Bacterial Community Structure In Sediments Research Articles

Bacterial Community Structure of Typical Lake Sediments in Yinchuan City and Its Response to Heavy Metals

Lake wetlands are extremely important and special ecosystems, which are important for regional water resource storage, environmental protection, and biodiversity maintenance. Sediment bacteria are an important component of lake ecosystems and are a major driver of biogeochemical cycling in lakes. In order to investigate the community structure of bacteria in typical lake sediments in Yinchuan City and their influencing factors, three typical lakes in Yinchuan City (Yuehai Lake, Mingcui Lake, and Xiniu Lake) were selected for the study and surface sediments were collected in January, April, July, and October 2021. The composition of the sediment bacterial community was examined using 16S rDNA high-throughput sequencing technology, and the response relationships between them and heavy metals were explored. The results showed that the ecological hazard coefficient for heavy metals in the sediments of three typical lakes in Yinchuan City was far less than 40, and the ecological hazard index was far less than 150, all of which indicated a minor ecological hazard. There were no significant differences in bacterial community diversity among the three lakes, but there were significant variations in diversity among the lakes in different seasons and significant differences in community composition. The dominant phyla (top three in terms of relative abundance) in Yuehai Lake, Mingcui Lake, and Xiniu Lake were Proteobacteria, Bacteroidetes, and Chloroflexi. The dominant lower orders were Gammaproteobacteria, Alphaproteobacteria, and Deltaproteobacteria. The main divergent species that occurred at the phylum level in typical lakes in Yinchuan were Proteobacteria, Bacteroidetes, Euryarchaeota, Firmicutes, Actinobacteria, and Acidobacteria. The sediment bacterial community structure of Yuehai Lake was significantly correlated with Cu, Fe, Mn, Zn, As, and Pb; the sediment bacterial community structure of Lake Mingcui was significantly correlated with Fe, Pb, and Cr; and the sediment bacterial community structure of Xiniu Lake was not significantly correlated with heavy metals. The types and contents of sediment heavy metals had a significant effect on the bacterial community structure of sediments in Yinchuan Yuehai Lake and Mingcui Lake and were important environmental factors that caused changes in the bacterial community structure of lake sediments.

Changes in Temporal Dynamics and Factors Influencing the Environment of the Bacterial Community in Mangrove Rhizosphere Sediments in Hainan

The structural characteristics of the rhizosphere soil’s microbial community is crucial to understanding the ecological function of mangroves. However, the mechanism influencing mangrove plants in soil microbial communities has yet to be determined. Here, the mangrove ecosystem of Xinying Mangrove National Wetland Park in Hainan Province was taken as the research object. The microbial communities, external regulatory factors, and the relationship between communities were analyzed using 16S rRNA high-throughput sequencing in the rhizosphere and non-rhizosphere sediments of mangrove forests under different spatiotemporal conditions. The results showed that there was no significant difference in the α-diversity of the bacterial community between the rhizosphere and non-rhizosphere sediments. However, β-diversity was significantly different. Redundancy analysis (RDA) showed that other environmental factors besides sulfide and Fe2+ affected the bacterial community structure in sediments. The co-occurrence pattern analysis of bacteria in the mangrove ecosystem indicates that the bacteria in rhizosphere sediments were more closely related than those in non-rhizosphere sediments. The results reveal significant differences between the rhizosphere and non-rhizosphere bacterial community diversity, structure, and their interaction in the mangrove ecosystem. Therefore, the ecological system of the mangrove wetland needs to be preserved and rehabilitated, which would have a tremendous impact on the sustainable development.

Effect of g-C3N4 on biodiversity and structure of bacterial community in sediment of Xiangjiang River under tetracycline pressure.

Photocatalysts have been widely prepared and used in wastewater treatment. Although the influence of photocatalyst application on survival and activity of organisms has been examined, its impact on composition and diversity of microbial community is not fully understood. In this study, the impact of photocatalyst g-C3N4 (Graphitic carbon nitride) on microbial communities in riverbed sediments polluted by antibiotic tetracycline (TC) was investigated. The sediment samples collected from the Xiangjiang River of China were exposed to different concentrations of TC, g-C3N4 and TC/g-C3N4 and the bacterial community were analyzed by Illumina sequencing. The results showed that the dominant bacterial phyla were Acidobacteriota, Proteobacteria, Actinobacteriota, and Chloroflexi in the study site. When compared to the control treatments, the application of TC, g-C3N4 and TC/g-C3N4 exhibited distinguishable effects on bacterial community structure in sediments. The presence of TC had greater influence on bacterial composition, while g-C3N4 and TC/g-C3N4 had less influence on bacteria. The diversity and richness of microorganisms in sediment increased under g-C3N4 application and reached the highest values when g-C3N4 was 75 mg/kg. The photocatalyst g-C3N4 restored bacterial community diversity affected by TC, reduced the TC residues in aquatic environment, and eliminated the side effects of TC application in sediments. Our study indicated that g-C3N4 was an environmentally friendly photocatalyst with lightly negative effects on microbial community in riverbed sediments, and could be used for effective remediation of TC-contaminated environments.

Effects of cyanobacterial growth and decline on the <i>phoD</i>-harboring bacterial community structure in sediments of Lake Chaohu

phoD基因编码的碱性磷酸酶驱动沉积物有机磷矿化并释放生物可利用磷，促进了富营养化湖泊蓝藻的生长与暴发，但对富营养化湖泊蓝藻生消周期phoD基因细菌群落动态变化的认识依然有限.本文研究了中国典型富营养化湖泊巢湖蓝藻生消过程沉积物碱性磷酸酶活性（APA）、phoD基因细菌多样性和群落结构的动态变化及其与环境的关系.结果显示：巢湖沉积物APA活性在蓝藻生长与暴发阶段显著升高，且与水温、pH、溶解氧（DO）等环境因子显著相关.蓝藻生消各阶段沉积物phoD基因细菌群落的优势菌属均由Pseudonocardia和Friedmanniella构成；与蓝藻潜伏期和衰亡期相比，生长初期与暴发期大多数样点沉积物Pseudonocardia的丰度显著降低而Friedmanniella显著升高.携带phoD基因的菌属丰度呈显著的时空变化，其中菌属丰度的空间异质性较高.蓝藻生长初期与暴发期的phoD基因细菌群落的Ace指数与Shannon多样性指数显著大于潜伏期与衰亡期.研究表明，携带phoD基因细菌群落结构的变化主要受APA、DO、叶绿素a、水温、总磷以及无机磷的驱动；春季蓝藻的生长消耗大量上覆水溶解性无机磷，激发了沉积物APA活性并诱发Friedmanniella生长从而缓解水体磷限制.;The alkaline phosphatase encoded by phoD gene drives the mineralization of organic phosphorus in sediments and thus the release of bioavailable phosphorus, and promotes the growth and blooms of cyanobacteria in eutrophic lakes. The dynamic variations of phoD-harboring bacterial community during the annual cyanobacterial growth and decline in eutrophic lakes, however, remain unclear. In this study, we analyzed the alkaline phosphatase activity (APA), phoD-harboring bacterial community diversity and structure and their associations with the physicochemical factors in a typical eutrophic lake (Lake Chaohu) in China during the entire cyanobacterial growth and decline. The results showed that the APA in sediments increased significantly during the initial growth and outbreaks of cyanobacteria. Pseudonocardia and Friedmanniella are the predominant phoD-harboring genera in sediments during the entire cyanobacterial growth and decline. In contrast to the abundance of Pseudonocardia and Friedmanniella in the incubation and decline stages of cyanobacteria, Pseudonocardia decreased significantly while Friedmanniella increased significantly in the early growth and outbreak stages. The abundance of phoD gene bacteria varies spatiotemporally, especially for its high spatial heterogeneity. The Ace and Shannon diversity index of phoD-harboring bacterial community during the early and outbreak stages of cyanobacteria were much higher than those in the incubation and decline stages. The changes of phoD-harboring bacterial community were mainly driven by APA, dissolved oxygen, chlorophyll-a, water temperature, total phosphorus and inorganic phosphorus. The rapid decline of dissolved inorganic phosphorus in overlying waters due to the increasing cyanobacterial photosynthesis in the early growth of cyanobacteria induces the APA, promotes the growth of Friedmanniella and alleviates the phosphorus restriction.

Mitigation of Eutrophication in a Shallow Lake: The Influences of Submerged Macrophytes on Phosphorus and Bacterial Community Structure in Sediments

Remediating water eutrophication is critical for maintaining healthy and sustainable development of lakes. The aim of this study was to explore the seasonal variation in phosphorus (P) speciation and bacterial community structure in sediments of Qin Lake (Taizhou, Jiangsu Province, China) associated with the growth of submerged macrophyte Vallisneria natans. The differences in sediment bacterial diversity and community structure between V. natans growing and control areas were analyzed over a period of one year. The results showed that V. natans growth reduced the total P and organic matter contents of the sediments and increased the bioavailable iron (Fe) and Fe-bound P contents. The α-diversity of sediment bacteria was significantly higher in the presence of V. natans than in the controls during the vigorous plant growth stage. In the presence of V. natans, there was a higher relative abundance of Proteobacteria and lower relative abundances of Chloroflexi and Acidobacteria. The Fe(II) content in the sediment had a larger influence on the spatial distribution of bacterial communities than sediment Fe-bound P, organic matter, and Fe(II) contents. V. natans growth could reshape sediment bacterial community structure in the shallow lake, which, in turn, enhanced P immobilization in the sediments and thereby improved the water quality.

Influences of nutritional conditions on degradation of dibutyl phthalate in coastal sediments with Cylindrotheca closterium

In this work, microphytobenthos Cylindrotheca closterium was planted on the surface of coastal sediments to investigate its influence on dibutyl phthalate (DBP) degradation in sediments under different nutritional conditions. The results indicated that C. closterium largely utilized nutrients from the overlying water. Addition of nitrogen, phosphorus or silicon increased algal biomass (as chlorophyll a) by 0.97–3.16, 1.75–2.36 and 1.61–3.09 times, respectively, meanwhile it changed bacterial community structure in sediments with C. closterium. Growth of C. closterium was more sensitive to nitrogen content in the overlying water. Inoculation of C. closterium increased the relative abundances of dominant aerobic bacteria by 10–67%. Compared with treatments without C. closterium, inoculation of C. closterium increased DBP degradation percentage in sediments (8.5–18.9% increment), which was positively correlated with chlorophyll a content. Thus, microphytobenthos showed the potential for improving the cleansing of polluted coastal sediments, which was obviously related to nutritional conditions in the overlying water.

Bacterial community dynamic associated with autochthonous bioaugmentation for enhanced Cu phytoremediation of salt-marsh sediments

Autochthonous bioaugmentation for metal phytoremediation is still little explored, particularly its application to estuarine salt marshes, but results obtained so far are promising. Nevertheless, understanding the behaviour of the microbial communities in the process of bioaugmentation and their role in improving metal phytoremediation is very important to fully validate the application of this biological technology. This study aimed to characterize the bacterial community dynamic associated with the application of autochthonous bioaugmentation in an experimentation which showed that Phragmites australis rhizosphere microorganisms could increase this salt marsh plant potential to phytoremediate Cu contaminated sediments. Bacterial communities present in the autochthonous microbial consortium resistant to Cu added to the medium and in the sediment at the beginning and at the end of the experiment were characterized by ARISA. Complementarily, the consortium and the sediment used for its production were characterized by next generation sequencing using the pyrosequencing platform 454. The microbial consortium resistant to Cu obtained from non-vegetated sediment was dominated by the genus Lactococcus (46%), Raoultella (25%), Bacillus (12%) and Acinetobacter (11%), whereas the one obtained form rhizosediment was dominated by the genus Gluconacetobacter (77%), Bacillus (17%) and Dyella (3%). Results clearly showed that, after two months of experiment, Cu caused a shift in the bacterial community structure of sediments, an effect that was observed either with or without addition of the metal resistant microbial consortium. Therefore, bioaugmentation application improved the process of phytoremediation (metal translocation by the plant was increased) without inducing long term changes in the bacterial community structure of the sediments. So, phytoremediation combined with autochthonous bioaugmentation can be a suitable technology for the recovery of estuarine areas, contributing for an efficient risk management strategy of these coastal zones.

Effects of Environmental Factors on Anammox Bacterial Community Structure in Sediments of a Freshwater Aquaculture Farm, Yangcheng Lake

ABSTRACTPrevious studies have reported wide distribution of anaerobic ammonia oxidation (anammox) bacteria in various ecosystems. However, little is known about the distribution of anammox bacteria under varying environmental conditions in intensive aquaculture systems. In Yangcheng Lake, a famous crab farm situated in the Yangtze River Delta, sediment samples were collected in October (feeding period) and January (nonfeeding period) to analyze the distribution and diversity of anammox bacteria and their relationships with environmental factors. Based on the functional biomarker of Anammox bacteria, hzo gene, anammox bacterial clone libraries were constructed and their abundances were determined by quantitative PCR (qPCR). The Anammox bacteria were detected in the lake with the abundances ranging from 0.70 × 105 to 6.05 × 105 copies per gram of sediment. Sequences from eight clone libraries yielded seven unique operational taxonomic units (OTUs), distantly related to the Candidatus Jettenia genera with a similarity of about 91%. The Anammox bacterial community structures, diversities and abundances varied spatiotemporally with environmental conditions. In October, the level of the nitrogen compounds, the diversity, evenness and abundance of Anammox bacteria were higher than in January. The predominant OTU of samples changed from HZO-OTU-1 (34.25%) in January to HZO-OTU-2 (28.90%) in October. Moreover, the site (SW) nearing to sewage inlet was lack of HZO-OTU-7 in January. Canonical correspondence analysis (CCA) showed that the pore water NO2− concentration, ammonium to nitrogen oxides ratio (NH4+/NOx−) and total organic carbon to total nitrogen ratio (TOC/TN) contributed most to Anammox bacterial community structures variances. Pearson correlations analysis revealed that the Anammox bacteria abundance had positive co-relationships with TN, NH4+, NO3− concentrations, and negative correlation with TOC/TN in porewater.

Effect of changes in the physicochemical properties of sand-alternatives on bacterial community structure in coastal sediments

Steel slag and its granulated agglomerates, and the granulated agglomerates of ash from thermal power stations are reserved for and partially used in the construction of sand-alternatives (SAs) in coastal restoration and creation projects. These SAs contain CaO and leach calcium and alkalis that may affect biological activity of microorganisms colonizing surrounding sediments. We evaluated the chemical behavior of four SAs, namely, decarburized slag (DCSlag), dephosphorized slag (DPSlag), granulated agglomerates of DCSlag (GSlag), and granulated agglomerates of coal fly ash (GAsh) in coastal sediment and the impact of these SAs on bacterial community structure in the sediment. The SAs eluted calcium with a decrease in the surface calcium content in the sediment. The elution from slag and slag-based SA (DCSlag, DPSlag, and GSlag) continued for 8 weeks, whereas the elution from GAsh continued for 24 weeks. The different elution periods are explained by the depth of eluted calcium found in the SAs; 0.19±0.07, 0.04±0.02, 0.27±0.12 and 2.4±0.97mm in DCSlag, DPSlag, GSlag and GAsh, respectively. After 1 year, the DGGE (Denaturing Gradient Gel Electrophoresis) profiles were different among all the SAs except for GSlag and GAsh. The taxon richness of bacterial communities was estimated by the number of DNA bands found in the sediment mixed with the SAs, and it was lower than that in the natural sediment. Physicochemical properties of the SA's have been shown to affect the bacterial community structure. On the other hand, the communities recovered to almost the same level as that in the natural sediment after 1 year. The long-term effects of chemicals eluted from the SAs on bacterial community structure would be limited or negligible.

PH levels drive bacterial community structure in sediments of the Qiantang River as determined by 454 pyrosequencing.

The Qiantang River is a typical freshwater ecosystem that acts as an irreplaceable water source in Zhejiang Province in southeastern China. However, the effects of environmental factors on the bacterial community of this freshwater ecosystem have not been determined. In this study, seven sediment samples were collected along the river. Their bacterial communities were identified using 454 high-throughput sequencing, and the primary environmental factors responsible for shaping the community structure were analyzed. The number of bacterial operational taxonomic units (OTUs) ranged from 2637 to 3933. Using a linear-regression analysis, the OTU numbers were significantly positively correlated with pH (r = 0.832, p < 0.05) and negatively correlated with nitrate concentration (r = −0.805, p < 0.05). A redundancy analysis (RDA) was also performed to test the relationship between the environmental factors and bacterial community composition. The results indicated that pH (p < 0.05) and nitrate concentration (p < 0.05) were the most significant factors that determined the community distribution of sediment bacteria.

Abundance and Diversity of Bacteria in Oxygen Minimum Drinking Water Reservoir Sediments Studied by Quantitative PCR and Pyrosequencing

Reservoir sediment is one of the most stressful environments for microorganisms due to periodically oxygen minimum conditions. In this study, the abundance and composition of bacteria associated with sediments from three drinking water reservoirs (Zhoucun, ZCR; Shibianyu, SBYR; and Jinpen, JPR) were investigated by quantitative polymerase chain reaction and 16S rRNA-based 454 pyrosequencing. The results of physico-chemical analysis of sediments showed that the organic matter and total nitrogen were significantly higher in ZCR as compared to JPR (P < 0.01). The bacterial abundance was 9.13 × 10(6), 1.14 × 10(7), and 6.35 × 10(6) copies/ng DNA in sediments of SBYR, ZCR, and JPR, respectively (P < 0.01). The pyrosequencing revealed a total of 9,673 operational taxonomic units, which were affiliated with 17 phyla. The dominant phylum was Firmicutes (56.83%) in JPR; whereas, the dominance of Proteobacteria was observed in SBYR with 40.38% and ZCR with 39.56%. The Shannon-Wiener diversity (H') was high in ZCR; whereas, Chao 1 richness was high in SBYR. The dominant genera were Clostridium with 42.15% and Bacillus with 20.44% in JPR. Meanwhile, Dechloromonas with 14.80% and Smithella with 7.20% were dominated in ZCR, and Bacillus with 45.45% and Acinetobacter with 5.15% in SBYR. The heat map profiles and redundancy analysis indicated substantial differences in sediment bacterial community composition among three reservoirs. Moreover, it appears from the results that physico-chemical variables of sediments including pH, organic matter, total nitrogen, and available phosphorous played key roles in shaping the bacterial community diversity. The results obtained from this study will broaden our understanding on the bacterial community structure of sediments in oxygen minimum and stressful freshwater environments.

Effect of redox conditions on bacterial community structure in Baltic Sea sediments with contrasting phosphorus fluxes.

Phosphorus release from sediments can exacerbate the effect of eutrophication in coastal marine ecosystems. The flux of phosphorus from marine sediments to the overlying water is highly dependent on the redox conditions at the sediment-water interface. Bacteria are key players in the biological processes that release or retain phosphorus in marine sediments. To gain more insight in the role of bacteria in phosphorus release from sediments, we assessed the effect of redox conditions on the structure of bacterial communities. To do so, we incubated surface sediments from four sampling sites in the Baltic Sea under oxic and anoxic conditions and analyzed the fingerprints of the bacterial community structures in these incubations and the original sediments. This paper describes the effects of redox conditions, sampling station, and sample type (DNA, RNA, or whole-cell sample) on bacterial community structure in sediments. Redox conditions explained only 5% of the variance in community structure, and bacterial communities from contrasting redox conditions showed considerable overlap. We conclude that benthic bacterial communities cannot be classified as being typical for oxic or anoxic conditions based on community structure fingerprints. Our results suggest that the overall structure of the benthic bacterial community has only a limited impact on benthic phosphate fluxes in the Baltic Sea.

Carbon, Metals, and Grain Size Correlate with Bacterial Community Structure in Sediments of a High Arsenic Aquifer

Bacterial communities can exert significant influence on the biogeochemical cycling of arsenic (As). This has globally important implications since As in drinking water affects the health of over 100 million people worldwide, including in the Ganges–Brahmaputra Delta region of Bangladesh where geogenic arsenic in groundwater can reach concentrations of more than 10 times the World Health Organization’s limit. Thus, the goal of this research was to investigate patterns in bacterial community composition across gradients in sediment texture and chemistry in an aquifer with elevated groundwater As concentrations in Araihazar, Bangladesh. We characterized the bacterial community by pyrosequencing 16S rRNA genes from aquifer sediment samples collected at three locations along a groundwater flow path at a range of depths between 1.5 and 15 m. We identified significant differences in bacterial community composition between locations in the aquifer. In addition, we found that bacterial community structure was significantly related to sediment grain size, and sediment carbon (C), manganese (Mn), and iron (Fe) concentrations. Deltaproteobacteria and Chloroflexi were found in higher proportions in silty sediments with higher concentrations of C, Fe, and Mn. By contrast, Alphaproteobacteria and Betaproteobacteria were in higher proportions in sandy sediments with lower concentrations of C and metals. Based on the phylogenetic affiliations of these taxa, these results may indicate a shift to more Fe-, Mn-, and humic substance-reducers in the high C and metal sediments. It is well-documented that C, Mn, and Fe may influence the mobility of groundwater arsenic, and it is intriguing that these constituents may also structure the bacterial community.

Structure and activity of lacustrine sediment bacteria involved in nutrient and iron cycles

Knowledge of the bacterial community structure in sediments is essential to better design restoration strategies for eutrophied lakes. In this regard, the aim of this study was to quantify the abundance and activity of bacteria involved in nutrient and iron cycling in sediments from four Azorean lakes with distinct trophic states (Verde, Azul, Furnas and Fogo). Inferred from quantitative PCR, bacteria performing anaerobic ammonia oxidation were the most abundant in the eutrophic lakes Verde, Azul and Furnas (4.5-16.6%), followed by nitrifying bacteria (0.8-13.0%), denitrifying bacteria (DNB) (0.5-6.8%), iron-reducing bacteria (0.2-1.4%) and phosphorus-accumulating organisms (<0.3%). In contrast, DNB dominated sediments from the oligo-mesotrophic lake Fogo (8.8%). Activity assays suggested that bacteria performing ammonia oxidation (aerobic and anaerobic), nitrite oxidation, heterothrophic nitrate reduction, iron reduction and biological phosphorus storage/release were present and active in all Azorean lake sediments. The present work also suggested that the activity of DNB might contribute to the release of phosphorus from sediments.

Bacterial community structure analysis of sediment in the Sagami River, Japan using a rapid approach based on two-dimensional DNA gel electrophoresis mapping with selective primer pairs

A rapid approach based on two-dimensional DNA gel electrophroesis (2-DGE) mapping with selective primer pairs was employed to analyze bacterial community structure in sediments from upstream, midstream and downstream of Sagami River in Japan. The 2-DGE maps indicated that Alpha- and Delta-proteobacteria were major bacterial populations in the upstream and midstream sediments. Further bacterial community structure analysis showed that richness proportion of Alpha- and Delta-proteobacterial groups reflected a trend toward decreasing from the upstream to downstream sediments. The biomass proportion of bacterial populations in the midstream sediment showed a significantly difference from that in the other sediments, suggesting that there may be an environmental pressure on the midstream bacterial community. Lorenz curves, together with Gini coefficients were successfully applied to the 2-DGE mapping data for resolving evenness of bacterial populations, and showed that the plotted curve from high-resolution 2-DGE mapping became less linear and more an exponential function than that of the 1-DGE methods such as chain length analysis and denaturing gradient gel electrophoresis, suggesting that the 2-DGE mapping may achieve a more detailed evaluation of bacterial community. In conclusion, the 2-DGE mapping combined with the selective primer pairs enables bacterial community structure analysis in river sediment and thus it can also monitor sediment pollution based on the change of bacterial community structure.

Bacterial Community Structure of Sediments of the Bizerte Lagoon (Tunisia), a Southern Mediterranean Coastal Anthropized Lagoon

In order to estimate how pollution affects the bacterial community structure and composition of sediments, chemical and molecular approaches were combined to investigate eight stations around the Bizerte lagoon. Terminal restriction fragment length polymorphism (T-RFLP) analysis of PCR-amplified 16S rRNA genes revealed that each station was characterized by a specific bacterial community structure. The combination of this data with those of chemical analysis showed a correlation between the bacterial fingerprint and the pollutant content, principally with hydrocarbon pollution. The composition of the bacterial community of two contrasted stations related to the pollution revealed sequences affiliated to alpha, beta, gamma, delta, epsilon subclass of the Proteobacteria, Actinobacteria, and Acidobacteria in both stations although in different extent. Gamma and delta subclass of the Proteobacteria were dominant and represent 70% of clones in the heavy-metal-contaminated station and 47% in the polyaromatic hydrocarbon (PAH)-contaminated. Nevertheless, most of the sequences found were unaffiliated to cultured bacteria. The adaptation of the bacterial community mainly to PAH compounds demonstrated here and the fact that these bacterial communities are mainly unknown suggest that the Bizerte lagoon is an interesting environment to understand the capacity of bacteria to cope with some pollutants.