Abstract
Phenol and formalin are major water pollutants that are frequently discharged into the aquatic milieu. These chemicals can affect broad domains of life, including microorganisms. Aquatic pollutants, unlike terrestrial pollutants, are easily diluted in water environments and exist at a sub-inhibitory concentration (sub-IC), thus not directly inhibiting bacterial growth. However, they can modulate gene expression profiles. The sub-IC values of phenol and formalin were measured by minimal inhibitory concentration (MIC) assay to be 0.146% (1.3 mM) and 0.0039% (0.38 mM), respectively, in Edwardsiella piscicida CK108, a Gram-negative fish pathogen. We investigated the differentially expressed genes (DEG) by RNA-seq when the cells were exposed to the sub-ICs of phenol and formalin. DEG analyses revealed that genes involved in major virulence factors (type I fimbriae, flagella, type III and type VI secretion system) and various cellular pathways (energy production, amino acid synthesis, carbohydrate metabolism and two-component regulatory systems) were up- or downregulated by both chemicals. The genome-wide gene expression data corresponded to the results of a quantitative reverse complementary-PCR and motility assay. This study not only provides insight into how a representative fish pathogen, E. piscicida CK108, responds to the sub-ICs of phenol and formalin but also shows the importance of controlling chemical pollutants in aquatic environments.
Highlights
Environmental pollutants are gradually increasing, along with the rising demands of chemical products and energy generation due to population growth and industrial development
A high concentration of terrestrial contaminants flowing into water environments can be fatal to microorganisms that thrive in aquatic habitats [1,2,3]
Fish lethality derived from the virulence factors of E. piscicida causes enormous economic losses so various types of antibiotics and chemicals are utilized in the aquaculture industry [11,12]
Summary
Environmental pollutants are gradually increasing, along with the rising demands of chemical products and energy generation due to population growth and industrial development. One type of the listed chemicals, are generated by natural processes and present in limited amounts in nature, the human-related large volume of phenol production and leakage from petroleum refining, the petrochemical industry, pharmaceutical companies, electronics factories and coal conversion factories is fatal to living organisms including humans [5,6]. Fish lethality derived from the virulence factors of E. piscicida causes enormous economic losses so various types of antibiotics and chemicals are utilized in the aquaculture industry [11,12]. We used genome-wide transcriptional profiling with RNA-seq to understand the metabolic alterations when E. piscicida CK108 is exposed to the sub-ICs of an aquatic pollutant and a disinfectant widely used in the fish industry—phenol and formalin, respectively. This work provides the fundamental transcriptomic knowledge of the marine pathogen when phenol and formalin are present and insights of the appropriate use of chemicals to prevent from potential side effects in marine ecosystems
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