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Cell-Cell Communication in Lactic Acid Bacteria
Published in Marcela Albuquerque Cavalcanti de Albuquerque, Alejandra de Moreno de LeBlanc, Jean Guy LeBlanc, Raquel Bedani, Lactic Acid Bacteria, 2020
Emília Maria França Lima, Beatriz Ximena Valencia Quecán, Luciana Rodrigues da Cunha, Bernadette Dora Gombossy de Melo Franco, Uelinton Manoel Pinto
The essential feature of LAB metabolism is efficient carbohydrate fermentation coupled to substrate-level phosphorylation. This group of bacteria exhibits an enormous capacity to degrade different carbohydrates and related compounds (Mozzi et al. 2010). Based on the end products of glucose metabolism they are classified as homofermentative and heterofermentative microorganisms (Ribeiro et al. 2014). Those that produce lactic acid as the major or sole products of glucose fermentation are designated homofermenters and include some Lactobacillus and most Enterococcus species, Lactococcus, Pediococcus, Streptococcus, Tetragenococcus and Vagococcus. Meanwhile, those that produce equal molar amounts of lactate, carbon dioxide, and ethanol from hexoses are designated heterofermentative, including Leuconostoc, some species of Lactobacillus, Oenococcus and Weissella (Jay et al. 2005). The apparent difference on the enzyme level between these two categories is the presence or absence of the key cleavage enzymes of the Embden-Meyerhof pathway (fructose 1,6-diphosphate) and the PK pathway (phosphoketolase).
Beneficial Lactic Acid Bacteria
Published in K. Balamurugan, U. Prithika, Pocket Guide to Bacterial Infections, 2019
LAB do not possess a functional respiratory system, so they derive the energy required for their metabolism from the oxidation of chemical compounds, mainly sugars. Sugars are fermented by LAB via homofermentative or heterofermentative pathways. Homofermentative bacteria produce lactic acid as the only product of glucose fermentation through glycolysis or Embden–Meyerhof–Parnas pathway. Heterofermentative bacteria use the pentose phosphate pathway generating carbon dioxide (CO2) and ethanol or acetate, besides lactic acid. Other hexoses are also fermented by LAB after preliminary isomerization or phosphorylation. In addition, LAB with heterofermentative type of fermentation successfully metabolize pentoses. Disaccharides are split enzymatically into monosaccharides entering the appropriate pathways (Von Wright and Axelsson 2011). Genus Bifidobacterium degrades hexose sugars through a particular metabolic pathway or bifid shunt allowing to produce more energy in the form of ATP. Bifidobacterial pathway yields 2.5 mol of ATP, 1.5 mol of acetate, and 1 mol of lactate from 1 mol of fermented glucose, while the homofermentative LAB produce 2 mol of ATP and 2 mol of lactic acid and heterofermentative LAB produce 1 mol each of lactic acid, ethanol, and ATP per 1 mol of fermented glucose. Fructose-6-phosphoketolase enzyme plays a key role in this pathway and is considered to be a taxonomic marker for the family of Bifidobacteriaceae (Pokusaeva 2011). Recently a novel metabolic pathway (galacto-N-biose (GNB)/lacto-N-biose (LNB) I pathway) that utilizes both human milk oligosaccharides and host glycoconjugates and is essential for colonization of the infant gastrointestinal tract was found in genus Bifidobacterium (Fushinobu 2010). This route was suggested to be specific for Bifidobacterium; however, further studies showed ability of some LAB to metabolize LNB and GNB. Nevertheless, metabolic pathways responsible for catabolism of these compounds in LAB are completely different from those described for Bifidobacterium species (Bidart et al. 2014).
Selection of fast and slow growing bacteria from fecal microbiota using continuous culture with changing dilution rate
Published in Microbial Ecology in Health and Disease, 2018
The bacterial dynamics was reflected in metabolite patterns as butyrate and propionate-producing bacteria preferably grew at low dilution rates. Enhanced propionate production at low specific growth rates was also reported by us and others in pure cultures of B. thetaiotaomicron [38,3940]. Production of propionate enables to save carbon and regenerate NAD+ through reductive TCA cycle which can be coupled with anaerobic respiration, that is more efficient compared to acetate production through phosphoketolase reaction, with the respective ATP yields 4 mol/mol glucose vs 2 mol/mol glucose [41]. Increase of propionate production at low dilution rates can be related to proportionally higher requirements of carbon to maintenance energy than for assimilation of carbon to the biomass [42]. Hence, formation of propionate is favored at slow growth as more ATP is required for the maintenance. Similar ratios of acetate:propionate:butyrate 50:42:8 on AG and 84:14:2 on citrus pectin as substrates, were reported by Englyst et al. [43] in batch cultures with fecal inoculum. Thus, AG might selectively promote the propionate-producing bacteria while AP supports fermentation of sugars to acetate, which is a good substrate for butyrate producing bacteria.
Acids produced by lactobacilli inhibit the growth of commensal Lachnospiraceae and S24-7 bacteria
Published in Gut Microbes, 2022
Emma J. E. Brownlie, Danica Chaharlangi, Erin Oi-Yan Wong, Deanna Kim, William Wiley Navarre
Members of the newly defined Lactobacillaceae family cluster into two distinct clades depending on whether they utilize homofermentative or heterofermentative metabolism.9,10 Homofermentative species metabolize hexoses via the Embden-Meyerhof pathway, producing pyruvate as a key metabolic intermediate and lactate as an end product. Heterofermentative species metabolize hexoses via the phosphoketolase pathway, producing pyruvate and acetyl-phosphate as key intermediates with lactate and acetate or ethanol as end products. The split between the two types of metabolism appears to have occurred early in the evolution of the Lactobacillaceae, and their fermentation types correlate almost perfectly with phylogeny.10