Search Results (16)

Salinization hinders the restoration of vegetation in salt-affected soils by negatively impacting plant growth and development. Halophytes play a key role in the restoration of saline and degraded lands due to unique features explaining their growth aptitude in such extreme ecosystems. Suaeda fruticosa is an euhalophyte well known for its medicinal properties and its potential for saline soil phytoremediation. However, excessive salt accumulation in soil limits the development of this species. Research findings increasingly advocate the use of extremophile rhizosphere bacteria as an effective approach to reclaim salinized soils, in conjunction with their salt-alleviating effect on plants. Here, a pot experiment was conducted to assess the role of a halotolerant plant growth-promoting actinobacterium, Glutamicibacter sp., on the growth, nutritional status, and shoot content of proline, total soluble carbohydrates, and phenolic compounds in the halophyte S. fruticosa grown for 60 d under high salinity (600 mM NaCl). Results showed that inoculation with Glutamicibacter sp. significantly promoted the growth of inoculated plants under stress conditions. More specifically, bacterial inoculation increased the shoot concentration of proline, total polyphenols, potassium (K⁺), nitrogen (N), and K⁺/Na⁺ ratio in shoots, while significantly decreasing Na⁺ concentrations. These mechanisms partly explain S. fruticosa tolerance to high saline concentrations. Our findings provide some mechanistic elements at the ecophysiological level, enabling a better understanding of the crucial role of plant growth-promoting rhizobacteria (PGPRs) in enhancing halophyte growth and highlight their potential for utilization in restoring vegetation in salt-affected soils. Full article

The Namib Desert is characterized by a number of abiotic stresses, including high temperature, high salinity, osmotic pressure, alkaline pH, and limited water availability. In such environments, dry soils typically exhibit a low water potential, scarce nutrients, and high concentrations of dissolved ions, collectively creating a challenging habitat for microbial life. In this study, 89 bacterial isolates belonging to 20 genera were identified. Bacteria demonstrated significant osmotolerance, with some strains thriving at polyethylene glycol (PEG) concentrations exceeding 20%. Furthermore, these bacteria demonstrated halotolerance, high pH tolerance, and capacity to produce plant growth-promoting (PGP) traits under conditions of osmotic stress. Osmotolerant bacteria exhibited higher proficiency in siderophore production, potassium solubilization, and phosphorus solubilization, all of which are critical for supporting plant growth in nutrient-scarce and stressful environments, such as deserts. However, alginate production was higher in isolates that were less osmotolerant, indicating the potential for a compensatory mechanism in strains that were more sensitive. These findings highlight the complex strategies employed by desert bacteria to survive and support host plants in extreme environments. The present study not only enhances our understanding of microbial adaptations in arid ecosystems, but also provides important information for the development of potential applications for these bacteria in the reclamation of arid land and agricultural practices aimed at improving crop resilience to abiotic stress. Full article

Deschampsia antarctica and Colobantus quitensis are the only two vascular plants colonized on the Antarctic continent, which is usually exposed to extreme environments. Endophytic bacteria residing within plant tissues can exhibit diverse adaptations that contribute to their ecological success and potential benefits for their plant hosts. This study aimed to characterize 12 endophytic bacterial strains isolated from these plants, focusing on their ecological adaptations and functional roles like plant growth promotion, antifungal activities, tolerance to salt and low-carbon environments, wide temperature range, and biofilm formation. Using 16S rRNA sequencing, we identified several strains, including novel species like Hafnia and Agreia. Many strains exhibited nitrogen-fixing ability, phosphate solubilization, ammonia, and IAA production, potentially benefiting their hosts. Additionally, halotolerance and carbon oligotrophy were also shown by studied bacteria. While some Antarctic bacteria remain strictly psychrophilic, others demonstrate a remarkable ability to tolerate a wider range of temperatures, suggesting that they have acquired mechanisms to cope with fluctuations in environmental temperature and developed adaptations to survive in intermediate hosts like mammals and/or birds. Such adaptations and high plasticity of metabolism of Antarctic endophytic bacteria provide a foundation for research and development of new promising products or mechanisms for use in agriculture and technology. Full article

Salinity constitutes a major abiotic factor that negatively affects crop productivity. Inoculation with plant growth-promoting bacteria (PGPB) is proven to increase plant tolerance to abiotic stresses and enhance plant growth, development and productivity. The present study aims to increase the resilience of crops to salinity using bacteria from the microbiome of plants growing in saline environments. For that, the halotolerance of bacteria present in the roots of natural plants growing on Sal Island, which is characterized by its arid environment and maritime influence, was determined, with some strains having extreme halotolerance. Their ability to produce plant growth-promoting traits was evaluated, with most strains increasing indole acetic acid (26–418%), siderophore (>300%) and alginate (2–66%) production and phosphate solubilization (13–100%) under salt stress. The strains evidencing the best performance were inoculated in maize (Zea mays L.) plants and their influence on plant growth and biochemical status was evaluated. Results evidenced bacterial ability to especially increase proline (55–191%), whose osmotic, antioxidant and protein-protecting properties reduced protein damage in salt-stressed maize plants, evidencing the potential of PGPB to reduce the impact of salinity on crops. Enhanced nutrition, phytohormone production and osmolyte synthesis along with antioxidant response all contribute to increasing plant tolerance to salt stress. Full article

Halophilic/halotolerant myxobacteria are extremely rare bacteria but an important source of novel bioactive secondary metabolites as drug leads. A slightly halophilic myxobacterium, “Paraliomyxa miuraensis” SMH-27-4, the producer of the antifungal antibiotic miuraenamide A, was considered to represent a novel genus. This study aimed to use the whole-genome sequence of this difficult-to-culture bacterium to provide genomic evidence supporting its taxonomy and to explore its potential as a novel secondary metabolite producer and its predicted gene functions. The draft genome was sequenced and de novo assembled into 164 contigs (11.8 Mbp). The 16S rRNA gene sequence-based and genome sequence-based phylogenetic analyses supported that this strain represents a novel genus of the family Nannocystaceae. Seventeen biosynthetic gene clusters (BGCs) were identified, and only five of them show some degree of similarity with the previously annotated BGCs, suggesting the great potential of producing novel secondary metabolites. The comparative genomic analysis within the family Nannocystaceae revealed the distribution of its members’ gene functions. This study unveiled the novel genomic features and potential of the secondary metabolite production of this myxobacterium. Full article

Soil salinity is a condition that limits crop growth and productivity, and soil-dwelling bacteria from halophytic plant roots may be a viable strategy to cope with low productivity due to salt stress. Halophilic and halotolerant bacteria of the root soil of Sesuvium verrucosum were analyzed in this study as there is little evidence regarding its associated microbiology. Soil was sampled from the roots of Sesuvium verrucosum to obtain the cultivable bacteria. Their morphological characteristics were identified and they were molecularly identified by the 16S sequence. The growth capacity of the bacteria was determined at different levels of pH and salinity, and several growth promotion characteristics were identified, such as phosphorus solubilization, indole acetic acid production by the tryptophan-dependent (AIAt) and tryptophan-independent (IAA) pathways, ammonium production from organic sources, solubilization of carbonates, and zinc and sodium capture capacity. In addition, the bacteria that presented the best characteristics for germination variables of Solanum lycopersicum were evaluated. A total of 20 bacteria from root soil of Sesuvium verrucosum Raf. belonging to the phyla Proteobacteria (50%), Firmicutes (45%) and Actinobacteria (5%) were identified, with each one having different morphological characteristics. Among the bacterial isolates, 45% had the ability to resist different levels of salinity and pH, ranging from 0 to 20% of NaCl, and pH between 5 and 11. Moreover, these bacteria had the capacity to solubilize carbonates, phosphorus and zinc, capture sodium, produce ammonium from organic substrates and IAA (indole acetic acid), and promote enzymatic activity of amylases, proteases, lipases and cellulases. The bacteria evaluated on the germination of Solanum lycopersicum had an influence on germination at different salinity levels, with greater influence at 100 mM NaCl. This demonstrated that halophilic bacteria belonging to the rhizosphere of Sesuvium verrucosum have the ability to promote growth in extreme salinity conditions, making them candidates for the recovery of productivity in saline soils. Full article

During a prokaryotic diversity study in Añana Salt Valley, a new Rhodobacteraceae member, designated ASV31^T, was isolated from Santa Engracia spring water. It was extremely halotolerant, tolerating up to 23% NaCl, and facultatively alkaliphilic, growing at pH 6.5–9.5 (optimum at 7.0–9.5). The isolate was a Gram-negative, rod-shaped, aerobic and non-motile bacterium that formed beige-to-pink colonies on marine agar. According to a 16S rRNA gene-based phylogenetic analysis, strain ASV31^T forms a distinct branch of the family Rhodobacteraceae, with Thioclava pacifica DSM 10166^T being its closest type strain (95.3%). This was confirmed with a phylogenomic tree and the values of ANI (73.9%), dDDH (19.3%), AAI (63.5%) and POCP (56.0%), which were below the genus/species level boundary. Additionally, an ability to degrade aromatic compounds and biosynthesise secondary metabolites was suggested by the genome of strain ASV31^T. Distinguishing fatty acid profiles and polar lipid content were also observed. The genome size was 3.6 Mbp, with a DNA G+C content of 65.7%. Based on the data obtained, it was considered that strain ASV31^T (=CECT 30309^T = LMG 32242^T) represents a new species of a new genus in the family Rhodobacteraceae, for which the name Anianabacter salinae gen. nov., sp. nov. is proposed. Full article

The evaporation of a localized, highly saline water body of the Boulder Clay debris-covered glacier, in the Northern Victoria Land, probably generated the accumulation of mirabilite (Na₂SO₄ × 10H₂O) and thenardite (Na₂SO₄) in a glacier salt-cone. Such an extremely cold and salty environment resembles the conditions on Mars, so it can be considered a terrestrial analog. The study was aimed at gaining a first glimpse at the prokaryotic community associated with Antarctic mirabilite and thenardite minerals and also to find clues about the origin of the salts. For this purpose, samples were analyzed by a next generation approach to investigate the prokaryotic (Bacteria and Archaea) diversity. Phylogenetic analysis allowed the identification of Bacteroidota, Actinobacteriota, Firmicutes, and Gammaproteobacteria as the main bacterial lineages, in addition to Archaea in the phylum Halobacterota. The genera Arthrobacter, Rhodoglobus, Gillisia, Marinobacter and Psychrobacter were particularly abundant. Interestingly, several bacterial and archaeal sequences were related to halotolerant and halophilic genera, previously reported in a variety of marine environments and saline habitats, also in Antarctica. The analyzed salt community also included members that are believed to play a major role in the sulfur cycle. Full article

Halotolerant bacteria with biosurfactant (BS) and bioemulsifiers (BE) activity can coexist in Karstic sinkholes with marine influence. Two sinkholes in the Yucatan peninsula were selected to isolate bacteria with BE and BS activity stable in NaCl. The optimal time, the effect of nitrogen and carbon source in the medium, and the conditions (agitation, pH and salinity) for the production of BS and BE compounds in planktonic and sessile (stimulate the formation of biofilms in cell roller) culture were determined. Eighty strains showed the highest emulsification activity (EI₂₄ ≥ 50%) and drop-collapse ≥ 4 mm. 87% of the strains are moderately halotolerant, and 21% bordered the limit of extreme halotolerance. Twenty-four strains maintained or improved their BS and BE activity under salinity conditions at 5% and 10%, being the most active genera Bacillus, Paenibacillus and Lysinibacillus, identified by sequencing of the 16S rRNA gene. The results show that the nitrogen source positively affects the BS and BE activity, regardless of the type of culture. The sessile culture markedly stimulated BS activity with significant differences. However, we did not find a greater influence on the culture conditions. The results suggest that halotolerant bacteria from sinkholes could be implemented in bioremediation and other biotechnological applications. Full article

Halophytes play a crucial ecological role in drought and saline–alkali environments. However, there is limited knowledge about the structure of bacterial communities and the potential microbial coexistence mechanism associated with halophytes. This study investigated the diversity and community structure of endophytic and rhizospheric bacteria associated with three halophytes by applying high-throughput sequencing and geochemistry analyses on the studied soils. We collected 18 plant and 21 soil samples, and sequenced the V3 and V4 hypervariable regions of the 16S rRNA gene using next-generation sequencing (NGS). We also assessed geochemistry of the studied soils. The research suggested that rhizospheric bacterial richness and diversity associated with three halophytes were all significantly higher than for endophytic bacteria. The microbial community analysis indicated that Actinobacteria, Firmicutes, Bacteroidetes and Proteobacteria were the dominating bacterial phyla. Most unassigned operational taxonomic units (OTUs) implied that the microbes associated with halophytes contained abundant potential novel taxa, which are significant microbial resources. The high-abundance OTU phylogenetic tree supported the above views as well. Additionally, network analysis indicated that some conditional rare taxa (CRT) also might be keystone taxa during halophyte microbial community construction. The results of non-metric multidimensional scaling (NMDS) ordination analysis indicated significant dissimilarities in the microbial community among different sample groups. Sixty-two biomarkers were detected from seven different sample groups by linear discriminant analysis effect size (LEFSe) analysis. Microbial functions predicted based on phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt2) demonstrated that the abundances of nitrogen metabolism genes of endophytic bacteria were significantly higher than in rhizobacteria. Environmental factor analysis confirmed that different soil properties have different degrees of influence on the abundance and composition of the microbiota. To better adapt to the extreme hypersaline environment, halophytes could specifically recruit some plant beneficial bacterial taxa, such as nitrogen-fixing bacteria and extremely halophilic or halotolerant bacteria, to help them robustly grow and proliferate. All our preliminary results highlight microbial diversity and community related to halophytes grown on saline–alkali land of arid areas. Simultaneously, this work also advanced our further understanding of the halophyte microbiome associated with plants, and their role in plant adaptation to the extremely hypersaline environment. Full article

The adaptation to adverse environmental conditions can lead to adapted microbial communities that may be screened for mechanisms involved in halophily and, in this case, metal tolerance. At a former uranium mining and milling site in Seelingstädt, Germany, microbial communities from surface waters and sediment soils were screened for isolates surviving high salt and metal concentrations. The high salt contents consisted mainly of chloride and sulfate, both in soil and riverbed sediment samples, accompanied by high metal loads with presence of cesium and strontium. The community structure was dominated by Chloroflexi, Proteobacteria and Acidobacteriota, while only at the highest contaminations did Firmicutes and Desulfobacterota reach appreciable percentages in the DNA-based community analysis. The extreme conditions providing high stress were mirrored by low numbers of cultivable strains. Thirty-four extremely halotolerant bacteria (23 Bacillus sp. and another 4 Bacillales, 5 Actinobacteria, and 1 Gamma-Proteobacterium) surviving 25 to 100 mM SrCl₂, CsCl, and Cs₂SO₄ were further analyzed. Mineral formation of strontium- or cesium-struvite could be observed, reducing bioavailability and thereby constituting the dominant metal and salt resistance strategy in this environment. Full article

Actinobacteria belonging to the genus Rubrobacter are known for their multi-extremophilic growth conditions—they are highly radiation-resistant, halotolerant, thermotolerant or even thermophilic. This work demonstrates that the members of the genus are capable of accumulating polyhydroxyalkanoates (PHA) since PHA-related genes are widely distributed among Rubrobacter spp. whose complete genome sequences are available in public databases. Interestingly, all Rubrobacter strains possess both class I and class III synthases (PhaC). We have experimentally investigated the PHA accumulation in two thermophilic species, R. xylanophilus and R. spartanus. The PHA content in both strains reached up to 50% of the cell dry mass, both bacteria were able to accumulate PHA consisting of 3-hydroxybutyrate and 3-hydroxyvalerate monomeric units, none other monomers were incorporated into the polymer chain. The capability of PHA accumulation likely contributes to the multi-extremophilic characteristics since it is known that PHA substantially enhances the stress robustness of bacteria. Hence, PHA can be considered as extremolytes enabling adaptation to extreme conditions. Furthermore, due to the high PHA content in biomass, a wide range of utilizable substrates, Gram-stain positivity, and thermophilic features, the Rubrobacter species, in particular Rubrobacter xylanophilus, could be also interesting candidates for industrial production of PHA within the concept of Next-Generation Industrial Biotechnology. Full article

Poly(3-hydroxybutyrate) (PHB) is a natural and biodegradable storage polyester, produced by numerous bacteria, which is considered a potential substituent for conventional plastics in the packaging industry. The improvement of the PHB material lifetime often involves mechanical and tribological characterization, which can be accurately performed on thin films. In this study, we aimed at the evaluation of the tribological properties, such as adhesion force, friction coefficient and wear resistance, of different polyester films, fabricated via the solvent casting method. Three polyester films were designed in this study, each containing 1% w/v constituents as follows: a PHBh film prepared out of the PHB, extracted from the extremely halotolerant bacteria, Halomonas elongata DSM2581^T, a PHBc film fabricated using a commercially available PHB, and a PHBVc film generated using the commercial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). The spectroscopy-in-point of AFM was used for adhesion force measurement based on multiple tests performed in a matrix, and the AFM lateral operating mode was applied for friction analysis under a controlled normal load. The fabricated PHBh film presented a thickness between 5 and 7 µm, a lower adhesion force (14 nN) as well as a smaller friction coefficient (0.15) compared to the PHBc and PHBVc. The tribological investigations of PHBh film revealed a biodegradable material with low roughness, as well as small adhesion and friction forces. Further optimization can be performed for the improvement of the PHBh film by copolymerization with other polymers, polyesters, and reinforcers, thus generating a feasible material with advanced tribo-mechanical features. Full article

Halophilic and halotolerant microorganisms represent promising sources of salt-tolerant enzymes that could be used in various biotechnological processes where high salt concentrations would otherwise inhibit enzymatic transformations. Considering the current need for more efficient biocatalysts, the present study aimed to explore the microbial diversity of five under- or uninvestigated salty lakes in Romania for novel sources of hydrolytic enzymes. Bacteria, archaea and fungi were obtained by culture-based approaches and screened for the production of six hydrolases (protease, lipase, amylase, cellulase, xylanase and pectinase) using agar plate-based assays. Moreover, the phylogeny of bacterial and archaeal isolates was studied through molecular methods. From a total of 244 microbial isolates, 182 (74.6%) were represented by bacteria, 22 (9%) by archaea, and 40 (16.4%) by fungi. While most bacteria synthesized protease and lipase, the most frequent hydrolase produced by fungi was pectinase. The archaeal isolates had limited hydrolytic activity, being able to produce only amylase and cellulase. Among the taxonomically identified isolates, the best hydrolytic activities were observed in halotolerant bacteria belonging to the genus Bacillus and in extremely halophilic archaea of the genera Haloterrigena and Halostagnicola. Therefore, the present study highlights that the investigated lakes harbor various promising species of microorganisms able to produce industrially valuable enzymes. Full article

The study of bacterial communities associated with extreme ecosystems is one of the most important tasks in modern microbial ecology. Despite a large number of studies being performed, the ecosystems that have not been sufficiently explored from the microbiological point of view still exist. Such research is needed for improving the understanding of the limits and mechanisms of bacterial survival under extreme conditions, and for revealing previously undescribed species and their role in global biospheric processes and their functional specifics. The results of the complex microbiological characteristics of permafrost and ice—collected on the Severniy Island in the northern part of the Novaya Zemlya archipelago—which have not previously been described from microbiological point of view, are presented in this article. The analysis included both culture-independent and culture-dependent methods, in particular, the spectra of metabolic activity range analysis in vitro under different temperature, pH and salinity conditions. High values for the total number of prokaryotes in situ (1.9 × 10⁸–3.5 × 10⁸ cells/g), a significant part of which was able to return to a metabolically active state after thawing, and moderate numbers of culturable bacteria (3.3 × 10⁶–7.8 × 10⁷ CFU/g) were revealed. Representatives of Proteobacteria, Actinobacteria, and Bacteroidetes were dominant in situ; Actinobacteria, Firmicutes, Proteobacteria, and Bacteroidetes were the most abundant phyla in vitro. Physiological assays revealed the mesophilic and neutrophilic optima of temperature and pH of culturing conditions, respectively, and wide temperature and pH ranges of culturable communities’ reproduction activity. Isolated strains were characterized by moderate halotolerant properties and antibiotic resistance, including multiple antibiotic resistance. It was found that almost all cultured bacterial diversity revealed (not just a few resistant species) had extremotolerant properties regarding a number of stress factors. This indicates the high adaptive potential of the studied microbial communities and their high sustainability and capability to retain functional activity under changing environmental (including climatic) conditions in wide ranges. Full article