Higher order taxa
Bacteria – Proteobacteria – Betaproteobacteria – Neisseriales – Neisseriaceae – Neisseria 
Neisseria flava Type strain: NRL 30,008
Description and significance
Neisseria are named after Albert Neisser, who discovered the microorganism responsible for gonorrhoea in 1879. Neisseria flava (from Latin flavus, yellow), or chromogenic group II as described by Elser and Huntoon in 1909, , is gram-negative coccus (spherical shape) of around 0.5-1.0 micrometres in diameter. They can occur as single coccus, or in pairs with adjacent sides flattened, and sometimes as tetrads due to division. While in Bergey’s Manual of Determinative Bacteriology, N. flava was described as a separate species, in Bergey’s Manual of Systematic Bacteriology, 2nd edition, it was included along with Neisseria perflava and Neisseria subflava under the species Neisseria subflava, where it was referred to as Neisseria subflava biovar flava, , although in other lists it is maintained as a distinct species.
Neisseria flava is normally found in the mucous membranes of the respiratory tract in humans and in the mouth. Culturing of Neisseria flava from the nasopharynx, and very rarely cerebrospinal fluid in cases of meningitis, can be done on blood agar, glucose agar, or chocolate agar. ,  On chocolate agar, the colonies are opaque and pale yellow, although the colour is difficult to detect unless grown on a lighter coloured medium. On blood agar, the colonies are small, yellowish, raised and smooth. Colonies are described similarly on glucose agar, except the colour is described as greenish-gray or greenish-yellow. The pigment is said to be best seen on Löffler’s blood serum medium or Dorsett’s egg medium, where it appears a greenish-yellow, although they grow well on ordinary culture media. Neisseria flava grows at 22C, and optimally at 37C. 
While N. flava is not one of the main disease-causing species of Neisseria in humans, its presence in blood cultures, along with other Neisseria species such as Neisseria subflava, Neisseria cinerea, and Neisseria canis, has been associated with serious infections such as endocarditis and meningitis. ,  N. flava is also a part of the human oral microbiome as described in the Human Oral Microbiome Database, and has also been identified in oral squamous cell carcinoma samples.
Whole genome sequence data is not available for N. flava, although there is supposedly little distinction between it and the other N. subflava biovars, for which more genome information is available. Partial sequences, of 16S ribosomal RNA genes for different N. flava strains, including the type strain NRL 30,008, are available. Complete coding sequences of genes for penicillin-binding protein 2 (penA) and transferrin binding protein B (tbpB) are available, along with the partial coding sequence of an opacity-related (opr) gene, and a porin precursor (por) gene.
Cell structure and metabolism
Neisseria are gram-negative bacteria, with an outer membrane consisting of phospholipids, proteins, and lipopolysaccharide (LPS). Their cell walls do not contain true waxes, and the peptidoglycan in N. flava is extensively O-acetylated, increasing resistance to peptidoglycan hydrolases in humans.  There is little information on the outer membrane proteins of N. flava, as most studies focus on the pathogenic species of Neisseria such as Neisseria gonorrhoeae and Neisseria meningitidis. However, for the opacity protein Opa, a membrane protein, opa-related genes were demonstrated in N. flava, although the corresponding protein was not found to be produced. Partial coding sequences of a porin precursor gene have been sequenced.
N. flava are early colonisers in biofilm formation. In an in-vivo study of dental biofilm formation, N. flava was identified in biofilm formed within the first 6 hours.
Neisseria spp. are chemoorganotrophs, oxidase and catalase positive (except for some Neisseria elongata strains), and produce carbonic anhydrase and nitrite reductase (all species except for N. gonorrhoeae and Neisseria canis). They do not produce thymidine, phosphorylase, thymidine kinase, or nucleoside deoxyribosyl transferase. N. flava has all required enzymes for the citric acid cycle, although an enzyme similar to a flavine adenine dinucleotide-dependent malate oxidase is used instead of a pyridine nucleotide-dependent malate dehydrogenase. Acid production from carbohydrates occurs by oxidation.  Neisseria flava produces acid from fructose, glucose, and maltose, but not from sucrose or mannitol .
N. flava are aerobic, and have been reported in the human mouth, specifically the nasopharynx. It is also found in the upper respiratory tract. It is occasionally isolated from cerebrospinal fluid in cases of meningitis, and infrequently from the genitourinary tract of patients with urethritis.
While N. flava are considered “non-pathogenic”, or commensals, (as opposed to the pathogenic N. gonorrhoeae and N. meningitidis), they have very occasionally been associated with human diseases,  such as meningitis – where they have been identified in cerebrospinal fluid – and endocarditis, as well as implicated in cases of urethritis and cervicitis.
Application to biotechnology
There are no mentions of the use of N. flava in biotechnology.
The most recent discoveries on N. flava relate to its presence in the human oral cavity and microbiome. The human microbiome, or the community of microorganisms that exist in and on the human body, assist in several metabolic and physiological functions, and have consequences for human health and disease. As a site providing access to the rest of the body, microbial communities in the oral cavity some of the most diverse, and have not only been shown to be responsible for several oral-related diseases, but have also been linked to other diseases including cardiovascular disease, diabetes, and pneumonia. The Human Oral Microbiome Database (HOMD) is an online database containing information, such as genome sequences, on prokaryote species that have been identified as part of the human oral microbiome. ,  There, N. flava was one of the species identified, and has Human Oral Taxon ID of 609. It has also been identified in human oral carcinoma samples.
7. Garrity GM, Bell JA, Lilburn T. 2005. Class II. Betaproteobacteria class. nov, p 575-922. In Brenner DJ, Krieg NR, Staley JT (ed), Bergey’s Manual® of Systematic Bacteriology, 2nd ed, vol 2. Springer-Verlag, Boston, MA.
13. Bennett JS, Jolley KA, Earle SG, Corton C, Bentley SD, Parkhill J, Maiden MCJ. 2012. A genomic approach to bacterial taxonomy: an examination and proposed reclassification of species within the genus “Neisseria”. Microbiology 158:1570-1580.
14. NCBI GenBank
15. Wolff K, Stern A. 1995. Identification and characterization of specific sequences encoding pathogenicity associated proteins in the genome of commensal Neisseria species. FEMS Microbiol Lett 125:255-263.
17. Ward’s Science
This page is written by <Quyen Vu> for the MICR3004 course, Semester 2, 2017