Evaluation of microbial agents as corrosion and scale inhibitor for industrial cooling water applications

Untargeted metabolomic analysis reveals the mechanism of Enterococcus faecium agent induced CaCO3 scale inhibition

In this study, a lactic acid bacterium, Enterococcus faecium, was found to prevent CaCO₃ precipitation through its metabolism. On analysis of all stages of E. faecium growth, static jar tests demonstrated that stationary phase E. faecium broth possessed the highest inhibition efficiency of 97.3% at a 0.4% inoculation dosage, followed by the decline and log phases with efficiencies of 90.03% and 76.07%, respectively. Biomineralization experiments indicated that E. faecium fermented the substrate to produce organic acid, which resulted in modulation of the pH and alkalinity of the environment and thus inhibited CaCO₃ precipitation. Surface characterization techniques indicated that the CaCO₃ crystals precipitated by the E. faecium broth tended to be significantly distorted and formed other organogenic calcite crystals. The scale inhibition mechanisms were revealed by untargeted metabolomic analysis on log and stationary phase E. faecium broth. In total, 264 metabolites were detected, 28 of which were differential metabolites (VIP ≥ 1 and p < 0.05). Of these, 15 metabolites were upregulated in stationary phase broth, and 13 metabolites were downregulated in log phase broth. Metabolic pathway analysis suggested that improved glycolysis and the TCA cycle were the main reasons for enhancement of the antiscaling performance of E. faecium broth. These findings have significant implications for microbial metabolism-induced CaCO₃ scale inhibition.

Biofilm-induced corrosion inhibition of Q235 carbon steel by anaerobic Bacillus cereus inoculum in simulated cooling water

In this study, the corrosion behavior of Q235 carbon steel (CS) under a Bacillus cereus (B. cereus) inoculum in simulated cooling water was evaluated. The weight loss study proved B. cereus inoculum possessed anticorrosion efficiencies of 92.84% and 73.88% for 3-day and 14-day rotation tests, respectively. The electrochemical measurements indicated that the added B. cereus inoculum increased the charge transfer resistance and reduced corrosion current density. B. cereus cells with strong biofilm-forming capacity were able to adhere onto the Q235 CS surface to form compact biofilms and cause biomineralization. Surface characterization analysis demonstrated that the presence of the B. cereus inoculum reduced the amount of Fe₂O₃ and simultaneously increased the amount of CaCO₃ in corrosion products. The corrosion inhibition mechanisms of the B. cereus inoculum involve forming biofilm, generating a biomineralized layer, and consuming dissolved oxygen. Thus, B. cereus inoculum provides a biological strategy for industrial cooling water anticorrosion application.

Synergistic inhibition of Pseudomonas fluorescens growth and proteases activities via sodium chlorite-based oxyhalogen

Pseudomonas fluorescens is considered among the main spoilage microorganisms due to its ability to produce proteases. Food deterioration caused by spoilage microorganisms has a major impact on food quality and the environment. The inactivation of Pseudomonas fluorescens growth and protease production was intensively investigated with the use of Salmide®, A Sodium Chlorite-Based Oxy-halogen Disinfectant. A unique M9 media was also developed to assure sufficient protease productions with different mutants of Pseudomonas fluorescens as a microbioreactor. Mutations were induced by classical whole-cell mutagenesis using N-methyl-N'- nitro-N-nitrosoguanidine (NTG). A dramatic decrease occurred in protease activity when different Salmide concentrations (5, 10, and 15 ppm) were added to the growth culture followed by a complete inhibition concentration (20, 25, 50, and 100 ppm) of Salmide. However, no significant inhibition occurred once it is secreted out of cells. Some mutants were resistant and remains highly stable with high protease production under stressful conditions of Sodium Chlorite-Based Oxy-halogen. The production of the protease showed a linear correlation with the increase in incubation time using a continuous culture bioreactor system and recorded maximum protease activity after 40 h. Our findings would offer alternative antimicrobial procedures for food and industrial sectors.