Polyhydroxyalkanoates (PHA) are storage polymers accumulated by numerous prokaryotes in form of intracellular granules. Native PHA granules are formed by amorphous polymer which reveals considerably higher elasticity and flexibility as compared to crystalline pure PHA polymers. The fact that bacteria store PHA in amorphous state has great biological consequences. It is not clear which mechanisms protect amorphous polymer in native granules from transition into thermodynamically favorable crystalline state. Here, we demonstrate that exposition of bacterial cells to particular stressors induces granules aggregation, which is the first but not sufficient condition for PHA crystallization. Crystallization of the polymer occurs only when the stressed bacterial cells are subsequently dried. The fact that both granules aggregation and cell drying must occur to induce crystallization of PHA indicates that both previously suggested hypotheses about mechanisms of stabilization of amorphous state of native PHA are valid and, in fact, both effects participate synergistically. It seems that the amorphous state of the polymer is stabilized kinetically by the low rate of crystallization in limited volume in small PHA granules and, moreover, water present in PHA granules seems to function as plasticizer protecting the polymer from crystallization, as confirmed experimentally for the first time by the present work.
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We acknowledge the program for large research infrastructures of the Ministry of Education, Youth and Sports within the project “National Infrastructure for Biological and Medicinal Imaging (Czech-Biolmaging LM2015062).
This study was funded by the projects “Materials Research Centre at FCH BUT - Sustainability and Development” No. LO1211 and “National Infrastructure for Biological and Medicinal Imaging” (Czech-Biolmaging LM2015062) of the Ministry of Education, Youth and Sports of the Czech Republic and by the project GP19-20697S of the Czech Science Foundation (GACR).
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Sedlacek, P., Slaninova, E., Enev, V. et al. What keeps polyhydroxyalkanoates in bacterial cells amorphous? A derivation from stress exposure experiments. Appl Microbiol Biotechnol 103, 1905–1917 (2019). https://doi.org/10.1007/s00253-018-09584-z
- Polyhydroxyalkanoates crystallization
- Intracellular granules
- Stress conditions