A widely distributed hydrogenase oxidises atmospheric H2 during bacterial growth

Diverse aerobic bacteria persist by consuming atmospheric hydrogen (H₂) using group 1h [NiFe]-hydrogenases. However, other hydrogenase classes are also distributed in aerobes, including the group 2a [NiFe]-hydrogenase. Based on studies focused on Cyanobacteria, the reported physiological role of the group 2a [NiFe]-hydrogenase is to recycle H₂ produced by nitrogenase. However, given this hydrogenase is also present in various heterotrophs and lithoautotrophs lacking nitrogenases, it may play a wider role in bacterial metabolism. Here we investigated the role of this enzyme in three species from different phylogenetic lineages and ecological niches: Acidithiobacillus ferrooxidans (phylum Proteobacteria), Chloroflexus aggregans (phylum Chloroflexota), and Gemmatimonas aurantiaca (phylum Gemmatimonadota). qRT-PCR analysis revealed that the group 2a [NiFe]-hydrogenase of all three species is significantly upregulated during exponential growth compared to stationary phase, in contrast to the profile of the persistence-linked group 1h [NiFe]-hydrogenase. Whole-cell biochemical assays confirmed that all three strains aerobically respire H₂ to sub-atmospheric levels, and oxidation rates were much higher during growth. Moreover, the oxidation of H₂ supported mixotrophic growth of the carbon-fixing strains C. aggregans and A. ferrooxidans. Finally, we used phylogenomic analyses to show that this hydrogenase is widely distributed and is encoded by 13 bacterial phyla. These findings challenge the current persistence-centric model of the physiological role of atmospheric H₂ oxidation and extend this process to two more phyla, Proteobacteria and Gemmatimonadota. In turn, these findings have broader relevance for understanding how bacteria conserve energy in different environments and control the biogeochemical cycling of atmospheric trace gases.Subject terms: Environmental microbiology, Biogeochemistry     

Investigation of synergistic action between coronatine and nitric oxide in alleviating arsenic-induced toxicity in sweet basil seedlings

The phytotoxin coronatine (COR) is a jasmonic acid mimic produced by several pathovars of plant pathogen. In this study, we evaluated the protective effect of COR and nitric oxide (NO) against the toxicity of sodium arsenate in sweet basil (Ocimum basilicum L.). According to the statistical analysis, arsenic had a significant adverse effect on length and biomass of plants. Seedlings that pretreated with COR and sodium nitroprusside (SNP), significantly reversed fresh and dry lose and relative water content decay induced by the metalloid. The protective effects of COR and SNP were indicated by extent of lipid peroxidation, increase glutathione (GSH), ascorbate and thiol (–SH) content, promote antioxidant enzymes and reduce H₂O₂ content in basil seedlings. The present observation suggested that reduction of excess arsenic As-induced toxicity in O. basilicum by COR and NO is through the activation of enzymes involved in ROS detoxification (CAT, SOD, POD, APX, GR) and maintenance contents of molecular antioxidant (GSH, ascorbate, non-protein thiol and protein-thiol). Moreover, the results revealed a mutually amplifying reaction between COR and NO in reducing As-induced damages.     

Genetically engineered phage harbouring the lethal catabolite gene activator protein gene with an inducer-independent promoter for biocontrol of Escherichia coli

Complications of chemotherapy, such as appearance of multidrug resistance, have persuaded researchers to consider phage therapy as a new method to combat bacterial infections. In vitro experiments were performed to assess the therapeutic value of genetically modified phages for controlling gastrointestinal Escherichia coli O157:H7 cells in Luria–Bertani (LB) media and contaminated cow milk. We constructed a modified nonreplicating M13-derived phage expressing a lethal catabolite gene activator protein (CAP) that is a Glu181Gln mutant of CAP. The modified phagemid was propagated in the lethal CAP-resistant strain XA3DII. Time–kill assay experiments showed a considerable reduction in the number of surviving bacteria in both LB media and contaminated cow milk. Our further study using other test strains demonstrated that the host range of lethal phage is limited to E. coli strains that produce pili. This study provides a possible strategy for the exploitation of genetically engineered nonlytic phages as bactericidal agents by minimizing the risk of release of progeny phages and endotoxins into the environment. The phage was engineered to remain lethal to its bacterial target, but incapable of replicating therein. Furthermore, the addition of an inducer to express the lethal protein is not required.     

Spell Checking Nature: Versatility of CRISPR/Cas9 for Developing Treatments for Inherited Disorders

Clustered regularly interspaced short palindromic repeat (CRISPR) has arisen as a frontrunner for efficient genome engineering. However, the potentially broad therapeutic implications are largely unexplored. Here, to investigate the therapeutic potential of CRISPR/Cas9 in a diverse set of genetic disorders, we establish a pipeline that uses readily obtainable cells from affected individuals. We show that an adapted version of CRISPR/Cas9 increases the amount of utrophin, a known disease modifier in Duchenne muscular dystrophy (DMD). Furthermore, we demonstrate preferential elimination of the dominant-negative FGFR3 c.1138G>A allele in fibroblasts of an individual affected by achondroplasia. Using a previously undescribed approach involving single guide RNA, we successfully removed large genome rearrangement in primary cells of an individual with an X chromosome duplication including MECP2. Moreover, removal of a duplication of DMD exons 18–30 in myotubes of an individual affected by DMD produced full-length dystrophin. Our findings establish the far-reaching therapeutic utility of CRISPR/Cas9, which can be tailored to target numerous inherited disorders.