Antimicrobial activity of tissue and associated bacteria from benthic sea anemone Stichodactyla haddoni against microbial pathogens

Associated bacteria from Stichodactyla haddoni are found maximum in tentacle tissues than the body tissue. There are eight associated bacterial species viz., Alcaligenes sp, Corynebacterium sp, Aeromonas sp, Sporosarcina sp, Renibacterium sp, Camobacterium sp1, Camobacterium sp2 and Salinococcus sp were recorded. The culture extracts from the associated bacterial species showed sensitivity against human bacterial and fungalpathogens. However, the hexane tissue extract of sea anemone showed maximum sensitivity (24 mm dia.) against the fish bacterial pathogen Aeromonas hydrophila than the other chosen pathogens. Comparatively the tissue extracts showed promising antimicrobial sensitivity than the cell free extracts of associated bacteria, and hence, the tissue samples from the sea anemone Stichodactyla haddoni is recommended for further exploration of novel antimicrobial drugs than the associated bacteria.     

Different niches of the Halophila stipulacea seagrass bed harbor distinct populations of nitrogen fixing bacteria

Halophila stipulacea beds in the northern Gulf of Elat (Red Sea) may be subdivided into three different sub-habitats, each harboring a distinct population of diazotrophs. Nitrogen (N₂) fixation in the phyllosphere and in the rhizomes/upper-sediment niche was light dependent, suggesting its dependence on photosynthesis. N₂ fixation in the phyllosphere was not affected by the addition of either glucose or 3-3,4-dichloro-phenyl-1,1-dimethyl-urea (DCMU), indicating that the diazotrophs involved carried out non-oxygenic photosynthesis. They may, thus, have been photosynthetic bacteria. N₂ fixation in the rhizomes/upper-sediment niche, however, was greatly enhanced by the addition of glucose, but was suppressed in the presence of DCMU. This indicates that the diazotrophs involved here probably possess two photosystems (I and II) and may be Cyanobacteria. The anaerobic rhizosphere, in which fixation rates in light were very slow but were greatly enhanced by the addition of glucose, is probably populated by heterotrophic diazotrophs. Plant and sediment samples used in the present study were collected from the Gulf of Elat between 1990 and 1992.     

Microbial activity and carbon, nitrogen, and phosphorus content in a subtropical seagrass estuary (Florida Bay): evidence for limited bacterial use of seagrass production

Bacterial abundance, production, and extracellular enzyme activity were determined in the shallow water column, in the epiphytic community of Thalassia testudinum, and at the sediment surface along with total carbon, nitrogen, and phosphorus in Florida Bay, a subtropical seagrass estuary. Data were statistically reduced by principle components analysis (PCA) and multidimensional scaling and related to T. testudinum leaf total phosphorus content and phytoplankton biomass. Each zone (i.e., pelagic, epiphytic, and surface sediment community) was significantly dissimilar to each other (Global R = 0.65). Pelagic aminopeptidase and sum of carbon hydrolytic enzyme (esterase, peptidase, and α- and β-glucosidase) activities ranged from 8 to 284 mg N m⁻² day⁻¹ and 113–1,671 mg C m⁻² day⁻¹, respectively, and were 1–3 orders of magnitude higher than epiphytic and sediment surface activities. Due to the phosphorus-limited nature of Florida Bay, alkaline phosphatase activity was similar between pelagic (51–710 mg P m⁻² day⁻¹) and sediment (77–224 mg P m⁻² day⁻¹) zones but lower in the epiphytes (1.1–5.2 mg P m⁻² day⁻¹). Total (and/or organic) C (111–311 g C m⁻²), N (9.4–27.2 g N m⁻²), and P (212–1,623 mg P m⁻²) content were the highest in the sediment surface and typically the lowest in the seagrass epiphytes, ranging from 0.6 to 8.7 g C m⁻², 0.02–0.99 g N m⁻², and 0.5–43.5 mg P m⁻². Unlike nutrient content and enzyme activities, bacterial production was highest in the epiphytes (8.0–235.1 mg C m⁻² day⁻¹) and sediment surface (11.5–233.2 mg C m⁻² day⁻¹) and low in the water column (1.6–85.6 mg C m⁻² day⁻¹). At an assumed 50% bacterial growth efficiency, for example, extracellular enzyme hydrolysis could supply 1.8 and 69% of epiphytic and sediment bacteria carbon demand, respectively, while pelagic bacteria could fulfill their carbon demand completely by enzyme-hydrolyzable organic matter. Similarly, previously measured T. testudinum extracellular photosynthetic carbon exudation rates could not satisfy epiphytic and sediment surface bacterial carbon demand, suggesting that epiphytic algae and microphytobenthos might provide usable substrates to support high benthic bacterial production rates. PCA revealed that T. testudinum nutrient content was related positively to epiphytic nutrient content and carbon hydrolase activity in the sediment, but unrelated to pelagic variables. Phytoplankton biomass correlated positively with all pelagic components and sediment aminopeptidase activity but negatively with epiphytic alkaline phosphatase activity. In conclusion, seagrass production and nutrient content was unrelated to pelagic bacteria activity, but did influence extracellular enzyme hydrolysis at the sediment surface and in the epiphytes. This study suggests that seagrass-derived organic matter is of secondary importance in Florida Bay and that bacteria rely primarily on algal/cyanobacteria production. Pelagic bacteria seem coupled to phytoplankton, while the benthic community appears supported by epiphytic and/or microphytobenthos production.     

Diel variation of bacterial productivity in seagrass (Zostera capricorni) beds measured by rate of thymidine incorporation into DNA

Diurnal variations occurred in bacterial growth rates in the sediment and water column associated with seagrass (mainly Zostera capricorni Aschers) beds in Moreton Bay, Queensland, Australia. Studies were carried out in March and June 1981. Cell production rates increased by 5- to 10-fold during the morning and decreased during the afternoon. No nocturnal variation was observed. Daily bacterial cell production rate in the aerobic zones of the seagrass bed was estimated to be 43 mg C m^-2. A minimum of 100 mg C m^-2 d^-1 would be required to support the bacterial production. This represents about 10% of net primary production. The incorporation of tritiated thymidine into DNA was used to measure bacterial growth. The validity of the method is discussed.     

Antimicrobial activities of extracts from Indo-Pacific marine plants against marine pathogens and saprophytes

This study is the second of two surveys designed to systematically screen extracts from marine plants for antimicrobial effects against ecologically relevant marine microorganisms, and to compare results on a geographical basis. In the preceding survey, extracts from tropical Atlantic marine algae and seagrasses were screened in growth inhibition assays against the pathogenic fungus Lindra thalassiae, the saprophytic fungus Dendryphiella salina, the saprophytic stramenopiles, Halophytophthora spinosa and Schizochytrium aggregatum, and the pathogenic bacterium Pseudoaltermonas bacteriolytica. In this study, the same assay microorganisms were used to examine the antimicrobial effects of lipophilic and hydrophilic extracts from 54 species of marine algae and two species of seagrasses collected from Indo-Pacific reef habitats. Overall, 95% of all species surveyed in this study yielded extracts that were active against one or more, and 77% yielded extracts that were active against two or more assay microorganisms. Broad-spectrum activity against three or four assay microbes was observed in the extracts from 50 to 21% of all species, respectively. Extracts from the green alga Bryopsis pennata and the red alga Portieria hornemannii inhibited the growth of all assay microorganisms. Given that antimicrobial activity was prevalent among extracts of Indo-Pacific marine plants, it is interesting to note that the inhibitory effects of each extract varied considerably between the assay microorganisms. Overall, H. spinosa and D. salina were the most susceptible while L. thalassiae, S. aggregatum, and P. bacteriolytica were the most resistant to the extracts tested. These results provide good evidence that antimicrobial chemical defenses are widespread among Indo-Pacific marine plants. Further, the activity profiles of plant extracts suggest that antimicrobial secondary metabolites can have pathogen-selective or broad-spectrum effects. To confirm these results, chemical studies will be needed to isolate and characterize the compounds responsible for the observed antimicrobial activities.     

An acoustic investigation of seagrass photosynthesis

The use of high-frequency acoustics has recently emerged as a viable method for mapping the areal coverage of seagrasses. Since the bubbles produced by seagrass plants are partly responsible for the observed acoustic signature, it is likely that sound transmission throughout a seagrass canopy varies on circadian cycles coinciding with photosynthetic bubble production. This study examined the propagation of high-frequency (100 kHz) sound energy through the seagrass canopies of Syringodium filiforme, Halodule wrightii and Thalassia testudinum in a shallow outdoor mesocosm. Relative changes in the received acoustic energy were recorded every hour during a 24-h period and compared to independently measured rates of oxygen production. The mean acoustic intensity of energy transmitted throughout the seagrass canopy varied by 3.5 dB for S. filiforme, 4.4 dB for T. testudinum and 4.7 dB for H. wrightii over a 24-h period. These transmission characteristics are encouraging for the future development of in situ acoustic assessments of seagrass photosynthesis.     

Antimicrobial activities of extracts from tropical Atlantic marine plants against marine pathogens and saprophytes

Studies investigating disease resistance in marine plants have indicated that secondary metabolites may have important defensive functions against harmful marine microorganisms. The goal of this study was to systematically screen extracts from marine plants for antimicrobial effects against marine pathogens and saprophytes. Lipophilic and hydrophilic extracts from species of 49 marine algae and 3 seagrasses collected in the tropical Atlantic were screened for antimicrobial activity against five ecologically relevant marine microorganisms from three separate kingdoms. These assay microbes consisted of the pathogenic fungus Lindra thalassiae, the saprophytic fungus Dendryphiella salina, the saprophytic stramenopiles, Halophytophthora spinosa and Schizochytrium aggregatum, and the pathogenic bacterium Pseudoaltermonas bacteriolytica. Overall, 90% of all species surveyed yielded extracts that were active against one or more, and 77% yielded extracts that were active against two or more assay microorganisms. Broad-spectrum activity against three or four assay microorganisms was observed in the extracts from 48 and 27% of all species, respectively. The green algae Halimeda copiosa and Penicillus capitatus (Chlorophyta) were the only species to yield extracts active against all assay microorganisms. Among all assay microorganisms, both fungi were the most resistant to the extracts tested, with less than 21% of all extracts inhibiting the growth of either L. thalassiae or D. salina. In contrast, over half of all lipophylic extracts were active against the stramenopiles H. spinosa and S. aggregatum, and the bacterium P. bacteriolytica. Growth sensitivity to hydrophilic extracts varied considerably between individual assay microorganisms. While 48% of all hydrophilic extracts were active against H. spinosa, 27% were active against P. bacteriolytica, and only 14% were active against S. aggregatum. Overall, more lipophilic extracts inhibited microbial growth than hydrophilic extracts. The variability observed in the antimicrobial effects of individual extracts against each assay microorganism reflects the importance of choosing appropriate test microbes in assays from which ecologically relevant information is sought. Results from this survey demonstrate that antimicrobial activities are prevalent among extracts from marine algae and seagrasses, suggesting that antimicrobial chemical defenses are widespread among marine plants.     

Effect of neem extract against the bacteria isolated from marine fish

Marine ornamental fishes are exceedingly valuable due to their high demand in domestic and international markets. There is a growing global interest to rear the fishes in captivity. But problem due to bacteria and fungi are the major hitch in captive condition. Since, the use of antibiotics is banned, an attempt was made to ascertain in vitro assay of the neem leaves extract against the bacterial pathogens isolated from infected fishes. Bacterial strains isolated from infected regions of the clown fishes Amphiprion sebae and A. ocellaris were identified as Aeromonas hydrophila, Enterobacter sp., E. coli, Pseudomonas aeruginosa, Proteus sp., Streptococcus sp., Vibrio cholerae, V. alginolyticus, V. parahaemolyticus and Yersinia enterocolitica. Ethanol and methanol extracts were highly inhibitory to the bacterial isolates when compared to other solvents. Ethanol extracts exhibited low minimum inhibitory concentration (75-250 microg ml(-1)) as compared to other extracts. The present finding revealed that the neem leaf extract significantly reduces the bacterial pathogens and their infection in marine ornamental fishes.     

Temporal variation of metals in the seagrass Posidonia australis and its potential as a sentinel accumulator near a lead smelter

Temporal variation in the concentrations of Cd, Cu, Mn, Ni, Pb and Zn in leaves of the seagrass Posidonia australis was studied at three sites near a lead smelter on the shore of Spencer Gulf, a large hypersaline marine embayment in South Australia, on four occasions from October 1980 to September 1981. Concentrations of Cd, Mn, Pb and Zn of up to 541, 537, 379 and 4241 g g^-1, respectively, were found in leaves collected from the site nearest to the smelter. A substantial temporal variation in the concentrations of these metals in samples from all sites resulted from the combined effect of leaf age and collection strategy. Concentrations of Cd, Cu and Zn in the leaf epibiota were lower than those in the leaves, but the reverse was true for Mn and Ni. The use of seagrass leaves as sentinel accumulators for Cd, Pb and Zn must be based on collections made at the same time of year, or otherwise account for the effect of leaf age on concentrations of the metals in the samples.     

Leaf epifauna of the seagrass Thalassia testudinum

The abundance, composition and trophic relationships of metazoan leaf epifauna of the marine angiosperm Thalassia testudinum König were studied in Barbados, West Indies. Approximately 90 species from 11 phyla consisted chiefly of nematodes, harpacticoid copepods, crustacean nauplii, ostracods, and turbellarians. Epiflora- and detritus-feeders dominated the epifauna. Increasing leaf epiphytism was accompanied by faunal changes, most notably increased nematode, harpacticoid and polychaete density. Faunal composition was very similar to that of the temperate seagrass analogue Zostera marina.     

The influence of bacterial quorum-sensing inhibitors against the formation of the diatom-biofilm

Quorum-sensing inhibitor (QSI) is one of the most promising and environmentally friendly agents for marine antifouling. In this study, the activities of three kinds of QSIs 3,4-dibromo-2(5)H-furanone, 4-nitropyridine-N-oxide and indole were evaluated on the growth of two marine diatoms Cylinthrotheca sp. and Nitzschia closterium. At the same time, the effects of QSIs on the formation of the diatom-biofilm were also discussed. All the results showed that QSIs significantly inhibited the growth, and the effects depended on the dose and diatom species. The extracellular polymeric substance contents in the diatom-biofilm were significantly reduced by QSIs. However, the contents of polysaccharide in culture mediums were increased, which might result in the destruction of diatom cells. Combined with the results of crystal violet staining-biofilm and images of scanning electron microscopy, it was further demonstrated that QSIs inhibited the biofilm formation of Cylindrotheca sp., and the inhibitory effect of 4-nitropyridine-N-oxide was superior to that of 3,4-dibromo-2(5)H-furanone and indole.     

The size distribution of airborne bacteria and human pathogenic bacteria in a commercial composting plant

•Bacterial concentrations from eight stages were 10⁴–10⁵copies/m³. •Diameter influenced clustering of bacterial and HPB lineages. •Dg of 8 HPB ranged from 2.42 to 5.09 μm in composting areas. •Dg of 8 HPB ranged from 3.70 to 8.96 μm in packaging areas. •HPB had high concentrations and small sizes in composting areas. Composting plants are regarded as one of the important sources of environmental bioaerosols. However, limitations in the size distribution of airborne bacteria have prevented our comprehensive understanding of their risk to human health and their dispersal behavior. In this study, different sizes of airborne bacteria were collected using an eight-stage impactor from a full-scale composting facility. Size-related abundance and communities of airborne bacteria as well as human pathogenic bacteria (HPB) were investigated using 16S rRNA gene sequencing coupled with droplet digital PCR. Our results indicate that the bacterial concentrations from the eight stages were approximately 10⁴–10⁵copies/m³. Although no statistical correlation was detected between the particle size and the Shannon index, the influence of size on bacterial lineages was observed in both composting and packaging areas. For airborne bacteria from different stages, the dominant phyla were Firmicutes, Proteobacteria, and Actinobacteria, and the dominant genera was Bacillus. Seven out of eight HPB with a small geometric mean aerodynamic diameter had a high concentration in composting areas. Based on diameters of 2.42 to 5.09 μm, most HPB in the composting areas were expected to be deposited on the bronchus and secondary bronchus. However, in the packaging areas, the deposition of HPB (diameters 3.70 to 8.96 μm) occurred in the upper part of the respiratory tract. Our results on the size distribution, abundance, and diversity of these bacteria offer important information for the systematic evaluation of bacterial pathogenicity and the potential health impacts on workers in composting plants and the surrounding residents.     

Investigation of bioremediation potential of zymogenous bacteria and fungi for crude oil degradation

Bioremediation potential of bacteria and fungi isolated from sludge samples has been investigated (Danube alluvium, Pančevo, Serbia). Total isolated microorganisms were divided into three parts. One part was added with actidione antifungicide. The second part was added with streptomycin antibiotic. The third part was without additives. Paraffinic type of crude oil was a substrate for assessment of bioremediation potential. The simulated oil biodegradation lasted 30, 60 and 90 days. Parallel with that, the experiments with blind trial were conducted. Extracts were isolated from the samples with chloroform in a separate funnel. They were assayed for the group composition (alkanes, aromatics, alcohols and fatty acids) by column chromatography. Alkane fraction was analysed by gas chromatography—mass spectrometry (GC–MS). The most intense oil degradation was achieved in the experiments with bacteria, somewhat weaker with consortium of fungi and bacteria, and the weakest bioremediation potential in these experiments was shown by fungi.     

Use of a seagrass residency index to apportion commercial fishery landing values and recreation fisheries expenditure to seagrass habitat service

Where they dominate coastlines, seagrass beds are thought to have a fundamental role in maintaining populations of exploited species. Thus, Mediterranean seagrass beds are afforded protection, yet no attempt to determine the contribution of these areas to both commercial fisheries landings and recreational fisheries expenditure has been made. There is evidence that seagrass extent continues to decline, but there is little understanding of the potential impacts of this decline. We used a seagrass residency index, that was trait and evidence based, to estimate the proportion of Mediterranean commercial fishery landings values and recreation fisheries total expenditure that can be attributed to seagrass during different life stages. The index was calculated as a weighted sum of the averages of the estimated residence time in seagrass (compared with other habitats) at each life stage of the fishery species found in seagrass. Seagrass‐associated species were estimated to contribute 30%–40% to the value of commercial fisheries landings and approximately 29% to recreational fisheries expenditure. These species predominantly rely on seagrass to survive juvenile stages. Seagrass beds had an estimated direct annual contribution during residency of €58–91 million (4% of commercial landing values) and €112 million (6% of recreation expenditure) to commercial and recreational fisheries, respectively, despite covering <2% of the area. These results suggest there is a clear cost of seagrass degradation associated with ineffective management of seagrass beds and that policy to manage both fisheries and seagrass beds should take into account the socioeconomic implications of seagrass loss to recreational and commercial fisheries.     

烷烃降解菌SY16的筛选、鉴定及降解能力测定

油田生产和运输中经常发生原油落地以及漏油现象,造成大量的石油进入地表土壤,从而产生环境污染。针对原油对土壤产生的环境污染问题,对微生物降解烷烃的能力进行了研究。在以正十六烷为唯一碳源的HDM培养基中,从扶余油田东区采油三厂经常被含油废水浸泡的土壤中,分离、筛选出一株高效降解正烷烃的菌株SY16。经形态学观察和生理生化特征研究,鉴定为施氏假单胞杆菌(Pseudomonas stutzeri)。通过摇瓶试验得出两菌株的最适生长条件为30℃,培养基初始pH 8.0,摇床转速为180 r/min,接种量为1.0%。在最适生长条件下,分别对不同初始质量浓度烷烃进行降解率试验。结果表明,两菌株降解正烷烃的能力显著,当培养基中初始正烷烃含量为50 mg/L时,24 h能全部降解。当混合烷烃中各烷烃的初始质量浓度为50 mg/L时,在24 h对正十烷、正十二烷、正十六烷和正十八烷的降解率分别达到47.0%、42.6%、38.8%、36.2%。     

Testing for thresholds of ecosystem collapse in seagrass meadows

Although the public desire for healthy environments is clear‐cut, the science and management of ecosystem health has not been as simple. Ecological systems can be dynamic and can shift abruptly from one ecosystem state to another. Such unpredictable shifts result when ecological thresholds are crossed; that is, small cumulative increases in an environmental stressor drive a much greater change than could be predicted from linear effects, suggesting an unforeseen tipping point is crossed. In coastal waters, broad‐scale seagrass loss often occurs as a sudden event associated with human‐driven nutrient enrichment (eutrophication). We tested whether the response of seagrass ecosystems to coastal nutrient enrichment is subject to a threshold effect. We exposed seagrass plots to different levels of nutrient enrichment (dissolved inorganic nitrogen) for 10 months and measured net production. Seagrass response exhibited a threshold pattern when nutrient enrichment exceeded moderate levels: there was an abrupt and large shift from positive to negative net leaf production (from approximately 0.04 leaf production to 0.02 leaf loss per day). Epiphyte load also increased as nutrient enrichment increased, which may have driven the shift in leaf production. Inadvertently crossing such thresholds, as can occur through ineffective management of land‐derived inputs such as wastewater and stormwater runoff along urbanized coasts, may account for the widely observed sudden loss of seagrass meadows. Identification of tipping points may improve not only adaptive‐management monitoring that seeks to avoid threshold effects, but also restoration approaches in systems that have crossed them.     

Characterization of boron tolerant bacteria isolated from a fly ash dumping site for bacterial boron remediation

Boron is an essential micronutrient for plants, but can above certain concentrations be toxic to living organisms. A major environmental concern is the removal of boron from contaminated water and fly ash. For this purpose, the samples were collected from a fly ash dumping site, Nagasaki prefecture, Japan. The chemical characteristics and heavy metal concentration of the samples were performed by X-ray fluorescent analysis and leaching test. For bacterial analysis, samples were collected in sterile plastic sheets and isolation was carried out by serial dilution method. The boron tolerant isolates that showed values of maximum inhibitory concentration toward boron ranging from 100 to 260 mM level were screened. Based on 16S rRNA sequencing and phylogenetic analysis, the isolates were most closely related to the genera Bacillus, Lysinibacillus, Microbacterium and Ralstonia. The boron tolerance of these strains was also associated with resistant to several heavy metals, such as As (III), Cr (VI), Cd, Cu, Pb, Ni, Se (III) and Zn. Indeed, these strains were arsenic oxidizing bacteria confirmed by silver nitrate test. These strains exhibited their salt resistances ranging from 4 to 15 % were determined in Trypticase soy agar medium. The boron tolerant strains were capable of removing 0.1–2.0 and 2.7–3.7 mg l^?1 boron from the medium and fly ash at 168 h. Thus, we have successfully identified the boron tolerant and removal bacteria from a fly ash dumping site for boron remediation.     

Pyruvate-utilizing bacteria as potential contributors to the food web in the Arabian Gulf

Water samples from the Kuwaiti coasts of the Arabian Gulf were used for counting and isolating bacteria capable of growth on low molecular weight organic compounds known to be released by picocyanobacteria. The compounds tested were potassium acetate, sodium pyruvate, fumaric acid, succinic acid, sodium citrate and glycerol. For comparison, the bacterial numbers on glucose (a conventional carbon source) and Tween 80 and crude oil (unconventional carbon sources), as sole sources of carbon and energy were also determined. Sodium pyruvate was, in most cases, the carbon and energy source most commonly utilized by the cultivable surface water bacteria. The most common cultivable bacterial genera on the test carbon sources were Pseudoalteromonas, Vibrio, Cobetia and Roseobacter. Less common genera were Rhodococcus, Pseudomonas and Bacillus. Quantification of heterotrophic bacteria associated with cultures of local picocyanobacterial strains, originally isolated from the Gulf surface water, also revealed that the carbon source most commonly utilized by cultivable bacteria was sodium pyruvate. However, a different bacterial composition was identified, with Alcanivorax, Stappia and Marinobacter as the major heterotrophic genera. All heterotrophic bacteria that grew on sodium pyruvate could also grow on β-alanine, as sole sources of carbon and energy. From this study we suggest that the Arabian Gulf bacteria utilizing picocyanobacterial low molecular weight compounds, particularly pyruvate may potentially contribute to the food web in this aquatic system. The experiments comply with the current laws of Kuwait.     

Antioxidative potential of metformin: Possible protective mechanism against generating OH radicals

• Metformin consumes O₂−• and OH• induced by PM are proposed. • OH• dominated the oxidation of metformin compared with O₂−• • Metformin can prevent the harm of ROS induced by PM to human health. • Antioxidative potential of metformin was first proposed to provide measures. Exposure to particulate matter (PM) can lead to the excessive accumulation of reactive oxygen species (ROS), which causes oxidative stress and endangers human health. In this study, the effects of metformin on PM-induced radicals were investigated, and the antioxidation reaction mechanism of metformin was analyzed by the density functional theory (DFT) method. The corresponding results revealed that the consumption rate of dithiothreitol (DTT) increased as the metformin concentration (0–40 mmol/L) increased under exposure to PM active components. Moreover, the OH radical content decreased as the metformin concentration increased. This result may be related to the consumption of PM-induced OH radicals by metformin, which promotes the DTT consumption rate. Additionally, because the initiation reaction has a high barrier, the oxidation reaction rate between metformin and •O₂− is not very fast, although various catalysts may be present in the human environment. Importantly, we found that the barrier of metformin induced by OH radicals is only 9.6 kcal/mol while the barrier of metformin induced by oxygen is 57.9 kcal/mol, which shows that the rate of the •OH-initiated oxidative reaction of metformin is much faster and that this reaction path occurs more easily. By sample analysis, the mean OH radical generation was 55 nmol/min/g (ranging from 5 to 105 nmol/min/g) on haze days and 30 nmol/min/g (ranging from 10 to 50 nmol/min/g) on non-haze days. Moreover, OH radical generation was higher on haze days than on neighboring non-haze days. Taken together, all data suggest that metformin could consume the PM-induced radicals, such as OH radicals and •O₂−, thereby providing health protection.