Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
102,896
result(s) for
"Bacteria - metabolism"
Sort by:
Anaerobic digestion : making biogas - making energy : the Earthscan expert guide
\"Hundreds of million tonnes of agricultural and food waste are produced each year around the world, most of which is just that, waste. Anaerobic digestion, biogas and the heat and electricity that can be produced from it is still a nascent industry in many countries, yet the benefits of AD spread throughout the community: - Gives good financial returns to farmers and eco-entrepreneurs. - Helps community leaders meet various policies and legislative targets. - Offers an environmentally sensitive waste disposal option. - Provides a local heat and power supply, & creates employment opportunities - Reduces greenhouse gas emissions, as well as providing an organic fertilizer. Although the process of AD itself is relatively simple there are several system options available to meet the demands of different feedstocks. This book describes, in simple, easy to read language the five common systems of AD; how they work, the impact of scale, the basic requirements, the costs and financial implications, and how to get involved in this rapidly growing green industry\"--Provided by publisher.
Book
Novel bile acid biosynthetic pathways are enriched in the microbiome of centenarians
Centenarians have a decreased susceptibility to ageing-associated illnesses, chronic inflammation and infectious diseases
1
–
3
. Here we show that centenarians have a distinct gut microbiome that is enriched in microorganisms that are capable of generating unique secondary bile acids, including various isoforms of lithocholic acid (LCA): iso-, 3-oxo-, allo-, 3-oxoallo- and isoallolithocholic acid. Among these bile acids, the biosynthetic pathway for isoalloLCA had not been described previously. By screening 68 bacterial isolates from the faecal microbiota of a centenarian, we identified Odoribacteraceae strains as effective producers of isoalloLCA both in vitro and in vivo. Furthermore, we found that the enzymes 5α-reductase (5AR) and 3β-hydroxysteroid dehydrogenase (3β-HSDH) were responsible for the production of isoalloLCA. IsoalloLCA exerted potent antimicrobial effects against Gram-positive (but not Gram-negative) multidrug-resistant pathogens, including
Clostridioides difficile
and
Enterococcus faecium
. These findings suggest that the metabolism of specific bile acids may be involved in reducing the risk of infection with pathobionts, thereby potentially contributing to the maintenance of intestinal homeostasis.
The microbiota of centenarians (aged 100 years and older) comprise gut microorganisms that are capable of generating unique secondary bile acids, including isoallolithocholic acid, a bile acid with potent antimicrobial effects against Gram-positive—but not Gram-negative—multidrug-resistant pathogens.
Journal Article
Similarities and Differences between Silver Ions and Silver in Nanoforms as Antibacterial Agents
Silver is considered as antibacterial agent with well-known mode of action and bacterial resistance against it is well described. The development of nanotechnology provided different methods for the modification of the chemical and physical structure of silver, which may increase its antibacterial potential. The physico-chemical properties of silver nanoparticles and their interaction with living cells differs substantially from those of silver ions. Moreover, the variety of the forms and characteristics of various silver nanoparticles are also responsible for differences in their antibacterial mode of action and probably bacterial mechanism of resistance. The paper discusses in details the aforementioned aspects of silver activity.
Journal Article
Photodynamic Inactivation of Bacteria with Porphyrin Derivatives: Effect of Charge, Lipophilicity, ROS Generation, and Cellular Uptake on Their Biological Activity In Vitro
Resistance of microorganisms to antibiotics has led to research on various therapeutic strategies with different mechanisms of action, including photodynamic inactivation (PDI). In this work, we evaluated a cationic, neutral, and anionic meso-tetraphenylporphyrin derivative’s ability to inactivate the Gram-negative and Gram-positive bacteria in a planktonic suspension under blue light irradiation. The spectroscopic, physicochemical, redox properties, as well as reactive oxygen species (ROS) generation capacity by a set of photosensitizers varying in lipophilicity were investigated. The theoretical calculations were performed to explain the distribution of the molecular charges in the evaluated compounds. Moreover, logP partition coefficients, cellular uptake, and phototoxicity of the photosensitizers towards bacteria were determined. The role of a specific microbial efflux pump inhibitor, verapamil hydrochloride, in PDI was also studied. The results showed that E. coli exhibited higher resistance to PDI than S. aureus (3–5 logs) with low light doses (1–10 J/cm2). In turn, the prolongation of irradiation (up to 100 J/cm2) remarkably improved the inactivation of pathogens (up to 7 logs) and revealed the importance of photosensitizer photostability. The PDI potentiation occurs after the addition of KI (more than 3 logs extra killing). Verapamil increased the uptake of photosensitizers (especially in E. coli) due to efflux pump inhibition. This effect suggests that PDI is mediated by ROS, the electrostatic charge interaction, and the efflux of photosensitizers (PSs) regulated by multidrug-resistance (MDR) systems. Thus, MDR inhibition combined with PDI gives opportunities to treat more resistant bacteria.
Journal Article
Two broadly conserved families of polyprenyl-phosphate transporters
Peptidoglycan and almost all surface glycopolymers in bacteria are built in the cytoplasm on the lipid carrier undecaprenyl phosphate (UndP)
1
–
4
. These UndP-linked precursors are transported across the membrane and polymerized or directly transferred to surface polymers, lipids or proteins. UndP is then flipped to regenerate the pool of cytoplasmic-facing UndP. The identity of the flippase that catalyses transport has remained unknown. Here, using the antibiotic amphomycin that targets UndP
5
–
7
, we identified two broadly conserved protein families that affect UndP recycling. One (UptA) is a member of the DedA superfamily
8
; the other (PopT) contains the domain DUF368. Genetic, cytological and syntenic analyses indicate that these proteins are UndP transporters. Notably, homologues from Gram-positive and Gram-negative bacteria promote UndP transport in
Bacillus subtilis
, indicating that recycling activity is broadly conserved among family members. Inhibitors of these flippases could potentiate the activity of antibiotics targeting the cell envelope.
A study identifies two broadly conserved families of flippases that catalyse the transport of undecaprenyl phosphate in bacteria and could function to recycle dolichol phosphate in eukaryotes and archaea.
Journal Article
Types and origins of bacterial membrane vesicles
Most bacteria release membrane vesicles (MVs) that contain specific cargo molecules and have diverse functions, including the transport of virulence factors, DNA transfer, interception of bacteriophages, antibiotics and eukaryotic host defence factors, cell detoxification and bacterial communication. MVs not only are abundant in nature but also show great promise for applications in biomedicine and nanotechnology. MVs were first discovered to originate from controlled blebbing of the outer membrane of Gram-negative bacteria and are therefore often called outer-membrane vesicles (OMVs). However, recent work has shown that Gram-positive bacteria can produce MVs, that different types of MVs besides OMVs exist and that, in addition to membrane blebbing, MVs can also be formed by endolysin-triggered cell lysis. In this Review, we provide an overview of the structures and compositions of the various vesicle types and discuss novel formation routes, which may lead to distinct vesicle types that serve particular functions.
Journal Article
From the regulation of peptidoglycan synthesis to bacterial growth and morphology
Key Points
Peptidoglycan synthesis is regulated at multiple levels to ensure shape-maintaining growth and cell division.
Peptidoglycan synthases and hydrolases coordinate to enlarge the sacculus. Coordinated enzyme activity is also required for cell division and morphogenesis.
Peptidoglycan synthesis and the localization and movement of cytoskeletal elements are interdependent.
Peptidoglycan synthases and hydrolases are also regulated by outer-membrane proteins.
Peptidoglycan growth is sensitive to mechanical force.
Peptidoglycan is remodelled in a growth-dependent manner, and its growth is tied to metabolic inputs.
The peptidoglycan sacculus maintains bacterial cell shape and provides mechanical strength to resist osmotic challenge. In this Review, Vollmer and colleagues describe recent insights into the mechanisms of peptidoglycan synthesis in Gram-negative bacteria and how this process is regulated by cytoskeletal and outer-membrane components.
How bacteria grow and divide while retaining a defined shape is a fundamental question in microbiology, but technological advances are now driving a new understanding of how the shape-maintaining bacterial peptidoglycan sacculus grows. In this Review, we highlight the relationship between peptidoglycan synthesis complexes and cytoskeletal elements, as well as recent evidence that peptidoglycan growth is regulated from outside the sacculus in Gram-negative bacteria. We also discuss how growth of the sacculus is sensitive to mechanical force and nutritional status, and describe the roles of peptidoglycan hydrolases in generating cell shape and of
D
-amino acids in sacculus remodelling.
Journal Article
Dead cells release a ‘necrosignal’ that activates antibiotic survival pathways in bacterial swarms
Swarming is a form of collective bacterial motion enabled by flagella on the surface of semi-solid media. Swarming populations exhibit non-genetic or adaptive resistance to antibiotics, despite sustaining considerable cell death. Here, we show that antibiotic-induced death of a sub-population benefits the swarm by enhancing adaptive resistance in the surviving cells. Killed cells release a resistance-enhancing factor that we identify as AcrA, a periplasmic component of RND efflux pumps. The released AcrA interacts on the surface of live cells with an outer membrane component of the efflux pump, TolC, stimulating drug efflux and inducing expression of other efflux pumps. This phenomenon, which we call ‘necrosignaling’, exists in other Gram-negative and Gram-positive bacteria and displays species-specificity. Given that adaptive resistance is a known incubator for evolving genetic resistance, our findings might be clinically relevant to the rise of multidrug resistance.
Swarming bacterial populations can exhibit antibiotic resistance, despite sustaining considerable cell death. Here, Bhattacharyya et al. show that killed cells release periplasmic protein AcrA, which activates efflux pumps on the surface of live cells, thus enhancing antibiotic resistance in the surviving cells.
Journal Article
Phylogenetic distribution of three pathways for propionate production within the human gut microbiota
Propionate is produced in the human large intestine by microbial fermentation and may help maintain human health. We have examined the distribution of three different pathways used by bacteria for propionate formation using genomic and metagenomic analysis of the human gut microbiota and by designing degenerate primer sets for the detection of diagnostic genes for these pathways. Degenerate primers for the acrylate pathway (detecting the
lcdA
gene, encoding lactoyl-CoA dehydratase) together with metagenomic mining revealed that this pathway is restricted to only a few human colonic species within the Lachnospiraceae and Negativicutes. The operation of this pathway for lactate utilisation in
Coprococcus catus
(Lachnospiraceae) was confirmed using stable isotope labelling. The propanediol pathway that processes deoxy sugars such as fucose and rhamnose was more abundant within the Lachnospiraceae (based on the
pduP
gene, which encodes propionaldehyde dehydrogenase), occurring in relatives of
Ruminococcus obeum
and in
Roseburia inulinivorans
. The dominant source of propionate from hexose sugars, however, was concluded to be the succinate pathway, as indicated by the widespread distribution of the
mmdA
gene that encodes methylmalonyl-CoA decarboxylase in the Bacteroidetes and in many Negativicutes. In general, the capacity to produce propionate or butyrate from hexose sugars resided in different species, although two species of Lachnospiraceae (
C. catus
and
R. inulinivorans
) are now known to be able to switch from butyrate to propionate production on different substrates. A better understanding of the microbial ecology of short-chain fatty acid formation may allow modulation of propionate formation by the human gut microbiota.
Journal Article
Undecaprenyl phosphate translocases confer conditional microbial fitness
The microbial cell wall is essential for maintenance of cell shape and resistance to external stressors
1
. The primary structural component of the cell wall is peptidoglycan, a glycopolymer with peptide crosslinks located outside of the cell membrane
1
. Peptidoglycan biosynthesis and structure are responsive to shifting environmental conditions such as pH and salinity
2
–
6
, but the mechanisms underlying such adaptations are incompletely understood. Precursors of peptidoglycan and other cell surface glycopolymers are synthesized in the cytoplasm and then delivered across the cell membrane bound to the recyclable lipid carrier undecaprenyl phosphate
7
(C55-P, also known as UndP). Here we identify the DUF368-containing and DedA transmembrane protein families as candidate C55-P translocases, filling a critical gap in knowledge of the proteins required for the biogenesis of microbial cell surface polymers. Gram-negative and Gram-positive bacteria lacking their cognate DUF368-containing protein exhibited alkaline-dependent cell wall and viability defects, along with increased cell surface C55-P levels. pH-dependent synthetic genetic interactions between DUF368-containing proteins and DedA family members suggest that C55-P transporter usage is dynamic and modulated by environmental inputs. C55-P transporter activity was required by the cholera pathogen for growth and cell shape maintenance in the intestine. We propose that conditional transporter reliance provides resilience in lipid carrier recycling, bolstering microbial fitness both inside and outside the host.
Members of the DUF368-containing and DedA transmembrane protein families have conditional roles in undecaprenyl phosphate translocation in Gram-negative and Gram-positive bacteria and may have a widely conserved function in the biogenesis of microbial cell surface glycopolymers.
Journal Article