Microbes living in the polar regions have some common and unique strategies to respond to thermal stress. Nevertheless, the amount of information available, especially at the molecular level is lacking for some organisms such as Antarctic psychrophilic yeast. For instance, it is not known whether molecular chaperones in Antarctic yeasts play similar roles to those from mesophilic yeasts when they are exposed to heat stress. Therefore, this project aimed to determine the gene expression patterns and roles of molecular chaperones in Antarctic psychrophilic Glaciozyma antarctica PI12 that was exposed to heat stress. G. antarctica PI12 was grown at its optimal growth temperature of 12ºC and later exposed to heat stresses at 16ºC and 20ºC for 6 hours. Transcriptomes of those cells were extracted, sequenced and analyzed. Thirty-three molecular chaperone genes demonstrated differential expression of which 23 were up-regulated while 10 were down-regulated. Functions of up-regulated molecular chaperone genes were related to protein binding, response to a stimulus, chaperone binding, cellular response to stress, oxidation, and reduction, ATP binding, DNA-damage response and regulation for cellular protein metabolic process. On the other hand, functions of down-regulated molecular chaperone genes were related to chaperone-mediated protein complex assembly, transcription, cellular macromolecule metabolic process, regulation of cell growth and ribosome biogenesis. The findings provided information on how molecular chaperones work together in a complex network to protect the cells under heat stress. It also highlights the evolutionary conserved protective role of molecular chaperones in psychrophilic yeast, G. antarctica, and mesophilic yeast, Saccharomyces cerevisiae.
The marine psychrophilic and endemic Antarctic yeast Leucosporidium antarcticum strain 171 synthesizes intracellular b-fructofuranosidase, and intra- and extracellular a-glucosidases. Each enzyme is maximally produced at 5°C , while the strain’s optimum growth temperature is 15°C . Invertase biosynthesis appeared regulated by catabolic repression, and induced by sucrose; the enzyme was extremely unstable ex vivo, and only EDTA, Mn2+, and BSA stabilized it for up to 12 h after yeast cell lysis. Thermal stability of the invertase was also low (30 min at temperatures up to 12°C). The optimum temperature for invertase activity was 30°C , and optimum pH was 4.55 to 4.75. The extracellular a-glucosidase was maximally active at 35°C and pH 6.70–7.50, and stable for 30 min up to 20°C.