Photoresponses of the purple nonsulfur bacteria Rhodospirillum centenum and Rhodobacter sphaeroides
Photoresponses of the purple nonsulfur bacteria Rhodospirillum centenum and Rhodobacter sphaeroides
复制标题
紫色非硫细菌Rhodospirillum centenum 和Rhodobacter sphaeroides 的光响应
作者：
M. Sackett;J. Armitage;E. Sherwood;T. Pitta
我们测量了两种紫色非硫细菌（球形红杆菌和 Centenum 红螺菌）在规定条件下，在与显微镜光轴成 90 度角传播的光束中的光响应。该光束使细胞在垂直于传播方向上具有陡峭的强度梯度，而在光传播方向上具有较浅的强度梯度。 R. centenum 是一种通过逆转来改变方向的物种，积聚在光束中，正如预期的“畏光”反应，而 R. sphaeroides 则停止而不是逆转，积聚在光束外。我们还比较了液体生长的 R. centenum（通过使用单个极鞭毛游泳）和表面生长的 R. centenum（通过使用许多侧鞭毛在琼脂上聚集）的行为，并且已被证明可以作为菌落向特定波长的光移动。当悬浮在液体介质中时，液体和表面生长的 R. centenum 对光梯度表现出相似的响应。在所有情况下，自由游动的细胞对陡峭的强度梯度有反应，但对浅的梯度没有反应，这表明它们无法感知光传播的方向，只能感知光的强度。在对照实验中，已知的趋光藻类莱茵衣藻 (Chlamydamonas Reinhardtii) 会沿着光传播的方向游动。
We have measured the photoresponse of two purple nonsulfur bacteria, Rhodobacter sphaeroides and Rhodospirillum centenum, under defined conditions in a light beam propagating at 90 degrees to the optical axis of the microscope. This beam presented cells with a steep gradient of intensity perpendicular to the direction of propagation and a shallow gradient in the direction of light propagation. R. centenum, a species that reverses to change direction, accumulated in the light beam, as expected for a "scotophobic" response, while R. sphaeroides, which stops rather than reverses, accumulated outside the light beam. We also compared the behavior of liquid-grown R. centenum, which swims by using a single polar flagellum, to that of surface-grown R. centenum, which swarms over agar by using many lateral flagella and has been shown to move as colonies toward specific wavelengths of light. When suspended in liquid medium, both liquid- and surface-grown R. centenum showed similar responses to the light gradient. In all cases, free-swimming cells responded to the steep gradient of intensity but not to the shallow gradient, indicating they cannot sense the direction of light propagation but only its intensity. In a control experiment, the known phototactic alga Chlamydamonas reinhardtii was shown to swim in the direction of light propagation.