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Abstract
Increase in soil salinity poses an enormous problem for agriculture and highlights the need for sustainable crop production solutions. Plant growth-promoting bacteria can be used to boost the growth of halophytes in saline soils. Salicornia is considered to be a promising salt-accumulating halophyte for capturing large amounts of carbon from the atmosphere. In addition, colonization and chemotaxis could play an important role in Salicornia-microbe interactions. In this study, the role of chemotaxis in the colonization of the halophilic siredophore-producing bacteria, Halomonas anticariensis FP35T, on Salicornia hispanica plants was investigated. The chemotactic response of FP35T to Salicornia root exudates showed optimum dependence at a salt concentration of 5 % NaCl (w/v). Oleanolic acid, the predominant compound in the exudates detected by HPLC and identified by UPLC-HRMS Q-TOF, acts as a chemoattractant. In vitro experiments demonstrated the enhanced positive effects of wild-type H. anticariensis strain FP35T on root length, shoot length, germination and the vigour index of S. hispanica. Furthermore, these positive effects partially depend on an active chemotaxis system, as the chemotaxis mutant H. anticariensis FP35 ΔcheA showed reduced plant growth promotion for all the parameters tested. Overall, our results suggest that chemotaxis responses to root exudates play an important role in interactions between Salicornia and halophilic bacteria, enhance their colonization and boost plant growth promotion. Preliminary results also indicate that root exudates have a positive impact on H. anticariensis FP35T biofilm formation under saline conditions, an effect which totally depends on the presence of the cheA gene.
Highlights
Increase in the salinization of arable soils is commonly found in semi-arid and arid areas
This study aims to analyse the effects of Salicornia root exudates on the chemotactic responses and biofilm formation of the halophilic bacterium H. anticariensis FP35T and to evaluate their impact on halophyte colonization
The chemotactic response of H. anticariensis FP35T and its mutant FP35 ∆cheA to Salicornia root exudates was first qualitatively analyzed in salt concentrations ranging from 2 to 12.5% (w/v) in order to determine the optimal saline concentration for bacterial chemotaxis
Summary
Increase in the salinization of arable soils is commonly found in semi-arid and arid areas. According to global change scenarios, agriculture under saline conditions has to be regarded as an alternative strategy for improving food production. The principal strategies used to improve crop yields in saline soils involve the use of halotolerant plant growth promoting rhizobacteria (PGPR) and/or halophytes [1]. The genus Salicornia (Chenopodiaceae) is composed of approximately 25–30 plant species which are extremely salt tolerant and widely dispersed in Eurasia, North America and South Africa [4,5]. Salicornia species have been the subject of considerable research, in relation to their use in food production [6], their medicinal applications [7,8], their use as a forage crop [9] and their salt tolerance mechanisms [10]. Salicornia is considered to be a promising salt-accumulating halophyte for capturing large amounts of carbon in the atmosphere [11]
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