This annotated bibliography contains summaries of 3 scientific papers on experiments conducted to study the extreme stress tolerance of tardigrades. [1] The first paper discusses experiments exposing tardigrades to cosmic radiation, microgravity, vacuum pressures, and cryogenic temperatures that found high survivability but unreliable microcosm results. [2] The second paper uses differential scanning calorimetry to show that tardigrade survival declines steeply after glass transition temperatures are reached. [3] The third paper uses proteomics to identify heat shock proteins in active and cryptobiotic tardigrades, finding unique proteins in cryptobiosis that aid suspension.

1. Tardigrades: An Annotated Bibliography
Edwin J. Alvarado
Department of Mathematics-Physics, University of Puerto Rico, Cayey, Puerto Rico
Persson D, Halberg KA, Jørgensen A, Ricci C, Møbjerg N, Kristensen RM. 2011. Extreme stress tolerance in
tardigrades: surviving space conditions in low earth orbit. J Zool Syst Evol Res [Internet]. Suppl
49:90—7.
doi: 10.1111/j.1439-0469.2010.00605.x
This paper discusses a series of experiments carried out on three species of tardigrades to
assess the organisms’ survivability and fecundity after being exposed to certain conditions.
These studies ranged from a microcosms experiment, which involved cosmic radiation and
microgravity exposition; a vacuum experiment, which consisted of subjecting specimens to
pressures around 2.9 × 10–8 Pa; and a cryogenic experiment, which involved baring the
tardigrades to temperatures around –196°C and absolute zero. The results from the microcosms
experiment are pretty much unreliable because of a flawed experimental protocol. This,
however, allows the authors to discuss several discrepancies in previous cosmic
experimentation on tardigrades. The aforementioned experimentation resulted in a highly
recorded survivability and fertility.
This article, although presenting erratic outcomes in some experiments, provides a great
starting point for tardigrade research, because not only does it present a generalized view of the
phylum’s tolerance, but also points out the need to carefully handle these organisms.
Hengherr S, Worland MR, Reuner A, Brϋmmer F, Schill RO. 2009. High-temperature tolerance in
anhydrobiotic
tardigrades is limited by glass transition. Physiol Biochem Zool [Internet]. 82(6):749—55.
doi: 10.1086/605954
Through the means of differential scanning calorimetry, the presence and role of glass transition
in extreme temperature exposure survival in tardigrades was researched. By submitting
tardigrades to various temperatures, researchers proved further the phylum’s extraordinary
resilience to desiccation and severe heat. Even though defective methodology partially tainted
the results, the study showed a steep decline in survival rate after a certain temperature was
reached. This temperature level assimilates glass transition, which interferes with safeguarding
measures. The study stresses the presence of glass components that interact with several of
the organism’s components during anhydrobiosis protecting damage-prone material. At the
point where these components reach glass transition, the survivability of tardigrades drops
drastically, allowing the appreciation of a maximum value for survival. In addition, the research
further evidenced the presence of water-replacement mechanisms, which play a crucial role in
preventing damage to tissue in tardigrades. It, however, questions the role of trehalose in tissue
preservation, and encourages its testing.

2. Schokraie E, Hotz-Wagenblatt A, Warnken U, Frohme M, Dandekar T, Schill RO, Schnölzer M. 2011.
Investigating
heat shock proteins of tardigrades in active versus anhydrobiotic state using shotgun proteomics. J
Zool Syst
Evol Res [Internet]. Suppl 49:111—9. doi: 10.1111/j.1439-0469.2010.00608.x
Heat shock proteins are chaperones that protect other polypeptides from denaturation,
degradation and aggregation. This study sought to identify the different Heat shock proteins
present in the active and cryptobiotic states of tardigrades. Through shotgun proteomics,
researchers were able to identify not only highly conserved Heat shock proteins whose
preservation stretched across animal taxonomy, but also unique polypeptides relatively
exclusive to tardigrades. Regarding the proteins present in the active versus the anhydrobiotic
state, the experiment showed various proteins present only when the specimen was in its
suspended state, meaning that these peptides are highly specialized. Such a simple research
experiment proved to be worthwhile for the understanding of the tardigrade suspension
mechanism. Future tardigrade research can definitely benefit from this research study because
it provides a clear inventory of the heat shock proteins and their relative functions within
tardigrades.