Perez Rebeca, Forchhammer Karl, Salerno Graciela, Maldener Iris
Department of Microbiology/Organismic Interactions, University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany.
FIBA-INBIOTEC, Vieytes 3103, Mar del Plata, Buenos Aires, Argentina.
Microbiology (Reading). 2016 Feb;162(2):214-223. doi: 10.1099/mic.0.000230. Epub 2015 Dec 17.
Akinetes are resting spore-like cells formed by some heterocyst-forming filamentous cyanobacteria for surviving long periods of unfavourable conditions. We studied the development of akinetes in two model strains of cyanobacterial cell differentiation, the planktonic freshwater Anabaena variabilis ATCC 29413 and the terrestrial or symbiotic Nostoc punctiforme ATCC 29133, in response to low light and phosphate starvation. The best trigger of akinete differentiation of Anabaena variabilis was low light; that of N. punctiforme was phosphate starvation. Light and electron microscopy revealed that akinetes of both species differed from vegetative cells by their larger size, different cell morphology and large number of intracellular granules. Anabaena variabilis akinetes had a multilayer envelope; those of N. punctiforme had a simpler envelope. During akinete development of Anabaena variabilis, the amount of the storage compounds cyanophycin and glycogen increased transiently, whereas in N. punctiforme, cyanophycin and lipid droplets increased transiently. Photosynthesis and respiration decreased during akinete differentiation in both species, and remained at a low level in mature akinetes. The clear differences in the metabolic and morphological adaptations of akinetes of the two species could be related to their different lifestyles. The results pave the way for genetic and functional studies of akinete differentiation in these species.
厚壁孢子是一些形成异形胞的丝状蓝细菌形成的类似休眠孢子的细胞，用于在长期不利条件下存活。我们研究了蓝细菌细胞分化的两个模式菌株——浮游淡水多变鱼腥藻ATCC 29413和陆生或共生的点状念珠藻ATCC 29133——中厚壁孢子对低光照和磷酸盐饥饿的发育响应。多变鱼腥藻厚壁孢子分化的最佳触发因素是低光照；点状念珠藻的则是磷酸盐饥饿。光学显微镜和电子显微镜观察显示，这两个物种的厚壁孢子与营养细胞不同，它们体积更大、细胞形态不同且细胞内颗粒数量众多。多变鱼腥藻的厚壁孢子有多层包膜；点状念珠藻的包膜则更简单。在多变鱼腥藻厚壁孢子发育过程中，储存化合物藻青素和糖原的量会短暂增加，而在点状念珠藻中，藻青素和脂滴会短暂增加。在这两个物种的厚壁孢子分化过程中，光合作用和呼吸作用均下降，并在成熟厚壁孢子中维持在较低水平。这两个物种厚壁孢子在代谢和形态适应方面的明显差异可能与它们不同的生活方式有关。这些结果为这些物种中厚壁孢子分化的遗传和功能研究铺平了道路。
