Endophytic bacteria of Mammillaria fraileana , an endemic rock-colonizing cactus of the southern Sonoran Desert
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ORIGINAL PAPER
Endophytic bacteria of Mammillaria fraileana, an endemic rock-colonizing cactus of the southern Sonoran Desert Blanca R. Lopez • Yoav Bashan • Macario Bacilio
Received: 20 July 2010 / Revised: 26 November 2010 / Accepted: 1 March 2011 / Published online: 29 March 2011 Ó Springer-Verlag 2011
Abstract The small cactus Mammillaria fraileana is a pioneer rock-colonizing plant harboring endophytic bacteria with the potential for nitrogen fixation and rock weathering (phosphate solubilization and rock degradation). In seeds, only a combination of culture-independent methods, such as fluorescence in situ hybridization, scanning electron microscopy, and fluorescence vital staining, detected significant amounts of non-culturable, but living, endophytic bacteria distributed underneath the membrane covering the embryo, in the undifferentiated tissue of the embryo, and in the vascular tissue. Large populations of culturable endophytic bacteria were detected in stems and roots of wild plants colonizing rocks in the southern Sonoran Desert, but not in seeds. Among 14 endophytic bacterial isolates found in roots, four isolates were identified by full sequencing of their 16S rRNA gene. In vitro tests indicated that Azotobacter vinelandii M2Per is a potent nitrogen fixer. Solubilization of inorganic phosphate was exhibited by Pseudomonas putida M5TSA, Enterobacter sakazakii M2PFe, and Bacillus megaterium M1PCa, while A. vinelandii M2Per, P. putida M5TSA, and B. megaterium M1PCa weathered rock by reducing the size of rock particles, probably by changing the pH of the liquid media.
Communicated by Ursula Priefer. B. R. Lopez Y. Bashan (&) M. Bacilio Environmental Microbiology Group, Northwestern Center for Biological Research (CIBNOR), Mar Bermejo 195, Colonia Playa Palo de Santa Rita, 23090 La Paz, BCS, Mexico e-mail: [email protected]; [email protected] Y. Bashan The Bashan Foundation, 3740 NW Harrison Blvd., Corvallis, OR 97330, USA
Cultivated seedlings of M. fraileana, derived from disinfected seeds and inoculated with endophytic bacteria, showed re-colonization 105 days after inoculation. Their densities decreased from the root toward the stem and apical zones. Functional traits in planta of culturable and non-culturable endophytic bacteria in seeds remain unknown. Keywords Cactus Plant colonization of rocks Endophytic bacteria Mammillaria Phosphate solubilization Rock weathering
Introduction Colonization, establishment, and continuing permanence of desert plants are part of biogenic processes that lead to accelerated weathering of rocks in arid zones of Central and North America (Puente et al. 2004a; Lopez et al. 2009). Some desert plants become established on bare rocks without the presence of soil in arid regions of Mexico (Bashan et al. 2002, 2006; Valverde et al. 2004; Lopez et al. 2009). Interactions with microorganisms assist desert plants to grow on rocks. These include association of many mycorrhizal fungi and plant growth-promoting bacteria (Puente et al. 2004b; Bashan et al. 2007)
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