Azospirillum spp. from Plant Growth-Promoting Bacteria to Their Use in Bioremediation.

Xenobiotic contamination, a worldwide environmental concern, poses risks for humans, animals, microbe health, and agriculture. Hydrocarbons and heavy metals top the list of toxins that represent a risk to nature. This review deals with the study of Azospirillum sp., widely reported as plant growth-promoting bacteria in various cultures. However, its adaptation properties in adverse environments make it a good candidate for studying remediation processes in environments polluted with hydrocarbons and heavy metals. This review includes studies that address its properties as a plant growth promoter, its genomics, and that evaluate its potential use in the remediation of hydrocarbons and heavy metals.

Candidatus Frankia Datiscae Dg1, the Actinobacterial Microsymbiont of Datisca glomerata, Expresses the Canonical nod Genes nodABC in Symbiosis with Its Host Plant.

Frankia strains are nitrogen-fixing soil actinobacteria that can form root symbioses with actinorhizal plants. Phylogenetically, symbiotic frankiae can be divided into three clusters, and this division also corresponds to host specificity groups. The strains of cluster II which form symbioses with actinorhizal Rosales and Cucurbitales, thus displaying a broad host range, show suprisingly low genetic diversity and to date can not be cultured. The genome of the first representative of this cluster, Candidatus Frankia datiscae Dg1 (Dg1), a microsymbiont of Datisca glomerata, was recently sequenced. A phylogenetic analysis of 50 different housekeeping genes of Dg1 and three published Frankia genomes showed that cluster II is basal among the symbiotic Frankia clusters. Detailed analysis showed that nodules of D. glomerata, independent of the origin of the inoculum, contain several closely related cluster II Frankia operational taxonomic units. Actinorhizal plants and legumes both belong to the nitrogen-fixing plant clade, and bacterial signaling in both groups involves the common symbiotic pathway also used by arbuscular mycorrhizal fungi. However, so far, no molecules resembling rhizobial Nod factors could be isolated from Frankia cultures. Alone among Frankia genomes available to date, the genome of Dg1 contains the canonical nod genes nodA, nodB and nodC known from rhizobia, and these genes are arranged in two operons which are expressed in D. glomerata nodules. Furthermore, Frankia Dg1 nodC was able to partially complement a Rhizobium leguminosarum A34 nodC::Tn5 mutant. Phylogenetic analysis showed that Dg1 Nod proteins are positioned at the root of both α- and ß-rhizobial NodABC proteins. NodA-like acyl transferases were found across the phylum Actinobacteria, but among Proteobacteria only in nodulators. Taken together, our evidence indicates an Actinobacterial origin of rhizobial Nod factors.

Polymerase chain reaction monitoring of transmission of Onchocerca volvulus in two endemic states in Mexico.

To investigate the impact of mass ivermectin treatments in Mexico on Onchocerca volvulus transmission, entomologic surveys were carried out in the two endemic states of Oaxaca and Chiapas. The data suggest that substantial progress towards the goal of elimination has been made. A comparison pre- and post-ivermectin data from a community in Southern Chiapas showed a 97% decrease in seasonal transmission potential, but some level of polymerase chain reaction positivity was still detectable. In other communities from northern Chiapas and Oaxaca where there are no baseline data, there was an absence or near absence of infective flies. Residual transmission was not evenly distributed because differences were seen in the infection and infective rates from different catch points. These findings suggest that while substantial progress towards elimination has been made in Mexico, it may be necessary to modify ivermectin distribution strategies to eliminate transmission in areas where transmission persists.

Cytotoxic, pro-apoptotic, pro-oxidant, and non-genotoxic activities of a novel copper(II) complex against human cervical cancer.

Cisplatin remains one of the most effective current chemotherapeutic agents; however, metal complexes synthesis has increased in order to produce new anti-neoplastic drugs with DNA binding and apoptotic activities in tumor cells and less toxicity for patients. In this study, we evaluated the cytotoxic activity of a novel copper(II) complex (LQM402) against cervical cancer cell lines and found that LQM402 exhibited selective cytotoxicity against HeLa and Ca Ski cells. FITC-annexin assay and DNA fragmentation indicated that apoptosis could be involved in HeLa cell death. Caspase 3/7 and cytochrome c analysis by immunoblotting suggest the intrinsic pathway. LQM402 is a lipid peroxidation inductor according to TBARS production. Additionally, the Ames and micronucleus tests demonstrated non-genotoxic activity for this compound in Salmonella typhimurium and CD1 mice, respectively. Therefore, LQM402 may be a promising and safe anti-cervical cancer compound.

New perspectives on nodule nitrogen assimilation in actinorhizal symbioses.

Nitrogen-fixing root nodules are plant organs specialised for symbiotic transfer of nitrogen and carbon between microsymbiont and host. The organisation of nitrogen assimilation, storage and transport processes is partitioned at the subcellular and tissue levels, in distinctive patterns depending on the symbiotic partners. In this review, recent advances in understanding of actinorhizal nodule nitrogen assimilation are presented. New findings indicate that Frankia within nodules of Datisca glomerata (Presl.) Baill. carries out both primary nitrogen assimilation and biosynthesis of arginine, rather than exporting ammonium. Arginine is a typical storage form of nitrogen in plant tissues, but is a novel nitrogen carrier molecule in root nodule symbioses. Thus Frankia within D. glomerata nodules exhibits considerable metabolic independence. Furthermore, nitrogen reassimilation is likely to take place in the host in the uninfected nodule cortical cells of this root nodule symbiosis, before amino acid export to host sink tissues via the xylem. The role of an augmented pericycle in carbon and nitrogen exchange in root nodules deserves further attention in actinorhizal symbiosis, and further highlights the importance of a comprehensive, structure-function approach to understanding function in root nodules. Moreover, the multiple patterns of compartmentalisation in relation to nitrogen flux within root nodules demonstrate the diversity of possible functional interactions between host and microsymbiont that have evolved in the nitrogen-fixing clade.

Cupriavidus and Burkholderia species associated with agricultural plants that grow in alkaline soils.

The presence of Burkholderia, Cupriavidus, and Ralstonia species in northeastern Mexico was investigated. An analysis of the root surrounding soil from different agricultural plants led to the isolation of Burkholderia and Cupriavidus species but no Ralstonia strains. Most Cupriavidus species were unknown and grouped into two clusters according to ARDRA profiles. The 16S rRNA sequence analysis showed that the Cupriavidus isolates were highly related among them and with different Cupriavidus species with validated names. However, SDS-PAGE profiles were distinct among the different ARDRA profiles and to other Cupriavidus species examined, suggesting new species in the genus. This shows that Cupriavidus is more widely associated with plants than previously appreciated. The BCC isolate was 99% similar to B. cenocepacia by recA sequence analysis. Additionally, most Cupriavidus strains from the two largest groups grew on media containing up to 0.1 mg/ml of copper, 10.0 mg/ml arsenic and 1.0 mg/ml zinc. Burkholderia strains grew on media containing up to 10.0 mg/ml zinc, 5.0 mg/ml arsenic and 0.1 mg/ml copper.