Rapid Flux of Osmolytes in Halotolerant Brevibacterium sp. JCM 6894 Exposed to Osmotic Shock
Kyoko ADACHI*a, Shinichi NAGATAb, and Kenichi MOCHIDAa
a Shimizu Laboratory, Marine Biotechnology Institute, 1900 Sodeshi-cho, Shimizu 424, Japan
b Kobe University of Mercantile Marine, 5-1-1 Fukae, Higashinada, Kobe 658, Japan
Halotolerant Brevibacterium sp. JCM 6894 is able to grow over wide concentration ranges of NaC1 (0-2.5 M). Our previous work demonstrated that Brevibacterium sp. accumulated ectoine and hydroxyectoine as compatible solutes and kept intracellular free Na+ concentrations low under hypersaline growth conditions (1, 2). When growing cells in the medium were subjected to osmotic shock, the concentration changes of the intracellular solutes within 24 hours depended on the medium components.
In this study, an extremely rapid flux of osmolytes in Brevibacterium sp. exposed to osmotic shock by washing with the solutions containing 0-2.0 M NaC1 was examined in comparison with that of E. coli ATCC 9637. The concentrations of K+ and organic osmolytes released from the cells were measured in the washing solutions by the potassium ion meter and 1H-NMR, respectively. The intracellular free Na+ concentration was measured by 23Na-NMR method with the shift reagent. The result which was characteristic for Brevibacterium sp. was that a rapid effiux of the accumulated K+ and organic osmolytes did not occurred, when cells were subjected to downshock at room temperature. However, Brevibacterium sp. subjected to cold downshock in ice water and E. coli subjected to downshock at each condition lost those solutes, probably due to the K+/H+ antiporter. The intracellular free Na+ concentrations in both Brevibacterium sp. and E. coli increased by not only an upshock but also a downshock.
In conclusion, it was found that the manner of rapid flux of both ionic and organic osmolytes in halotolerant Brevibacterium sp. exposed to osmotic shock was different from that of E. coli. And the behavior of the intracellular free Na+ seems interesting so that the mechanism has been under consideration.
1. Nagata, S., Adachi, K., Shirai, K., and Sano, H. (1995) Microbiology, 141,729-736.
2. Nagata, S., Adachi, K., and Sano, H. (1996) Microbiology, 142, 3355-3362.
