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Endophytic bacterial population was isolated from Spartina maritima tissues, a heavy metal bioaccumulator cordgrass growing in the estuaries of Tinto, Odiel, and Piedras River (south west Spain), one of the most polluted areas in the world. Strains were identified and ability to tolerate salt and heavy metals along with plant growth promoting and enzymatic properties were analyzed. A high proportion of these bacteria were resistant toward one or several heavy metals and metalloids including As, Cu, and Zn, the most abundant in plant tissues and soil. These strains also exhibited multiple enzymatic properties as amylase, cellulase, chitinase, protease and lipase, as well as plant growth promoting properties, including nitrogen fixation, phosphates solubilization, and production of indole-3-acetic acid (IAA), siderophores and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. The best performing strains (Micrococcus yunnanensis SMJ12, Vibrio sagamiensis SMJ18, and Salinicola peritrichatus SMJ30) were selected and tested as a consortium by inoculating S. maritima wild plantlets in greenhouse conditions along with wild polluted soil. After 30 days, bacterial inoculation improved plant photosynthetic traits and favored intrinsic water use efficiency. However, far from stimulating plant metal uptake, endophytic inoculation lessened metal accumulation in above and belowground tissues. These results suggest that inoculation of S. maritima with indigenous metal-resistant endophytes could mean a useful approach in order to accelerate both adaption and growth of this indigenous cordgrass in polluted estuaries in restorative operations, but may not be suitable for rhizoaccumulation purposes.

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Background and aims A glasshouse experiment was conceived to assess the role of a bacterial consortium (Pseudomonas composti SDT3, Aeromonasaquariorum SDT 13 and Bacillus sp. SDT14) isolated from the rizhosphere of S. densiflora on its growth and physiological tolerance to the physicochemical properties of marsh soils. Methods Two inoculation treatments (with and without inoculation) in combination with two soil types (from Piedras and Odiel marshes, SW Spain) were assigned for 50 days. Growth parameters, combined with measurements of gas exchange, efficiency of PSII biochemistry, photosynthetic pigments and leaf water content were measured. In addition, the accumulation of nutrients and trace elements were determined. ResultsThe inoculation improved growth of S. densiflora through a beneficial effect on its photochemical apparatus due to its impact on chlorophyll concentration. This enhancement happened under both soil conditions and was mainly reflected in a greater length and diameter of roots. Also, inoculation favoured leaf water content through the decline in stomatal conductance and increment in root-to-shoot ratio. Moreover, this consortium was able to stimulate ion accumulation in roots and leaves. Conclusions Selected rhizospheric bacteria appear to play a significant role in S. densiflora growth response and tolerance to the physicochemical properties of marshes soils.

Soil bacterial community dynamics was assessed in some of the most polluted estuaries by heavy metals of the world. The influence of seasons, heavy metal pollution, and Spartina maritima rhizosphere throughout an entire year were compared in Tinto, Odiel, and Piedras salt marshes from Huelva, Spain. The less contaminated estuary showed the highest bacterial biodiversity, especially in rhizosphere, which was deeply affected by seasonal changes. On the contrary, bacterial diversity in the most polluted salt marsh was lower and neither plant roots nor seasons had a marked effect on their annual dynamics. This work provided evidence that soil bacterial communities in south western Spain estuarine sediments were not completely related to the plant species they inhabit with, but to environmental conditions, prioritizing pollution levels. These results may be considered for conducting planned restoration strategies using native plant growth promoting rhizobacteria together with heavy metal hyperaccumulator S. maritima to preserve these endangered ecosystems.