Immediate response mechanisms of Gram-negative solvent-tolerant bacteria to cope with environmental stress: cis-trans isomerization of unsaturated fatty acids and outer membrane vesicle secretion

Abstract

Bacteria have evolved an array of adaptive mechanisms enabling them to survive and grow in the presence of different environmental stresses. These mechanisms include either modifications of the membrane or changes in the overall energy status, cell morphology, and cell surface properties. Long-term adaptations are dependent on transcriptional regulation, the induction of anabolic pathways, and cell growth. However, to survive sudden environmental changes, bacterial short-term responses are essential to keep the cells alive after the occurrence of an environmental stress factor such as heat shock or the presence of toxic organic solvents. Thus far, two main short-term responses are known. On the one hand, a fast isomerization of cis into trans unsaturated fatty leads to a quick rigidification of the cell membrane, a mechanism known in some genera of Gram-negative bacteria. On the other hand, a fast, effective, and ubiquitously present countermeasure is the release of outer membrane vesicles (OMVs) from the cell surface leading to a rapid increase in cell surface hydrophobicity and finally to the formation of cell aggregates and biofilms. These immediate response mechanisms just allow the bacteria to stay physiologically active and to employ long-term responses to assure viability upon changing environmental conditions. Here, we provide insight into the two aforementioned rapid adaptive mechanisms affecting ultimately the cell envelope of Gram-negative bacteria.

Transcriptional regulation of fatty acid cis–trans isomerization in the solvent‐tolerant soil bacterium, Pseudomonas putida F1

“…The previously reported constitutive cti expression in solvent-treated bacteria led to the establishment of a Cti regulation model, according to which Cti activity is not controlled at the transcriptional level, but rather by simply allowing or prohibiting the active center of the enzyme to reach the double bond, which would depend only on membrane fluidity (Heipieper et al, 2010;Eberlein et al, 2018). The activation of cti expression in octanol-treated P. putida F1 cultures observed in our studies C. β-Galactosidase activity of pFCtiPP1 showing than Crp represses cti expression in P. putida F1.…”

“…Cti, which located in the cellular periplasm (Pedrotta and Witholt, 1999), is a cytochrome c-type protein, bearing a heme-binding motif essential for the cis to trans isomerization reaction (Holtwick et al, 1999). Moreover, the highest levels of the trans-UFA were found 30 min after the initiated stress, demonstrating cis-trans isomerization to be a fast adaptive response Eberlein et al, 2018).…”

“…It is generally accepted that cti is constitutively expressed in Pseudomonas spp. (Kiran et al, 2004) and proposed to be regulated only post-translationally by the membrane fluidity (Eberlein et al, 2018). However, Bernal and colleagues (2007) reported the upregulation of P. putida cti expression in response to the toluene addition, raising the question about a possible transcriptional cti regulation in this bacterium.…”

Toward Biorecycling: Isolation of a Soil Bacterium That Grows on a Polyurethane Oligomer and Monomer

“…The fatty acid composition and pattern of TDA1 was the same as the one of strain P. putida KT2440 which was used as a control and benchmark. In addition, the gene for the cis-trans isomerase of unsaturated fatty acids (CTI), an important marker gene for the genus Pseudomonas (Palleroni, 2015;Eberlein et al, 2018), is present in the TDA1 genome (gene 13840) revealing more than 90% amino acid sequence identity with several Pseudomonas CTIs already present in the protein BLAST database (for example: Accession numbers Q8RJN7, A0A059V043, and F8FYU0). Also, the CTI phenotype, regularly given as solvent stress-depending increase in the trans/cis ratio of unsaturated fatty acids, was detected in the presence of 2,4-TDA in P. putida KT2440 (Figure 2).…”

Membrane Rigidity and Phosphatidic Acid (PtdOH) Signal: Two Important Events in Acinetobacter guillouiae SFC 500‐1A Exposed to Chromium(VI) and Phenol

“…In microorganisms like bacteria, PLA 2 is activated under diverse stress conditions (Belosludtsev et al, 2014;Istivan and Coloe, 2006;Zheng et al, 2017). However, few studies have reported bacterial membrane changes under stress by heavy metals and aromatic compounds, and even fewer have described the changes in PL head groups or acyl chains under simultaneous Cr(VI) and phenol treatment (Eberlein et al, 2018;Markowicz et al, 2010;Pepi et al, 2008;Waranusantigul et al, 2011). The presence of these and other pollutants generates environmental signals whose perception is considered to occur at the cell membrane level (Sohlenkamp and Geiger, 2015).…”