Differential Effects of Permeating and Nonpermeating Solutes on the Fatty Acid Composition of Pseudomonas putida

Abstract

We examined the effect of reduced water availability on the fatty acid composition of Pseudomonas putida strain mt-2 grown in a defined medium in which the water potential was lowered with the permeating solutes NaCl or polyethylene glycol (PEG) with a molecular weight of 200 (PEG 200) or the nonpermeating solute PEG 8000. Transmission electron microscopy showed that ؊1.0-MPa PEG 8000-treated cells had convoluted outer membranes, whereas ؊1.0-MPa NaCl-treated or control cells did not. At the range of water potential (؊0.25 to ؊1.5 MPa) that we examined, reduced water availability imposed by PEG 8000, but not by NaCl or PEG 200, significantly altered the amounts of trans and cis isomers of monounsaturated fatty acids that were present in whole-cell fatty acid extracts. Cells grown in basal medium or under the ؊0.25-MPa water potential imposed by NaCl or PEG 200 had a higher trans:cis ratio than ؊0.25-MPa PEG 8000-treated cells. As the water potential was lowered further with PEG 8000 amendments, there was an increase in the amount of trans isomers, resulting in a higher trans:cis ratio. Similar results were observed in cells grown physically separated from PEG 8000, indicating that these changes were not due to PEG toxicity. When cells grown in ؊1.5-MPa PEG 8000 amendments were exposed to a rapid water potential increase of 1.5 MPa or to a thermodynamically equivalent concentration of the permeating solute, NaCl, there was a decrease in the amount of trans fatty acids with a corresponding increase in the cis isomer. The decrease in the trans/cis ratio following hypoosomotic shock did not occur in the presence of the lipid synthesis inhibitor cerulenin or the growth inhibitors chloramphenicol and rifampicin, which indicates a constitutively operating enzyme system. These results indicate that thermodynamically equivalent concentrations of permeating and nonpermeating solutes have unique effects on membrane fatty acid composition.

Reduced Water Availability Influences the Dynamics, Development, and Ultrastructural Properties of Pseudomonas putida Biofilms

“…In order to visualize unsaturated biofilms, we tagged P. putida mt-2 with the green fluorescent protein by transferring a stable, broad-host-range plasmid pPROBE-KT (18) containing the gfp gene fused to the constitutive neomycin-phosphotransferase (P nptII ) promoter. We used a permeating solute (NaCl, KCl, sucrose, polyethylene glycol 200 [PEG 200; i.e., a PEG with a molecular weight of 200]) and a nonpermeating solute (PEG 8000) to simulate the solute and matric components of the soil water potential, respectively, as described previously (11,12). Bacteria were cultivated on 50%-strength Luria-Bertani solid medium without NaCl and amended with (per liter) 1 g of MgSO 4 ⅐ 7H 2 O, 1.38 g of KH 2 PO 4 , 0.2 g of calcofluor white (Sigma Chemical Co., St. Louis, Mo.…”

Influence of reduced water availability on Pseudomonas putida unsaturated biofilms and the role of alginate in desiccation tolerance

“…In this study, many wdc loci identified were differentially regulated by solute and matric stress, although some genes were induced by both stresses. This result suggests that when the stresses are thermodynamically equivalent, cells are differently affected by each form of reduced water availability (66,67,124), and hence they employ different adaptive responses to matric and solute stresses.…”

“…From a bacterial perspective, the major difference between these two stresses is that with an osmotic stress microbes are bathed in water of diminished activity, whereas with a matric stress microbes become dehydrated by the physical removal of water from their environment and the availability of the remaining water is reduced through its sorptive interaction with soil constituents (66). In fact, as soils dry the matric potential becomes the predominant component contributing to the total water potential (67,115).…”

“…As cell membranes become dehydrated, they undergo a series of phase transitions from liquid crystalline to gel-like phases; the membranes become less fluid as they are dehydrated and decreasing membrane fluidity can restrict the diffusion of nutrient and waste products (33,124). Recently, it has been shown that cis-to-trans isomerization of membrane fatty acids by a constitutively expressed cis-trans isomerase (Cti) (77, 78, 83, 119) is a rapid means by which P. putida can mitigate the dehydration-mediated disruption of membrane integrity (66). In addition to altering membrane fatty acids, bacteria may employ an adaptive strategy by exporting trehalose or sucrose to stabilize dehydrated membranes (53,124).…”

“…However, its toxicity and permeability of membranes results in a perturbed cytoplasmic membrane structure and function (174), which may not reflect authentic dehydrating situations. Alternatively, high molecular weight (MW) (i.e., a MW of >3,000) polyethylene glycols (PEGs) have been used to study microbial and plant responses to reduced water content, because they are inert, non-ionic, and too large to penetrate cell walls and can cause reduction in water content available to microbes by binding water molecules tightly (21,66,67,104). Thus, these high MW PEG amended media could better reflect in situ dry soil habitats at the given water potential than those amended with ethanol.…”