Screening of microbial genomes towards new enzymes for the synthesis of compatible solutes

生物体对高盐浓度的适应通常包括相容溶质的积累。相容溶质是一种有机小分子的官能团，可以在不干扰新陈代谢的情况下在细胞内大量积累。除了碳水化合物、多元醇、氨基酸及其衍生物外，在含盐的古菌、细菌、藻类和植物的细胞中也经常发现一组杂苷(糖和多元醇的结合)。与其他相容溶质相比，杂多糖苷的研究总体上还不够深入。但由于嵌合的化学本质，它们会产生有趣的生理效应。与海藻糖等碳水化合物一样，它们可以调节细胞膜和蛋白质的稳定，但它们似乎具有更高的渗透保护效率，如真正的多元醇。通过对与异苷合成酶相似的蛋白质进行同源性搜索，在最近测序的原核生物基因组中发现了大量可能的新酶。系统发育分析揭示了一种意想不到的模式，这可能表明侧向基因转移参与了这类抗盐基因的分布。在我们的研究项目范围内，我们将对这些基因进行功能性分析。这些结果将加深我们对基本盐驯化策略机理的认识，并可能有助于提高作物的耐盐性和干旱性。

Acclimation of organisms to high salt concentrations usually includes the accumulation of compatible solutes. Compatible solutes are a functional group of small organic molecules, which can be accumulated in high cellular amounts without disturbing metabolism. Beside carbohydrates, polyols, amino acids and their derivates the group of heterosides (combination of sugar and polyol) is often found in cells of salt-loaded archaea, bacteria, algae and plants. Compared to other compatible solutes, heterosides are not well studied in general. But due to the chimeric chemical nature they cause interesting physiological effects. Like carbohydrates such as trehalose they mediate membrane and protein stabilization but seem to have higher osmoprotective efficiency such as true polyols. By a homology search for proteins with similarities to heteroside-synthesizing enzymes a high number of putative new enzymes was discovered in recently sequenced prokaryotic genomes. The phylogenetic analyses revealed an unexpected pattern, which may indicate that lateral gene transfer was involved in the distribution of this class of salt resistance genes . Within the scope of our research project we will functionally analyze those genes. Such results will improve our knowledge on mechanisms of basic salt acclimation strategies and may be useful to improve salt and desiccation tolerance of crop plants.