Pseudochrobactrum asaccharolyticum mitigates arsenic induced oxidative stress of maize plant by enhancing water status and antioxidant defense system.

BACKGROUND: Oxidative stress mediated by reactive oxygen species (ROS) is a common denominator in arsenic toxicity. Arsenic stress in soil affects the water absorption, decrease stomatal conductance, reduction in osmotic, and leaf water potential, which restrict water uptake and osmotic stress in plants. Arsenic-induced osmotic stress triggers the overproduction of ROS, which causes a number of germination, physiological, biochemical, and antioxidant alterations. Antioxidants with potential to reduce ROS levels ameliorate the arsenic-induced lesions. Plant growth promoting rhizobacteria (PGPR) increase the total soluble sugars and proline, which scavenging OH radicals thereby prevent the oxidative damages cause by ROS. The main objective of this study was to evaluate the potential role of Arsenic resistant PGPR in growth of maize by mitigating arsenic stress. METHODOLOGY: Arsenic tolerant PGPR strain MD3 (Pseudochrobactrum asaccharolyticum) was used to dismiss the 'As' induced oxidative stress in maize grown at concentrations of 50 and 100 mg/kg. Previously isolated arsenic tolerant bacterial strain MD3 "Pseudochrobactrum asaccharolyticum was used for this experiment. Further, growth promoting potential of MD3 was done by germination and physio-biochemical analysis of maize seeds. Experimental units were arranged in Completely Randomized Design (CRD). A total of 6 sets of treatments viz., control, arsenic treated (50 & 100 mg/kg), bacterial inoculated (MD3), and arsenic stress plus bacterial inoculated with three replicates were used for Petri plates and pot experiments. After treating with this MD3 strain, seeds of corn were grown in pots filled with or without 50 mg/kg and 100 mg/kg sodium arsenate. RESULTS: The plants under arsenic stress (100 mg/kg) decreased the osmotic potential (0.8 MPa) as compared to control indicated the osmotic stress, which caused the reduction in growth, physiological parameters, proline accumulation, alteration in antioxidant enzymes (Superoxide dismutase-SOD, catalase-CAT, peroxidase-POD), increased MDA content, and H2O2 in maize plants. As-tolerant Pseudochrobactrum asaccharolyticum improved the plant growth by reducing the oxidation stress and antioxidant enzymes by proline accumulation. PCA analysis revealed that all six treatments scattered differently across the PC1 and PC2, having 85.51% and 9.72% data variance, respectively. This indicating the efficiency of As-tolerant strains. The heatmap supported the As-tolerant strains were positively correlated with growth parameters and physiological activities of the maize plants. CONCLUSION: This study concluded that Pseudochrobactrum asaccharolyticum reduced the 'As' toxicity in maize plant through the augmentation of the antioxidant defense system. Thus, MD3 (Pseudochrobactrum asaccharolyticum) strain can be considered as bio-fertilizer.

New insights into aniline toxicity: Aniline exposure triggers envelope stress and extracellular polymeric substance formation in Rubrivivax benzoatilyticus JA2.

Aniline is a major environmental pollutant of serious concern due to its toxicity. Although microbial metabolism of aniline is well-studied, its toxic effects and physiological responses of microorganisms to aniline are largely unexplored. Rubrivivax benzoatilyticus JA2, an aniline non-degrading bacterium, tolerates high concentrations of aniline and produces extracellular polymeric substance(EPS). Surprisingly, strain JA2 forms EPS only when exposed to aniline and other toxic compounds like organic solvents and heavy metals indicating that EPS formation is coupled to cell toxicity. Further, extensive reanalysis of the previous proteomic data of aniline exposed cells revealed up-regulation of envelope stress response(ESR) proteins such as periplasmic protein folding, envelope integrity, transmembrane complex, and cell-wall remodelling proteins. In silico analysis and molecular modeling of three highly up-regulated proteins revealed that these proteins were homologous to CpxARP proteins of ESR signalling pathway. Furthermore, EPS formation to known ESR activators(Triton-X-100, EDTA) suggests that envelope stress possibly regulating the EPS production. The present study suggests that aniline triggers envelope stress; to counter this strain JA2 activates ESR pathway and EPS production. Our study revealed the hitherto unknown toxic effects of aniline as an acute envelope stressor thus toxicity of aniline may be more profound to life-forms than previously thought.

Silver and Copper Acute Effects on Membrane Proteins and Impact on Photosynthetic and Respiratory Complexes in Bacteria.

Silver (Ag+) and copper (Cu+) ions have been used for centuries in industry, as well as antimicrobial agents in agriculture and health care. Nowadays, Ag+ is also widely used in the field of nanotechnology. Yet, the underlying mechanisms driving toxicity of Ag+ ions in vivo are poorly characterized. It is well known that exposure to excess metal impairs the photosynthetic apparatus of plants and algae. Here, we show that the light-harvesting complex II (LH2) is the primary target of Ag+ and Cu+ exposure in the purple bacterium Rubrivivax gelatinosus Ag+ and Cu+ specifically inactivate the 800-nm absorbing bacteriochlorophyll a (B800), while Ni2+ or Cd2+ treatment had no effect. This was further supported by analyses of CuSO4- or AgNO3-treated membrane proteins. Indeed, this treatment induced changes in the LH2 absorption spectrum related to the disruption of the interaction of B800 molecules with the LH2 protein. This caused the release of B800 molecules and subsequently impacted the spectral properties of the carotenoids within the 850-nm absorbing LH2. Moreover, previous studies have suggested that Ag+ can affect the respiratory chain in mitochondria and bacteria. Our data demonstrated that exposure to Ag+, both in vivo and in vitro, caused a decrease of cytochrome c oxidase and succinate dehydrogenase activities. Ag+ inhibition of these respiratory complexes was also observed in Escherichia coli, but not in Bacillus subtilisIMPORTANCE The use of metal ions represents a serious threat to the environment and to all living organisms because of the acute toxicity of these ions. Nowadays, silver nanoparticles are one of the most widely used nanoparticles in various industrial and health applications. The antimicrobial effect of nanoparticles is in part related to the released Ag+ ions and their ability to interact with bacterial membranes. Here, we identify, both in vitro and in vivo, specific targets of Ag+ ions within the membrane of bacteria. This include complexes involved in photosynthesis, but also complexes involved in respiration.

Comparison of biofilm formation and motility processes in arsenic-resistant Thiomonas spp. strains revealed divergent response to arsenite.

Bacteria of the genus Thiomonas are found ubiquitously in arsenic contaminated waters such as acid mine drainage (AMD), where they contribute to the precipitation and the natural bioremediation of arsenic. In these environments, these bacteria have developed a large range of resistance strategies among which the capacity to form particular biofilm structures. The biofilm formation is one of the most ubiquitous adaptive response observed in prokaryotes to various stresses, such as those induced in the presence of toxic compounds. This study focused on the process of biofilm formation in three Thiomonas strains (CB1, CB2 and CB3) isolated from the same AMD. The results obtained here show that these bacteria are all capable of forming biofilms, but the architecture and the kinetics of formation of these biofilms differ depending on whether arsenite is present in the environment and from one strain to another. Indeed, two strains favoured biofilm formation, whereas one favoured motility in the presence of arsenite. To identify the underlying mechanisms, the patterns of expression of some genes possibly involved in the process of biofilm formation were investigated in Thiomonas sp. CB2 in the presence and absence of arsenite, using a transcriptomic approach (RNA-seq). The findings obtained here shed interesting light on how the formation of biofilms, and the motility processes contribute to the adaptation of Thiomonas strains to extreme environments.