Cellular response mechanisms inPseudomonas aeruginosaPseA during growth in organic solvents

Abstract

Aims: Solvent‐tolerant bacteria have emerged as a new class of micro‐organisms able to grow at high concentrations of toxic solvents. Such bacteria and their solvent‐stable enzymes are perceived to be useful for biotransformations in nonaqueous media. In the present study, the solvent‐responsive features of a lipase–producing, solvent‐tolerant strain Pseudomonas aeruginosa PseA have been investigated to understand the cellular mechanisms followed under solvent‐rich conditions. Methods and Results: The solvents, cyclohexane and tetradecane with differing log P‐values (3·2 and 7·6 respectively), have been used as model systems. Effect of solvents on (i) the cell morphology and structure (ii) surface hydrophobicity and (iii) permeability of cell membrane have been examined using transmission electron microscopy, atomic force microscopy and other biochemical techniques. The results show that (i) less hydrophobic (low log P‐value) solvent cyclohexane alters the cell membrane integrity and (ii) cells adapt to organic solvents by changing morphology, size, permeability and surface hydrophobicity. However, no such changes were observed in the cells grown in tetradecane. Conclusions: It may be concluded that P. aeruginosa PseA responds differently to solvents of different hydrophobicities. Bacterial cell membrane is more permeable to less hydrophobic solvents that eventually accumulate in the cytoplasm, while highly hydrophobic solvents have lesser tendency to access the membrane. Significance and Impact of the Study: To the best of our knowledge, these are first time observations that show that way of bacterial solvent adaptability depends on nature of solvent. Difference in cellular responses towards solvents of varying log P‐values (hydrophobicity) might prove useful to search for a suitable solvent for carrying out whole‐cell biocatalysis.

A Proteomic Approach to Understand the Role of the Outer Membrane Porins in the Organic Solvent-Tolerance of Pseudomonas aeruginosa PseA

“…The up-regulation of Opr86 in the present case may be due to the damage to the outer membrane caused by the solvents and an imminent need thereof, for its repair. In our previous studies related to the solvent effect on the cells of P. aeruginosa , we have shown the damage caused to the membrane in presence of toxic solvents and also the intracellular accumulation of solvents [13]. Hence, the up-regulation of OprH in presence of organic solvents of lower log P ow value and of Opr86 in all the solvent-treated samples, supports our previous observation.…”

“…It has been well characterized for its solvent-tolerant traits [2], [12], [13]. A previous study on the cellular mechanisms for solvent tolerance of this strain revealed that cyclohexane (log P ow ) altered the cell growth, morphology, size, membrane integrity, permeability and surface hydrophobicity, whereas n-tetradecane (log P ow ) did not affect any of these parameters [18].…”

Highly Solvent Tolerance in Serratia marcescens IBBPo15

“…Cell membrane permeability was determined using the method indicated by Gaur and Khare 14 . The absorbance of cell-free culture broths was measured at 260 nm using a SPECORD 200 UVvisible spectrophotometer (Analytik Jena, Jena, Germany).…”

“…However, toxic organic solvents are able to penetrate into cytoplasmic membrane resulting in swelling of the membrane and increase of membrane fluidity which leads to the loss of membrane functionality and to the damage of bacterial cell. The leakage of DNA macromolecules was previously described 14 for the bacterial cells grown in the presence of toxic organic solvents. Bacterial cells try to undertake proper responses to reduce the disruptive effect of organic compounds by readjustment of membrane fluidity 3 .…”

Extremophiles: An Overview of Microorganism from Extreme Environment

“…protein engineering (Martinez and Arnold, 1991;Gerike et al, 2001), chemical modification (Tyagi and Gupta, 1998;Gaur and Khare, 2009;Gupta and Khare, 2009), directed evolution (Arnold and Moore, 1998) and immobilization (Gaur et al, 2008;Datta et al, 2013). Some of these are also promising but loss in enzyme activity and cost of stabilization are major drawbacks.…”