Abstract
Paludifilum halophilum DSM 102817T is the first member of the genus Paludifilum in the Thermoactinomycetaceae family. The thermohalophilic bacterium was isolated from the solar saltern of Sfax, Tunisia and was shown to be able to produce ectoines with a relatively high-yield and to cope with salt stress conditions. In this study, the whole genome of P. halophilum was sequenced and analysed. Analysis revealed 3,789,765 base pairs with an average GC% content of 51.5%. A total of 3775 genes were predicted of which 3616 were protein-coding genes and 73 were RNA genes. The genes encoding key enzymes for ectoines (ectoine and hydroxyectoine) synthesis (ectABCD) were identified from the bacterial genome next to a gene cluster (ehuABCD) encoding a binding-protein-dependent ABC transport system responsible for ectoines mobility through the cell membrane. With the aid of KEGG analysis, we found that the central catabolic network of P. halophilum comprises the pathways of glycolysis, tricarboxylic acid cycle, and pentose phosphate. In addition, anaplerotic pathways replenishing oxaloacetate and glutamate synthesis from central metabolism needed for high ectoines biosynthetic fluxes were identified through several key enzymes. Furthermore, a total of 18 antiSMASH-predicted putative biosynthetic gene clusters for secondary metabolites with high novelty and diversity were identified in P. halophilum genome, including biosynthesis of colabomycine-A, fusaricidin-E, zwittermycin A, streptomycin, mycosubtilin and meilingmycin. Based on these data, P. halophilum emerged as a promising source for ectoines and antimicrobials with the potential to be scaled up for industrial production, which could benefit the pharmaceutical and cosmetic industries.
Highlights
Among extreme niches, natural and artificial hypersaline habitats were shown to harbor several species of halotolerant and halophilic bacteria (Boujelben et al 2015; Gibtan et al 2017)
P. halophilum depends on a considerable salt concentration for its growth but it can cope with a broad spectrum of salinities
This work presents the first insight into the genome of the highly salt resistant bacterium P. halophilum
Summary
Natural and artificial hypersaline habitats were shown to harbor several species of halotolerant and halophilic bacteria (Boujelben et al 2015; Gibtan et al 2017). Besides their primary function of protecting cells against harch conditions, the most powerful stabilizing properties on biological macromolecules (enzymes, DNA, antibodies, and even whole cells) confer ectoines attractive potentials in fields of skin caring, food processing, molecular biology, agriculture, biotechnology, and medical values in human diseases (Kanapathipillai et al 2005; Graf et al 2008; Pastor et al 2010; Abdelaziz et al 20013; Hahn et al 2017) This led to the development of the first industrial-scale production process using the salt-tolerant bacterium Halomonas elongata as the production host (Schwibbert et al 2011; Kunte et al 2014). Some microorganisms are able to synthesize a hydroxylated derivative of ectoine, the 5-hydroxyectoine catalyzed by the ectoine hydroxylase (EctD) (Prabhu et al 2004; Garcia-Estepa et al 2006; Höppner et al 2014)
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