Basic Microbiology
Philip A. Geis in Cosmetic Microbiology, 2020
Facultative anaerobes have evolved mechanisms to produce ATP (although in smaller amounts) by breaking down sugars when O2 is absent. Collectively referred to as fermentation, these mechanisms produce ATP along with a number of interesting byproducts depending on the species. Many of these byproducts are important commercially. The mechanisms of fermentation are categorized based on the major acid or alcohol byproducts that are produced. Homolactic fermentation—Produces lactic acid exclusively as a byproduct of fermentation.Heterolactic fermentation—Produces lactic acid in addition to ethanol and CO2.Alcoholic fermentation—In this mechanism, ethanol is the primary byproduct in addition to CO2.Mixed acid fermentation—Produces multiple byproducts including acetic acid, lactic acid, succinic acid, and formic acids as well as ethanol.Butanediol fermentation—In this mechanism, butanediol and ethanol are produced in large amounts along with lactic acid.
Biology of microbes
Philip A. Geis in Cosmetic Microbiology, 2006
When several other products (including ethanol and CO2) are formed in addition to lactic acid, the reaction is known as heterolactic fermentation. Lactic acid fermentors include various Lactobacillus spp. and some Streptococcus spp. Pyruvate may also be reduced to form formic acid, ethanol, and a variety of other acids (e.g., acetic, lactic, succinic). In this case, the reaction is designated mixed acid fermentation and is typical of many enteric bacteria such as Escherichia, Salmonella, and Proteus. If formate hydrogenylase is present, the formate will be further converted to hydrogen and carbon dioxide. Alternatively, the pyruvate may be converted to acetoin that is then reduced to butanediol using NADH. Organisms that perform this fermentation are Enterobacter, Serratia, and Bacillus spp. These processes help identify the various organisms that perform them and can be used as diagnostic tools. Other fermentations may also take place, for example, the formation of propionic acid (Propionibacterium), isopropanol, butanol, and butyrate (Clostridium). These latter fermentations may be applied to the manufacture of foods and fuels.
The duodenal mucosa associated microbiome, visceral sensory function, immune activation and psychological comorbidities in functional gastrointestinal disorders with and without self-reported non-celiac wheat sensitivity
Published in Gut Microbes, 2022
Ayesha Shah, Seungha Kang, Nicholas J Talley, Anh Do, Marjorie M Walker, Erin R Shanahan, Natasha A Koloski, Michael P Jones, Simon Keely, Mark Morrison, Gerald J Holtmann
In this study, we have compared all the FGID subjects with the controls using three distinct statistical approaches: edgeR, sPLS-DA (ASV-level), and factor analysis (genus-level). One or more of these approaches identified specific ASVs representing Prevotella, Alloprevotella, Neisseria, Veillonella, Peptostreptococcus, and Leptotrichia to be increased for the FGID patients compared to the control group. These differences are likely to support a mixed acid fermentation including succinate and propionate production, which in turn provides substrates that can support the growth of asaccharolytic Veillonella spp. and Neisseria spp.,41 respectively. As such, these alterations in the d-MAM profiles of FGID patients without SR-NCWS are microbiologically intuitive and aligned with other findings. Indeed, a previous study focussing on IBS patients observed in the small intestine significantly increased the abundance of Prevotella spp, and Prevotella and Veillonella spp. abundance was significantly correlated.42
Human vaginal pH and microbiota: an update
Published in Gynecological Endocrinology, 2018
Keshav Godha, Kelly M. Tucker, Colton Biehl, David F. Archer, Sebastian Mirkin
The pH of the vagina has been an ongoing area of interest in the understanding of vaginal physiology, disease, and drug development. More than a century ago, in 1892, Albert Döderlein, a German obstetrician and gynecologist, was the first to describe a Gram-positive bacterium from the vagina, Döderlein’s bacillus (Lactobacilli genus), that was characterized by its ability to produce lactic acid through glycogen fermentation [2]. The resulting acidic pH of a healthy human vagina (normal range of 3.8–4.5) was found to provide protection against urinary tract infections (UTI) vaginitis, and deterring the overgrowth of pathogenic microbes [3]. Since then, other non-Lactobacillus species have been discovered that contribute to the acidic pH through homolactic and mixed acid fermentation [4]. Döderlein’s discovery brought awareness to the microorganisms that colonize the human vagina, currently defined as the vaginal microbiota.
Development of the gut microbiota in healthy children in the first ten years of life: associations with internalizing and externalizing behavior
Published in Gut Microbes, 2022
Yangwenshan Ou, Clara Belzer, Hauke Smidt, Carolina de Weerth
We further investigated potential functional differences of the gut microbiota between bacterial clusters in an exploratory manner by using the Picrust2 approach. In general, we noticed that multiple predicted metabolic functions (i.e., KEGG orthologs and MetaCyc pathways) varied between bacterial clusters in infancy and childhood. For example, in infancy, we observed that the level of KEGG ortholog beta-galactosidase, an enzyme catalyzing the hydrolysis of beta-galactosides like lactose, was lower in Infancy_3 in comparison with the other two infant bacterial clusters. Beta-galactosidase has been found prevalent in Bifidobacterium species.55 Consistent with this, Infancy_3 showed the lowest level of Bifidobacterium; hence, the depletion of Bifidobacterium may explain the reduction of beta-galactosidase in Infancy_3. In childhood, we found that the relative abundance of the KEGG ortholog beta-glucosidase, an enzyme hydrolysing various glycosides like cellulose coming from plant foods, was highest in bacterial cluster Childhood_2. Childhood_2 was enriched in a fiber-favoring bacterium Prevotella_9. As a consequence, this cluster can be considered to have a higher ability of utilizing cellulose, which is in line with our finding. As for differences in MetaCyc pathways, we observed that the biosynthesis of precursors (i.e., aromatic amino acids) for neurotransmitters (i.e., serotonin, dopamine and norepinephrine), was decreased in Infancy_3. This bacterial cluster also showed decreases in mixed acid fermentation and Bifidobacterium shunt, which might indicate a reduction in short-chain fatty acids (SCFAs) production. Although the role of SCFAs on the MGBA has not been clearly elucidated, they are speculated to have considerable impacts.56 In both Infancy_3 and Childhood_2, we noticed decreased levels in predicted functions of L-arginine biosynthesis I and II. L-arginine supplementation has been reported to stimulate glutamate decarboxylation in Lactococcus lactis, which in turn increases the production of the neurotransmitter gamma-aminobutyric acid (GABA).57 However, it is unknown if other bacteria have similar interactions of L-arginine with GABA. Finally, note that there are two main limitations of any function prediction tool based on marker genes such as Picrust2.47 The first is the bias caused by the reference database, and the second is that the resolution cannot distinguish strain-specific functionality. Hence, these findings of predicted functions must be seen as exploratory and interpreted with caution.
Related Knowledge Centers
- Acid
- Anaerobic Organism
- Bacteria
- Biochemistry
- Enterobacteriaceae
- Fermentation
- Glucose
- Metabolism
- Carbohydrate
- Gram-Negative Bacteria