Satlari Graells, Anna

Universitat Autònoma de Barcelona. Facultat de Biociències

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ObjectivesThe aim of this review is to know bacterial strategies against highconcentrations of arsenic in water and which of these mechanisms areuseful for bioremediation. Also, it compares natural and geneticallymodified bacteria for their application in bioremediation.BackgroundArsenic contamination is a global problem. According to WHO,arsenic is one of the most dangerous substances for public health. Inaddition, inorganic arsenic is considered carcinogen.It is estimated that 150 million people are exposed to this metalloidand the most affected regions are Bangladesh, West Bengal andTaiwan. In these zones the arsenic levels in groundwater are higherthan WHO’s recommendation, which has stablished a recommendedlimit of 10 μg/L (10 ppb) of arsenic in drinking water.Arsenic as a ContaminantArsenic is found in more than 200 minerals andit reaches the water due to the erosion of rocksand several anthropogenic activities that haveintensified arsenic contamination in water too.In natural waters, inorganic arsenic is found asarsenite As+3 and arsenate As+5. The trivalentform is considered the most toxic.Bacteria play an important role in arsenicbiogeochemical cycle due to the oxidation andreduction reactions with inorganic arsenic.Thus, arsenic is a causative of severeepidemiological, cytotoxic and genotoxicaffectations.Microbial Strategies for the Bioremediation of Arsenic in Polluted WaterAnna Satlari GraellsBachelor’s Degree in MicrobiologyPathways of Arsenic Uptake and ResistanceTable 1. Summary of the most important arsenic affectations in humans 1Future Prospects & ConclusionsMost studies are made in laboratories  need to prove them on an industrial scale to verify its economicviability.Difficulty to implement modified microorganisms. Branco et al. proposed a method for the immobilizationof O. tritici double mutant obtained in Sousa’s et al. study  surface as arsenic biofilter for bioremediationprocessesBiological treatment promising option due to many advantages of bacteriaAs+3 and As+5 uptake• By non-specific phosphate transporters GlpF and Pit orPst respectively• Arsenate uptake is increased in low phosphateconcentrationsOxidation• By Aio/Arx arsenite oxidase• As+3 oxidation to As+5• Ochrobactrum tritici, Gallionella ferruginea andLeptothrix ochraceaReduction• By Arr arsenate reductase• As+5 reduction to As+3• Geospirillum arsenophilus, Bacillus arsenicoselenatisand Crysiogenes arsenatisars operon• ArsA: ATPase found together with ArsB• ArsB: integral membrane permease that forms anefflux pump and extrudes arsenite outside the cell• ArsC: cytosolic arsenate reductase• ArsR: operon regulator• Escherichia coli, Herminiimonas arsenicoxydans,Thiomonas sp. and Corynebacterium glutamicumMethylation • By ArsM methyltransferase• Formation of volatile products• Penicillium sp., Aeromonas sp., Corynebacterium sp., E.coli and Methanobacterium bryantiiEpidemiology Dermal disease Cardiovascular diseaseSkin and bladder cancer CytotoxicityProblems in cell differentiation  ApoptosisExcessive cell proliferationAutophagy Genotoxicity DeletionsOxidative DNA damageDNA strand breaksChromosomal aberrations Isolation of Arsenic Resistant BacteriaAbbas et al. (2014). Samples of contaminated water from Pakistan• Three bacterial species isolated: Enterobacter sp., Klebsiellapneumoniae 1 and Klebsiella pneumoniae 2• All were arsenite oxidizing bacteriaSarkar et al. (2013). Samples of contaminated water from West Bengal• 64 arsenic-resistant bacteria were isolated, with a predominance ofAgrobacterium, Ochrobactrum and Achromobacter• Resistant to concentrations of 40 mM of As+3Paul et al. (2015). Samples of contaminated water from West Bengal• Bacterial community formed by Pseudomonas, Flavobacterium,Brevudimonas, Polaromonas, Rhodococcus, Methyloversatilis andMethyloteneraDevelopment of Genetically Modified BacteriaDiscussionA large group of bacteria is naturally resistant to high concentrations of arsenicin water. Arsenite oxidizing bacteria are useful for bioremediation, since theytransform As+3 to As+5 biotransformation assembled to a conventional As+5absorbance method.It is also proposed a water treatment based in bioreactors with H.arsenicoxydans biofilms: the arsenic is sequestered due to the segregation ofexopolymers.On the other hand, genetically modifications in the ars operon allows theachievement of improved bacteria capable to optimize the assimilation,resistance and accumulation of inorganic arsenic  great bio-tool forbioremediation.Genetically modified organisms are more effective as arsenic bioaccumulatorsand they can resist higher arsenic levels than autochthonous bacteria.Corynebacterium glutamicum modification by Mateos et al. (2006) Ochrobactrum tritici modification by Sousa et al. (2015)Corynebacterium glutamicum modification by Villadangos etal. (2015)• Increase of arsenate uptake low phosphateconcentrations (A)• Mutation on the efflux pumpgene  absence of ArsBpermease• Inability to extrude arsenite(B)• Accumulation of arsenite inthe cell bioaccumulation• Resistant to 60 mM of As+3• 6 different mutants wereobtained• Double mutantarsB/Acr3_1 accumulatesmore arsenite than theothers  useful as abioaccumulator• Mutation on the efflux pumpgene  absence of Acr3permease• Mutation on arsC gene  nopresence of arsenate reductase• Consortium with twodetoxification phases:1. O. tritici oxidizes As+3 to As+5(a)2. As+5 and As+3 are accumulatedby C. glutamicum double mutant(b)Relevant References1. Shankar, S., Shanker, U. & Shikha. Arsenic contamination of groundwater: a review of sources, prevalence, health risks, and strategies for mitigation. Sci. World J. 2014, 304– 524 (2014). 2. Kruger, M. C., Bertin, P. N., Heipieper, H. J. & Arsène-Ploetze, F. Bacterial metabolism of environmental arsenic - Mechanisms and biotechnological applications. Appl.Microbiol. Biotechnol. 97, 3827–3841 (2013). 3. Mateos, L. M., Ordóñez, E., Letek, M. & Gil, J. A. Corynebacterium glutamicum as a model bacterium for the bioremediation of arsenic. Int. Microbiol. 9, 207–215 (2006). 4. Villadangos, A. F. et al. Engineered coryneform bacteria as a bio-tool for arsenic remediation. Appl. Microbiol. Biotechnol. 98, 10143–10152 (2014). 5. Sousa, T., Branco, R., Piedade, A. P. & Morais, P. V. Hyper Accumulation of Arsenic in Mutants of Ochrobactrum tritici Silenced for Arsenite Efflux Pumps. PLoS One 1–14 (2015). 6. Lièvremont, D., Bertin, P. N. & Lett, M. C. Arsenic in contaminated waters: Biogeochemical cycle, microbial metabolism and biotreatment processes. Biochimie 91,1229–1237 (2009). 7. Abbas, S. Z. et al. Isolation and characterization of arsenic resistant bacteria from wastewater. Brazilian J. Microbiol. 45, 1309–15 (2014). 8. Mukhopadhyay, R., Rosen, B. P., Phung, L. T. & Silver, S. Microbial arsenic: From geocycles to genes and enzymes. FEMS Microbiol. Rev. 26, 311–325 (2002). 9. Kaur, S., Kamli, M. R. & Ali, A. Role ofarsenic and its resistance in nature. Can. J. Microbiol. 57, 769–774 (2011). 10. Paul, D., Kazy, S. K., Gupta, A. K., Pal, T. & Sar, P. Diversity , Metabolic Properties and Arsenic Mobilization Potential of Indigenous Bacteria in Arsenic Contaminated Groundwater of. 10, (2015). 11. Sarkar, A., Kazy, S. K. & Sar, P. Characterization of arsenic resistant bacteria fromarsenic rich groundwater of West Bengal, India. Ecotoxicology 22, 363–376 (2013). 12. Branco, R., Sousa, T., Piedade, A. P. & Morais, P. V. Immobilization of Ochrobactrum tritici As5 on PTFE thin films for arsenite biofiltration. Chemosphere 146, 330–337 (2016).• Specificity• Economical• Environmentally friendly• Safe• Reduction of wasteFigure 1. Bacterial interactions with arsenic 2Figure 2. C. glutamicum mutant 3 Figure 3. ars operons from O. tritici 5Figure 4. Consortium of O. tritici wild type and C. glutamicum mutant 4

Microbial strategies for the bioremediation of arsenic in polluted water

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Microbial strategies for the bioremediation of arsenic in polluted water

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