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IntroductionLow temperature inhibits the growth of most microorganisms. However, some microbes can grow well in a low temperature, even a freezing temperature.MethodsIn this study, the mechanisms conferring cold resistance in the cryophylactic yeast Metschnikowia (M.) pulcherrima MS612, an isolate of the epidermis of ice grapes, were investigated based on comparative transcriptome analysis.ResultsA total of 6018 genes and 374 differentially expressed genes (> 2-fold, p < 0.05) were identified using RNA-Seq. The differentially expressed genes were mainly involved in carbohydrate and energy metabolism, transport mechanisms, antifreeze protection, lipid synthesis, and signal transduction. M. pulcherrima MS612 maintained normal growth at low temperature (5°C) by enhancing energy metabolism, sterol synthesis, metal ion homeostasis, amino acid and MDR transport, while increased synthesis of glycerol and proline transport to improve its resistance to the freezing temperature (−5°C). Furthermore, cAMP-PKA and ERAD signaling pathways contribute to resist the low temperature and the freezing temperature, respectively.ConclusionThis study provides new insights into cold resistance in cryophylactic microorganisms for maneuvering various metabolism to resist different cold environment.

Kazak cheese is a traditional dairy product fermented by lactic acid bacteria (LAB) in Xinjiang. To investigate the LAB in Kazak cheese and their contributions to cheese fermentation, four representative LAB, Streptococcus thermophilus B8, Lactobacillus helveticus B6, Weissella confusa B14, and Lactobacillus rhamnosus B10, were isolated from Kazak cheese and subsequently used to ferment cheeses, which were named StC, LhC, WcC, and LrC, respectively. The result showed that most of the physical and chemical indicators had no significant difference, except for moisture and fat. W. confusa B14 was beneficial to the production of amino acids, whereas S. thermophilus B8 promoted the formation of organic acids and contributed to formation ideal texture property. Furthermore, the four cheeses all possessed a strong fruity aroma, with brandy, sweet, herbaceous, pungent, and fatty aromas being the most prominent in WcC. This is because L. helveticus B6 produced a high concentration of hexanal, nonanal, octanal, 3-methylbutanoic acid, ethyl acetate, ethyl butanoate, isoamyl acetate, and ethyl hexanoate in LhC. Research on the fermentation mechanism of LAB in cheese will provide a theoretical basis for the quality control and industrial production of Kazak cheese.