The Root Microbiome of Salicornia ramosissima as a Seedbank for Plant-Growth Promoting Halotolerant Bacteria

Abstract

Root−associated microbial communities play important roles in the process of adaptation of plant hosts to environment stressors, and in this perspective, the microbiome of halophytes represents a valuable model for understanding the contribution of microorganisms to plant tolerance to salt. Although considered as the most promising halophyte candidate to crop cultivation, Salicornia ramosissima is one of the least-studied species in terms of microbiome composition and the effect of sediment properties on the diversity of plant-growth promoting bacteria associated with the roots. In this work, we aimed at isolating and characterizing halotolerant bacteria associated with the rhizosphere and root tissues of S. ramosissima, envisaging their application in saline agriculture. Endophytic and rhizosphere bacteria were isolated from wild and crop cultivated plants, growing in different estuarine conditions. Isolates were identified based on 16S rRNA sequences and screened for plant-growth promotion traits. The subsets of isolates from different sampling sites were very different in terms of composition but consistent in terms of the plant-growth promoting traits represented. Bacillus was the most represented genus and expressed the wider range of extracellular enzymatic activities. Halotolerant strains of Salinicola, Pseudomonas, Oceanobacillus, Halomonas, Providencia, Bacillus, Psychrobacter and Brevibacterium also exhibited several plant-growth promotion traits (e.g., 3-indole acetic acid (IAA), 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, siderophores, phosphate solubilization). Considering the taxonomic diversity and the plant-growth promotion potential of the isolates, the collection represents a valuable resource that can be used to optimize the crop cultivation of Salicornia under different environmental conditions and for the attenuation of salt stress in non-halophytes, considering the global threat of arable soil salinization.

Bioaugmentation Improves Phytoprotection in <em>Halimione Portulacoides </em>Exposed to Mild Salt Stress: Perspectives for Salinized Soil Restoration

“…The augmentation of the tolerance to excess salt is of great value considering the potential halotolerant species have in the bio-reclamation of salt-damaged soils [33]. In this work, bioaugmentation was achieved by the root inoculation of a consortium formed by competent salt marsh PGB-bacteria that were obtained and evaluated in a previous study [26].…”

“…Moreover, endophytes, plant root colonizing bacteria, that establish direct interactions with the host root cells, in the same way as rhizobacteria, has been shown to stimulate not only plant growth but stress resistance and tolerance mechanisms [20,21]. Additionally, it is increasingly more common the usage of PGPR consortia instead of a single strain to achieve or elicit all the intended responses [22,23]. Effective PGPR usage is constrained by a number of variables such as climate, water, soil characteristics, target species, etc.…”

“…[24], and it is understood that these bacteria have growth conditions where they can be more or less effective, for example, it was found that some PGPR with increasing salinity, and with no relation with bacterial death, did not display their plant-growth promoting attributes [25]. Nonetheless, several studies have not only identified salt tolerate PGPR but also associated PGPR consortia specific for salt-stressed plants [21,23]. Halophytes like H. portulacoides can inhabit high salinity areas, but it is well-known that even salt tolerate species have their NaCl limitations, salt exposure that exceeds the tolerance limit provokes physiological and biochemical alterations affecting growth and potentially causing death [8].…”

“…For this study, several salt marshes acquired PGPRs, specifically Bacillus aryabhattai, Stenotrophomonas rhizophila, Pseudomonas oryzihabitans, and Salinicola endophyticus have been selected in order to build a potentially effective consortium. Recent promising findings were taken into consideration in the identification and selection of those rhizobacteria with the purpose of salt stress amelioration in halophyte plants [26][27][28][29]. This present work aims to evaluate the physiological fitness and phytoprotection improvement by salt marsh PGPR in H. portulacoides under mild and severe salt stress.…”

Plant Growth Promoting Microorganisms Useful for Soil Desalinization

“…The authors were able to isolate 13 rhizobacteria from the plant rhizosphere, cultivated in soil amended with compost and watered with high concentrations of NaCl; some of these showed several biochemical PGP features. The key role of PGPB was also highlighted in the paper of Ferreira et al [5]. In fact, even in this work, the authors aimed at isolating and characterizing halotolerant bacteria, associated with the rhizosphere and root tissues of Scaevola ramosissima (Sm.)…”