Publication Date: 2016.
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.
Author affiliation: Perez, Rebeca. University of Tübingen; Alemania
Author affiliation: Forchhammer, Karl. University of Tübingen; Alemania
Author affiliation: Salerno, Graciela Lidia. Fundación para Investigaciones Biológicas Aplicadas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones en Biodiversidad y Biotecnología; Argentina
Author affiliation: Maldener, Iris. University of Tübingen; Alemania
Repository: CONICET Digital (CONICET). Consejo Nacional de Investigaciones Científicas y Técnicas
Publication Date: 2007.
Polyhydroxyalkanoates (PHAs) are accumulated as intracellular granules by many bacteria under unfavorable conditions, enhancing their fitness and stress resistance. Poly(3-hydroxybutyrate) (PHB) is the most widespread and best-known PHA. Apart from the genes that catalyze polymer biosynthesis, natural PHA producers have several genes for proteins involved in granule formation and/or with regulatory functions, such as phasins, that have been shown to affect polymer synthesis. This study evaluates the effect of PhaP, a phasin, on bacterial growth and PHB accumulation from glycerol in bioreactor cultures of recombinant Escherichia coli carrying phaBAC from Azotobacter sp. strain FA8. Cells expressing phaP grew more, and accumulated more PHB, both using glucose and using glycerol as carbon sources. When cultures were grown in a bioreactor using glycerol, PhaP-bearing cells produced more polymer (2.6 times) and more biomass (1.9 times) than did those without the phasin. The effect of this protein on growth promotion and polymer accumulation is expected to be even greater in high-density cultures, such as those used in the industrial production of the polymer. The recombinant strain presented in this work has been successfully used for the production of PHB from glycerol in bioreactor studies, allowing the production of 7.9 g/liter of the polymer in a semisynthetic medium in 48-h batch cultures. The development of bacterial strains that can efficiently use this substrate can help to make the industrial production of PHAs economically feasible. Copyright © 2007, American Society for Microbiology. All Rights Reserved.
Author affiliation: De Almeida, A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Author affiliation: Pettinari, M.J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Keywords: Bacteria; Biomass; Bioreactors; Biosynthesis; Escherichia coli; Glycerol; Intracellular granules; Polyhydroxyalkanoates (PHAs); Semisynthetic medium; Stress resistance; Proteins; bacterial protein; carbon; glucose; glycerol; poly(3 hydroxybutyric acid); polyhydroxyalkanoic acid; polymer; regulator protein; bacterium; fitness; gene; growth; polymer; protein; stress resistance; article; Azotobacter; bacterial growth; bacterial strain; bacterium culture; bioreactor; biosynthesis; catalysis; cell granule; controlled study; Escherichia coli; nonhuman; protein expression; protein function; stress; Azotobacter; Bacterial Proteins; Biomass; Bioreactors; DNA-Binding Proteins; Escherichia coli; Fermentation; Glucose; Glycerol; Hydroxybutyrates; Polyesters; Azotobacter; Bacteria (microorganisms); Escherichia coli.
Repository: Biblioteca Digital (UBA-FCEN). Universidad Nacional de Buenos Aires. Facultad de Ciencias Exactas y Naturales