(American Society for Microbiology, 2020) Velázquez Suárez, Cristina; Luque, I.; Herrero, A.; Genética; Agencia Estatal de Investigación. España; European Union (UE); Gobierno de España
ABSTRACT The model cyanobacterium Anabaena sp. PCC 7120 exhibits a phototrophic metabolism relying on oxygenic photosynthesis and a complex morphology. The organismic unit is a filament of communicated cells that may include cells specialized in different nutritional tasks, thus representing a paradigm of multicellular bacteria. In Anabaena, the inorganic carbon and nitrogen regime influenced not only growth, but also cell size, cell shape, and filament length, which also varied through the growth cycle. When using combined nitrogen, especially with abundant carbon, cells enlarged and elongated during active growth. When fixing N2, which imposed lower growth rates, shorter and smaller cells were maintained. In Anabaena, gene homologs to mreB, mreC, and mreD form an operon that was expressed at higher levels during the phase of fastest growth. In an ntcA mutant, mre transcript levels were higher than in the wild type and, consistently, cells were longer. Negative regulation by NtcA can explain that Anabaena cells were longer in the presence of combined nitrogen than in diazotrophic cultures, in which the levels of NtcA are higher. mreB, mreC, and mreD mutants could grow with combined nitrogen, but only the latter mutant could grow diazotrophically. Cells were always larger and shorter than wild-type cells, and their orientation in the filament was inverted. Consistent with increased peptidoglycan width and incorporation in the intercellular septa, filaments were longer in the mutants, suggesting a role for MreB, MreC, and MreD in the construction of septal peptidoglycan that could affect intercellular communication required for diazotrophic growth.
IMPORTANCE Most studies on the determination of bacterial cell morphology have been conducted in heterotrophic organisms. Here, we present a study of how the availability of inorganic nitrogen and carbon sources influence cell size and morphology in the context of a phototrophic metabolism, as found in the multicellular cyanobacterium Anabaena. In Anabaena, the expression of the MreB, MreC, and MreD proteins, which influence cell size and length, are regulated by NtcA, a transcription factor that globally coordinates cellular responses to the C-to-N balance of the cells. Moreover, MreB, MreC, and MreD also influence septal peptidoglycan construction, thus affecting filament length and, possibly, intercellular molecular exchange that is required for diazotrophic growth. Thus, here we identified new roles for Mre proteins in relation to the phototrophic and multicellular character of a cyanobacterium, Anabaena.
(Sage, 2012) Hierro Recio, Luis Ángel; Gómez-Álvarez Díaz, Rosario; Atienza Montero, Pedro; Economía e Historia Económica
The aim of this work is to solve the problem of nonadditivity revealed by work that calculates the redistributive effects of the budget or public policies made up of different instruments of income or public spending. To do this, the authors use the Shapley value. This technique allows us to consistently, symmetrically, and directly decompose the redistributive effect and the vertical and horizontal effects. This method is consistent because the total effects can be explained by the sum of the individual contributions; it is symmetrical because it does not depend on the aggregation ranking of the instruments; and it is direct because each index can be calculated without the need to calculate the rest. The main result obtained for the case of taxes and social transfers in the United States is that previous calculations undervalued the redistributive effects and their vertical and horizontal components for taxes and transfers. Undervaluation is more important for taxes.
