Inactivation combined with cell lysis of Pseudomonas putida using a low pressure carbon dioxide microbubble technology

Dissolved iron released from nanoscale zero-valent iron (nZVI) activates the defense system in bacterium Pseudomonas putida, leading to high tolerance to oxidative stress

Nanoscale zero-valent iron (nZVI) has increasingly been applied to remediate aquifers polluted by organochlorines or heavy metals. As a result, bacteria in the vicinity of remediate action can be stressed by surplus iron released from nZVI. However, the understanding of the iron stress defense pathways during this process is currently incomplete. Therefore, we aimed to elucidate the physiological and transcriptomic response of the bacterium, Pseudomonas putida NCTC 10936, to 100 mg/L of nZVI and 44.5 µg/L of dissolved iron obtained from nZVI suspension. Cell viability was neither affected by nZVI nor dissolved iron, although the dissolved iron caused stress that altered the cell physiology and caused the generation of smaller cells, whereas cells were elongated in the presence of nZVI. Transcriptomic analysis confirmed the observed stronger physiological effect caused by dissolved iron (in total 3839 differentially expressed genes [DEGs]) than by nZVI (945 DEGs). Dissolved iron (but not nZVI) activated genes involved in oxidative stress-related pathways, antioxidant activity, carbohydrate and energy metabolism, but downregulated genes associated with flagellar assembly proteins and two-component systems involved in sensing external stimuli. As a result, bacteria very effectively faced oxidative insults and cell viability was not affected.

Determination of the Lethal Injury on the Inactivation of Saccharomyces pastorianus Cells by Low-pressure Carbon Dioxide Microbubbles

To clarify the lethal injury related to the inactivation of Saccharomyces pastorianus cells by low-pressure carbon dioxide microbubble (CO₂MB) treatment, surviving number, leakage of nucleic acids and proteins, fluorescence polarisation (FP) of the cell membrane, activity of alkaline phosphatase (AP), intracellular pH (pH_in), mitochondrial membrane potential (MMP), cell surface hydrophobicity (CSH) and oxidative stress of S. pastorianus treated with CO₂MB at various temperatures were measured. The number of surviving S. pastorianus cells decreased below the detection limit after CO₂MB treatment at temperatures of 40, 45 and 50 ℃, inducing a 2-log reduction at 35 ℃. The S. pastorianus cells treated with CO₂MB at temperatures above 40 ℃ showed an increase in FP and leakage of nucleic acids and proteins. The AP in S. pastorianus cells treated with CO₂MB at a temperature of 35 ℃ was also activated but inactivated at temperatures above 40 ℃. Furthermore, the decrease in pH_in and MMP and the increase in CSH of S. pastorianus were caused by CO₂MB treatment at temperatures above 35 ℃. Oxidative stress in S. pastorianus cells was also increased by CO₂MB treatment without warming but decreased at temperatures above 35 ℃. Our results lead us to infer that the type of cell injury in S. pastorianus induced by CO₂MB treatment differed from that caused by the treatment temperature and that the lethal injury was enzyme inactivation.

On the Ability of Perfluorohexane Sulfonate (PFHxS) Bioaccumulation by Two Pseudomonas sp. Strains Isolated from PFAS-Contaminated Environmental Matrices

PFASs (perfluoroalkyl and polyfluoroalkyl substances) are highly fluorinated, aliphatic, synthetic compounds with high thermal and chemical stability as well as unique amphiphilic properties which make them ingredients in a range of industrial processes. PFASs have attracted consideration due to their persistence, toxicity and bioaccumulation tendency in the environment. Recently, attention has begun to be addressed to shorter-chain PFASs, such as perfluorohexane sulfonate [PFHxS], apparently less toxic to and more easily eliminated from lab animals. However, short-chain PFASs represent end-products from the transformation of fluorotelomers whose biotic breakdown reactions have not been identified to date. This means that such emergent pollutants will tend to accumulate and persist in ecosystems. Since we are just learning about the interaction between short-chain PFASs and microorganisms, this study reports on the response to PFHxS of two Pseudomonas sp. strains isolated from environmental matrices contaminated by PFASs. The PFHxS bioaccumulation potential of these strains was unveiled by exploiting different physiological conditions as either axenic or mixed cultures under alkanothrofic settings. Moreover, electron microscopy revealed nonorthodox features of the bacterial cells, as a consequence of the stress caused by both organic solvents and PFHxS in the culturing substrate.

Viability of Molds and Bacteria in Tempeh Processed with Supercritical Carbon Dioxides during Storage

Application of supercritical carbon dioxide for processing of food products has an impact on microbial inactivation and food quality. This technique is used to preserve tempeh due to no heat involved. The quality of tempeh is highly influenced by mold growth because of its role in forming a compact texture, white color, and functional properties as well as consumer acceptance. This study aims to observe viability of molds and bacteria in tempeh after processed with supercritical CO₂ and to determine the best processing conditions which can maintain mold growth and reduce the number of bacteria in tempeh. For that purpose, tempeh was treated using high pressure CO₂ at 7.6 MPa (supercritical CO₂) and at 6.3 MPa (sub/near supercritical CO₂) with incubation period of 5, 10, 15, and 20 min. The best treatment obtained was used to process tempeh for storage study. The results showed that there was a significant interaction between pressure and incubation period for bacterial and mold viability at ρ>0.05. Reduction of bacteria and molds increased with longer incubation period. Molds were undetectable after treatment for 20 min with either supercritical CO₂ or sub-supercritical, and bacteria significantly reduced up to 2.40 log CFU/g. On the other hand, sub-supercritical CO₂ for 10 min was the best processing method because molds survived 4.3x10⁴ CFU/gram after treatment and were able to grow during storage at 30°C, producing white mycelium as indicated by increasing the L⁎ color value and tempeh acceptability. The inactivation of mold was reversible causing it to grow back during storage under suitable conditions. Tempeh matrix composition can provide protection against the destructive effects of supercritical CO₂. Gram-positive bacteria were more resistant than Gram-negative. In conclusion, sub-supercritical CO₂ can act as a method of cold pasteurization of tempeh and can be used as an alternative method to preserve tempeh.

Ethanol addition on inactivation of Saccharomyces pastorianus by a two-stage system with low-pressure carbon dioxide microbubbles can accelerate the cell membrane injury

The effect of ethanol on the inactivation of Saccharomyces pastorianus by a two-stage system with low-pressure carbon dioxide microbubbles (two-stage MBCO₂ ) was investigated. Zero and >5 log reductions of S. pastorianus populations suspended in physiological saline (PS) containing 0% and 10% ethanol, respectively, occurred by the two-stage MBCO₂ at a mixing vessel pressure of 1 MPa and a heating coil temperature of 40°C. Conversely, the detected number of surviving S. pastorianus cells in PS containing 5% ethanol was higher in yeast and mold agar (YMA, an optimum agar) than YMA with 2.5% sodium chloride, followed by yeast nitrogen base agar (YNBA, a minimum agar). The fluorescence polarization of S. pastorianus in PS containing 5% and 10% ethanol increased similarly with exposure time in the heating coil of two-stage MBCO₂ and was correlated with the surviving cell number measured in YNBA. The intracellular pH (pH_in ) of S. pastorianus in PS containing 5% ethanol decreased linearly with exposure time in the heating coil of two-stage MBCO₂ . Also, the pH_in -lowering of S. pastorianus in PS containing 10% ethanol was drastically caused by two-stage MBCO₂ at 1 min exposure time in the heating coil but then stayed constant until 5 min, agreeing with the inactivation efficiency. Therefore, ethanol in S. pastorianus suspension was suggested to accelerate the cell membrane injury caused by two-stage MBCO₂ . © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:282-286, 2018.