CYANOBACTERIA

Unicellular or colonial aggregates held together by additional cell wall layers

Section I Reproduction by binary fission or budding

Synechococcus, Synechocystis, Gloeobacter, Gloeocapsa, Gloeothece, Chamaesiphon

Section II Reproduction by multiple fission giving rise to small daughter cells, BAEOCYTES, or by both multiple fission and binary fission

Dermocarpa, Xenococcus, Myxosarcina, Pleurocapsa, Chroococcidiopsis

Filamentous; a TRICHOME or chain of cells which grows by intercalary cell division; reproduction by random trichome breakage, by formation of HORMOGONIA, or by germination of AKINETES (Sections IV and V only)

Trichome always composed only of vegetative cells

Section III Division in only one plane

Spirulina, Oscillatoria, Lyngbya, Plectonema, Phormidium, Pseudanabaena, Microcoleus

In the absence of combined nitrogen, trichome contains heterocysts (N2 fixation) ; some also produce akinetes (resting cells)

Section IV Division in only one plane

Anabaena, Nodularia, Cylindrospermum, Nostoc, Scytonema, Calothrix

Section V Division in more than one plane

Fischerella, Chlorogloeopsis

CYANOBACTERIAL DNA PROPERTIES

G + C CONTENT

Section I: 35 to 71 mol% G + C

Section III 40 to 67 mol% G + C

Sections II, IV and V: 38 to 47 mol% G + C

All bacteria: 29 to 74 mol% G + C

GENOME SIZE

Section I 3000 to 10,000 kbp (Mean: 4450)

Section II 5100 to 7900 kbp (Mean: 6200)

Section III 4100 to 10,000 kbp

Section IV 5300 to 14,000 kbp

Section V 6000 to 8600 kbp

It has been suggested that genomes may have evolved by a series of fusions of smaller genomes (each about 2000 kbp) to form genomes containing 4000 kbp, 6000 kbp, 8000 kbp and 12,000 kbp

Synechocystis sp. PCC 6803

Unicellular, non-nitrogen fixing, heavy capsule

Freshwater

Naturally transformable

Capable of dark heterotrophic growth on glucose

Prefers lower light intensity, Topt ~34°C; optimum doubling time = ~12 hours

Synechococcus sp. PCC 7002

Unicellular (probably a natural short-chain mutant of a Phormidium), non-nitrogen fixing, light capsule

Marine/euryhaline (brackish water)

Naturally transformable

Capable of dark heterotrophic growth on glycerol

High-light tolerant; Topt ~39°C; optimum doubling time = 3.5 hours


Synechocystis sp. PCC 6803 Genome

G + C Content = 47.7%

3168 potential protein coding sequences

145 (4.6%) genes already reported and characterized

933 (29.4%) homologs of known genes

324 (10.2%) similarity to known genes

340 (10.8%) similarity to hypothetical genes

1,426 (45%) no significant similarity to any known gene

87% of Genome was coding sequence (1 gene per 1.1 kb)

Smallest protein: 28 aa Largest potential protein: 4,199 aa

Average protein = 326 amino acids

99 ORFs with similarity to transposases

Stable RNAs

Two rrn clusters identified, which were identical in sequence

42 tRNA genes were identified

rnpB (RNA component of RNase P)


A FEW POTENTIALLY INTERESTING OBSERVATIONS

Although some evidence for operons is observed, clustering of related genes is not very extensive. This differs from E. coli, B. subtilis, etc. Similar observations being made in other sequenced genomes.

Photosynthesis ~4% of genome

Gene regulation ~4% of genome (2% 2-comp.)

Insertion sequences, etc. ~3% of genome

Sigma Factors 9 total identified 1 Group 1

4 Group 2

4 Group 3 (3 RpoE-like)

No RpoN, RpoH, or RpoS

Twitching Motility (Type IV Pili) and Chemotaxis genes present.

Several protein classes found in eucaryotes (e.g., kinases, WD repeat proteins, phytochrome-like proteins, "cyanoglobin" )

Only one set of sec genes was found. Suggests thylakoid lumen and periplasmic space are topographically identical. However, two LepB's and one LspA.

3 DnaKs, 2 GroELs, 4 DnaJs, 3 NifSs

Multiple ndh genes for ndhF (4) and ndhD (5)

Multiple petC genes (Rieske Fe-S protein) (3)

Three oxidases: cydBD genes (putative plastoquinol oxidase), and two cytochrome oxidase gene sets; also genes with similarity to succinate dehydrogenase, fumarate reductase, and uptake hydrogenase. 5 presumed 2Fe-2S Ferredoxins

Two DNA polymerases (Polymerases I and III).

WHY SO MANY GENES??

Developmentally among the most complex procaryotes known

Heterocysts Anaerobic cells for N2 fixation

terminally differentiated cells with a specified pattern (like a tissue)

Akinetes Resting cells

Hormogonia Swarmer cells for dispersal; formed upon akinete germination

Relationships Among Genomes

66% of the H. influenzae genes (1130 of 1703 sequences) have E. coli homologs

>50% of the H. pylori genes (more than 800 of 1590 sequences) have hits in E. coli

51.5% of the A. aeolicus genes (777 of 1508 sequences) have hits in E. coli (~38% similarity on average)

25% of the A. aeolicus genes (379 of 1508 sequences) have hits in M. jannaschii (~35% similarity on average)

21% of the Synechocystis sp. PCC 6803 genes (675 of 3168 sequences) have hits in E. coli

13% of the M. jannaschii genes have hits to E. coli (231 of 1738 sequences) have hits in E. coli

~13% of the Synechocystis sp. PCC 6803 genes have hits in M. jannaschii (407 of 3168)

4.3% of the Saccharomyces cerevisiae proteins (254 of 5885 sequences) have hits in E. coli Ɛ뺎p#KS,+A"NPY9=?/gwZ[_*\j.tZ_Rh2zfgdz^rsU~`~XuJԴSEgӵ]F(#0d^/]QWU