At industrial scale, they are used in cheese making, especially Swiss hard cheeses, as dominant starter cultures. There is a rising trend to use propionibacteria in fermented milks as probiotic. The current paper reviews the characteristics of propionibacteria related to their use in fermented milks either as starter culture or probiotic, methods for the enumeration of propionibacteria, and their functional in vivo efficiency.
The authors thank the Shahid Beheshti Medical Science University for library and research facilities. Skip to Main Content. Search in: This Journal Anywhere. Advanced search. Submit an article Journal homepage.
Pages Accepted author version posted online: 12 Feb Original Articles. Incorporation of Propionibacteria in Fermented Milks as a Probiotic. Article Metrics Views. With a wider insight, propionibacteria may be assayed as probiotics for other ruminants like goats and sheep since their milk-derived products are highly appreciated by consumers. It should be emphasized that much of the health benefits described above could be related to the ability of propionibacteria to remain in high numbers in the gastrointestinal tract by surviving the adverse environmental conditions and adhering to the intestinal mucosa.
On the basis of the GRAS status of dairy propionibacteria and the positive results obtained by us and other authors, further studies are encouraged in order to select the appropriate strains for developing new functional foods that include these bacteria for human and animal nutrition. They have a peculiar metabolism leading to the formation of propionic acid as main end-product of fermentation.see url
Incorporation of Propionibacteria in Fermented Milks as a Probiotic
By the beginning of the XX th century, E. Since then, new species were described on the basis of their morphological and biochemical characteristics such as their typical pattern of Chinese characters, propionic acid production, and carbohydrate fermentation profile. In , Johnson and Cummins [ 6 ], classified strains with several common features into eight homology groups based on DNA-DNA hybridization and peptidoglycan characteristics.
Four dairy species were recognized in this edition: P. In , on the basis of 16S rRNA sequences, the species Arachnia propionica was reclassified as Propionibacterium propionicus [ 7 ]. Other species like P. In the last two decades six new species were isolated: P. Recently, a new species isolated from human humerus, P. The current taxonomic position of propionibacteria is the following [ 2 ]: Phylum Actinobacteria; Class Actinobacteria; Subclass Actinobacteridae; Order Actinomycetales; Suborder Propionibacterineae; Family Propionibacteriaceae; Genus Propionibacterium. In the more conventional and general way, propionibacteria are divided based on habitat of origin, in two main groups:.
Classical propionibacteria include among their main habitats: raw milk and cheese [ 1 , 2 ] but have been obtained also from silages and vegetables for human consumption [ 15 ], and from ruminal content and feces of cows and calves [ 16 ]. Furthermore, they are not limited to the gastrointestinal tract of ruminants being also isolated from the intestine of pigs and laying hens [ 17 ]. On the other side, cutaneous species are found mainly in the human skin, but have been isolated also from the intestine of humans, chicken and pigs [ 1 , 2 , 18 ], being best represented by the acne bacillus, Propionibacterium acnes.
The 13 species known up to now are listed in Table 1. From a safety point of view, classical species have a long history of safe application on industrial processes whereas members of the cutaneous group are commonly considered opportunistic pathogens in compromised hosts. In consequence, the economic relevance of propionibacteria derives mainly from the industrial application of dairy species as cheese starters and as biological producers of propionic acid and other metabolites with a more recent interest on their usage as health promoters.
Isolation and enumeration of propionibacteria can be made by microbial culture and molecular methods [ 19 ]. Various agarized media with different degrees of selectivity have been used for detection and enumeration of classical propionibacteria in dairy environments, animal and human fecal samples. Although these media may be successful for the isolation of classical and cutaneous strains of Propionibacterium , they have limitations for selective enumeration of bacteria in very complex ecosystems like intestinal microbiota.
- Propionibacterium | Definition of Propionibacterium at tioromismiper.tk;
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- Propionibacteria also have Probiotic Potential;
Molecular methods are a valuable alternative to plating assays, being far more specific, and unhindered by the presence of non-target microorganisms. Genus and species-specific primers targeted to the genes encoding 16S rRNA for PCR-based assays were also designed for detection of dairy propionibacteria [ 29 ]. A FISH protocol and oligonucleotide probes targeting the 16S rRNA of dairy propionibacteria were developed in our laboratory [ 32 ] and successfully used for enumeration of P.
Finally, a real-time PCR method, based on the transcription of the enzyme transcarboxylase involved in propionic fermentation, was successfully used to detect a strain of P. The members of the genus Propionibacterium possess a circular-shaped chromosome like most bacteria that varies in size between 2. The presence of two types of bacteriophages has also been described for propionibacteria.
One of them, the bacteriophage B22, belongs to the Group B1 of Bradley classification, whereas the other, bacteriophage B5, would be the first infectious filamentous virus described in a Gram positive bacterium [ 38 ]. Up to few years ago, the only completely sequenced and publicly available genome within the genus Propionibacterium was that of the commensal cutaneous species P. However, in the year , the complete genome of a species that belongs to the taxonomic group of dairy propionibacteria was described for the first time.
The genome of the type strain, P. The chromosome is predicted to contain protein-coding genes and also contains 22 different insertion sequences that represent 3. Insertion sequences and transposable elements may promote genome plasticity and induce phenotypic changes that contribute to bacterial adaptation to different environments; being particular for propionibacteria the synthesis of capsular EPS and the ability to ferment lactose [ 40 ]. The genome sequence also showed that P. Although propionibacteria are usually described as anaerobes, all the genes encoding enzymes required for aerobic respiration such as NADH dehydrogenase, succinate dehydrogenase, cytochrome bd complex, ATPase and the complete pathway for heme synthesis have been identified in the genome of P.
With respect to technological application in dairy industries, various pathways for formation of cheese flavor compounds were identified in the genome of this strain such as the enzymes involved in the production of propionic acid, volatile branched chain fatty acids from amino acid degradation, and free fatty acids and esters from lipids catabolism. In relation to probiotic functionality, it has been identified the complete biosynthesis pathway for a bifidogenic compound DHNA as well as the sequences corresponding to a high number of surface proteins involved in the interactions with the host like adhesion and immunomodulation.
By comparative genomics with P. Propionibacteria are heterotrophic microorganisms that mean they need an organic carbon source to grow and posses a fermentative metabolism [ 41 - 43 ]. They degrade carbohydrates like glucose, galactose, lactose, fructose and other sugars; poliols like glycerol; erythritol and others; and organic acids such as lactic and gluconic acids producing propionic, acetic and CO 2 as the main fermentation end-products [ 1 ]. The production of propionic acid by these bacteria involves a complex metabolic cycle with several reactions in which substrates are metabolized to pyruvate via glycolysis, pentose phosphate or the Entner-Doudoroff pathways, generating ATP and reduced co-enzymes.
Pyruvate is then oxidised to acetate and CO 2 or reduced to propionate.
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The latter transformation occurs via the Wood-Werkman cycle or transcarboxilase cycle which represents the key component of the central carbon metabolic pathway in propionibacteria [ 41 ]. The most important reaction of this cycle is transcarboxylation that transfers a carboxyl group from methyllmalonyl-CoA to pyruvate to form oxaloacetate and propionyl-CoA, without ATP consumption.
The enzyme catalyzing this reaction is a methylmalonyl-CoA carboxytransferase that has been fully characterized and its structure resolved [34; 40]. Then, oxaloacetate is reduced to succinate, via malate and fumarate in two NADH requiring reactions. Succinate is then converted to propionate via methylmalonyl-CoA intermediates succinyl-CoA and propionyl-CoA ; the carboxyl group removed from methylmalonyl-CoA is transferred to pyruvate to yield oxaloacetate, thus completing one cycle. Methylmalonyl-CoA is also regenerated from succinyl-CoA during propionate production, thus creating the second of the two transcarboxylase cycles, and can react with a new molecule of pyruvate.
All the reactions of this cycle are reversible. It must be emphasized that the Wood Werkman cycle used by propionibacteria to produce propionate is coupled to oxidative phosphorylation and yields more ATP than in the other bacteria producing propionic acid [ 42 , 43 ]. Depending on the strains, the substrate used, and the environmental conditions, propionibacteria modulate the proportions of pyruvate either reduced to propionate, or oxidised to acetate and CO 2 , to maintain the redox balance [ 43 ]. In this way the oxidation of glucose and lactic acid leads to a molar ratio of propionate:acetate of whereas the oxidation of glycerol leads to the formation of propionate only.
During lactate fermentation, aspartate is deaminated to fumarate by an aspartate ammonia lyase; fumarate is then converted to succinate, with a concomitant production of NAD and ATP. Their nutritional requirements are low and almost the same for all the species. Dairy propionibacteria like P. They can grow in a minimal medium containing ammonium as the sole nitrogen source, but a higher growth is observed in media containing amino acids [ 45 ].
Although P. Some proteinases have been described for Propionibacterium, one cell wall associated and one intracellular or membrane bound but their activities are weak. By contrast, different peptidases such as aminopeptidases, proline iminopeptidase, proline imidopeptidase, X-prolyl-dipeptidyl-amino-peptidase, endopeptidases and carboxypeptidase, have been described.
Amino acids, especially aspartic acid, alanine, serine and glycine, are degraded by Propionibacterium , with variations among species and strain [ 47 ]. On the other side, cutaneous propionibacteria, have the ability to hydrolyze different proteins, like gelatin and fibronectin, and to promote damages and inflammation of the host tissues. Regarding vitamins, all propionibacteria strains require pantothenate vitamin B5 and biotin vitamin H.
In addition, some strains require thiamine B1 and p-aminobenzoic acid [ 40 , 41 ]. It is known that propionibacteria are able to adapt and survive to different stresses like industrial processes and the gastrointestinal transit, as well as to remain active for long periods of time in such adverse environments [ 43 ].
The transit through the digestive tract also suppose stressful conditions for bacteria such as gastric acidity and the presence of other aggressive intestinal fluids like bile and pancreatic enzymes. Interestingly, the cell machinery involved in general stress adaptation in P.
The redundancy and inducibility of this chaperone and protease machinery is in agreement with the ability of P. The stress adaptation proteins were particularly investigated in P. Acid and bile stresses, induce the synthesis of the following proteins: pyruvate-flavodoxin oxidoreductase and succinate dehydrogenase which are involved in electron transport and ATP synthesis, as well as glutamate decarboxylase and aspartate ammonia-lyase, which are involved in intracellular pH homeostasis. Bile also induces oxidative stress so that survival and activity within the gut depend on remediation of oxidative damages.
Moreover, in response to bile salts, P. Other inducible proteins involved in protection and repair of DNA damages include Ssb protein which is involved in DNA recombination and repair, as well as Dps which protects DNA against oxidative stress are stress-induced in P.
Stress tolerance and cross-protection in strains of Propionibacterium freudenreichii were examined after exposure to heat, acid, bile and osmotic stresses. Cross-protection between bile salts and heat adaptation was demonstrated. By contrast, some other heterologous pretreatments hypothermic and hyperosmotic had no effect on tolerance to bile salts.