Biological functions of nirS in Pseudomonas aeruginosa ATCC 9027 under aerobic conditions

Through our previous study, we found an up-regulation in the expression of nitrite reductase (nirS) in the isothiazolone-resistant strain of Pseudomonas aeruginosa. However, the definitive molecular role of nirS in ascribing the resistance remained elusive. In the present study, the nirS gene was deleted from the chromosome of P. aeruginosa ATCC 9027 and the resulting phenotypic changes of ΔnirS were studied alongside the wild-type (WT) strain under aerobic conditions. The results demonstrated a decline in the formations of biofilms but not planktonic growth by ΔnirS as compared to WT, especially in the presence of benzisothiazolinone (BIT). Meanwhile, the deletion of nirS impaired swimming motility of P. aeruginosa under the stress of BIT. To assess the influence of nirS on the transcriptome of P. aeruginosa, RNA-seq experiments comparing the ΔnirS with WT were also performed. A total of 694 genes were found to be differentially expressed in ΔnirS, of which 192 were up-regulated, while 502 were down-regulated. In addition, these differently expressed genes were noted to significantly enrich the carbon metabolism along with glyoxylate and dicarboxylate metabolisms. Meanwhile, results from RT-PCR suggested the contribution of mexEF-oprN to the development of BIT resistance by ΔnirS. Further, c-di-GMP was less in ΔnirS than in WT, as revealed by HPLC. Taken together, our results confirm that nirS of P. aeruginosa ATCC 9027 plays a role in BIT resistance along with biofilm formation and further affects several metabolic patterns under aerobic conditions.

Isothiazolone emissions from building products

Adding biocides to dispersion products is a well-known practice to control microbial deterioration. Isothiazolones are among the most commonly used preservatives, in particular a mixture of 2-methyl-2H-isothiazol-3-one (MIT) and 5-chloro-2-methyl-2H-isothiazol-3-one (CIT). In recent years, for health reasons, due to its strong sensitizing effect, CIT has been replaced by 1,2-benzisothiazol-3-one (BIT). Furthermore, numerous products are now available for interiors containing the fungicidal active substance 2-octyl-2H-isothiazol-3-one (OIT). So far nearly nothing is known of the emission behavior of BIT and OIT. An analytical method was developed for these two isothiazolones and interior products containing BIT respectively OIT have been investigated in an emission chamber and in test rooms. The chamber tests revealed maximum concentrations of 6.7 μg OIT/m3, 1.9 μg BIT/m3, and 187 μg MIT/m3. Concentrations obtained in the test rooms were at levels up to 1.4 μg OIT/m3 and 29 μg MIT/m3. A noticeable finding was the very slight subsidence of OIT and BIT levels over several weeks. While MIT outgassed quickly, OIT in particular showed low concentrations, but prolonged evaporation.

Three-phase hollow-fiber liquid-phase microextraction combined with HPLC-UV for the determination of isothiazolinone biocides in adhesives used for food packaging materials

The present study deals with the development of a liquid microextraction procedure for enhancing the sensitivity of the determination of 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one in adhesives. The procedure involves a three-phase hollow-fiber liquid-phase microextraction using a semipermeable polypropylene membrane, which contained 1-octanol as the organic phase in the pores of the membrane. The donor and acceptor phases are aqueous acidic and alkaline media, respectively, and the final liquid phase (acceptor) is analyzed by HPLC coupled with diode array detection. The most appropriate conditions were extraction time 20 min, stirring speed 1400 rpm, extraction temperature 50°C. The quantification limits of the method were 0.123 and 0.490 μg/g for 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one, respectively. Three different adhesive samples were successfully analyzed. The procedure was compared to direct analysis using ultra high pressure liquid chromatography coupled with TOF-MS, where the identification of the compounds and the quantification values were confirmed.