Azospirillum brasilense AbV5/6 encapsulation in dual-crosslinked beads based on cationic starch.

The main challenge of agriculture is feeding the growing population and at the same time providing environmental sustainability. Using Azospirillum brasilense as a biofertilizer has proved to be a promising solution. However, its prevalence in soil has not been efficient due to biotic and abiotic stresses. Thus, to overcome this drawback, we encapsulated the A. brasilense AbV5 and AbV6 strains in a dual-crosslinked bead based on cationic starch. The starch was previously modified with ethylenediamine by an alkylation approach. Then, the beads were obtained by a dripping technique, crosslinking sodium tripolyphosphate with a blend containing starch, cationic starch, and chitosan. The AbV5/6 strains were encapsulated into the hydrogel beads by a swelling diffusion method followed by desiccation. Plants treated with encapsulated AbV5/6 cells showed an increase in the root length by 19 %, shoot fresh weight by 17 %, and the content of chlorophyll b by 71 %. The encapsulation of AbV5/6 strains showed to keep A. brasilense viability for at least 60 days and efficiency to promote maize growth.

MAW point mutation impairs H. Seropedicae RecA ATP hydrolysis and DNA repair without inducing large conformational changes in its structure.

RecA is a multifunctional protein that plays a central role in DNA repair in bacteria. The structural Make ATP Work motif (MAW) is proposed to control the ATPase activity of RecA. In the present work, we report the biochemical activity and structural effects of the L53Q mutation at the MAW motif of the RecA protein from H. seropedicae (HsRecA L53Q). In vitro studies showed that HsRecA L53Q can bind ADP, ATP, and ssDNA, as does wild-type RecA. However, the ATPase and DNA-strand exchange activities were completely lost. In vivo studies showed that the expression of HsRecA L53Q in E. coli recA1 does not change its phenotype when cells were challenged with MMS and UV. Molecular dynamics simulations showed the L53Q point mutation did not cause large conformational changes in the HsRecA structure. However, there is a difference on dynamical cross-correlation movements of the residues involved in contacts within the ATP binding site and regions that hold the DNA binding sites. Additionally, a new hydrogen bond, formed between Q53 and T49, was hypothesized to allow an independent motion of the MAW motif from the hydrophobic core, what could explain the observed loss of activity of HsRecA L53Q.

Structural and Functional Studies of H. seropedicae RecA Protein - Insights into the Polymerization of RecA Protein as Nucleoprotein Filament.

The bacterial RecA protein plays a role in the complex system of DNA damage repair. Here, we report the functional and structural characterization of the Herbaspirillum seropedicae RecA protein (HsRecA). HsRecA protein is more efficient at displacing SSB protein from ssDNA than Escherichia coli RecA protein. HsRecA also promotes DNA strand exchange more efficiently. The three dimensional structure of HsRecA-ADP/ATP complex has been solved to 1.7 Å resolution. HsRecA protein contains a small N-terminal domain, a central core ATPase domain and a large C-terminal domain, that are similar to homologous bacterial RecA proteins. Comparative structural analysis showed that the N-terminal polymerization motif of archaeal and eukaryotic RecA family proteins are also present in bacterial RecAs. Reconstruction of electrostatic potential from the hexameric structure of HsRecA-ADP/ATP revealed a high positive charge along the inner side, where ssDNA is bound inside the filament. The properties of this surface may explain the greater capacity of HsRecA protein to bind ssDNA, forming a contiguous nucleoprotein filament, displace SSB and promote DNA exchange relative to EcRecA. Our functional and structural analyses provide insight into the molecular mechanisms of polymerization of bacterial RecA as a helical nucleoprotein filament.