Isolation and molecular characterization ofFrankiastrains resistant to some heavy metals

Significance of nitrogen-fixing actinorhizal symbioses for restoration of depleted, degraded, and contaminated soil

Atmospheric nitrogen (N2)-fixing legume trees are frequently used for the restoration of depleted, degraded, and contaminated soils. However, biological N2 fixation (BNF) can also be performed by so-called actinorhizal plants. Actinorhizal plants include a high diversity of woody species and therefore can be applied in a broad spectrum of environments. In contrast to N2-fixing legumes, the potential of actinorhizal plants for soil restoration remains largely unexplored. In this Opinion, we propose related basic research requirements for the characterization of environmental stress responses that determine the restoration potential of actinorhizal plants for depleted, degraded, and contaminated soils. We identify advantages and unexplored processes of actinorhizal plants and describe a mainly uncharted avenue of future research for this important group of plant species.

Complete genome of Nakamurella sp. PAMC28650: genomic insights into its environmental adaptation and biotechnological potential

The mechanisms underlying the survival of bacteria in low temperature and high radiation are not yet fully understood. Nakamurella sp. PAMC28650 was isolated from a glacier of Rwenzori Mountain, Uganda, which species belonged to Nakamurella genus based on 16S rRNA phylogeny, ANI (average nucleotide identity), and BLAST Ring Image Generator (BRIG) analysis among Frankineae suborder. We conducted the whole genome sequencing and comparative genomics of Nakamurella sp. PAMC28650, to understand the genomic features pertaining to survival in cold environment, along with high UV (ultraviolet) radiation. This study highlights the role of polysaccharide in cold adaptation, mining of the UV protection-related secondary metabolites and other related to cold adaptation mechanism through different bioinformatics tools, and providing a brief overview of the genes present in DNA repair systems. Nakamurella sp. PAMC28650 contained glycogen and cellulose metabolism pathways, mycosporine-like amino acids and isorenieratene-synthesizing gene cluster, and a number of DNA repair systems. Also, the genome analysis showed osmoregulation-related genes and cold shock proteins. We infer these genomic features are linked to bacterial survival in cold and UV radiation.

The effects of biochar aging on rhizosphere microbial communities in cadmium-contaminated acid soil

Biochars are widely used in the remediation of Cd-contaminated soils. However, changes in the bacterial communities in the rhizosphere contaminated with Cd in response to biochar aging are poorly studied. Addressing this gap in knowledge is important to improving micro-ecological services on healthy growth of plants with mitigation strategies against Cd contamination. An aging experiment (270 days) was conducted with biochars derived from poultry litter and sugar-gum wood added to a Cd-contaminated acid soil. Bacterial communities in the rhizosphere of Brassica rapa and bulk soils were investigated after 1, 90 and 270 days of biochar aging. There was no significant difference (P > 0.05) in bacterial Shannon and Simpson indices between the control and biochar treatments. However, compared to the no-Cd control, the addition of Cd decreased the relative abundances of Firmicutes, Chloroflexi and Acidobacteriota but increased those of Actinobacteriota and Proteobacteria. Poultry-litter biochar had the largest effect on bacterial community composition, especially in the rhizosphere. Aging of poultry-litter biochar increased the abundance of Armatimonadota over time more than the sugar-gum-wood biochar, which was attributed to a lower pH and higher bioavailability of Cd in the sugar-gum-wood biochar treatment. The addition of poultry-litter biochar to the contaminated soil mitigated the bioaccumulation of Cd by increasing soil pH and restoring soil bacterial ecology in contaminated acid soils over time.

Paradigms of actinorhizal symbiosis under the regime of global climatic changes: New insights and perspectives

Nitrogen occurs as inert and inaccessible dinitrogen gaseous form (N₂ ) in the atmosphere. Biological nitrogen fixation is a chief process that makes this dinitrogen (N₂ ) accessible and bioavailable in the form of ammonium (NH₄ ⁺ ) ions. The key organisms to fix nitrogen are certain prokaryotes, called diazotrophs either in the free-living form or establishing significant mutual relationships with a variety of plants. On such examples is ~95-100 MY old incomparable symbiosis between dicotyledonous trees and a unique actinobacterial diazotroph in diverse ecosystems. In this association, the root of the certain dicotyledonous tree (~25 genera and 225 species) belonging to three different taxonomic orders, Fagales, Cucurbitales, and Rosales (FaCuRo) known as actinorhizal trees can host a diazotroph, Frankia of order Frankiales. Frankia is gram-positive, branched, filamentous, sporulating, and free-living soil actinobacterium. It resides in the specialized, multilobed, and coralloid organs (lateral roots but without caps), the root nodules of actinorhizal tress. This review aims to provide systematic information on the distribution and the phylogenetic diversity of hosts from FaCuRo and their micro-endosymbionts (Frankia spp.), colonization mechanisms, and signaling pathways. We also aim to provide details on developmental and physiological imperatives for gene regulation and functional genomics of symbiosis, phenomenal restoration ecology, influences of contemporary global climatic changes, and anthropogenic impacts on plant-Frankia interactions for the functioning of ecosystems and the biosphere.

Frankobactin Metallophores Produced by Nitrogen-Fixing Frankia Actinobacteria Function in Toxic Metal Sequestration

A series of new metallophores, referred to as frankobactins, were extracted from cultures of the symbiotic and nitrogen-fixing actinobacterium Frankia sp. CH37. Structure elucidation revealed a 2-hydroxyphenyl-substituted oxazoline core and a chain composed of five proteinogenic and nonproteinogenic amino acids, suggesting nonribosomal peptide synthesis as the biosynthetic origin. By whole-genome sequencing, bioinformatic analysis, and comparison with other Frankia strains, the genetic locus responsible for the biosynthesis was detected. Spectrophotometric titration of frankobactin with Fe(III) and Cu(II) and mass spectrometry established the 1:1 (metal:frankobactin) coordination. Uptake experiments suggested that frankobactin A₁ (1) did not serve to recruit iron, but to detoxify Cu(II). As frankobactin A₁ prevents the cellular entry of Cu(II), it could play a crucial role in the symbiosis of Frankia sp. and its host in the reclamation of copper-contaminated soil.

Metallophore profiling of nitrogen-fixingFrankiaspp. to understand metal management in the rhizosphere of actinorhizal plants

Frankiaspp. are widespread nitrogen-fixing and metallophore releasing soil bacteria, which often live in symbiosis with a broad spectrum of hosts.