User:S4438663

Name Chew Zi Huai (s4438663) Bench ID C Date 23/09/2016 ^[1]

Classification

Higher order taxa

Bacteria – Firmicutes – Negativicutes – Selenomonadales – Veillonellaceae – Veillonella

Species

Species name and type strain: Veillonella parvula DM2008

Description and significance

Veillonella parvula (V. parvula) first isolated by Veillon and Zuber in 1898 and falls under the 6 species of anaerobic gram-negative cocci under the genus ‘’Veillonella’’. ^[1]

Veillonella parvula are small (roughly 0.3-0.5 µm in diameter), non-fermentative and nonsporulating coccus that forms part of the normal flora of humans in the oropharynx (tongue,dental plaque, buccal mucosa, gastrointestinal tract and female genital tract and are harmless in general. Oral V. parvula plays a role in the early development of periodontal disease.^[2] V. parvula are rare opportunistic pathogens that are implicated in infections of sinuses, lungs, heart bone and central nervous system.^[1] V. parvula can coaggregate with other aerobic and anaerobic bacterias. With the ability of V. parvula to grow in a biofilm with other bacterium could allow the survival of other bacteria in antimicrobial treatment. Caries and periodontitis are polymicrobial disease where multiple bacterium plays a role and that the presence of V. parvulagives other bacteria and itself a survival advantage by being more resistant to antimicrobial treatment.^[3] In the dental plague,V. parvula cannot adhere by itself to the surface of the teeth and does so by attaching to Streptococcus mutans and these two forms a mutualististic relationship with each other.

V. parvula are culture positive organisms can be cultured on lactate agar media forming colonies that are diamond or heartshaped, opaque, smooth, butyrous and grayish white and also culture in blood agar and are non-hemolytic. With incubation time of 48 hours and temperature between 30-37 degree C in an anaerobic environment of pH=6.5-8.0.^[4]

Genome structure

Veillonella parvula DSM 2008 has one main circular DNA chromosome with 38.6% GC content. With a total of 2132142 base pair, 1920 predicted genes, 1859 protein genes, 61 RNA genes and 15 pseudogenes.^[5]

Cell structure and metabolism

V. parvulacell wall comprises of an outer membrane made up of lipopolysaccharide that has an unusual presence of cadaverine and putrescine. The cell wall is highly endotoxic which might play a role in virulence. Major components of cytoplasmic membrane are plasmalogens which are ether lipids that play an important role in regulation of membrane fluidity.^[5] V. parvula DSM 2008 are early colonizers in dental biofilm and resident members in the oral microbial communities and are immobile as they lack flagella for motility. ^[4]

V. parvula are not able to ferment carbohydrates and uses organic acid by-products of carbohydrate processing microorganisms instead for its own metabolism and so can be considered as a benevolent bacteria. V. parvula are lactate fermenters and their main source of energy and metabolites comes from the conversion of lactate into propionate and acetate with little adenosine triphosphate (ATP) produced..^[6]V. parvula has an unusual metabolism that uses methylmalonyl-CoA decarboxylase, converting free energy from decarboxylation reactions into sodium ions electrochemical gradient that comes from the metabolism of succinate in the presence of lactate.^[5] The stoichiometry of using the methylmalonyl-CoA pathway for the fermentation of lactate to propionate and acetate is shown:^[7] Lactate → acetate + 2 propionate + CO2 + H2O

Ecology

V. parvula is found as part of the normal flora in mouth, gastrointestinal tract and vagina in humans. In oral V.parvula, the primary habitats are the tongue, dental plaque and buccal mucosa.^[1] In healthy subgingival sites, up to 98% of V.parvula can be cultivated. ^[5] Oral V. paruvala is most strongly associated with Streptococcus mutans(S. mutans) in oral biofilm as they have limited adherence properties to host and require other species with better adhering ability to help itself adhere to host. Study of oral V.parvula in the mouths of rats showed that V.parvula are unable to establish a single-species biofilm but when S. mutans were added in, there was a 1,000 fold increase in the amount of V.parvula.^[8] Another reason why V.parvula is greatly associated with S. mutans because it not able to ferment carbohydrates but able to use organic acids such as lactic acid which are byproducts heavily produce by S. mutans metabolic activity.^[9]

Pathology

Normally, V. parvula are not considered as pathogens but in the oral cavity can cause caries and periodontitis.> However, in rare case, V parvula can cause meningitis, endocarditis, osteomyelitis, epidural abscess, lumbar discitis and septicemia. ^[10]^[11]^[12]^[13]^[14]^[15]V. parvula are also shown to be resistant to antibiotics. Other more pathogenic microbes, for an example, S. mutans are able to use the biofilm formed with V. parvula for virulence in periodontal disease, thus V. parvula could indirectly involved in the pathogenesis of other microbes.^[3] As well as the the endotoxin lipopolysaccharide that could play a role in septicemia.^[5]

Application to biotechnology

A study of V. parvula genome reveals that it has a complete metabolic pathway for porphyrin and vitamin B12 metabolism and this pathway can be exploited for the development of probiotics. Currently, commercial available health-promoting competitive exclusion culture for poultry are made from mixed culture containing veillonella and lactic acid bacteria from ceca of chickens that inhibits enteropathogenic bacteria. In the age of antibiotic resistant ,such application or the genome may be used in the development of novel strategies using veillonella to prevent colonization of pathogenic bacteria.^[16]

Current research

There are many ongoing research to try to understand the mechanism and interaction of V. parvula with other aerobic and anaerobic microbes as V. parvula are well known for their coaggregation properties. For an example, in the respiratory tract of cystic fibrosis (CF) patients, Pseudomonas aeruginosa (P. aeruginosa) is the most dominant bacteria and that has been found to interact with V. parvula.^[17] Perhaps, just like with the coaggregation with S. mutans that make S. mutans less susceptible to chemical antiseptics, V. parvula works the same with P. aeruginosa. Another huge health problem which V. parvula is one of the key players in the development of dental caries that affects 60-90% of school-aged child and vast majority of adults.^[17] Since then, there is an interest to understand how a commensal bacteria can ultimately cause caries and other more severe infections.