parameters tested were survival to: (i) long-term storage at ambient conditions, (ii) simulated Galactic Cosmic Radiation and Solar Particle Event radiation provided by the NASA Space Radiation Laboratory, (iii) exposure to simulated gastric fluid, and (iv) exposure to simulated intestinal fluid. We found that radiation exposure produced minimal effects on the probiotic strains. However, we found that that the shelf-lives of the three strains, and their survival during passage through simulations of the upper GI tract, differed dramatically. We observed that only spores of B. subtilis were capable of surviving all conditions and maintaining a titer of >109 spores per capsule. The results indicate that probiotics consisting of bacterial spores could be a viable option for long-duration human space travel.

RETRACTED: Expression of SARS-CoV-2 Spike Protein Receptor Binding Domain on Recombinant B. subtilis on Spore Surface: A Potential COVID-19 Oral Vaccine Candidate

“…It can also tolerate the acidic environment in the digestive tract and heat [77], which enables effective delivery to the gut and enhanced stability during storage and transportation. Fajardo-Cavazos and Nicholson reported that freeze-dried B. subtilis spores in capsules can survive up to 3 years, not only in ambient conditions, but also in a round trip voyage to Mars with the presence of Galactic cosmic radiation and solar particle-event radiations [52]. In addition, B. subtilis is easy to modify genetically [78], which makes it easier to design recombinant spores targeting both the original SARS-CoV-2 and mutant viruses (Figure 1).…”

“…B. subtilis vaccines also have a lower production cost. Freeze-dried B. subtilis spores in capsules are stable for long-term storage under ambient conditions [52]. Therefore, we believe that oral B. subtilis vaccines could be a potential candidate for the treatment of COVID-19.…”

Immunomodulatory and Antioxidant Properties of a Novel Potential Probiotic Bacillus clausii CSI08

“…can survive aggressive gastric conditions and reach the small intestine in large numbers where they germinate into vegetative form [ 9 ]. Spore-based probiotic formulations have a long shelf life and do not require refrigeration during storage [ 10 , 11 ]. Moreover, Bacillus spp.…”

Oral vaccination of fish against vibriosis using spore-display technology

“…The extreme resistance of B. subtilis spores, which guarantees passage through the harsh gut environment without losing characteristics ( 63 ), is the basis for their oral applications as probiotics or as delivery vehicles ( 20 , 24 , 26 – 29 , 31 , 32 , 60 , 64 – 68 ). Spores’ direct incorporation into animal feed, circumventing further protection processes, such as encapsulation, together with their simple production and long shelf-life without needing refrigeration ( 51 , 69 ), are also attractive characteristics from the industrial point of view ( 70 ). Adding to this “needle-free” and “refrigeration-free” potential, B. subtilis spores adjuvant properties ( 18 , 19 , 71 – 73 ) and contribution to GALT (gut associated lymphoid tissue) development ( 67 , 74 – 76 ), increases their potential as oral delivery systems of antigens.…”