Phenotypic structure of Pseudomonas populations is altered under elevated pCO2 in the rhizosphere of perennial grasses

Abstract

The increasing atmospheric CO 2 content (pCO 2 ) is likely to modify the ecosystem functioning including rhizosphere bacteria that are directly dependent on rhizodeposition. This may include alteration of Pseudomonas populations that display phenotypic traits in relation with plant fitness. In the present study, 1228 Pseudomonas strains were isolated from the non-rhizosphere soil, rhizosphere soil and root fractions of perennial grassland systems: Lolium perenne and Molinia coerulea. Both plants were grown under ambient (36 Pa) and elevated (60 Pa) pCO 2 in the Swiss Free Air CO 2 Enrichment (FACE) system. Pseudomonas spp. were tested for their ability to produce auxin, siderophores and hydrogen cyanide, and to dissimilate nitrate. No effect of root proximity and elevated pCO 2 was observed on the proportions of auxin producers. For L. perenne and M. coerulea, siderophore and hydrogen cyanide Pseudomonas producers were stimulated in the root fraction. In contrast lower frequencies of nitrate reducers were observed in the root fraction compared to non-rhizosphere soil. The frequencies of siderophore producers and nitrate dissimilating strains were higher, and those of hydrogen cyanide producers lower, under elevated pCO 2 for L. perenne. This alteration of the phenotypic structure of Pseudomonas guild in the root fraction is discussed in relation with the physico-biochemical modifications of the rhizosphere condition via rhizodeposition and environmental changes occurring under elevated pCO 2 .

Bio-inoculation of yerba mate seedlings (Ilex paraguariensis St. Hill.) with native plant growth-promoting rhizobacteria: a sustainable alternative to improve crop yield

“…Synthesis of arylsulphatases was evaluated by the formation of a blue coloration around colonies on modified Angle agar plates with 40 mg L −1 X-sulfate and 710 mg L −1 Na 2 SO 4 as sulfur sources (Kertesz and Mirleau 2004). Synthesis of indole-3-acetic acidlike compounds (IAA-like) was estimated by the colorimetric technique specific for the detection of indolic compounds (Bric et al 1991) as described in Tarnawski et al (2006). The intensity of the coloration was measured at a wavelength of 535 nm using a Genesys 10S UV-VIS spectrophotometer (Thermo Scientific).…”

“…The value reported was normalized to bacterial growth using cellular abundance measured at 600 nm. Production of hydrogen cyanide (HCN) was tested on a synthetic medium containing glutamate, glycine, and methionine as precursors of HCN (Castric and Castric 1983) as described in Tarnawski et al (2006). Inhibition of the growth of fungi and protists responsible for damping-off attack (often encountered in plantations and in nursery) was evaluated in a dual culture assay on PDA by inoculating 10 μl of fresh bacterial cultures in triplicate at equidistant points around the perimeter of the plate.…”

“…Numerous bacterial species, principally those associated with plant rhizosphere or root tissues, have been reported to have a positive impact on plant growth and health (Kloepper et al 1989;Dobbelaere et al 1999). These bacteria, collectively known as plant growth-promoting rhizobacteria (PGPR), improve plant growth through different mechanisms as biofertilizers ( Kloepper et al 1980;Cattelan et al 1999;Rodrigues et al 2008;Tarnawski 2008), phytostimulators (Mehnaz et al 2001), or bio-control agents (Compant et al 2005;Pieterse et al 2009). The rhizosphere and roots of several crops are relevant microniches for the isolation of native PGPR strains adapted to endemic soil conditions from which effective bio-inoculants can be formulated.…”

Effects of Elevated CO2 on Communities of Denitrifying Bacteria and Methanogens in a Temperate Marsh Microcosm

“…In terms of bacteria, the effects of elevated CO 2 on bacterial biomass, number, respiration, activity, trace gas emission (e.g., denitrification and methanogenesis), and species composition have been examined by several researchers [3,4,14,15,19,29,30,32,35,55]. Most of these studies, however, were performed in grassland or agricultural soil, while limited information is available about the response of the bacterial communities involved in denitrification and methanogenesis to the elevated CO 2 in wetland ecosystems.…”

Tratamento de sementes com rizobactérias na produção de cebola

“…As rizobactérias exercem efeito benéfico sobre as plantas por diferentes mecanismos de ação, diretos ou indiretos, como, por exemplo, a antibiose, o parasitismo, a competição, a produção de sideróforos e a indução de resistência (RAMAMOORTHY et al, 2001;TARNAWSKI et al, 2006). As rizobactérias são capazes de se multiplicar e colonizar rapidamente o sistema radicular, prevenindo a invasão de patógenos pela produção de metabólitos secundários que inibem outros microrganismos deletérios (KLOEPPER et al, 2004).…”