Abstract
The extensive use of acids in a variety of manufacturing industries results in the increase of discharged acidic waste stream into the environment. Such co-pollution of acids and other organic pollutants limits the biodegradation capability of neutrophilic degraders. With high-throughput genetic techniques, we aim to improve the acid tolerance of a pollutant-degrading bacterium, Pseudomonas putida S16 by genetically engineering it with the glutamate decarboxylase (GAD)-dependent system and the global regulator (IrrE) of extreme radiation resistance. The engineered strains holding either GAD system or irrE regulator could grow under pH 4.5, compared to the wild type. They could also degrade over 90% of a selected pollutant (benzoate or nicotine) under pH 5.0 in 48 h, while no biodegradation was detected with the wild type under the same conditions. We conclude that acid stress tolerance by the possession of the GAD system or IrrE regulator in pollutant-degrading bacteria would be a promising approach to enhance their viability and biodegrading activities in bioremediation of acidic wastes.
Highlights
Co-pollution between acids and organic wastes often occurs in the effluents discharged from agriculture and manufacturing industries, and persistence of such pollutants are harmful to any living organisms (Kjeldsen et al, 2002; Foo and Hameed, 2009)
The recombinant plasmid pME-Gad constructed by insertion of a 3.3-kb fragment containing the gene gadBC and 230 bp upstream from the initiation site of gadB is shown in Supplementary Figure S1A, while the recombinant plasmid pME-GirrE holding the gene IrrE regulator (irrE) and the promoter GroESL is shown in Supplementary Figure S1C
The possession of the gene expressing gadBC or irrE was confirmed with PCR (Supplementary Figures S1B,D) and DNA sequencing
Summary
Co-pollution between acids and organic wastes often occurs in the effluents discharged from agriculture and manufacturing industries, and persistence of such pollutants are harmful to any living organisms (Kjeldsen et al, 2002; Foo and Hameed, 2009). Benzoate is a typical aromatic pollutant found in the waste stream at typical pH 4.0 (Oie et al, 2007; Xie et al, 2009) Another example is nicotine, which is a predominant compound contaminated in the effluent from tobacco factories. Enhancing Acid Tolerance of Pseudomonas putida stream at shallow pH values (pH < 5) (Dixon et al, 2000; Zhong et al, 2010; Li et al, 2019) These acidic conditions limit the survival and biodegradation activities of neutrophilic pollutantdegrading bacteria like pseudomonads that generally dominate the polluted sites. Genetics improvement of these bacteria by enhancing their acid stress resistance would be a promising strategy to optimize biological waste treatments
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