Search

The response of Staphylococcus aureus to hypochlorous acid (HOCI) exposure was investigated. HOCI challenges were performed on cultures interrupted in the exponential phase. Pretreatment with HOCI conferred resistance to hydrogen peroxide in a PerR-dependent manner. Derepression of the PerR regulon was observed at low HOCI concentration (survival > 50%), using several fusions of different stress promoters to lacZ reporter genes. At least four members of the PerR regulon (katA, mrgA, bcp and trxA) encoding proteins with antioxidant properties were strongly induced following exposure to various HOCI concentrations. A striking result was the link between the derepression of the PerR regulon and the decreased superoxide dismutase (SOD) activity following exposure to increased HOCl concentrations. The soda mutant was more resistant than the wild-type and also had a higher level of 3-phosphoglycerate dehydrogenase (a measure of PerR regulon activity) without exposure to HOCI. Together, these results imply that derepression of PerR by HOCI is dependent on the level of SOD and protects exponentially arrested cells against HOCI stress.

The behaviour of Aeromonas hydrophila in nutrient-poor filter-sterilized seawater was investigated at 23 and 5 [degrees]C with respect to its growth phase. At both temperatures, the culturable A. hydrophila population declined below the detection level (0*1 c.f.u, [ml.sup.-1]) after 3-5 weeks, depending on the initial physiological state of the cells. During the first week, starved A. hydrophila cells appeared more resistant to the seawater stress at 5 [degrees]C than cells initially in the exponential growth phase. This difference was not observed at 23 [degrees]C, where de novo protein synthesis seemed to be required for long-term adaptation of cells from the exponential growth phase. Over the duration of the experiments, intact and total cell concentrations were not significantly affected, indicating that bacteria had entered a so-called viable but nonculturable state (VBNC). However, the incubated bacteria rapidly became heterogeneous with respect to their nucleic acid content, and their cell size decreased faster at 23 than at 5 [degrees]C. Resuscitation of VBNC cells was attempted by a temperature shift from 5 to 23 [degrees]C without exogenous nutrient addition. Comparison of the growth rates of the stressed population and of the untreated bacteria growing in the same autoclaved initial cell suspension showed significantly faster growth for the stressed cells, suggesting that in addition to growth of the few culturable stressed cells, a proportion of injured cells became culturable.

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. [ABSTRACT FROM AUTHOR]

A total of 54 halophilic strains were isolated from crystallizer TS18 (26 strains) and non-crystallizer M1 (28 strains) ponds and screened for their ability to produce protease, amylase, and lipase activities. Enzymatic assays allowed the selection of thirty-two active strains, among them, the ETR14 strain from TS18 showed maximum protease production yields and therefore, selected for further analysis. The results from 16S rRNA gene sequence analysis revealed that the strain belonged to Halorubrum ezzemoulense ( Hrr. ezzemoulense) species. Further results indicated that optimum growth and protease production yields were obtained with 10-15% NaCl concentrations in the DSC-97 medium. The enzyme was also able to maintain high levels of protease activity at salt concentrations of up to 25%. While readily available carbon sources were noted to significantly reduce protease production, the combination between yeast extract and peptone enhanced protease excretion, which reached a maximum of 284 U ml−1 at the end of the exponential growth phase. The enzyme exhibited optimum activity at pH 9 and 60°C. The halophilic protease retained 87% of its initial activity after 1 h incubation at 70 °C and showed high stability over a wide range of pH, ranging from 7 to 10. This protease exhibited good temperature, pH, and salinity tolerance, which distinguishes it from other proteases previously described from other members of the holoarchaea genera and makes it a promising candidate for application in various industries. [ABSTRACT FROM AUTHOR]

An extremely halophilic archaeon, strain ETD6, was isolated from a marine solar saltern in Sfax, Tunisia. Analysis of the 16S rRNA gene sequence showed that the isolate was phylogenetically related to species of the genus Halorubrum among the family Halobacteriaceae, with a close relationship to Hrr. xinjiangense (99.77% of identity). However, value for DNA-DNA hybridization between strain ETD6 and Hrr. xinjiangense were about 24.5%. The G+C content of the genomic DNA was 65.1mol% (T(m)). Strain ETD6 grew in 15-35% (w/v) NaCl. The temperature and pH ranges for growth were 20-55°C and 6-9, respectively. Optimal growth occurred at 25% NaCl, 37°C, and pH 7.4. The results of the DNA hybridization against Hrr. xinjiangense and physiological and biochemical tests allowed genotypic and phenotypic differentiation of strain ETD6 from other Hrr. species. Therefore, strain ETD6 represents a novel species of the genus Halorubrum, for which the name Hrr. sfaxense sp. nov. is proposed. The Genbank EMBL-EBI accession number is GU724599. [ABSTRACT FROM AUTHOR]

In this study, a novel fatty acid anhydride, named phalarisin 1, was successfully isolated from the ethyl acetate extract of Phalaris canariensis growing in Tunisia. The structural characterisation of the compound was achieved through various spectroscopic techniques including FT-IR, 1D and 2D-NMR spectroscopy, as well as acidic hydrolysis analyses. Remarkably, phalarisin exhibited potent antimicrobial properties against a range of pathogens including Micrococcus luteus , Bacillus subtilis , Fusarium oxysporum , and Fusarium phylophylum , with minimum inhibitory concentrations (MICs) ranging from 31.25 to 62.5 μg/mL. To grasp the antimicrobial potential of compound 1, molecular docking studies were performed and they furnished evidence indicating its ability to bind to proteins in bacteria and fungi that are pivotal for drug resistance.