Bacteria, Membranes And Environmental Challenges

Amazoniac

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Karma, karma, karma-chameleons;

A brief review on how bacteria adapt to their environment, including the alteration of their membrane fatty acid saturation to resist challenges. Note that this is under extreme (but stable) circumstances; the microbes that adapt better can thrive without much competition, unlike inside a humanoid.

Multiple responses of Gram-negative bacteria to organic solvents - Segura - 1999 - Environmental Microbiology - Wiley Online Library

"The main function of the cell membrane of microorganisms is to form a permeability barrier, regulating the passage of solutes between the cell and the external environment (Nikaido, 1999). The barrier properties of the cytoplasmic membrane are of special importance for the energy transduction of the cell (Sikkema et al., 1995). The major damage caused by organic solvents on the cell membrane is the impairment of vital functions, e.g. loss of ions, metabolites, lipids and proteins, the dissipation of the pH gradient and electrical potential or the inhibition of membrane protein functions. This is often followed, in turn, by cell lysis and death (de Smet et al., 1978; Sikkema et al., 1995).”

*From Sigma Aldrich's website:
"Common aromatic hydrocarbon solvents used in paints and coatings are benzene, toluene, ethylbenzene, mixed xylenes (BTEX) and high flash aromatic naphthas. Additional information can be found under our Petrochemical Industry VOCs guide. Aromatic solvents are also widely used in printing inks, pesticides, insecticides, and agricultural chemicals."

They then suggest that bacteria have three main strategies to deal with toxic insults. 1, transform to a safer compound; 2, alter the structure of the membrane, so they are less permeable and more rigid; 3, excrete relying on energy to do that.

Commenting later that the strategy #1 is not significant because some bacteria can tolerate extreme insults despite not being able to metabolize and transform the compound. #2-3 are the focus of the review.


" There are two major mechanisms for changing the ester-linked fatty acid composition, and thus membrane fluidity, in bacterial lipid bilayers: the cis/trans isomerization of fatty acids as a short-term response; and the change in the saturated–unsaturated fatty acid ratio as a long-term response to solvent exposure. Additionally, the ratio of long-chain to short-chain fatty acids can also be altered to regulate membrane fluidity. Figure 1 shows that the steric behaviour of trans fatty acids and saturated fatty acids is very similar, as both possess a long extended conformation allowing a denser packing of the membrane. In contrast, the cis configuration of the acyl-chain has a non-movable bend of 30°, which causes steric hindrance and disturbs the highly ordered fatty acid package. The cis fatty acids have a lower phase transition temperature than the corresponding trans isomers (Keweloh and Heipieper, 1996).”

In other words, as an immediate response they try to mimic the rigidity of SaFA by altering the conformation of their unsaturated fatty acid membranes.

"Organic solvents increase membrane fluidity, and an increment in trans fatty acid content could counteract the alteration in membrane fluidity."

"The major importance of the cis/trans conversion lies in the fact that the constitutively expressed enzyme Cti can thus trigger an immediate emergency response to overcome initial membrane damage. By doing this, the cells gain time for a more precise adjustment to the new environmental conditions. In the meantime, a long-term response can be triggered."

" A temperature increase, which has a fluidizing effect on the lipid bilayer like some organic solvents, has been shown to lead to an upregulation of saturated fatty acids in the psychrophilic Vibrio sp., E. coli and P. putida P8, whereas a decrease in temperature promoted the formation of unsaturated fatty acids (Cronan, 1968; Hamamoto et al., 1994; Loffeld and Keweloh, 1996). This widespread strategy to regulate membrane fluidity depends on the de novo synthesis of fatty acids, a process that is time-consuming and might not be quick enough to enable bacteria to survive a solvent or heat shock, especially if they are slow growing. An augmentation in the saturated fatty acid content in P. putida strain Idaho was observed as late as 15 min after solvent exposure (Pinkart and White, 1997); this adaptation mechanism is considered to be a long-term response.”

“The change in phospholipid headgroups is a less well- studied phenomenon, and few data on it are available. The composition of the phospholipid headgroup influences membrane fluidity (Weber and de Bont, 1996).

In the presence of toluene, changes in the phospholipid headgroup composition were observed for P. putida S-12 in a chemostat. In the phospholipid headgroup, phosphatidylethanolamine (PE) decreased and diphosphatidylglycerol (DPG) as well as phosphatidylglycerol (PG) increased. DPG has a higher transition temperature than PE (10°C higher), which lowers membrane fluidity, producing a stabilizing effect (Weber and de Bont, 1996).”

“A detailed analysis of the phospholipid headgroup biosynthesis in the presence of xylene in P. putida strain Idaho revealed an increase in the level of PE and a decrease in the level of PG. PE has a higher melting point than PG and, thus, its increase tends to stabilize the cell membrane. Therefore, different Pseudomonas strains seem to have developed different strategies for changing phospholipid headgroup composition to increase membrane rigidity and, in this way, to overcome the damaging effects of solvents.”

“Changes in outer membrane proteins and lipopolysaccharides (LPS) after exposure to solvents have been monitored in various bacteria (Pinkart et al., 1996; Weber and de Bont, 1996). LPS molecules are made up of a polysaccharide chain and several saturated fatty acids and have low permeability for hydrophobic compounds.”

“The presence of divalent cations (e.g. Mg2+ and Ca2+ ions) was found to improve survival when added to the growth medium supplemented with organic solvents in several P. putida strains (Inoue et al., 1991; Ramos et al., 1995; Weber and de Bont, 1996). It is likely that the divalent cations electrostatically linked adjacent polyanionic LPS molecules and reduced charge repulsion. This allowed a denser packing of the anionic membrane molecules, and the membrane became more hydrophobic, which affected membrane stability and the access of solvents to the membrane.”
Biofilms and Mg-Ca

“An increase in the protein–lipid content has been observed in E. coli when exposed to ethanol or phenol (Ingram, 1977; Keweloh et al., 1990). A higher protein content has a rigidifying effect on membranes, as proteins hinder lipid motion (Weber and de Bont, 1996).”

“During evolutionary history, bacteria have been exposed to different toxic compounds, such as natural toxins, endogenous metabolic end-products, antibiotics, etc. To protect themselves, microorganisms have evolved devices that detoxify and extrude these substances. This phenomenon leads to the occurrence of multidrug resistance (MDR), which is a unidirectional efflux system that catalyses the active extrusion of a large number of structurally and functionally unrelated compounds from the bacterial cytoplasm (or internal membrane) to the external medium.”

“Experiments carried out with the toluene-tolerant P. putida strains S12 and DOT-T1 indicate that the amount of [14C]-toluene and [14C-1,2,4]-trichlorobenzene accumulating in cells cultivated in the presence of toluene (adapted) was two- to fivefold lower than in the non-adapted bacteria. When the respiratory chain inhibitor potassium cyanide or the proton conductor carbonyl cyanide m-chlorophenyhydrazone (CCCP) was added, the results showed that, in adapted cells, the presence of either inhibitor resulted in significantly higher amounts of accumulation of the aromatic hydrocarbon in P. putida cells. The results support the hypothesis that, in these strains, cells growing in the presence of a given organic solvent could be using an energy-dependent exclusion system that may decrease the level of solvent in the membranes (Isken and de Bont, 1996; Ramos et al., 1997; 1998).”

“In Gram-negative bacteria, a number of responses have been found to counteract the effect of organic solvents that are directed towards the rigidification of the cell membrane and the extrusion of the toxic chemical. In a number of Pseudomonas strains, a rapid response to challenging agents is the isomerization of the naturally synthesized cis-isomer of unsaturated lipids to the trans-isomer, a reaction catalysed by a membrane-bound Cti isomerase. Long-term exposure of Pseudomonas spp., E. coli and other microorganisms to non-lethal concentrations of solvents often leads to an increase in the total amount of phospholipids and to a higher proportion of saturated long-chain lipids. These changes are concomitant with alterations in the level of different phospholipid headgroups. All the above changes are directed towards the rigidification of the cell membrane.”


--
On the same line but much more detailed in case someone’s interested:

Multiple responses of gram-positive and gram-negative bacteria to mixture of hydrocarbons

“Because of the highly impermeable outer membrane of Gram-negative bacteria, it was generally accepted that this type of bacteria are more tolerant to hydrocarbons than Gram-positive bacteria (3, 25, 32, 34, 79). However, several Gram-positive bacteria seems to been more resistant (43, 48, 50, 58, 71, 89). Because of the different experimental set-ups used in the published literature, it has been difficult to compare the hydrocarbons tolerance of different strains, and extremely difficult to compare hydrocarbons tolerance between Gram-positive and Gram-negative strains (71).”

“The resistance of Gram-positive (Mycobacterium sp. IBBPo1, Oerskovia sp. IBBPo2, Corynebacterium sp. IBBPo3) and Gram-negative (Chryseomonas sp. IBBPo7, Pseudomonas sp. IBBPo10, Burkholderia sp. IBBPo12) bacterial strains to antibiotics (ampicillin, kanamycin) and toxic compounds (sodium dodecyl sulfate, rhodamine 6G) differs from one strain to another (Table 1). Antimicrobial effect of all these compounds was more pronounced for Gram-positive (MIC90 = 40 - 800 µg ml-1) bacteria, probably due to the lack of additional permeability barriers, particularly the outer membrane of Gram-negative (MIC90 = 45 - 1000 µg ml-1) bacteria. Nevertheless, the outer membrane itself does not provide resistance to antimicrobial agents as it only decreases permeability. The resistance to antimicrobial agents is dependent on the other resistance mechanisms such as efflux but these mechanisms have enhanced effectiveness in the presence of the outer membrane in Gram-negative bacteria. The synergy between the efflux pumps and the outer membrane probably explains the variable effectiveness of related multidrug efflux systems in providing resistance in organisms with differences in intrinsic outer membrane permeability properties (60, 81).”
 
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Amazoniac

Amazoniac

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Capoeira fighter,

Bottom line ? Your hypothesis ?
There's no hypothesis, pboy George.. I'm learning along :ss
But this confirms what we read on Ray's articles; about saturated fats being more protective in nature, life leaning towards it as temperature increases, about the resilience of bacteria and how fast they adapt, about energy being required to eliminate undesired compounds, also keeping the environment dynamic (because they are able to adapt to every circumstance), being careful with antibiotics, etc..
 
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Makrosky

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There's no hypothesis, pboy George.. I'm learning along :ss
But this confirms what we read on Ray's articles; about saturated fats being more protective in nature, life leaning towards it as temperature increases, about the resilience of bacteria and how fast they adapt, about energy being required to eliminate undesired compounds, also keeping the environment dynamic (because they are able to adapt to every circumstance), being careful with antibiotics, etc..
:D:thumbup
 

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