Antioxidant response of a novel Streptomyces sp. M3004 isolated from legume rhizosphere to H2O2 and paraquat

The role of oxidative stress in genome destabilization and adaptive evolution of bacteria

The review is devoted to bacterial genome destabilization by oxidative stress. The article discusses the main groups of substances causing such stress. Stress regulons involved in destabilization of genetic material and mechanisms enhancing mutagenesis, bacterial genome rearrangements, and horizontal gene transfer, induced by oxidative damage to cell components are also considered. Based on the analysis of publications, it can be claimed that rapid development of new food substrates and ecological niches by microorganisms occurs due to acceleration of genetic changes induced by oxidative stress, mediated by several stress regulons (SOS, RpoS and RpoE) and under selective pressure. The authors conclude that non-lethal oxidative stress is probably-one of the fundamental processes that guide evolution of prokaryotes and a powerful universal trigger for adaptive destabilization of bacterial genome under changing environmental conditions.

Strepolyketide D, a new SEK15-derived polyketide compound from salt-lake-derived Streptomyces sp. DBC5

A new SEK15-derived polyketide compound, strepolyketide D (1), was isolated from salt-lake-derived Streptomyces sp. DBC5, together with two known analogues (2-3). Their structures were elucidated based on spectroscopic analysis of IR, MS, 1 D and 2 D NMR. Compound 2 elicited moderate antioxidation with IC₅₀ value of 39.26 μg/ml. The results of the study revealed that salt-lake actinomycetes of Lake Dabancheng appear to have immense potential as a source of polyketide compounds.

Long-chain flavodoxin FldX1 improves Paraburkholderia xenovorans LB400 tolerance to oxidative stress caused by paraquat and H2O2

Flavodoxins are small electron transfer proteins containing flavin mononucleotide (FMN) as a prosthetic group, which play an important role during oxidative stress or iron limitation. The aims of this study were the identification and characterization of flavodoxins in the model aromatic-degrader Paraburkholderia xenovorans LB400 and the analyses of their protective effects during oxidative stress induced by paraquat and H2O2. Two genes (BxeA0278 and BxeB0391) encoding flavodoxins (hereafter referred to as fldX for flavodoxin from P. xenovorans), were identified at the LB400 major and minor chromosome. Genomic context of the flavodoxin-encoding genes showed genes encoding membrane proteins, transporters, and proteins involved in redox processes and biosynthesis of macromolecules. A secondary structure prediction of both LB400 flavodoxins showed the characteristic flavodoxin structure of five ß-sheets intercalated with five α-helices. FldX1 contains a loop intercalated in the fifth β-strand, which indicates that it belongs to the long-chain flavodoxins, whereas FldX2 is a short-chain flavodoxin. A phylogenetic analysis of 73 flavodoxins from 43 bacterial genera revealed eight clusters (I-VIII), while FldX1 and FldX2 grouped separately within a long-chain and a short-chain flavodoxin clades. FldX1 and FldX2 were overexpressed in P. xenovorans. Interestingly, the strain overexpressing the long-chain flavodoxin FldX1 (p2-fldX1) showed a faster growth in glucose than the control strain. The recombinant strain overexpressing the long-chain flavodoxin FldX1 (p2-fldx1) exposed to paraquat (20 mM) possessed lower susceptibility to growth inhibition on plates and higher survival in liquid medium than the control strain. The strains overexpressing the flavodoxins FldX1 and FldX2 showed higher survival during exposure to 1 mM paraquat (>95%) than the control strain (68%). Compared to the control strain, strains overexpressing FldX1 and FldX2 showed lower lipid peroxidation (>20%) after exposure to 1 mM paraquat and a lower protein carbonylation (~30%) after exposure to 1 mM H2O2 was observed. During exposure to paraquat, strain p2-fldx1 downregulated the katG4, hpf, trxB1 and ohr genes (> 2-fold), whereas strain p2-fldx2 upregulated the oxyR and ahpC1 genes (> 2-fold). In conclusion, the flavodoxins FldX1 and FldX2 of P. xenovorans LB400 conferred protection to cells exposed to the oxidizing agents paraquat and H2O2.

Bacillus megaterium strains derived from water and soil exhibit differential responses to the herbicide mesotrione

The intense use of herbicides for weed control in agriculture causes selection pressure on soil microbiota and water ecosystems, possibly resulting in changes to microbial processes, such as biogeochemical cycles. These xenobiotics may increase the production of reactive oxygen species and consequently affect the survival of microorganisms, which need to develop strategies to adapt to these conditions and maintain their ecological functionality. This study analyzed the adaptive responses of bacterial isolates belonging to the same species, originating from two different environments (water and soil), and subjected to selection pressure by herbicides. The effects of herbicide Callisto and its active ingredient, mesotrione, induced different adaptation strategies on the cellular, enzymatic, and structural systems of two Bacillus megaterium isolates obtained from these environments. The lipid saturation patterns observed may have affected membrane permeability in response to this herbicide. Moreover, this may have led to different levels of responses involving superoxide dismutase and catalase activities, and enzyme polymorphisms. Due to these response systems, the strain isolated from water exhibited higher growth rates than did the soil strain, in evaluations made in oligotrophic culture media, which would be more like that found in semi-pristine aquatic environments. The influence of the intracellular oxidizing environments, which changed the mode of degradation of mesotrione in our experimental model and produced different metabolites, can also be observed in soil and water at sites related to agriculture. Since the different metabolites may present different levels of toxicity, we suggest that this fact should be considered in studies on the fate of agrochemicals in different environments.

Enhancement of ε-poly-L-lysine synthesis in Streptomyces by exogenous glutathione

Our previous work indicated that the vigor of Streptomyces decreased at the later stage of ε-poly-L-lysine (ε-PL) fermentation. In this study, we observed that the level of reactive oxygen species (ROS) in vivo increased sharply after 24 h, and the addition of an antioxidant glutathione (GSH) before this increase in ROS stimulated ε-PL synthesis in shake-flask fermentation. The enhancement of ε-PL production by GSH was further verified in batch and fed-batch fermentations. On a 5-l fermenter scale, the highest increasement was 68.8% in batch fermentation and the highest ε-PL level was 46.5 g l^- 1 in fed-batch fermentation. The RT-qPCR analysis showed that the transcriptional level of the catalase gene was down-regulated, and the decrease in cell activity was alleviated by the addition of GSH. The results revealed that exogenous antioxidant might maintain the cell vigor by reducing the excess ROS which provided a novel approach to regulate ε-PL synthesis.

Oxidative stress response in atrazine-degrading bacteria exposed to atrazine

Rhodobacter sphaeroides W16 and Acinetobacter lwoffii DNS32 which were isolated from soil in cold area subjected to a long-term atrazine application in Heilongjiang Province (China) can degrade atrazine efficiently. The investigation of their antioxidant properties will be useful for bioremediation and engineering applications of atrazine-degrading bacteria. Superoxide dismutase (SOD) and catalase (CAT) from two atrazine-degrading bacteria and one non-atrazine-degrading bacterium were tested for response to the oxidative stress caused by atrazine. Atrazine produced a greater inhibition of growth in Bacillus subtilis B19. The three bacteria apparently produced two activity peaks of SOD and CAT. The results demonstrated all three bacteria possessed a mechanism for atrazine tolerance that may include controlling the cellular redox balance by producing reactive oxygen species (ROS) and the subsequent scavenging of the ROS, but such response was more rapid and at lower levels in the two atrazine-degrading bacteria, suggesting less oxidative damage in these cells upon atrazine exposure. Compared to B. subtilis B19, atrazine-degrading bacteria had relatively high tolerance to atrazine stress, especially R. sphaeroides W16. Therefore, R. sphaeroides W16 and A. lwoffii DNS32 have a good application prospect of bioremediation project for soil contaminated by atrazine in cold area in Heilongjiang Province.

Oxidative stress response in two representative bacteria exposed to atrazine

Bacteria are present extensively in the environment. Investigation of their antioxidant properties will be useful for further study on atrazine stress tolerance of bacteria and the defense mechanism of antioxidant enzymes against atrazine or other triazine herbicides. Superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST) and total antioxidant capacity (T-AOC) from one Gram-negative representative strain Escherichia coli K12 and one Gram-positive representative strain Bacillus subtilis B19, respectively, were tested for response to atrazine stress. The results indicated that SOD, CAT, GST and T-AOC were induced upon exposure to atrazine. The growth of two bacteria was better in the absence than in the presence of atrazine, indicating that atrazine can decrease bacterial growth. The changes of enzyme activities indicate the presence of oxidative stress. Oxidative stress induced by atrazine may be due to imbalance of redox potential in bacterial cells, which leads to bacterial metabolic disorder.

Carbohydrate metabolite pathways and antibiotic production variations of a novel Streptomyces sp. M3004 depending on the concentrations of carbon sources

To determine the variations of growth, some key enzyme activities such as glucose kinase (GK), glucose-6-phosphate dehydrogenase (G6PDH), α-ketoglutarate dehydrogenase (KGDH), and isocitrate lyase (ICL) besides metabolite levels of pyruvate and antibiotic production of newly isolated Streptomyces sp. M3004 were grown in culture media which contain 10-20 g/l concentration with either glucose or glycerol as carbon source. Biomass and intracellular glucose and glycerol levels of Streptomyces sp. M3004 showed positive correlation with the concentration of these carbon sources, and these levels were higher in glucose compared with the glycerol-supplemented mediums. GK, G6PDH, and KGDH activities showed marked correlation with the concentration of both glucose and glycerol, and the activity levels were 4.14-, 1.47-, and 1.27-fold higher in glucose than glycerol. A key enzyme of the glyoxalate cycle, ICL activities decreased with increasing glucose concentrations from 10 to 20 g/l, but increased up to 15 g/l of glycerol. The positive correlations were also determined between intracellular glucose and glycerol levels besides pyruvate and protein variations with respect to concentrations of the carbon sources. Antibacterial activities of Streptomyces sp. M3004 reached maximum on the stationary phase, while it did not change significantly with respect to glucose and glycerol.

Actinobacterial peroxidases: an unexplored resource for biocatalysis

Peroxidases are redox enzymes that can be found in all forms of life where they play diverse roles. It is therefore not surprising that they can also be applied in a wide range of industrial applications. Peroxidases have been extensively studied with particular emphasis on those isolated from fungi and plants. In general, peroxidases can be grouped into haem-containing and non-haem-containing peroxidases, each containing protein families that share sequence similarity. The order Actinomycetales comprises a large group of bacteria that are often exploited for their diverse metabolic capabilities, and with recent increases in the number of sequenced genomes, it has become clear that this metabolically diverse group of organisms also represents a large resource for redox enzymes. It is therefore surprising that, to date, no review article has been written on the wide range of peroxidases found within the actinobacteria. In this review article, we focus on the different types of peroxidases found in actinobacteria, their natural role in these organisms and how they compare with the more well-described peroxidases. Finally, we also focus on work remaining to be done in this research field in order for peroxidases from actinobacteria to be applied in industrial processes.