Rhizosphere Of Halophytes Research Articles

Isolation and Characterization of Plant Growth Promoting and Metal Resistant Archaea Associated with the Rhizosphere of Salsola stocksii and Atriplex amnicola

Halophilic microorganisms play a crucial role in plant health and growth in salinity affected lands. The objective of this study was to evaluate the haloarchaeal diversity from the rhizosphere of halophytes and plant growth promoting abilities of these strains. The whole genome sequences of two haloarchaeal strains, Halorubrum lacusprofundi HL1RP11 and Halobacterium noricense NRS2HaP9, were analyzed, and genes related to plant growth promoting traits were identified. Phylogenetic analysis showed that archaeal strains of Halococcus, Halorubrum, Halobacterium and Natrinema were dominant in the rhizosphere of halophytes. More than 60% of the strains were positive for phosphate solubilization and IAA production. About 33% were siderophore producers. More than 40% of haloarchaeal strains showed the heavy metal resistance for Nickel, Cadmium, Chromium and Zinc at a concentration of 5 mM. Genes involved in plant growth promotion were identified through annotation. Gene clusters related to secondary metabolites including phenazine, siderophore production and terpene were also identified in this study. Our results suggested that these haloarchaeal strains can be used as an eco-friendly biofertilizer to improve growth and productivity in hypersaline environment.

Thriving against the odds: Exploring halotolerant rhizobacteria in the saline rhizosphere of Tuzla lagoon's halophytes

Soil salinization poses a significant threat to global crop production, affecting around 20% of agricultural fields with the challenges of osmotic and ionic stress. The reclamation of salinity-affected agricultural lands is a pressing concern. To bridge existing gaps in our understanding of halotolerant plant growth-promoting rhizobacteria (PGPR), this research strategically focuses on isolating and characterizing these beneficial bacteria from the rhizosphere of halophytes in the Tuzla lagoon area. The objective is to contribute essential insights, fostering a deeper understanding of halotolerant PGPR for application in sustainable agricultural practices, particularly in alleviating salinity-induced stress in plants.All nine isolates demonstrated remarkable abilities, including the synthesis of siderophores, with isolates B15, C20, E2, and H9 showcasing phosphate solubilization. Additionally, isolates E2 and H9 displayed phytase production, and five isolates exhibited indole acetic acid synthesis. Although 1-aminocyclopropane-1-carboxylate deaminase production was absent, hydrogen cyanide synthesis was evident in all isolates except H9. Isolate E2 did not demonstrate cellulase synthesis, but biofilm formation was observed in all isolates except C23.To assess the salinity stress mitigation potential of the isolates, a randomized complete block design bioassay was conducted with ten treatments (nine bacterial isolates and a control) across four salt concentrations (0 mM, 100 mM, 200 mM, and 300 mM). While the isolates successfully demonstrated multiple plant growth-promoting traits, their capacity to significantly alleviate the effects of salinity stress on wheat plants suggests the need for further exploration. Comprehensive greenhouse/field trials under diverse physiological and environmental conditions are recommended to unlock the full potential of these isolates in effectively mitigating salinity stress in crops.

Halophytes increase rhizosphere microbial diversity, network complexity and function in inland saline ecosystem

Salinization is an important global environmental problem influencing sustainable development of terrestrial ecosystems. Salt-tolerant halophytes are often used as a promising approach to remedy the saline soils. Yet, how rhizosphere microbes' association and functions vary with halophytes in saline ecosystems remains unclear, restricting our ability to assess the role of halophytes in remedying saline ecosystems. Herein, we examined bacterial and fungal diversities, compositions, and co-occurrence networks in the rhizospheres of six halophytes and bulk soils in a semiarid inland saline ecosystem, and related these parameters to microbial functions. The microbiomes were more diverse and complex and microbial activity and residues were higher in rhizospheres than bulk soils. The connections of taxa in the rhizosphere microbial communities increased with fungi-fungi and bacteria-fungi connections and fungal diversity. The proportion of the fungi-related central connections were larger in rhizospheres (13–73%) than bulk soils (3%). Moreover, microbial activity and residues were significantly correlated with microbial composition and co-occurrence network complexity. These results indicated that enhanced association between fungi and bacteria increased microbial co-occurring network complexity in halophytes rhizosphere, which contributed to the higher microbial functions (microbial activities and residue) in this inland saline ecosystem.

Rhizosphere bacteria community and functions under typical natural halophyte communities in North China salinized areas.

Soil salinity is a serious environmental issue in arid China. Halophytes show extreme salt tolerance and are grow in saline-alkaline environments. There rhizosphere have complex bacterial communities, which mediate a variety of interactions between plants and soil. High-throughput sequencing was used to investigated rhizosphere bacterial community changes under the typical halophyte species in arid China. Three typical halophytes were Leymus chinensis (LC), Puccinellia tenuiflora (PT), Suaeda glauca (SG). The dominant phyla were Proteobacteria, Actinobacteria, Chloroflexi, Gemmatimonadetes, Acidobacteria and Bacteroidetes, Suaeda glauca rhizosphere has stronger enrichment of Nitrospirae and Cyanobacteria. The Ace, Chao and Shannon indices were significantly higher in soils under LC and SG (P<0.05). Functional predictions, based on 16S rRNA gene by PICRUSt, indicated that Energy metabolism, Amino acid metabolism, Carbohydrate metabolism and Fatty acid metabolism are dominant bacterial functions in three halophytes rhizosphere soil. Carbon metabolism, Oxidative phosphorylation, Methane metabolism, Sulfur metabolism and Nitrogen metabolism in SG were significantly higher than that in LC and PT. Regression analysis revealed that rhizosphere soil bacterial community structure is influenced by soil organic matter (SOM) and soil water content (SWC), while soil bacterial community diversity is affected by soil pH. This study contributes to our understanding of the distribution characteristics and metabolic functions under different halophyte rhizosphere bacterial communities, and will provide references for the use of rhizosphere bacteria to regulate the growth of halophytes and ecological restoration of saline soil.

Aquaponics using a fish farm effluent shifts bacterial communities profile in halophytes rhizosphere and endosphere

The intensification of marine aquaculture raises multiple sustainability issues, namely the handling of nutrient-rich effluents that can adversely impact ecosystems. As integrated multi-trophic aquaculture (IMTA) gains momentum, the use of halophyte plants to phytoremediate aquaculture effluents has received growing attention, particularly in aquaponics. It is, therefore, important to obtain a more in-depth knowledge of the microbial communities present in the root systems of these plants, both in their natural environment (sediment) and in aquaponics, in order to understand their nutrient removal potential. The present study used denaturing gradient gel electrophoresis (DGGE) and barcoded pyrosequencing to assess the bacterial community present in the endosphere and rhizosphere of three halophyte plants: Halimione portulacoides, Salicornia ramosissima and Sarcocornia perennis. Species-specific effects were recorded in the profile and diversity of the bacterial communities present in halophyte roots, with significant differences also recorded for the same halophyte species grown in contrasting environments (sediment vs. aquaponics). In aquaponics the most abundant groups belonged to the orders Rhodocyclales, Campylobacterales, Rhodobacterales and Desulfobacterales, while in the natural environment (sediment) the most abundant groups belonged to the orders Rhizobiales, Sphingomonadales and Alteromonadales. An overall enrichment in bacterial taxa involved in nutrient cycling was recorded in the roots of halophytes grown in aquaponics (such as Denitromonas, Mesorhizobium, Colwellia, Dokdonella and Arcobacter), thereby highlighting their potential to reduce the nutrient loads from aquaculture effluents.

Phylogenetic analysis of halophyte-associated rhizobacteria and effect of halotolerant and halophilic phosphate-solubilizing biofertilizers on maize growth under salinity stress conditions.

The main objective of the present work was to evaluate plant growth-promoting abilities of bacterial strains from the rhizosphere of halophytes and their effect on maize growth under salinity stress. Halophilic bacteria were identified using 16S rRNA sequence analysis and their plant growth-promoting abilities were characterized. Phylogenetic analysis showed that bacterial strains belonging to Bacillus, Halobacillus and Pseudomonas were dominant in the rhizosphere of halophytes. More than 93% strains showed P-solubilization activity and IAA production. About 54% strains were able to produce ACC deaminase, 29% strains showed positive results for nitrogen fixation, 41 and 21% strains showed siderophores and HCN production ability respectively. More than 90% strains showed antifungal activity against more than two fungal pathogens and production of different hydrolytic enzymes. To study the plant growth-promoting effect on maize, five bacterial strains Bacillus safensis HL1HP11 and Bacillus pumilus HL3RS14, Kocuria rosea HL1RP8, Enterobacter aerogenes AT1HP4 and Aeromonas veronii AT1RP10 were used as inoculants; in the form of seed coat and enriched soil-based phosphate biofertilizers. All bacterial strains positively affected the maize growth as compared to non-inoculated control+NaCl plants. Plants inoculated with Bacillus HL3RS14-based soil biofertilizers showed maximum increase in dry weights of root (48-124%) and shoot (52-131%) as compared to control+NaCl (soil+rock phosphate, no inoculum). PGPR inoculations under salinity stress conditions showed high concentrations of proline, glycine betaine and malondialdehyde. These results indicated that under saline soil conditions, halophilic PGPR strains combined with carrier materials are promising candidates as biofertilizers.

Identification of plasmid encoded osmoregulatory genes from halophilic bacteria isolated from the rhizosphere of halophytes

Bacterial plasmids carry genes that code for additional traits such as osmoregulation, CO2 fixation, antibiotic and heavy metal resistance, root nodulation and nitrogen fixation. The main objective of the current study was to identify plasmid-conferring osmoregulatory genes in bacteria isolated from rhizospheric and non-rhizospheric soils of halophytes (Salsola stocksii and Atriplex amnicola). More than 55% of halophilic bacteria from the rhizosphere and 70% from non-rhizospheric soils were able to grow at 3 M salt concentrations. All the strains showed optimum growth at 1.5–3.0 M NaCl. Bacterial strains from the Salsola rhizosphere showed maximum (31%) plasmid elimination during curing experiments as compared to bacterial strains from the Atriplex rhizosphere and non-rhizospheric soils. Two plasmid cured strains Bacillus HL2HP6 and Oceanobacillus HL2RP7 lost their ability to grow in halophilic medium, but they grew well on LB medium. The plasmid cured strains also showed a change in sensitivity to specific antibiotics. These plasmids were isolated and transformed into E. coli strains and growth response of wild-type and transformed E. coli strains was compared at 1.5–4 M NaCl concentrations. Chromosomal DNA and plasmids from Bacillus filamentosus HL2HP6 were sequenced by using high throughput sequencing approach. Results of functional analysis of plasmid sequences showed different proteins and enzymes involved in osmoregulation of bacteria, such as trehalose, ectoine synthetase, porins, proline, alanine, inorganic ion transporters, dehydrogenases and peptidases. Our results suggested that plasmid conferring osmoregulatory genes play a vital role to maintain internal osmotic balance of bacterial cells and these genes can be used to develop salt tolerant transgenic crops.

Isolation and characterization of bacteria associated with the rhizosphere of halophytes (Salsola stocksii and Atriplex amnicola) for production of hydrolytic enzymes.

Microbes from hypersaline environments are useful in biotechnology as sources of novel enzymes and proteins. The current study aimed to characterize halophilic bacteria from the rhizosphere of halophytes (Salsola stocksii and Atriplex amnicola), non-rhizospheric, and brine lake-bank soils collected from Khewra Salt Mine and screening of these bacterial strains for industrially important enzymes. A total of 45 bacterial isolates from the rhizosphere of Salsola, 38 isolates from Atriplex, 24 isolates from non-rhizospheric, and 25 isolates from lake-bank soils were identified by using 16S rRNA gene analysis. Phylogenetic analysis showed that bacterial strains belonging to Bacillus, Halobacillus, and Kocuria were dominant in the rhizosphere of halophytes (Salsola and Atriplex), and Halobacillus and Halomonas were dominating genera from non-rhizospheric and lake-bank soils. Mostly identified strains were moderately halophilic bacteria with optimum growth at 1.5-3.0M salt concentrations. Most of the bacterial exhibited lipase, protease, cellulase, amylase, gelatinase, and catalase activities. Halophilic and halotolerant Bacilli (AT2RP4, HL1RS13, NRS4HaP9, and LK3HaP7) identified in this study showed optimum lipase, protease, cellulase, and amylase activities at 1.0-1.5M NaCl concentration, pH 7-8, and temperature 37°C. These results indicated that halophilic and halotolerant bacteria can be used for bioconversion of organic compounds to useful products under extreme conditions.

SCREENING OF DIFFERENT ISOLATES OF AZOSPIRILLUMFOR GROWTH AT DIFFERENT SALT (NACL) CONCENTRATIONS

Azospirillum was abundant in the rhizosphere of halophytes collected from El- Thaliga salt marsh near Benghazi, Libya. More than twenty five isolated of Azospirillum were isolated from rhizosphere by enrichement method using DN semisolid medium with or without salt. After several transfer for purification, 13 isolates were screened to select the most efficient strains in a microcosms experiment with wheat. According to the cultural, morphological and biochemical experiments Azospirillum isolated were belonging to A. brasilense and isolated was belonging to A. lipoferum, Azospirillum isolates were screened for growth at different NaCl concentration in liquid DN medium.

Impact of soil salinity on the microbial structure of halophyte rhizosphere microbiome.

The rhizosphere microbiome plays a significant role in the life of plants in promoting plant survival under adverse conditions. However, limited information is available about microbial diversity in saline environments. In the current study, we compared the composition of the rhizosphere microbiomes of the halophytes Urochloa, Kochia, Salsola, and Atriplex living in moderate and high salinity environments (Khewra salt mines; Pakistan) with that of the non-halophyte Triticum. Soil microbiomes analysis using pyrosequencing of 16S rRNA gene indicated that Actinobacteria were dominant in saline soil samples whereas Proteobacteria predominated in non-saline soil samples. Firmicutes, Acidobacteria, Bacteriodetes and Thaumarchaeota were predominant phyla in saline and non-saline soils, whereas Cyanobacteria, Verrucomicrobia, Gemmatimonadetes and the unclassified WPS-2 were less abundant. Sequences from Euryarchaeota, Ignavibacteriae, and Nanohaloarchaeota were identified only from the rhizosphere of halophytes. Dominant halophilic bacteria and archaea identified in this study included Agrococcus, Armatimonadetes gp4, Halalkalicoccus, Haloferula and Halobacterium. Our analysis showed that increases in soil salinity correlated with significant differences in the alpha and beta diversity of the microbial communities across saline and non-saline soil samples. Having a complete inventory of the soil bacteria from different saline environments in Pakistan will help in the discovery of potential inoculants for crops growing on salt-affected land.

Nutrients, microbial community structure and functional gene abundance of rhizosphere and bulk soils of halophytes

Salt marshes occupy the transition zone between terrestrial and marine ecosystem and provide habitat for salt tolerant plant species-halophytes. Dominant halophytes such as Salicornia brachiata, Aeluropus lagopoides and Suaeda maritima play significant role in carbon sequestration, nutrient mineralization, nutrient cycling and improving micro-environment. There are scanty reports on the rhizosphere microbial communities of halophytes. Whether the rhizosphere of halophytes harbors unique microbial communities or has species specificity is yet to be established. In the present study, we have determined microbial community structure and functional genes abundance as well as major nutrients and three key enzyme activities in both rhizosphere and bulk soil of three halophytes (Salicornia, Aeluropus and Suaeda) growing on salty marsh of coastal Gujarat, India. The NH4-N and available K were significantly higher in the rhizosphere than in the bulk soil in all the cases. The rhizosphere of Suaeda was characterized by significantly higher concentrations of organic carbon, total N, NH4-N and available P as compared to other two halophytes. The rhizopsheric soil had significantly higher concentrations of total PLFA, GM+ve, GM−ve and total bacterial PLFA biomarkers compared to the bulk soil. Among halophytes, significantly higher concentrations of total PLFA, GM+ve, GM−ve, total bacterial and actinomycetes biomarker PLFAs were recorded in Suaeda and Aeluropus in comparison to Salicornia. The NMS analysis of PLFA profiles revealed a significant difference in microbial community structure in Salicornia compared to Aeluropus and Suaeda. Similarly, rhizosphere microbial community structure of Salicornia was significantly different from Suaeda and Aeluropus. In rhizosphere soils, significantly higher abundance (molar%) of GM−ve, GM+ve, total bacterial and actinomycetes PLFAs were observed in Aeluropus and Suaeda compared to Salicornia. Activities of β-glucosidase and urease were significantly higher in rhizosphere than in the bulk soil. The abundance of 16S rRNA, cbbL and nifH genes, detected by the quantitative RT-PCR was significantly varied among soils and halophytes. The results exhibited high bacterial diversity, abundance of CO2 and N-fixing bacteria, which can be explored further for their role in C and N cycling for sustainable agriculture and environment management.

Biological control of postharvest diseases of apples, peaches and nectarines by Bacillus subtilis S16 isolated from halophytes rhizosphere

Penicillium expansum, Botrytis cinerea and Colletotrichum acutatum are the most common postharvest pathogens of apples, peaches and nectarines. In this study, 96 bacteria were isolated from halophytes rhizosphere and assayed for biocontrol activity under in vitro conditions. Among the 96 isolates tested, isolate S16 effectively inhibited the growth of P. expansum, B. cinerea and C. acutatum. The isolate S16 has reduced 78.33±1.53 to 82.98±2.13% of disease severity in apples, peaches and nectarines. Matrix-assisted laser desorption ionisation-time of flight mass spectrometry of the antifungal compounds revealed three lipopeptide complexes, namely surfactins, iturins and fengycins. Lipopeptides and hydrolytic enzymes produced by the isolate S16 play an important role in the antifungal activity. Polymerase chain reaction analysis using ituD, srfAD, fenD and fenE gene-specific primers showed that the isolate S16 carry sequences similar to ituD, srfAD, fenD and fenE genes. Based on the 16S rDNA sequencing, the effective isolate S16 was identified as Bacillus subtilis.