Growth and survival of bacteria depend on homeostasis of membrane lipids, and the capacity to adjust lipid composition to adapt to various environmental stresses. Membrane fluidity is regulated in part by the ratio of unsaturated to saturated fatty acids present in membrane lipids. Here, we studied the effects of high growth temperature and salinity (NaCl) stress, separately or in combination, on fatty acids composition and de novo synthesis in two peanut-nodulating Bradyrhizobium strains (fast-growing TAL1000 and slow-growing SEMIA6144). Both strains contained the fatty acids palmitic, stearic, and cis-vaccenic + oleic. TAL1000 also contained eicosatrienoic acid and cyclopropane fatty acid. The most striking change, in both strains, was a decreased percentage of cis-vaccenic + oleic (≥ 80% for TAL1000), and an associated increase in saturated fatty acids, under high growth temperature or combined conditions. Cyclopropane fatty acid was significantly increased in TAL1000 under the above conditions. De novo synthesis of fatty acids was shifted to the synthesis of a higher proportion of saturated fatty acids under all tested conditions, but to a lesser degree for SEMIA6144 compared to TAL1000. The major adaptive response of these rhizobial strains to increased temperature and salinity was an altered degree of fatty acid unsaturation, to maintain the normal physical state of membrane lipids.

The polyphosphoinositides from Trypanosoma cruzi were isolated by preparative thin-layer chromatography (TLC) and identified. When myo-[3H]inositol was present in the culture medium for five days, analyses showed the presence of phosphatidylinositol (PI), lysophosphatidylinositol (lysoPI), phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2). Short-term incubation with 32Pi led to higher percentages of incorporation into phosphatidylethanolamine (PE), lysophosphatidylethanolamine (lysoPE) and PI compared to the other glycerophospholipids. The phosphoinositides (PI, PIP and PIP2) contained a larger proportion of unsaturated than saturated fatty acids. High proportions of 18:2 were found in the three phosphoinositides analyzed, whereas the major saturated fatty acid was 18:0. Water-soluble inositol phosphates (IP, IP2 and IP3) were also identified.

Phospholipids provide the membrane with its barrier function and play a role in a variety of processes in the bacterial cell, as responding to environmental changes. The aim of the present study was to characterize the physiological and metabolic response of Bradyrhizobium SEMIA 6144 to saline and temperature stress. This study provides metabolic and compositional evidence that nodulating peanut Bradyrhizobium SEMIA 6144 is able to synthesize fatty acids, to incorporate them into its phospholipids (PL), and then modify them in response to stress conditions such as temperature and salinity. The fatty acids were formed from [1-(14)C]acetate and mostly incorporated in PL (95%). Phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and cardiolipin (CL) were found to be the major phospholipids in the bacteria analyzed. The amount and the labeling of each individual PL was increased by NaCl, while they were decreased by temperature stress. The amount of PC, PE, and PG under the combined stresses decreased, as in the temperature effect. The results indicate that synthesized PL of Bradyrhizobium SEMIA 6144 are modified under the tested conditions. Because in all conditions tested the PC amount was always modified and PC was the major PL, we suggest that this PL may be involved in the bacteria response to environmental conditions.

Uptake and metabolism of saturated (16:0, 18:0) and unsaturated [18:1(n-9), 18:2(n-6), 18:3(n-3)] fatty acids by cultured epimastigotes of Trypanosoma cruzi were studied. Between 17.5 and 33.5% of the total radioactivity of [1-14C]labeled fatty acids initially added to the culture medium was incorporated into the lipids of T. cruzi and mostly choline and ethanolamine phospholipids. As demonstrated by argentation thin layer chromatography, gas liquid chromatography and ozonolysis of the fatty acids synthesized, exogenous palmitic acid was elongated to stearic acid, and the latter was desaturated to oleic acid and 18:2 fatty acid. The 18:2 fatty acid was tentatively identified as linoleic acid with the first bond in the delta 9 position and the second bond toward the terminal methyl end. Exogenous stearic acid was also desaturated to oleic and 18:2 fatty acid, while oleic acid was only converted into 18:2. All of the saturated and unsaturated fatty acids investigated were also converted to a small extent (2-4%) into polyunsaturated fatty acids. No radioactive aldehyde methyl ester fragments of less than nine carbon atoms were detected after ozonolysis of any of the fatty acids studied. These results demonstrate the existence of delta 9 and either delta 12 or delta 15 desaturases, or both, in T. cruzi and suggest that delta 6 desaturase or other desaturases of the animal type are likely absent in cultured forms of this organism.

Phosphatidylcholine, the major phospholipid in eukaryotes, is found in rhizobia and in many other bacteria interacting with eukaryotic hosts. Phosphatidylcholine has been shown to be required for a successful interaction of Bradyrhizobium japonicum USDA 110 with soybean roots. Our aim was to study the role of bacterial phosphatidylcholine in the Bradyrhizobium-peanut (Arachis hypogaea) symbiosis. Phospholipid N-methyltransferase (Pmt) and minor phosphatidylcholine synthase (Pcs) activities were detected in crude extracts of the peanut-nodulating strain Bradyrhizobium sp. SEMIA 6144. Our results suggest that phosphatidylcholine formation in Bradyrhizobium sp. SEMIA 6144 is mainly due to the phospholipid methylation pathway. Southern blot analysis using pmt- and pcs-probes of B. japonicum USDA 110 revealed a pcs and multiple pmt homologues in Bradyrhizobium sp. SEMIA 6144. A pmtA knockout mutant was constructed in Bradyrhizobium sp. SEMIA 6144 that showed a 50% decrease in the phosphatidylcholine content in comparison with the wild-type strain. The mutant was severely affected in motility and cell size, but formed wild-type-like nodules on its host plant. However, in coinoculation experiments, the pmtA-deficient mutant was less competitive than the wild type, suggesting that wild-type levels of phosphatidylcholine are required for full competitivity of Bradyrhizobium in symbiosis with peanut plants.