5% w/v. This is in contrast to glucose, where concentrations above 0.2% w/v resulted in the saturation of growth (Fig. 1a). Casamino concentrations higher than 0.5% w/v were not tested because the resulting OD of more than 0.7 is already rather high for turbidity measurements and higher values selleck products would be imprecise. When high cell masses are needed, for example for biochemical experiments, casamino acid concentrations higher than 0.5% w/v should be used. As a next application of growth in microtiter plates, the usage of seven different carbon sources was investigated (Fig. 1c). Haloferax volcanii did not grow at all on mannose, but to a variable extent on the other six carbon

sources. The best growth was obtained on glucose and fructose, followed by glycerin (and pyruvate, data not shown), xylose and arabinose, and the slowest growth was obtained with acetate as the sole carbon and energy source. These results, together with the very fast growth on casamino acids (Fig. S2), underscore the versatile metabolism of H. volcanii that can grow on a variety of different sugars, sugar alcohols, acids, amino acids and peptides. It will be interesting to test further and more unusual carbon sources like various polymers

or man-made chemicals. The next aim was to selleck screening library unravel the vitamin dependence of H. volcanii. About 20 years ago, it was reported that H. volcanii stops growing after two or three serial dilutions in a synthetic medium, suggesting that vitamins are missing, and that the addition of biotin and thiamine is enough to allow prolonged growth in a synthetic medium (Kauri et al., 1990). At that time, we were working with H. volcanii strain WR340 and found that the addition of biotin and thiamine did not yield reproducible and satisfactory results; therefore, we started to add 0.01% w/v yeast extract Dimethyl sulfoxide as a vitamin source. However, several groups regularly reported the growth of H. volcanii in a synthetic medium with biotin and thiamine as the sole vitamin sources (e.g. Allers et al., 2004; Blaby et al., 2010); therefore, we used microtiter-based

growth to reinvestigate the vitamin dependence of H. volcanii. Much to our surprise, repeated serial dilutions of precultures in the absence of added vitamins did not lead to growth arrest and H. volcanii and it grew rather well in the absence of vitamins (Fig. 2), in contrast to earlier observations (Kauri et al., 1990). This clearly showed that H. volcanii is able to synthesize all coenzymes and prosthetic groups and does not depend on vitamin addition. However, the addition of both biotin and thiamine enhanced the growth rate, indicating that the biosynthesis rates of both substances limited the maximal growth rate. However, the effect was not additive; the addition of both biotin and thiamine led to a growth rate lower than that obtained with the addition of thiamine alone, but the difference was rather small (Fig. 2).