Effects of Halophyte Root Exudates and Their Components on Chemotaxis, Biofilm Formation and Colonization of the Halophilic Bacterium Halomonas Anticariensis FP35T

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.

The role of root‐associated microbes in growth stimulation of plants under saline conditions

“…Increase the biomass, water uptake, K + , and nitrogen metabolism Dong et al (2019) flavonoid and antioxidant enzymes, and regulated K + /Na + homeostasis to ameliorate salinity stress damage for the host. Sampedro et al (2020) reached a similar conclusion, as it was found that S. europaea root exudates (oleanolic acid) acted as chemoattractants for the halophilic bacterium Halomonas anticariensis FP35T, which could enhance the recruitment of halophilic bacteria in the rhizosphere and promote S. europaea growth. The production of other substances including proline, sugar and plant hormones by plant roots under salt stress, may indirectly increase the solubility of insoluble nutrients by increasing the activity of salt tolerant microbes (Vives-Peris, Molina, Segura, G omez-Cadenas, & Pérez-Clemente, 2018).…”

Dominance of Bacillus species in the wheat (Triticum aestivum L.) rhizosphere and their plant growth promoting potential under salt stress conditions

“…After removing the dye, the wells were rinsed with sterile water. Then 150 µL of 95% ethanol was added to solubilize crystal violet stain and the amount of dye was measured using a plate reader at the wavelength of 570 nm ( Sampedro et al, 2020 ).…”

Probing the potential of salinity-tolerant endophytic bacteria to improve the growth of mungbean [Vigna radiata (L.) Wilczek]

“…Crystal violet dye absorbed by the wells was solubilized by adding 150 μL of 95% ethanol. Biofilm formation was quantified by measuring the amount of absorbed dye at OD 570 nm in a microtiter plate reader ( Sampedro et al, 2020 ; Jhuma et al, 2021 ).…”