Microbial Populations and Activities in the Rhizoplane of Rock‐Weathering Desert Plants. I. Root Colonization and Weathering of Igneous Rocks

Abstract

Dense layers of bacteria and fungi in the rhizoplane of three species of cactus (Pachycereus pringlei, Stenocereus thurberi, Opuntia cholla) and a wild fig tree (Ficus palmeri) growing in rocks devoid of soil were revealed by bright-field and fluorescence microscopy and field emission scanning electron microscopy. These desert plants are responsible for rock weathering in an ancient lava flow at La Purisima-San Isidro and in sedimentary rock in the Sierra de La Paz, both in Baja California Sur, Mexico. The dominant bacterial groups colonizing the rhizoplane were fluorescent pseudomonads and bacilli. Seven of these bacterial species were identified by the 16S rRNA molecular method. Unidentified fungal and actimomycete species were also present. Some of the root-colonizing microorganisms fixed in vitro N(2), produced volatile and non-volatile organic acids that subsequently reduced the pH of the rock medium in which the bacteria grew, and significantly dissolved insoluble phosphates, extrusive igneous rock, marble, and limestone. The bacteria were able to release significant amounts of useful minerals, such as P, K, Mg, Mn, Fe, Cu, and Zn from the rocks and were thermo-tolerant, halo-tolerant, and drought-tolerant. The microbial community survived in the rhizoplane of cacti during the annual 10-month dry season. This study indicates that rhizoplane bacteria on cacti roots in rock may be involved in chemical weathering in hot, subtropical deserts.

Characterization of endophytic bacteria associated with rose plant (Rosa damascena trigintipeta) during flowering stage and their plant growth promoting traits

“…This deficiency can be compensated by bacteria for its inorganic phosphatesolubilizing ability (Zaidi et al 2006). In present work, the estimation of phosphate solublization in vitro showed that all the six endophytic bacteria isolates had the capacity to solublize phosphate (Table 3) when the solid medium was supplemented with Ca 3 (PO 4 ) 2 (Puente et al 2004), strain TUB5 showed a high capacity for phosphate solublization than other tested strains. Furthermore, these particular bacteria have more potential as a PGPE strategy in arid region plants than the PGPB used in agriculture.…”

“…The capability of the bacteria to solubilize phosphates was tested by measuring the diameter of the solubilized zone around bacterial colonies grown on a solid medium supplemented with freshly precipitated Ca 3 (PO 4 ) 2 (Puente et al 2004) Exoenzyme activity tests The tests included (1) starch hydrolysis on starch plates (Claus 1988); (2) Lipid hydrolysis using both egg yolk agar (Claus 1988) and Tributyrin agar (Lusty and Doudorof 1966); (3) proteolysis as hydrolysis of skim milk (Claus 1988), and gelatin (Biling 1970); cellulose degradation (Farkas et al 1985); Pectolysis with either polygalaturonate or sodium polypectate as substrates after the method of Collmer et al (1988) and chitin hydrolysis as described by Zhou et al (1999). Bacterial cultures were streaked on the medium and incubated at 308C for 48 hours.…”

Characteristics of metal-tolerant plant growth-promoting yeast (Cryptococcus sp. NSE1) and its influence on Cd hyperaccumulator Sedum plumbizincicola

“…2). Within these experiments, the pH value of the solution changed inversely to the concentration of soluble P. The solubilization of P is commonly associated with a decrease in pH (Puente et al 2004) and has been reported in fungi as a result of production of various organic acids, including citric acid, gluconic acid (Reyes et al 2001;Whitelaw et al 1999), and oxalic acid (Gharieb 2000). As seen in Fig.…”

Cu-resistant Kocuria sp. CRB15: a potential PGPR isolated from the dry tailing of Rakha copper mine

“…The major mechanism associated with the solubilization of insoluble phosphate is the organic acid production, accompanied by acidification of the medium (Puente et al 2004). The present study represents that a gradual increase in solubilized phosphate concentration was observed from 24 to 120 h. Phosphate concentration varied from 15.78 to 39.37 lg ml -1 in the culture filtrates of CRB15.…”