Members of the family Halobacteriaceae in the domain Archaea are obligate extreme halophiles. They occupy a variety of hypersaline environments, and their cellular biochemistry functions in a nearly saturated salty milieu. Despite extensive study, a detailed analysis of their growth kinetics is missing. To remedy this, Arrhenius plots for 14 type species of the family were generated. These organisms had maximum growth temperatures ranging from 49 to 58°C. Nine of the organisms exhibited a single temperature optimum, while five grew optimally at more than one temperature. Generation times at these optimal temperatures ranged from 1.5 h (Haloterrigena turkmenica) to 3.0 h (Haloarcula vallismortis and Halorubrum saccharovorum). All shared an inflection point at 31 ؎ 4°C, and the temperature characteristics for 12 of the 14 type species were nearly parallel. The other two species (Natronomonas pharaonis and Natronorubrum bangense) had significantly different temperature characteristics, suggesting that the physiology of these strains is different. In addition, these data show that the type species for the family Halobacteriaceae share similar growth kinetics and are capable of much faster growth at higher temperatures than those previously reported.The family Halobacteriaceae in the domain Archaea presently is comprised of 18 genera and 49 validly described species (International Committee on Systematics of Prokaryotes [http://www.the-icsp.org]). All members are extreme halophiles, requiring at least 1.5 M NaCl for growth, but grow optimally in 2.0 to 4.5 M NaCl (6, 20). All have exceptionally high internal cation concentrations that approach 6 M in some species (e.g., Halobacterium salinarum) (21). In addition to exhibiting halophilicity, four genera (Natronococcus, Natronomonas, Natronorubrum, and Natronobacterium) are also alkaliphilic, growing optimally between pH 9.5 and 10.0 (20). These organisms have been isolated from a wide variety of environments, including the sediment of a cold, hypersaline lake in Antarctica (Halorubrum lacusprofundi) (3), the Dead Sea (Haloferax volcanii) (16), the Great Salt Lake (Halorabdus utahensis) (31), a hypersaline soda lake in Egypt (Natronomonas pharaonis) (27), and a salt crystal from a Permian halite deposit (Halosimplex carlsbadense) (30). There is also a report of haloarchaeal 16S rDNA amplified from inside a black smoker (28), but no haloarchaeons have been cultured from this source. All haloarchaea grow aerobically, and one species (Halobacterium salinarum) can grow phototrophically using bacteriorhodopsin as a light-driven proton pump (19).Since ". . .growth is the core of bacterial physiology. . ." (11) and since all experiments in cellular regulation are fundamentally physiological, it is essential to understand the growth physiology of the organism one is studying. Toward this goal we generated a complete Arrhenius plot for the haloarchaeon Haloferax mediterranei (22, 25; J. L. Robinson and R. F. Shand, unpublished data [http://jan.ucc.nau.edu/ϳshand]). This growth ...
