Effect of growth temperature on the fatty acid composition of Mycobacterium phlei

Genetic and chemical control of tuberculostearic acid production in Mycobacterium avium subspecies paratuberculosis

Tuberculostearic acid (TBSA) is a fatty acid unique to mycobacteria and some corynebacteria and has been studied due to its diagnostic value, biofuel properties, and role in membrane dynamics. In this study, we demonstrate that TBSA production can be abrogated either by addition of pivalic acid to mycobacterial growth cultures or by a bfaA gene knockout encoding a flavin adenine dinucleotide (FAD)-binding oxidoreductase. Mycobacterium avium subspecies paratuberculosis (Map) growth and TBSA production were inhibited in 0.5-mg/mL pivalic acid-supplemented cultures, but higher concentrations were needed to have a similar effect in other mycobacteria, including Mycobacterium smegmatis. While Map C-type strains, isolated from cattle and other ruminants, will produce TBSA in the absence of pivalic acid, the S-type Map strains, typically isolated from sheep, do not produce TBSA in any condition. A SAM-dependent methyltransferase encoded by bfaB and FAD-binding oxidoreductase are both required in the two-step biosynthesis of TBSA. However, S-type strains contain a single-nucleotide polymorphism in the bfaA gene, rendering the oxidoreductase enzyme vestigial. This results in the production of an intermediate, termed 10-methylene stearate, which is detected only in S-type strains. Fatty acid methyl ester analysis of a C-type Map bfaA knockout revealed the loss of TBSA production, but the intermediate was present, similar to the S-type strains. Collectively, these results demonstrate the subtle biochemical differences between two primary genetic lineages of Map and other mycobacteria as well as explain the resulting phenotype at the genetic level. These data also suggest that TBSA should not be used as a diagnostic marker for Map.IMPORTANCEBranched-chain fatty acids are a predominant cell wall component among species belonging to the Mycobacterium genus. One of these is TBSA, which is a long-chain middle-branched fatty acid used as a diagnostic marker for Mycobacterium tuberculosis. This fatty acid is also an excellent biolubricant. Control of its production is important for industrial purposes as well as understanding the biology of mycobacteria. In this study, we discovered that a carboxylic acid compound termed pivalic acid inhibits TBSA production in mycobacteria. Furthermore, Map strains from two separate genetic lineages (C-type and S-type) showed differential production of TBSA. Cattle-type strains of Mycobacterium avium subspecies paratuberculosis produce TBSA, while the sheep-type strains do not. This important phenotypic difference is attributed to a single-nucleotide deletion in sheep-type strains of Map. This work sheds further light on the mechanism used by mycobacteria to produce tuberculostearic acid.

Tuberculostearic Acid Controls Mycobacterial Membrane Compartmentalization

The intracellular membrane domain (IMD) is a laterally discrete region of the mycobacterial plasma membrane, enriched in the subpolar region of the rod-shaped cell. Here, we report genome-wide transposon sequencing to discover the controllers of membrane compartmentalization in Mycobacterium smegmatis. The putative gene cfa showed the most significant effect on recovery from membrane compartment disruption by dibucaine. Enzymatic analysis of Cfa and lipidomic analysis of a cfa deletion mutant (Δcfa) demonstrated that Cfa is an essential methyltransferase for the synthesis of major membrane phospholipids containing a C19:0 monomethyl-branched stearic acid, also known as tuberculostearic acid (TBSA). TBSA has been intensively studied due to its abundant and genus-specific production in mycobacteria, but its biosynthetic enzymes had remained elusive. Cfa catalyzed the S-adenosyl-l-methionine-dependent methyltransferase reaction using oleic acid-containing lipid as a substrate, and Δcfa accumulated C18:1 oleic acid, suggesting that Cfa commits oleic acid to TBSA biosynthesis, likely contributing directly to lateral membrane partitioning. Consistent with this model, Δcfa displayed delayed restoration of subpolar IMD and delayed outgrowth after bacteriostatic dibucaine treatment. These results reveal the physiological significance of TBSA in controlling lateral membrane partitioning in mycobacteria. IMPORTANCE As its common name implies, tuberculostearic acid is an abundant and genus-specific branched-chain fatty acid in mycobacterial membranes. This fatty acid, 10-methyl octadecanoic acid, has been an intense focus of research, particularly as a diagnostic marker for tuberculosis. It was discovered in 1934, and yet the enzymes that mediate the biosynthesis of this fatty acid and the functions of this unusual fatty acid in cells have remained elusive. Through a genome-wide transposon sequencing screen, enzyme assay, and global lipidomic analysis, we show that Cfa is the long-sought enzyme that is specifically involved in the first step of generating tuberculostearic acid. By characterizing a cfa deletion mutant, we further demonstrate that tuberculostearic acid actively regulates lateral membrane heterogeneity in mycobacteria. These findings indicate the role of branched fatty acids in controlling the functions of the plasma membrane, a critical barrier for the pathogen to survive in its human host.

Thermally enhanced bioremediation: A review of the fundamentals and applications in soil and groundwater remediation

Thermally enhanced bioremediation (TEB), a new concept proposed in recent years, explores the combination of thermal treatment and bioremediation to address the challenges of the low efficiency and long duration of bioremediation. This study presented a comprehensive review regarding the fundamentals of TEB and its applications in soil and groundwater remediation. The temperature effects on the bioremediation of contaminants were systematically reviewed. The thermal effects on the physical, chemical and biological characteristics of soil, and the corresponding changes of contaminants bioavailability and microbial metabolic activities were summarized. Specifically, the increase in temperature within a suitable range can proliferate enzymes enrichment, extracellular polysaccharides and biosurfactants production, and further enhancing bioremediation. Furthermore, a systematic evaluation of TEB applications by utilizing traditional in situ heating technologies, as well as renewable energy (e.g., stored aquifer thermal energy and solar energy), was provided. Additionally, TEB has been applied as a biological polishing technology post thermal treatment, which can be a cost-effective method to address the contaminants rebounds in groundwater remediation. However, there are still various challenges to be addressed in TEB, and future research perspectives to further improve the basic understanding and applications of TEB for the remediation of contaminated soil and groundwater are presented.

Essential Roles of PPARs in Lipid Metabolism during Mycobacterial Infection

The mycobacterial cell wall is composed of large amounts of lipids with varying moieties. Some mycobacteria species hijack host cells and promote lipid droplet accumulation to build the cellular environment essential for their intracellular survival. Thus, lipids are thought to be important for mycobacteria survival as well as for the invasion, parasitization, and proliferation within host cells. However, their physiological roles have not been fully elucidated. Recent studies have revealed that mycobacteria modulate the peroxisome proliferator-activated receptor (PPAR) signaling and utilize host-derived triacylglycerol (TAG) and cholesterol as both nutrient sources and evasion from the host immune system. In this review, we discuss recent findings that describe the activation of PPARs by mycobacterial infections and their role in determining the fate of bacilli by inducing lipid metabolism, anti-inflammatory function, and autophagy.

Identification and characterization of a novel anti-inflammatory lipid isolated from Mycobacterium vaccae, a soil-derived bacterium with immunoregulatory and stress resilience properties

RATIONALE

Mycobacterium vaccae (NCTC 11659) is an environmental saprophytic bacterium with anti-inflammatory, immunoregulatory, and stress resilience properties. Previous studies have shown that whole, heat-killed preparations of M. vaccae prevent allergic airway inflammation in a murine model of allergic asthma. Recent studies also demonstrate that immunization with M. vaccae prevents stress-induced exaggeration of proinflammatory cytokine secretion from mesenteric lymph node cells stimulated ex vivo, prevents stress-induced exaggeration of chemically induced colitis in a model of inflammatory bowel disease, and prevents stress-induced anxiety-like defensive behavioral responses. Furthermore, immunization with M. vaccae induces anti-inflammatory responses in the brain and prevents stress-induced exaggeration of microglial priming. However, the molecular mechanisms underlying anti-inflammatory effects of M. vaccae are not known.

OBJECTIVES

Our objective was to identify and characterize novel anti-inflammatory molecules from M. vaccae NCTC 11659.

METHODS

We have purified and identified a unique anti-inflammatory triglyceride, 1,2,3-tri [Z-10-hexadecenoyl] glycerol, from M. vaccae and evaluated its effects in freshly isolated murine peritoneal macrophages.

RESULTS

The free fatty acid form of 1,2,3-tri [Z-10-hexadecenoyl] glycerol, 10(Z)-hexadecenoic acid, decreased lipopolysaccharide-stimulated secretion of the proinflammatory cytokine IL-6 ex vivo. Meanwhile, next-generation RNA sequencing revealed that pretreatment with 10(Z)-hexadecenoic acid upregulated genes associated with peroxisome proliferator-activated receptor alpha (PPARα) signaling in lipopolysaccharide-stimulated macrophages, in association with a broad transcriptional repression of inflammatory markers. We confirmed using luciferase-based transfection assays that 10(Z)-hexadecenoic acid activated PPARα signaling, but not PPARγ, PPARδ, or retinoic acid receptor (RAR) α signaling. The effects of 10(Z)-hexadecenoic acid on lipopolysaccharide-stimulated secretion of IL-6 were prevented by PPARα antagonists and absent in PPARα-deficient mice.

CONCLUSION

Future studies should evaluate the effects of 10(Z)-hexadecenoic acid on stress-induced exaggeration of peripheral inflammatory signaling, central neuroinflammatory signaling, and anxiety- and fear-related defensive behavioral responses.

Overview of strategies for enhanced treatment of municipal/domestic wastewater at low temperature

Biological wastewater treatment has been widely applied to municipal/domestic wastewater treatment systems. However, low temperature significantly decreases process performance. Furthermore, increasingly stringent effluent discharge standards are causing wastewater treatment facilities to have to improve and maintain contaminants removal under low temperature. Hence, this review aims to summarize strategies for enhanced treatment of municipal/domestic wastewater at low temperature. First, mechanisms of the effects of low temperature on wastewater treatment, including physiological characteristics, microbial growth rate, microbial activity, microbial community structure and sludge settleability, are analyzed. Strategies for performance intensifications at low temperature, mainly operational parameters regulation, bioaugmentation, biofilm technology, chemical phosphorus precipitation and application of novel process technologies, are then reviewed. Finally, future directions to address low temperature wastewater are highlighted. A special emphasis is given to the application of novel process/technology configurations to enhance process performance at low temperature in practical engineering.

Mycobacterial Response to Organic Solvents and Possible Implications on Cross-Resistance With Antimicrobial Agents

Mycobacterium vaccae, a bacterium found in soil, has been receiving attention as adjuvant to antituberculosis treatment, vaccines and immunotherapies and even as antidepressant. This bacterium is also able to degrade several pollutants, including aromatic compounds. The increasing presence of organic solvents in the environment may lead to M. vaccae adapted populations. A possible relationship between solvent tolerance and decreased susceptibility to other types of chemicals, including antibiotics, may pose a problem during opportunistic infections. The present study thus aimed at assessing if solvent adapted cells presented higher tolerance to antibiotics and efflux pump inhibitors (EPIs). M. vaccae cells were able to thrive and grow in the presence of up 20% (v/v) glycerol, 5% (v/v) ethanol, 1% (v/v) methyl tert-butyl ether (MTBE) and 0.1% (v/v) toluene. During adaptation to increasing concentration of ethanol and MTBE, the cells changed their fatty acid profile, zeta potential and morphology. Adapted cells acquired an improved tolerance toward the EPIs thioridazine and omeprazole, but became more susceptible to the antibiotics levofloxacin and teicoplanin when compared with non-adapted cells.

Depth, soil type, water table, and site effects on microbial community composition in sediments of pesticide-contaminated aquifer

Microbial community compositions in pesticide-contaminated aquifers have not been studied, although such information is important for remediation and maintaining freshwater sources clean under changing climate. Therefore, phospholipid (PLFAs), glycolipid (GLFAs), and neutral lipid (NLFAs) fatty acids were determined from sand and clay sediments at depths of 0.3-24.8 m, all contaminated with triazines and dichlobenil/2,6-dichlorobenzamide. The portion of fungi and Gram-negative bacteria at 0.3 m was greater than at 0.8 m, where the percentage of Gram-positive bacteria, actinobacteria, and sulfate-reducing bacteria (SRB) increased. In deeper sediments, microbial biomass, activity, and diversity decreased. Clay sediments seemed to serve as a reservoir for slow pesticide elution to groundwater, and their biomarker portion for all bacteria except actinobacteria was greater than in sand sediments. The slow pesticide dissipation seemed to occur in the main groundwater flow zone, resulting in nitrogen release simultaneously with organic matter elution from gardening and bank filtration. As a result, microbial biomass, activity, and diversity were increased. This shift in conditions towards that in surface soil may be appropriate for enhanced natural attenuation of pesticides in groundwater sources.

Temperature-induced plasticity in membrane and storage lipid composition: thermal reaction norms across five different temperatures

Temperature is a key environmental factor inducing phenotypic plasticity in a wide range of behavioral, morphological, and life history traits in ectotherms. The strength of temperature-induced responses in fitness-related traits may be determined by plasticity of the underlying physiological or biochemical traits. Lipid composition may be an important trait underlying fitness response to temperature, because it affects membrane fluidity as well as availability of stored energy reserves. Here, we investigate the effect of temperature on lipid composition of the springtail Orchesella cincta by measuring thermal reaction norms across five different temperatures after four weeks of cold or warm acclimation. Fatty acid composition in storage and membrane lipids showed a highly plastic response to temperature, but the responses of single fatty acids revealed deviations from the expectations based on HVA theory. We found an accumulation of C(18:2n6) and C(18:3n3) at higher temperatures and the preservation of C(20:4n6) across temperatures, which is contrary to the expectation of decreased unsaturation at higher temperatures. The thermal response of these fatty acids in O. cincta differed from the findings in other species, and therefore shows there is interspecific variation in how single fatty acids contribute to HVA. Future research should determine the consequences of such variation in terms of costs and benefits for the thermal performance of species.

Effect of growth in biofilms on chlorine susceptibility of Mycobacterium avium and Mycobacterium intracellulare

Mycobacterium avium and Mycobacterium intracellulare were grown in suspension and in biofilms, and their susceptibilities to chlorine were measured. M. avium and M. intracellulare readily adhered within 2 h, and numbers increased 10-fold in 30 days at room temperature in biofilms on both polystyrene flasks and glass beads. The chlorine resistance of M. avium and M. intracellulare cells grown and exposed to chlorine in biofilms was significantly higher than that of cells grown in suspension. Survival curves showed no evidence of a resistant, persisting population after 6 h of exposure to 1 mug chlorine/ml. The chlorine susceptibility of cells grown in biofilms and exposed in suspension (cells detached from bead surfaces) was also significantly higher than that of cells grown and exposed in suspension (planktonic cells), although it was lower than that of cells grown and exposed in biofilms. The higher resistance of the detached biofilm-grown cells was reversed upon their growth in suspension. There was a strong correlation between the chlorine susceptibility of cells of both M. avium and M. intracellulare and cell surface hydrophobicity measured by contact angle for both biofilm- and suspension-grown cells.

Comparative analysis of phenotypic and genotypic characteristics of two desulfurizing bacterial strains, Mycobacterium phlei SM120-1 and Mycobacterium phlei GTIS10

AIM

To compare few phenotypic and genotypic characteristics of two desulfurizing bacterial strains, Mycobacterium phlei SM120-1 and Mycobacterium phlei GTIS10.

METHODS AND RESULTS

In the present study, dibenzothiophene (DBT) desulfurizing activity, composition of fatty acids of cell membranes, DBT sulfone monoxygenase gene (bdsA) and the selection pressure applied during the growth and enrichment of the bacterial strains M. phlei SM120-1 and M. phlei GTIS10 were compared in our laboratory. The DBT desulfurization activity of M. phlei SM120-1 was found to be 0.17 +/- 0.02 micromol 2-HBP min(-1) (gram dry cell weight)(-1) and that of the bacterial strain M. phlei GTIS10 was 1.09 +/- 0.05 micromol 2-HBP min(-1) (gram dry cell weight)(-1). Fatty acid methyl ester analysis of cell membranes of these two bacterial strains in the presence of light gas oil showed that both the strains had different fatty acid profiles in their cell membranes. Comparison of the full gene sequences of the desulfurization gene bdsA in the two bacterial strains showed significant difference in the bdsA gene sequences. There was a significant difference observed in the selection pressure applied during the growth and enrichment of the two bacterial strains.

CONCLUSIONS

The results of the comparative study of the bacterial strains, M. phlei SM120-1 and M. phlei GTIS10 showed that there were considerable differences in the phenotypic and genotypic characteristics of these two strains.

SIGNIFICANCE AND IMPACT OF STUDY

The present study would broaden the understanding of biodesulfurization trait at intra-species level.

Temperature-dependent biosynthesis of glucose monomycolate and its recognition by CD1-restricted T cells

Mycolic acids are long chain fatty acids that constitute the lipid-rich cell wall framework of mycobacteria. Upon infection, mycobacteria begin to synthesize glucose monomycolate (GMM), a glucosylated species of mycolic acids, by utilizing host-derived glucose as sugar source. Accordingly, GMM production serves as a good indicator for local invasion of mycobacteria, and its detection by the host immune system would favor efficient monitoring of mycobacterial infection. Here, we found that GMM was produced abundantly at 30 degrees C rather than at 37 degrees C and recognized by a GMM-specific, CD1-restricted T cell line that was isolated from mycobacteria-infected human skin. Since the common portal sites for mycobacterial infection include ventilating alveoli of the lung and the externally exposed skin that often render invading microbes survive at reduced temperature, sampling GMM by CD1 lipid antigen-presenting molecules may allow the host to detect mycobacterial infection at its early phases.

Impact of membrane fatty acid composition on the uncoupling sensitivity of the energy conservation of Comamonas testosteroni ATCC 17454

The fatty acid composition of pyruvate-grown Comamonas testosteroni ATCC 17454 was analyzed after growth at 30 and 20 degrees C and after half-maximum growth inhibition caused by different membrane-active chemicals at 30 degrees C. Palmitic acid (16:0), palmitoleic acid (16:1 omega7c) and vaccenic acid (18:1 omega7c) were the dominant fatty acids. At 20 degrees C, the proportion of palmitic acid decreased and those of palmitoleic and vaccenic acid increased. Saturation degree was also lowered when half-maximum growth inhibition was caused by 4-chlorosalicylic acid, 2,4-dichlorophenoxyacetic acid and 2,4-dinitrophenol and, to a lesser extent, in the presence of 2,4-dichlorophenol, phenol and ethanol. It appeared that the dissociated forms of the former group of chemicals were preferentially incorporated near the head group region of the lipid bilayer, thereby somewhat extending the outer region of the membranes, and that the increased amount of bent, unsaturated fatty acids helped to maintain membrane integrity. Irrespective of how the decrease of the saturation degree was triggered, it caused electron transport phosphorylation (adenosine triphosphate synthesis driven by n-hexanol oxidation) to become more sensitive to uncoupling. Apparently, the viscosity and phase stability of the cytoplasmic membrane of C. testosteroni were maintained at the price of a reduced protection against energy toxicity.

Factors influencing the chlorine susceptibility of Mycobacterium avium, Mycobacterium intracellulare, and Mycobacterium scrofulaceum

The susceptibility of representative strains of Mycobacterium avium, Mycobacterium intracellulare, and Mycobacterium scrofulaceum (the MAIS group) to chlorine was studied to identify factors related to culture conditions and growth phase that influenced susceptibility. M. avium and M. intracellulare strains were more resistant to chlorine than were strains of M. scrofulaceum. Transparent and unpigmented colony variants were more resistant to chlorine than were their isogenic opaque and pigmented variants (respectively). Depending on growth stage and growth rate, MAIS strains differed in their chlorine susceptibilities. Cells from strains of all three species growing in early log phase at the highest growth rates were more susceptible than cells in log and stationary phase. Rapidly growing cells were more susceptible to chlorine than slowly growing cells. The chlorine susceptibility of M. avium cells grown at 30 degrees C was increased when cells were exposed to chlorine at 40 degrees C compared to susceptibility after exposure at 30 degrees C. Cells of M. avium grown in 6% oxygen were significantly more chlorine susceptible than cells grown in air. Chlorine-resistant MAIS strains were more hydrophobic and resistant to Tween 80, para-nitrobenzoate, hydroxylamine, and nitrite than were the chlorine-sensitive strains.

Generation and evaluation of a large mutational library from the Escherichia coli mechanosensitive channel of large conductance, MscL: implications for channel gating and evolutionary design

Random mutagenesis of the mechanosensitive channel of large conductance (MscL) from Escherichia coli coupled with a high-throughput functional screen has provided new insights into channel structure and function. Complementary interactions of conserved residues proposed in a computational model for gating have been evaluated, and important functional regions of the channel have been identified. Mutational analysis shows that the proposed S1 helix, despite having several highly conserved residues, can be heavily mutated without significantly altering channel function. The pattern of mutations that make MscL more difficult to gate suggests that MscL senses tension with residues located near the lipid headgroups of the bilayer. The range of phenotypical changes seen has implications for a proposed model for the evolutionary origin of mechanosensitive channels.

Gas chromatographic-mass spectrometric detection of 2- and 3-hydroxy fatty acids as methyl esters from soil, sediment and biofilm

Hydroxy fatty acids (OH-FAs) can be used in the characterization of microbial communities, especially Gram-negative bacteria. We prepared methyl esters of 2- and 3-OH-FAs from the lipid extraction residue of soil, sediment, and biofilm samples without further purification or derivatization of hydroxyl groups. OH-FA methyl esters were analyzed using a gas chromatograph equipped with a mass selective detector (GC-MS). The ions followed in MS were m/z 103 for 3-OH-FAs and m/z 90 and M-59 for 2-OH-FAs. The rapid determination of 3- and 2-OH-FAs concomitantly with phospholipid fatty acids provided more detailed information on the microbial communities present in soil, sediment, and drinking water biofilm.

Nontuberculous mycobacteria in the environment

It is likely that the incidence of infection by environmental opportunistic mycobacteria will continue to rise. Part of the rise will be caused by the increased awareness of these microbes as human pathogens and improvements in methods of detection and culture. Clinicians and microbiologists will continue to be challenged by the introduction of new species to the already long list of mycobacterial opportunists (see Table 3). The incidence of infection will also rise because an increasing proportion of the population is aging or subject to some type of immunosuppression. A second reason for an increase in the incidence of environmental mycobacterial infection is that these microbes are everywhere. They are present in water, biofilms, soil, and aerosols. They are natural inhabitants of the human environment, especially drinking water distribution systems. Thus, it is likely that everyone is exposed on a daily basis. It is likely that certain human activities can lead to selection of mycobacteria. Important lessons have been taught by study of cases of hypersensitivity pneumonitis associated with exposure to metalworking fluid. First, the implicated metalworking fluids contained water, the likely source of the mycobacteria. Second, the metalworking fluids contain hydrocarbons (e.g., pine oils) and biocides (e.g., morpholine) both of which are substrates for the growth of mycobacteria [53,193]. Third, outbreak of disease followed disinfection of the metalworking fluid [136,137]. Although the metalworking fluid was contaminated with microorganisms, it was only after disinfection that symptoms developed in the workers. Because mycobacteria are resistant to disinfectants, it is likely that the recovery of the mycobacteria from the metalworking fluid [137] was caused by their selection. Disinfection may also contribute, in part, to the persistence of M avium and M intracellulare in drinking water distribution systems [33,89,240]. M avium and M intracellulare are many times more resistant to chlorine, chloramine, chlorine dioxide, and ozone than are other water-borne microorganisms [141,236]. Consequently, disinfection of drinking water results in selection of mycobacteria. In the absence of competitors, even the slowly growing mycobacteria can grow in the distribution system [33]. It is likely that hypersensitivity pneumonitis in lifeguards and therapy pool attendants [139] is caused by a similar scenario.

Suitability of the trans/cis ratio of unsaturated fatty acids in Pseudomonas putida NCTC 10936 as an indicator of the acute toxicity of chemicals

This study explored the suitability of using the trans/cis ratio of unsaturated fatty acids as an indicator of the acute toxicity of membrane active hazardous chemicals. The conversion of cis into trans fatty acids in Pseudomonas putida NCTC 10936 in response to 4-chlorophenol and temperature changes was compared with the results from another kind of toxicity test using the same organism, based on the sensitivity of its xylose oxidation-driven ATP synthesis to uncoupling. The response of both indicators is believed to be largely due to changes in the fluidity of the cytoplasmic membrane. However, the electron transport phosphorylation reacted faster and more sensitively to the fluidizing effect of 4-chlorophenol than the isomerization of unsaturated fatty acids. Therefore, measuring the trans/cis ratio does not provide as good early warning signals of acute toxicity as monitoring the response of the electron transport phosphorylation. If used as an indicator of chemostress, with Pseudomonas species as test organisms, the ratio should only be used in conjunction with other parameters reflecting the energetic state of the cells.

Effect of low temperature on microbial growth: lowered affinity for substrates limits growth at low temperature

The effect of environmental temperature on the affinity of microorganisms for substrates is discussed in relation to measurements of affinity by either K(s) values or specific affinity (a(A)). It can be shown for psychrophiles, mesophiles and thermophiles that when a(A) is used as the measure of affinity, affinity decreases consistently as temperature drops below the optimum temperature for growth. This effect may be because of stiffening of the lipids of the membrane below the temperature optimum, leading to decreased efficiency of transport proteins embedded in the membrane. The lower temperature limit for growth is, therefore, that temperature at which an organism is no longer able to supply the maintenance requirement of the growth rate-limiting nutrient because of loss of affinity for that substrate. This linking of temperature and affinity for substrates taken up by active transport (a temperature-modulated substrate affinity model) includes uptake of both organic and inorganic substrates. This effect of decreased substrate affinity at low temperature may have profound implications on the availability of substrates in the natural environment as environmental temperatures change. At temperatures below their optimum for growth microorganisms will become increasingly unable to sequester substrates from their environment because of lowered affinity, exacerbating the anyway near-starvation conditions in many natural environments.

Effect of aromatic compounds on cellular fatty acid composition of Rhodococcus opacus

In cells of Rhodococcus opacus GM-14, GM-29, and 1CP, the contents of branched (10-methyl) fatty acids increased from 3% to 15 to 34% of the total fatty acids when the cells were grown on benzene, phenol, 4-chlorophenol, chlorobenzene, or toluene as the sole source of carbon and energy, in comparison with cells grown on fructose. In addition, the content of trans-hexadecenoic acid increased from 5% to 8 to 18% with phenol or chlorophenol as the carbon source. The 10-methyl branched fatty acid content of R. opacus GM-14 cells increased in a dose-related manner following exposure to phenol or toluene when toluene was not utilized as the growth substrate. The results suggest that 10-methyl branched fatty acids may participate in the adaptation of R. opacus to lipophilic aromatic compounds.

Streptomyces spp. Isolated from Potato Scab Lesions Under Nordic Conditions in Finland

Actinomycetes isolated from scab lesions of potato tubers in Finland (60°-68°N, 21°-31°E) were characterized using physiological tests and production of necrosis on potato minitubers. Seven strains were additionally analyzed for their whole cell fatty acid profiles. The majority of the pathogenic strains were similar to the Streptomyces scabies type strain ATCC 49173 that is characterized by gray to brown colonies, gray spores, spiral sporophores, melanin production, and utilization of the International Streptomyces Project (ISP) sugars. However, two groups of strains (designated as Group 4, 38 strains; and Group 5, nine strains), each containing several pathogenic isolates, differed from S. scabies ATCC 49173 in at least two phenotypic traits. Additionally, a single, highly virulent strain (SSC 122) differed from all other strains for its phenotypic traits. The fatty acid compositions of the three pathogenic strains of Group 4 and the strain SSC 122 differed from S. scabies ATCC 49173 and S. acidiscabies ATCC 49003. In SSC 122, the ratio of saturated and unsaturated and the iso and anteiso forms of fatty acids were different from all other streptomycetes analyzed. Thus, the strains of Group 4 and 5 and SSC 122 may represent three novel Streptomyces spp. pathogenic on potato. SSC 122 and the pathogenic strains identified to S. scabies grew at pH 5.0 but not at pH 4.6, whereas the pathogenic strains of Group 4 and 5 grew at pH 4.6 or 4.4 but not at pH 4.2.

Microbial fatty acids and thermal adaptation

The existing literature on the role of fatty acids in microbial temperature adaptation is reviewed. Several modes of change of cellular fatty acids at varying environmental temperatures are shown to exist in yeasts and fungi, Gram-negative bacteria, and bacteria containing iso- and anteiso-branched fatty acids, as well as in a few Gram-positive bacteria. Consequently, the degree of fatty acid unsaturation and cyclization, fatty acid chain length, branching, and cellular fatty acid content increase, decrease, or remain unaltered on lowering the temperature. Moreover, microorganisms seem to be able to change from one mode or alter the cellular fatty acid profile temperature dependently to another on lowering the temperature, as well as even within the same growth temperature range, depending on growth conditions. Therefore, the effect of the temperature on cellular fatty acids appears to be more complicated than known earlier. However, similarities found in the modes of change of cellular fatty acids at varying environmental temperatures in several microorganisms within the above mentioned groups support the existence of a limited amount of common regulatory mechanisms. The models presented enable the prediction of temperature-induced changes occurring in the fatty acids of microorganisms, and enzymatic steps of the fatty acid biosynthesis that possibly are under temperature control.