Diversity of Pseudomonas spp. Isolated from Rice Rhizosphere Populations Grown along a Salinity Gradient

Abstract

Along the coastline of Tamil Nadu, five sites were chosen to assess the diversity of Pseudomonas populations isolated from rice (Oryza sativa) cultivated along a salinity gradient. One of these sites was under organic farming while the other four were under inorganic farming. A total of 256 Pseudomonas strains isolated from these five sites were analyzed using both phenotypic (substrate utilization patterns and antibiotic resistance assay) and genotypic (PCR-RFLP of 16S rDNA) characteristics. The results derived from this study indicate that soil salinity affects rhizosphere Pseudomonas populations. It was observed that increasing salinity led to decreasing diversity. Fluorescent pseudomonads were the dominant species found in the non-saline site, while in the saline sites they were replaced by salt-tolerant species, in particular Pseudomonas alcaligenes and P. pseudoalcaligenes. An interesting observation was the increase in diversity found in the saline site under organic farming. Organic farming was found to be capable of mitigating the harmful effects of saline stress to a large extent, and restoring the Pseudomonas diversity, thereby making it comparable with the diversity encountered in the non-saline site.

Salt-tolerant and plant growth-promoting bacteria isolated from Zn/Cd contaminated soil: identification and effect on rice under saline conditions

“…Pseudomonas spp. have a widespread distribution in saline and non-saline soils (Rangarajan et al 2002), and some salt-tolerant Pseudomonas spp. had the ability to colonize the rice rhizosphere and ability to suppress bacterial leaf blight and sheath blight pathogens of rice (Rangarajan et al 2003).…”

Effect of soil salinity and nutrient levels on the community structure of the root-associated bacteria of the facultative halophyte, <i>Tamarix ramosissima</i>, in southwestern United States

“…These results indicate that, at least, a portion of the RB species observed in T. ramosissima was halotolerant. In addition, P. alcaligenes and P. pseudoalcaligenes have been isolated from the rhizosphere of plants (Egamberdiyeva and Höflich, 2004;Rangarajan et al, 2002). P. alcaligenes has been reported to result in growth-promoting effects and improvement of nutrient uptake in plants (Costa et al, 2006;Egamberdiyeva, 2007;Egamberdiyeva and Höflich, 2004), indicating that the Pseudomonas species in our study may also have such beneficial effects on T. ramosissima.…”

“…The numbers at the nodes indicate percent (≥50%) bootstrap support (1000 replications) (RB, root-associated bacteria; T-RF, terminal restriction fragment). Rangarajan et al (2002) have examined the effect of salt and showed that close relatives of Pseudomonas in our study, P. alcaligenes and P. pseudoalcaligenes, had a salt tolerance and were predominant in saline conditions. These results indicate that, at least, a portion of the RB species observed in T. ramosissima was halotolerant.…”

Molecular and phenotypic characterization of potential plant growth-promoting Pseudomonas from rice and maize rhizospheres

“…The forward primer Ps-for (20-mer [5 0 -GGTCTGAGAGGATGAT-CAGT-3 0 ]) and reverse primer Ps-rev (18-mer [5 0 -TTAG CTCCACCTCGCGGC-3 0 ]) (Cirvilleri et al 2005;Rangarajan et al 2002) were used to amplify the total genomic DNA. The total volume of the reaction mixture was 25 ll containing 10-50 ng of template DNA, 109 reaction buffer, 2.5 mM dNTPs, 20 pmol of each primer, and 1 U taq DNA polymerase (invitrogen).…”

“…The total volume of the reaction mixture was 25 ll containing 10-50 ng of template DNA, 109 reaction buffer, 2.5 mM dNTPs, 20 pmol of each primer, and 1 U taq DNA polymerase (invitrogen). PCR amplification was performed as detailed in previously study (Rangarajan et al 2002). To estimate the product size, the products were run on 1% agarose gels along with 1 kb ladder as marker and stained with ethidium bromide.…”