Discriminant analysis of cellular fatty acids of Candida species, Torulopsis glabrata, and Cryptococcus neoformans determined by gas-liquid chromatography

Detection of Species-Specific Lipids by Routine MALDI TOF Mass Spectrometry to Unlock the Challenges of Microbial Identification and Antimicrobial Susceptibility Testing

MALDI-TOF mass spectrometry has revolutionized clinical microbiology diagnostics by delivering accurate, fast, and reliable identification of microorganisms. It is conventionally based on the detection of intracellular molecules, mainly ribosomal proteins, for identification at the species-level and/or genus-level. Nevertheless, for some microorganisms (e.g., for mycobacteria) extensive protocols are necessary in order to extract intracellular proteins, and in some cases a protein-based approach cannot provide sufficient evidence to accurately identify the microorganisms within the same genus (e.g., Shigella sp. vs E. coli and the species of the M. tuberculosis complex). Consequently lipids, along with proteins are also molecules of interest. Lipids are ubiquitous, but their structural diversity delivers complementary information to the conventional protein-based clinical microbiology matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) based approaches currently used. Lipid modifications, such as the ones found on lipid A related to polymyxin resistance in Gram-negative pathogens (e.g., phosphoethanolamine and aminoarabinose), not only play a role in the detection of microorganisms by routine MALDI-TOF mass spectrometry but can also be used as a read-out of drug susceptibility. In this review, we will demonstrate that in combination with proteins, lipids are a game-changer in both the rapid detection of pathogens and the determination of their drug susceptibility using routine MALDI-TOF mass spectrometry systems.

Resource Partitioning between Bacteria, Fungi, and Protists in the Detritusphere of an Agricultural Soil

The flow of plant-derived carbon in soil is a key component of global carbon cycling. Conceptual models of trophic carbon fluxes in soil have assumed separate bacterial and fungal energy channels in the detritusphere, controlled by both substrate complexity and recalcitrance. However, detailed understanding of the key populations involved and niche-partitioning between them is limited. Here, a microcosm experiment was performed to trace the flow of detritusphere C from substrate analogs (glucose, cellulose) and plant biomass amendments (maize leaves, roots) in an agricultural soil. Carbon flow was traced by rRNA stable isotope probing and amplicon sequencing across three microbial kingdoms. Distinct lineages within the Actinobacteria, Bacteroidetes, Gammaproteobacteria, Basidiomycota, Ascomycota as well as Peronosporomycetes were identified as important primary substrate consumers. A dynamic succession of primary consumers was observed especially in the cellulose treatments, but also in plant amendments over time. While intra-kingdom niche partitioning was clearly observed, distinct bacterial and fungal energy channels were not apparent. Furthermore, while the diversity of primary substrate consumers did not notably increase with substrate complexity, consumer succession and secondary trophic links to bacterivorous and fungivorous microbes resulted in increased food web complexity in the more recalcitrant substrates. This suggests that rather than substrate-defined energy channels, consumer succession as well as intra- and inter-kingdom cross-feeding should be considered as mechanisms supporting food web complexity in the detritusphere.

Crz1p Regulates pH Homeostasis in Candida glabrata by Altering Membrane Lipid Composition

The asexual facultative aerobic haploid yeast Candida glabrata is widely used in the industrial production of various organic acids. To elucidate the physiological function of the C. glabrata transcription factor Crz1p (CgCrz1p) and its role in tolerance to acid stress, we deleted or overexpressed the corresponding gene, CgCRZ1 Deletion of CgCRZ1 resulted in a 60% decrease in the dry weight of cells (DCW) and a 50% drop in cell viability compared with those of the wild type at pH 2.0. Expression of lipid metabolism-associated genes was also significantly downregulated. Consequently, the proportion of C_18:1 fatty acids, the ratio of unsaturated to saturated fatty acids, and the ergosterol content decreased by 30%, 46%, and 30%, respectively. Additionally, membrane integrity, fluidity, and H⁺-ATPase activity were reduced by 45%, 9%, and 50%, respectively. In contrast, overexpression of CgCrz1p increased C_18:1 and ergosterol contents by 16% and 40%, respectively. Overexpression also enhanced membrane integrity, fluidity, and H⁺-ATPase activity by 31%, 6%, and 20%, respectively. Moreover, in the absence of pH buffering, the DCW and pyruvate titers increased by 48% and 60%, respectively, compared to that of the wild type. Together, these results suggest that CgCrz1p regulates tolerance to acidic conditions by altering membrane lipid composition in C. glabrataIMPORTANCE This study provides insight into the metabolism of Candida glabrata under acidic conditions, such as those encountered during the industrial production of organic acids. We found that overexpression of the transcription factor CgCrz1p improved viability, biomass, and pyruvate yields at a low pH. Analysis of plasma membrane lipid composition indicated that CgCrz1p might play an important role in its integrity and fluidity and that it enhanced the pumping of protons in acidic environments. We propose that altering the structure of the cell membrane may provide a successful strategy for increasing C. glabrata productivity at a low pH.

Paracoccidioides brasiliensis uses endogenous and exogenous arachidonic acid for PGE x production

Paracoccidioides brasiliensis is the agent of paracoccidioidomycosis, the most prevalent deep mycosis in Latin America. Production of eicosanoids during fungal infections plays a critical role on fungal biology as well as on host immune response modulation. The purpose of our study was to assess whether P. brasiliensis strains with different degree of virulence (Pb18, Pb265, Bt79, Pb192) produce prostaglandin E(x) (PGE(x)). Moreover, we asked if P. brasiliensis could use exogenous sources of arachidonic acid (AA), as well as metabolic pathways dependent on cyclooxygenase (COX) enzyme, as reported for mammalian cells. A possible association between this prostanoid and fungus viability was also assessed. Our results showed that all strains, independently of their virulence, produce high PGE(x) levels on 4 h culture that were reduced after 8 h. However, in both culture times, higher prostanoid levels were detected after supplementation of medium with exogenous AA. Treatment with indomethacin, a COX inhibitor, induced a reduction on PGEx, as well as in fungus viability. The data provide evidence that P. brasiliensis produces prostaglandin-like molecules by metabolizing either endogenous or exogenous AA. Moreover, the results suggest the involvement of these mediators on fungal viability.

Prostaglandin E(2) production by high and low virulent strains of Paracoccidioides brasiliensis

The production of prostaglandins (PGs) during fungal infections could be an important suppressor factor of host immune response. Host cells are one source of prostaglandin E(2) (PGE(2)); however another potential source of PGE(2) is the fungal pathogen itself. Thus, both host and fungal PGE2 production is theorized to play a role in pathogenesis, being critical for growth of the fungus and to modulate the host immune response. The purpose of this work was to investigate if high and low virulent strains of Paracoccidioides brasiliensis have the capacity to produce PGE(2) in vitro, and if this production was related to the fungal growth. The results demonstrated that both strains of P. brasiliensis produce high levels of PGE(2) and the treatment with indomethacin, a cyclooxygenase inhibitor, significantly reduced the production of this mediator, as well as the viability of the fungus. Thus, our data indicate that PGE(2) is produced by P. brasiliensis by a cyclooxygenase-dependent metabolic pathway, and its production is required for fungal survival. This discovery reveals an important factor that has potentially great implications for understanding the mechanisms of immune deviation during infection.

Phenotypic characterization of food waste degradingBacillus strains isolated from aerobic bioreactors

A phenotypic characterization of seventeen Bacillus strains isolated from aerobic thermophilic bioreactors of a food waste processing company was carried out, using fatty acid and enzymatic activity profiles. It was observed that each species possessed a typical fatty acid and enzymatic production profile. Bacillus licheniformis strains exhibited the most significant enzyme production. Numerical analyses (principal component and hierarchical cluster analyses) revealed that Bacillus licheniformis strains were homogeneous regarding their fatty acid profiles whilst B. subtilis and Bacillus pumilus strains showed some phenotypic differences. However, enzymatic activities numerical analyses indicated that these three Bacillus species were more homogeneous regarding this phenotypic characteristic.

Differentiation between Candida species isolated from diabetic foot by fatty acid methyl ester analysis using gas chromatography

Gas chromatography (GC) was used to differentiate 100 isolates of Candida species (Candida parapsilosis, Candida albicans, Candida tropicalis, Candida famata and Candida glabrata) from 22 of 509 diabetic patients in whom the same species had been isolated from ulcer and interdigital spaces of the same and/or the other foot. All clinical isolates were identified by quantitative differences in the composition of six cell fatty acids (CFA). The values of the coefficients of variability (CV) of CFA show that the isolates from foot ulcers and interdigital spaces of the same diabetic patient probably belong to different chemotypes of the same Candida species.

Pathogenic yeasts Cryptococcus neoformans and Candida albicans produce immunomodulatory prostaglandins

Enhanced prostaglandin production during fungal infection could be an important factor in promoting fungal colonization and chronic infection. Host cells are one source of prostaglandins; however, another potential source of prostaglandins is the fungal pathogen itself. Our objective was to determine if the pathogenic yeasts Cryptococcus neoformans and Candida albicans produce prostaglandins and, if so, to begin to define the role of these bioactive lipids in yeast biology and disease pathogenesis. C. neoformans and C. albicans both secreted prostaglandins de novo or via conversion of exogenous arachidonic acid. Treatment with cyclooxygenase inhibitors dramatically reduced the viability of the yeast and the production of prostaglandins, suggesting that an essential cyclooxygenase like enzyme may be responsible for fungal prostaglandin production. A PGE series lipid was purified from both C. albicans and C. neoformans and was biologically active on both fungal and mammalian cells. Fungal PGE(x) and synthetic PGE(2) enhanced the yeast-to-hypha transition in C. albicans. Furthermore, in mammalian cells, fungal PGE(x) down-modulated chemokine production, tumor necrosis factor alpha production, and splenocyte proliferation while up-regulating interleukin 10 production. These are all activities previously documented for mammalian PGE(2). Thus, eicosanoids are produced by pathogenic fungi, are critical for growth of the fungi, and can modulate host immune functions. The discovery that pathogenic fungi produce and respond to immunomodulatory eicosanoids reveals a virulence mechanism that has potentially great implications for understanding the mechanisms of chronic fungal infection, immune deviation, and fungi as disease cofactors.

Characterization and differentiation of filamentous fungi based on Fatty Acid composition

Cellular fatty acid composition of 100 different filamentous fungi, including oomycetes, zygomycetes, ascomycetes, basidiomycetes, and sterile mycelia, was analyzed to determine if they can be differentiated from one another on this basis and how minor variations in culture temperature and age affect this characteristic. Many fungi were found to possess the same fatty acids but produced different relative concentrations of each. Some fungi differed in both the fatty acids produced and in the relative concentrations of others. Multivariate discriminant analysis demonstrated that all of the species included in this study had significantly different (P < 0.001) fatty acid profiles. Each of the three phyla from which representative species were analyzed and the sterile forms had distinctive fatty acid profiles. Significant differences in fatty acid composition were also found at the intraspecific level. Both culture temperature and age affected fatty acid composition in the fungi examined, but when these factors were held constant, variance in fatty acid composition was not a problem and fungal fatty acid profiles could be differentiated statistically.

Total cellular fatty acid composition of cultured Pneumocystis carinii

Oleic acid makes up > 50% of the total fatty acids of Pneumocystis carinii grown on WI-38 cells. Oleic acid levels increased in parallel with increasing trophozoites over 7 days in culture. The fatty acid composition of P. carinii resembles that of certain fungi but differs from those of lung surfactant lipid, host cells, and fetal bovine serum.

Strain delineation and epidemiology of Candida (Clavispora) lusitaniae

Electrophoretic karyotype (EK) patterns, determined by using contour-clamped homogeneous pulsed-field electrophoresis, and isoenzyme (IZ) profiles were evaluated as methods for strain delineation among 35 isolates of Candida lusitaniae recovered from 15 patients. All isolates were identified to the species level by using conventional morphologic and physiologic criteria, and the identification was confirmed by gas-liquid chromatography analysis of the cellular fatty acids. The isolates were then typed without knowledge of the patient source. The IZ profiles showed all isolates to be closely related. Fifteen EK patterns were found; each pattern was restricted to isolates recovered from a single patient. In contrast, on the basis of heterogeneity in phosphatases, beta-glucosidases, esterases, and catalases, 10 IZ profiles were found; 4 were shared by isolates recovered from more than one patient. Multiple isolates from six patients were analyzed, and for each patient, a single EK- and IZ-defined type was found. The types of isolates obtained from two patients, after the emergence of resistance to amphotericin B, remained the same as the types of isolates obtained earlier. The data suggest that a patient becomes colonized by a single strain of C. lusitaniae which may disseminate to multiple sites, that the colonizing strain can persist during the patient's hospitalization, and that it may develop resistance to amphotericin B. Both EK patterns and IZ profiles can be used to delineate strains of C. lusitaniae, but the EK pattern provides more discriminatory power.

Applications of cellular fatty acid analysis

More than ever, new technology is having an impact on the tools of clinical microbiologists. The analysis of cellular fatty acids by gas-liquid chromatography (GLC) has become markedly more practical with the advent of the fused-silica capillary column, computer-controlled chromatography and data analysis, simplified sample preparation, and a commercially available GLC system dedicated to microbiological applications. Experience with applications in diagnostic microbiology ranges from substantial success in work with mycobacteria, legionellae, and nonfermentative gram-negative bacilli to minimal involvement with fungi and other nonbacterial agents. GLC is a good alternative to other means for the identification of mycobacteria or legionellae because it is rapid, specific, and independent of other specialized testing, e.g., DNA hybridization. Nonfermenters show features in their cellular fatty acid content that are useful in identifying species and, in some cases, subspecies. Less frequently encountered nonfermenters, including those belonging to unclassified groups, can ideally be characterized by GLC. Information is just beginning to materialize on the usefulness of cellular fatty acids for the identification of gram-positive bacteria and anaerobes, despite the traditional role of GLC in detecting metabolic products as an aid to identification of anaerobes. When species identification of coagulase-negative staphylococci is called for, GLC may offer an alternative to biochemical testing. Methods for direct analysis of clinical material have been developed, but in practical and economic terms they are not yet ready for use in the clinical laboratory. Direct analysis holds promise for detecting markers of infection due to an uncultivable agent or in clinical specimens that presently require cultures and prolonged incubation to yield an etiologic agent.

Fatty acid analysis of different Candida species by capillary column gas-liquid chromatography

Gas-liquid chromatography was used to analyse the fatty acid composition of whole-cell hydrolysates of 40 yeast strains representing 5 Candida species and Torulopsis glabrata, T. glabrata could be easily distinguished from all other Candida spp. by the absence of C18:3. Candida albicans, C. krusei, C. parapsilosis, C. pseudotropicalis and C. tropicalis showed 10 major peaks in characteristic proportions. C. parapsilosis showed a high C16:0/C16:1 ratio (greater than 4.5), whereas C. pseudotropicalis was characterized by a C18:1/C16:0 ratio of less than 2.0. A high C18:3 concentration (greater than 10%) was typical for C. krusei (C18:2/C18:3 ratio less than or equal to 1.0). Our data reveal characteristic patterns of cellular fatty acid composition of T. glabrata, C. krusei, C. parapsilosis and C. pseudotropicalis which can be used for laboratory identification.