School of Sciences, Indira Gandhi National Open University, New Delhi, 110 068 India.
Indian J Microbiol. 2007 Sep;47(3):241-50. doi: 10.1007/s12088-007-0045-3. Epub 2007 Oct 4.
Stable mutants of Aspergillus nidulans, resistant to 1 mM Ni were developed by step-by-step repeated culturing of the fungus on the medium containing increasing concentrations of nickel chloride. Characterization of mutants could differentiate them into two categories Ni(R) I and Ni(R) II. Each category of mutants exhibited alterations in growth, conidial germination and melanin secretion both in Ni-free and Ni-containing media. Ni(R) II mutants were little slow in growth with sparse mycelia and conidiation but showed high melanin secretion and higher Ni-uptake in comparison to Ni(R) I mutant. Studies involving metabolic and translational inhibitors could prove that Ni-accumulation was biphasic. The initial energy independent surface accumulation was found to be followed by energy dependent intarcellular uptake. Increase in the concentration of the metal in the medium or the time of exposure did not proportionately increase the metal uptake by the mutants. Ni-uptake followed Michaelis-Menton saturation kinetics, which was enhanced under optimum pH of 6.5-7.5 and reduced complexity of the medium due to free availability of ions. Resistance to Ni was found to be constitutive in Ni(R)I mutant, and could be induced in Ni(R)II mutant.
通过在含有逐渐增加氯化镍浓度的培养基上逐步重复培养真菌，开发出对 1mM Ni 具有抗性的稳传 Aspergillus nidulans 突变体。突变体的特征可将其分为两类：Ni(R)I 和 Ni(R)II。每种类的突变体在不含 Ni 和含 Ni 的培养基中，其生长、分生孢子萌发和黑色素分泌均发生改变。与 Ni(R)I 突变体相比，Ni(R)II 突变体生长缓慢，菌丝稀疏，分生孢子少，但黑色素分泌高，Ni 摄取量高。涉及代谢和翻译抑制剂的研究可以证明 Ni 积累是双相的。发现初始的能量非依赖性表面积累随后是能量依赖性细胞内摄取。培养基中金属浓度的增加或暴露时间的增加并没有使突变体的金属摄取成比例增加。Ni 摄取遵循米氏-门顿饱和动力学，在最佳 pH 值 6.5-7.5 下增强，由于离子自由可用性，培养基的复杂性降低。在 Ni(R)I 突变体中发现对 Ni 的抗性是组成型的，在 Ni(R)II 突变体中可以诱导。
