微生物学

Lipid membranes are essential cellular elements as they provide cellular integrity and selective permeability under a broad range of environmental settings upon cell growth. In particular, Archaea are commonly recognized for their tolerance to extreme conditions, which is now widely accepted to stem from the unique structure of their lipids. While enhancing the stability of the archaeal cell membrane, the exceptional properties of archaeal lipids also hinder their extraction using regular procedures initially developed for bacterial and eukaryotic lipids. The protocol described here circumvents these issues by directly hydrolyzing the polar head group(s) of archaeal lipids and extracting the resulting core lipids. Although leading to a loss of information on the nature of polar heads, this procedure allows the quantitative extraction of core lipids for most types of archaeal cells in an efficient, reproducible, and rapid manner.

Bacteria are surrounded by a protective peptidoglycan cell wall. Provided that this structure and the enzymes involved are the preferred target for our most successful antibiotics, determining its structural and chemical complexity is of the highest interest. Traditionally, high-performance liquid chromatography (HPLC) analyses have been performed, but these methods are very time consuming in terms of sample preparation and chromatographic separation. Here we describe an optimized method for preparation of Gram-negative bacteria peptidoglycan and its subsequent analysis by ultra-performance liquid chromatography (UPLC). The use of UPLC in peptidoglycan analyses provides a dramatic reduction of the sample volume and hands-on time required and, furthermore, permits in-line mass spectrometry (MS) of the UPLC resolved muropeptides, thus facilitating their identification. This method improves our capability to perform high throughput analysis to better understand the cell-wall biology.

The yeast Saccharomyces cerevisiae has been perceived over decades as a highly valuable model organism for the investigation of ion homeostasis. Indeed, many of the genes and biological systems that function in yeast ion homeostasis are conserved throughout unicellular eukaryotes to humans. In this context, measurement of the yeast cellular ionic content provides information regarding yeast response to gene deletion or exposure to chemicals for instance. We propose here a protocol that we tested for the analysis of 12 elements (Ba²⁺, Ca²⁺, Cd²⁺, Co²⁺, Cu²⁺, Fe²⁺, K⁺, Mg²⁺, Mn²⁺, Na⁺, Ni²⁺, Zn²⁺) in yeast using Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). This technique enables determination of the cellular content of numerous ions from one biological sample.

Leishmaniasis is a parasitic disease caused by the obligatory intracellular protozoa Leishmania spp. Current therapeutic options are limited and thus, drug discovery against leishmaniasis is very important. Nevertheless, there is a great difficulty to develop therapeutic strategies against the disease because the parasite deploys various mechanisms to evade the immune system and multiply inside the host. Among the main factors of the immunity that are recruited to confront the Leishmania infection are the macrophages (MΦs) that produce effector molecules such as Nitric Oxide (NO) and Reactive Oxygen Species (ROS). Therefore, efficient drug agents should combine the antileishmanial effect of these gaseous transmitters along with the enhancement of the host’s adaptive immunity. In the quest of therapeutic alternatives, natural products have been extensively studied and are considered as candidate antileishmanial agents since they exhibit specific properties in modulating the host’s immune response towards an effective anti-leishmanial cell-mediated immunity capable to eliminate parasitic dissemination. In the current protocol, Leishmania-infected MΦs (J774A.1 cell line) that have been treated with various increasing concentrations of a natural compound, are tested for the production of the aforementioned molecules. In order to detect NO production, we employ the Griess colorimetric nitrite assay and quantification relies on the construction of an accurate standard curve using appropriate standards of known concentration. ROS detection and quantification is achieved by flow cytometry and relies on the use of carboxy-H₂DCFDA, an indicator that converts to a fluorescent form when interacts with ROS molecules.

Candida albicans is the most common cause of fungal infections worldwide. Infection by C. albicans is closely associated with its ability to form a biofilm, closely packed communities of cells attached to the surfaces of human tissues and implanted devices, in or on the host. When tested for susceptibility to antifungals, such as polyenes, azoles, and allylamines, C. albicanscells in a biofilm are more resistant to antifungal agents than C. albicans cells in the planktonic form. Cyclic Adenosine monophosphate (cAMP) is one of the key elements for triggering hyphal and biofilm formation in C. albicans. It is hard to detect or extract molecular markers (e.g., cAMP) from C. albicans biofilms because the biofilms have a complex three-dimensional architecture with an extracellular matrix surrounding the cell walls of the cells in the biofilm. Here, we present an improved protocol that can effectively measure the level of intracellular cAMP in C. albicans biofilms.

D-amino acid transaminase (D-AAT) is able to synthesize both D-glutamate and D-alanine, according to the following reaction: D-alanine + α-ketoglutarate ⇌ D-glutamate + pyruvate. These two D-amino acids are essential components of the peptidoglycan layer of bacteria. In our recently published work, MSMEG_5795 from Mycobacterium smegmatis was identified as having D-amino acid transaminase (D-AAT) activity, although it has primarily been annotated as 4-amino-4-deoxychorismate lyase (ADCL). To unequivocally demonstrate D-AAT activity from MSMEG_5795 protein two coupled enzyme assays were performed in series. First, D-alanine and α-ketoglutarate were converted to D-glutamate and pyruvate by MSMEG_5795 using the D-AAT assay. Next, the products of this reaction, following removal of all protein, were used as input into an assay for glutamate racemase in which D-glutamate is converted to L-glutamate by glutamate racemase (Gallo and Knowles, 1993; Poen et al., 2016). As the only source of D-glutamate in this assay would be from the reaction of D-alanine with MSMEG_5795, positive results from this assay would confirm the D-AAT activity of MSMEG_5795 and of any enzyme tested in this manner.

Teichoic acids (TA) are anionic polymers comprised of polyol phosphate repeat units that are abundant in the cell wall of Gram-positive bacteria. Both wall teichoic acid (WTA) and lipoteichoic acid (LTA) play important roles in regulating cell wall remodeling as well as conferring antibiotic resistance. To analyze TA, we describe a polyacrylamide gel electrophoresis (PAGE) method for both WTA and LTA. To extract crude WTA, the peptidoglycan sacculus is first isolated and WTA is then liberated by hydrolysis. LTA is extracted by 1-butanol and pre-treated with lipase to prevent aggregation and improve single-band resolution by PAGE. Crude extracts of both TAs are then subjected to PAGE followed by Alcian blue and silver staining. These protocols are easily adoptable by laboratories interested in rapidly analyzing TAs and can be used determine the relative abundance, relative polymer length and whether TAs are glycosylated. More detailed TA structural and compositional information can be obtained using the described purification protocols by nuclear magnetic resonance (NMR) and electrospray ionization mass spectrometry (ESI-MS) analysis.

Polyphosphate (polyP), a universally conserved biomolecule, is composed of up to 1,000 phosphate monomers linked via phosphoanhydride bonds. Reaching levels in bacteria that are in the high nmoles per mg protein range, polyP plays important roles in biofilm formation and colonization, general stress protection and virulence. Various protocols for the detection of polyP in bacteria have been reported. These methods primarily differ in the ways that polyP is extracted and/or detected. Here, we report an improved method, in which we combine polyP extraction via binding to glassmilk with a very sensitive PolyP kinase/luciferase-based detection system. By using this procedure, we significantly enhanced the sensitivity of polyP detection, making it potentially applicable for mammalian tissues.

Ralstonia eutropha H16 produces and mobilizes (re-utilizes) intracellular polyhydroxybutyrate (PHB) granules during growth. This protocol describes the visualization of intracellular Nile red stained PHB granules and the quantification of PHB by gas chromatography. Our first method describes how to analyze PHB granules by fluorescence microscopy qualitatively. Our second approach enables the conversion of PHB to volatile hydroxycarboxylic acid methyl esters by acidic methanolysis and their quantification by gas chromatography. Through this method, it is possible to obtain an absolute quantification of PHB, e.g., per cell dry weight.

Increased antibiotic resistance of plants and human pathogens and continuous use of chemical fertilizers has pushed microbiologists to explore new microbial sources as potential antagonists. In this study, eight strains of Pseudomonas aurantiaca and Pseudomonas chlororaphis, have been isolated from different plant sources and screened for their antagonistic and plant growth promoting potential (Shahid et al., 2017). All strains were compared with reference strain PB-St2 and their secondary metabolites were isolated by the use of solvent partitioning and subjected to LC/ESI/MS for confirmation of compounds. The ESI-mass spectra obtained were used to characterize the surfactants ionization behavior and [M + H]⁺ and [M + Na]⁺ ions were monitored for phenazines, derivatives of lahorenoic acid and cyclic lipopeptide (WLIP). LC-MS and HPLC methods were developed to see the elution of dominant metabolites in a single run to avoid the labor and separate methods of detection for all compounds. The method was found suitable and distinctively separated the compounds at different retention times in gradient flow. This method can be helpful to explore the metabolome of Pseudomonas sp. overall and in identification and quantification of strain specific metabolites.