Baldwin W W, Myer R, Kung T, Anderson E, Koch A L
Northwest Center for Medical Education, Indiana University School of Medicine, Bloomington 47405.
J Bacteriol. 1995 Jan;177(1):235-7. doi: 10.1128/jb.177.1.235-237.1995.
The growth and buoyant densities of two closely related strains of Escherichia coli in M9-glucose medium that was diluted to produce osmolarities that varied from as low as 5 to 500 mosM were monitored. At 15 mosM, the lowest osmolarity at which buoyant density could be measured reproducibly in Percoll gradients, both ML3 and ML308 had a buoyant density of about 1.079 g/ml. As the osmolarity of the medium was increased, the buoyant density also increased linearly up to about 125 mosM, at which the buoyant density was 1.089 g/ml. From 150 up to 500 mosM, the buoyant density again increased linearly but with a different slope from that seen at the lower osmolarities. The buoyant density at 150 mosM was about 1.091 g/ml, and at 500 mosM it was 1.101 g/ml. Both strains of E. coli could be grown in M9 medium diluted 1:1 with water, with an osmolarity of 120 mosM, but neither strain grew in 1:2-diluted M9 if the cells were pregrown in undiluted M9. (Note: undiluted M9 as prepared here has an osmolarity of about 250 mosM.) However, if the cells were pregrown in 30% M9, about 75 mosM, they would then grow in M9 at 45 mosM and above but not below 40 mosM. To determine which constituent of M9 medium was being diluted to such a low level that it inhibited growth, diluted M9 was prepared with each constituent added back singly. From this study, it was determined that both Ca2+ and Mg2+ could stimulate growth below 40 mosM. With Ca2+ - and Mg2+ -supplemented diluted M9 and cells pregrown in 75 mosM M9, it was possible to grow ML308 in 15 mosM M9. Strain ML3 would only haltingly grow at 15 mosM. Four attempts were made to grow both ML3 and ML308 at 5 mosM. In three of the experiments, ML308 grew, while strain ML3 grew in one experiment. While our experiments were designed to effect variations in medium osmolarity by using NaCl as an osmotic agent, osmolarity and salinity were changed concurrently. Therefore, from this study, we believe that E. coli might be defined as an euryhalinic and/or euryosmotic bacterium because of its ability to grow in a wide range of salinities and osmolarities.
监测了两种密切相关的大肠杆菌菌株在M9 - 葡萄糖培养基中的生长情况及浮力密度，该培养基经稀释后产生的渗透压范围从低至5到500毫渗摩尔/升不等。在15毫渗摩尔/升时（这是在Percoll梯度中可重复测量浮力密度的最低渗透压），ML3和ML308的浮力密度均约为1.079克/毫升。随着培养基渗透压的增加，浮力密度也呈线性增加，直至约125毫渗摩尔/升，此时浮力密度为1.089克/毫升。从150到500毫渗摩尔/升，浮力密度再次呈线性增加，但斜率与较低渗透压时不同。150毫渗摩尔/升时的浮力密度约为1.091克/毫升，500毫渗摩尔/升时为1.101克/毫升。两种大肠杆菌菌株都能在用水1:1稀释的M9培养基中生长，渗透压为120毫渗摩尔/升，但如果细胞在未稀释的M9中预培养，两种菌株在1:2稀释的M9中均不生长。（注意：此处制备的未稀释M9的渗透压约为250毫渗摩尔/升。）然而，如果细胞在30%的M9（约75毫渗摩尔/升）中预培养，那么它们随后能在45毫渗摩尔/升及以上的M9中生长，但在40毫渗摩尔/升及以下则不能生长。为了确定M9培养基中的哪种成分被稀释到如此低的水平以至于抑制了生长，制备了分别单独添加每种成分的稀释M9。通过这项研究确定，Ca2+和Mg2+都能在40毫渗摩尔/升以下刺激生长。使用添加了Ca2+和Mg2+的稀释M9以及在75毫渗摩尔/升M9中预培养的细胞，有可能在15毫渗摩尔/升的M9中培养ML308。菌株ML3在15毫渗摩尔/升时只会缓慢生长。进行了四次尝试在5毫渗摩尔/升下培养ML3和ML308。在三次实验中，ML308生长了，而菌株ML3在一次实验中生长。虽然我们的实验旨在通过使用NaCl作为渗透剂来改变培养基渗透压，但渗透压和盐度是同时变化的。因此，通过这项研究，我们认为大肠杆菌可能因其能够在广泛的盐度和渗透压范围内生长而被定义为广盐性和/或广渗透压细菌。
