Parker L L, Hall B G
Department of Molecular and Cell Biology, University of Connecticut, Storrs 06268.
Genetics. 1988 Jul;119(3):485-90. doi: 10.1093/genetics/119.3.485.
Escherichia coli K12 is being used to study the potential for adaptive evolution that is present in the genome of a single organism. Wild-type E. coli K12 do not utilize any of the beta-glucoside sugars arbutin, salicin or cellobiose. It has been shown that mutations at three cryptic loci allow utilization of these sugars. Mutations in the bgl operon allow inducible growth on arbutin and salicin while cel mutations allow constitutive utilization of cellobiose as well as arbutin and salicin. Mutations in a third cryptic locus, arbT, allow the transport of arbutin. A salicin+ arbutin+ cellobiose+ mutant has been isolated from a strain which is deleted for the both the bgl and cel operons. Because the mutant utilized salicin and cellobiose as well as arbutin, it is unlikely it is the result of a mutation in arbT. A second step mutant exhibited enhanced growth on salicin and a third step mutant showed better growth on cellobiose. A fourfold level of induction in response to arbutin and a twofold level of induction in response to salicin was observed when these mutants were assayed on the artificial substrate p-nitrophenyl-beta-D-glucoside. Although growth on cellobiose minimal medium can be detected after prolonged periods of time, these strains are severely inhibited by cellobiose in liquid medium. This system has been cloned and does not hybridize to either bgl or cel specific probes. We have designated this gene system the sac locus. The sac locus is a fourth set of genes with the potential for evolving to provide beta-glucoside utilization.
大肠杆菌K12正被用于研究单个生物体基因组中存在的适应性进化潜力。野生型大肠杆菌K12不能利用任何一种β-葡萄糖苷糖，如熊果苷、水杨苷或纤维二糖。研究表明，三个隐蔽位点发生突变后可利用这些糖。bgl操纵子中的突变使细菌能在熊果苷和水杨苷上进行诱导生长，而cel突变则使细菌能组成型利用纤维二糖以及熊果苷和水杨苷。第三个隐蔽位点arbT发生突变后可使熊果苷得以转运。从一个缺失bgl和cel操纵子的菌株中分离出了一株水杨苷+熊果苷+纤维二糖+突变体。由于该突变体既能利用水杨苷、纤维二糖，也能利用熊果苷，所以不太可能是arbT发生突变的结果。第二步突变体在水杨苷上的生长增强，第三步突变体在纤维二糖上的生长更好。当这些突变体在人工底物对硝基苯基-β-D-葡萄糖苷上进行检测时，观察到对熊果苷的诱导水平提高了四倍，对水杨苷的诱导水平提高了两倍。虽然在纤维二糖基本培养基上长时间培养后可检测到生长，但这些菌株在液体培养基中会受到纤维二糖的严重抑制。这个基因系统已被克隆，且不与bgl或cel特异性探针杂交。我们将这个基因系统命名为sac位点。sac位点是第四组具有进化潜力以提供β-葡萄糖苷利用能力的基因。
