Acidobacteria strains from subdivision 1 act as plant growth-promoting bacteria
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ORIGINAL PAPER
Acidobacteria strains from subdivision 1 act as plant growth‑promoting bacteria Anna M. Kielak1 · Matheus A. P. Cipriano1 · Eiko E. Kuramae1
Received: 21 March 2016 / Revised: 9 June 2016 / Accepted: 15 June 2016 © The Author(s) 2016. This article is published with open access at Springerlink.com
Abstract Acidobacteria is one of the most abundant phyla in soils and has been detected in rhizosphere mainly based on cultivation-independent approaches such as 16S rRNA gene survey. Although putative interaction of Acidobacteria with plants was suggested, so far no plant–bacterial interactions were shown. Therefore, we performed several in vitro tests to evaluate Acidobacteria–plant interactions and the possible mechanisms involved in such interaction. We observed that Arabidopsis thaliana inoculated with three strains belonging to Acidobacteria subdivision 1 showed increase in biomass of roots and shoots as well as morphological changes in root system. Our results indicate that the plant hormone indole-3-acetic acid production and iron acquisition are plausibly involved in the plant and Acidobacteria interactions. Here, we confirm for the first time that Acidobacteria can actively interact with plants and act as plant growth-promoting bacteria. In addition, we show that Acidobacteria strains produce exopolysaccharide which supports the adhesion of bacteria to the root surfaces. Keywords Acidobacteria · PGPB · IAA · Root biomass · Arabidopsis thaliana
Communicated by Erko Stackebrandt. * Eiko E. Kuramae [email protected] 1
Department of Microbial Ecology, Netherlands Institute of Ecology (NIOO-KNAW), P.O. Box 50, Droevendaalsesteeg 10, 6708 PB Wageningen, The Netherlands
Introduction Acidobacteria is a very diverse and ubiquitous bacterial phylum. Furthermore, those bacteria seem to be especially well adapted to soil environment, often representing one the most abundant bacterial phylum (Janssen 2006; Lee et al. 2008). Although there are inconsistencies in reports regarding the preference of Acidobacteria in inhabiting bulk versus rhizosphere soils (Fierer et al. 2007; Singh et al. 2007; Kielak et al. 2008), there are clear evidences for the association of some Acidobacteria with plants (da Rocha et al. 2010, 2013). The enormous phylogenetic diversity within the phylum also suggests that Acidobacteria are genetically and, most likely, metabolically dissimilar; thus, the results of single studies cannot be generalized and easily extrapolated to the whole phylum. Due to the still low number of sequenced genomes and difficulties associated with cultivation, the ecological role of this phylum remains rather unknown (Kielak et al. 2016). Nevertheless, a number of studies have compared distribution and diversity of Acidobacteria in relation to plant root proximity (Chow et al. 2002; Filion et al. 2004; da Rocha et al. 2010; Chaparro et al. 2014) and/or plant exudates (Shi et al. 2011; Mao et al. 2014). For example, acidobacterial strains have been obtained from internal plant tissues hinting to
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