Mine tailings are man-made environments characterized by low levels of organic carbon and assimilable nitrogen, as well as moderate concentrations of heavy metals. For the introduction of nitrogen into these environments, a key role is played by ammonia-oligotrophic/diazotrophic heavy metal-resistant guilds. In mine tailings from Zacatecas, Mexico, Serratia liquefaciens was the dominant heterotrophic culturable species isolated in N-free media from bulk mine tailings as well as the rhizosphere, roots, and aerial parts of pioneer plants. S. liquefaciens strains proved to be a meta-population with high intraspecific genetic diversity and a potential to respond to these extreme conditions. The phenotypic and genotypic features of these strains reveal the potential adaptation of S. liquefaciens to oligotrophic and nitrogen-limited mine tailings with high concentrations of heavy metals. These features include ammonia-oligotrophic growth, nitrogen fixation, siderophore and indoleacetic acid production, phosphate solubilization, biofilm formation, moderate tolerance to heavy metals under conditions of diverse nitrogen availability, and the presence of zntA, amtB, and nifH genes. The acetylene reduction assay suggests low nitrogen-fixing activity. The nifH gene was harbored in a plasmid of ∼60 kb and probably was acquired by a horizontal gene transfer event from Klebsiella variicola.
Se presenta una descripción morfológica del género Mimophytum Greenm. (Boraginaceae), datos referentes a su distribución geográfica y ecológica y una clave dicotómica para identificar sus elementos. Asimismo, se describen las dos especies conocidas de este grupo vegetal endémico de la Sierra Madre Oriental de México; una de ellas, M. benitomartinezii se propone como nueva para la ciencia, pues difiere de M. omphalodoides en que lleva el tallo rizomatoso-estolonífero, el haz de la hoja glabro, la lámina foliar con 3 nervios basales, la inflorescencia en forma de cima escorpiodea, ebracteada, los pedicelos más cortos; además, los frutos de la nueva especie tienen los gloquidios dispuestos periféricamente.
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