L14 - Cyanobacteria

Question 1

What are cyanobacteria?

Answer 1

They are large, morphologically, ecologically heterogeneous group of oxygenic, phototrophic bacteria.

Question 2

What is the difference in DNA dispersion in cyanobacteria prokaryotic cells?

Answer 2

DNA dispersed within cell, photosynthetic lamellae occur freely in the cytoplasm.

Question 3

What is the difference in DNA dispersion in cyanobacteria eukaryotic cells?

Answer 3

DNA localised within a nucleus; essentially similar to those of higher plants. Photosynthetic lamellae are confined within membranes as well as defined chloroplasts

Question 4

What are cyanobacteria on?

Answer 4

A bacterial phylum, phylogenetic tree of the major phyla of cultivated bacteria.

Question 5

What are cyanobacteria?

Answer 5

Blue-green algae. Gram-negative bacteria. Only photosynthetic prokaryotes to produce O2. 0.2 - 2 um, but can be 40 um in diameter. Characteristic colour: phycocyanin. Extremely diverse (in freshwater, marine, terrestrial and extreme environments.

Question 6

Why are cyanobacteria important?

Answer 6

Pivotal to life on earth - important in evolutionary history. First time oxygen found in the atm ~ 2.5 billion years ago. Without them there would be no plants and no us… no life.

Question 7

What is the evolutionary importance of cyanobacteria?

Answer 7

2.8 to 2.5 billion years old. Important in shaping evolutionary change throughout earth’s history. First organisms capable of oxygenic photosynthesis. Main driving force in converting a very reducing and anaerobic atmosphere to one with oxygen.

Question 8

What are stromatolites?

Answer 8

Rock like structures made of cyanobacteria. Earth’s oldest fossil - important in informing on evolution. Stromatolites are modern-day examples of life in precambrian times.

Question 9

How are prokaryotes pivotal to the evolution of life?

Answer 9

Prokaryotes gave rise to the first eukaryotic cells via endosymbiosis. Phagotrophic cell came along, engulfed cyanobacteria which then became the chloroplast in eukaryotes.

Question 10

What happens in further endosymbiosis?

Answer 10

The number of membranes help determine classification. However, still topic of research

Question 11

Tree of eukaryotes?

Answer 11

Algae have evolved many times in the tree of life. Higher plants just the once from green algae. Very diverse in their form and function. Fungi, bacteria, cyanobacteria, animals all come off on single branches. We don’t have a good single definition for algae because its evolution is so broad

Question 12

What is the physiology of cyanobacteria?

Answer 12

Oxygenic phototrophs with both FeS and Q-type photosystems. All fix CO2 by the calvin cycle. Many fix N2. Most synthesise own vitamins. Harvest energy from light and fix CO2 during day. Generate energy by fermentation or aerobic respiration of carbon storage products (e.g. glycogen) at night. Some can assimilate simple organic compounds in light (photoheterotrophy). Some can switch to anoxygenic photosynthesis using H2S as electron donor.

Question 13

What is inside a cyanobacterial cell?

Answer 13

Ribosomes, thylakoids, nucleoid (DNA ring), RuBisCO, carboxysome, slime coat, capsule, mucoid sheath, peptidoglycan layer, outer membrane, cell membrane, cell wall, phycobilisome, thylakoid membrane

Question 14

What are thylakoids?

Answer 14

Specialised membrane systems that increase ability to harvest light energy, typically arranged in concentric circles around cytoplasm periphery.

Question 15

What is the physiology of photosynthetic membranes?

Answer 15

Cyanobacteria produce pigments: chlorophyll a, phycobilins (accessory pigments) - Phycocyanin are blue making together with chlorophyll a the blue-green colour of cyanobacteria. Phycoerthryin is a red phycobilin making the producer species red or brown. Prochlorophytes (e.g. Prochlorococcus and Prochloron) contain chlorophyll a and b but no phycobilins.

Question 16

Photosynthesis in cyanobacteria?

Answer 16

In addition to photosystems 1 and 2, cyanobacteria contain phycobilisomes which contain phycoerythrin and phycocyanin

Question 17

Chloroplasts vs cyanobacteria?

Answer 17

Chloroplasts - intermembrane space (viridiplantaean chloroplasts and rhodoplasts), granum (higher plants)
Shared - outer membrane, inner membrane, nucleoid, thylakoids, lipid droplet, ribosomes.
Cyanobacterium - peptidoglycan wall (also in muroplasts), mucoid sheath, capsule, slime coat.

Question 18

What is the cell structure and motility of cyanobacteria?

Answer 18

Cell walls contain peptidoglycan, possess several motility mechanisms but no flagella. Many cyanobacteria display gliding motility when in contact with solid surface, another cell, or filament. Most show phototaxis (towards light); chemotaxis may occur.

Question 19

What is the function of gas vesicles?

Answer 19

Regulate buoyancy important in positioning in water column where light intensity is optimal. Many produce sheaths (mucilaginous envelopes) that bind groups of cells or filaments together. Some form hormogonia (short, motile filaments that break off to facilitate dispersal under stress). There is no sexual reproduction in cyanobacteria. Some form akinetes (resting structures with thickened outer walls that protect the organism from darkness, desiccation or cold. Many form cyanophycin (nitrogen storage product). Many form Nostocales and Stigonematales form heterocysts.

Question 20

What is nitrogenase?

Answer 20

It is sensitive to oxygen, so fixation cannot occur along with oxygenic photosynthesis. Several regulatory mechanisms separate nitrogenase from photosynthesis - many unicellular cyanobacteria fix nitrogen only at night, some transiently suppress photosynthetic activity within filaments, many filamentous cyanobacteria form heterocysts.

Question 21

What are heterocysts?

Answer 21

Arise from differentiation of vegetative cells, surrounded by thickened cell wall that slows diffusion of O2 and provides an anoxic environment. Lack photosystem, cannot fix CO2. Fixed carbon is imported from adjacent cells and oxidised to yield electrons for nitrogen fixation. Fixed nitrogen moves to vegetative cells.

Question 22

Heterocysts & Nitrogen fixation - types of microscopy?

Answer 22

Phase contrast and fluorescence microscopy.

Question 23

What are the different types of cells in filamentous cyanobacteria?

Answer 23

Akinete (resting stage with granular - thick wall), Heterocysts (nitrogen fixation), hormogonia.

Question 24

What is the ecology of cyanobacteria?

Answer 24

Important for productivity of oceans - Synechococcus and Prochlorococcus are most abundant ocean phototrophs, contributing 80 percent of marine photosynthesis and 35 percent of total photosynthesis. Cyanobacterial nitrogen fixation is dominant input of new nitrogen in oceans.

Question 25

Nitrogen fixation in cyanobacteria in the oceans?

Answer 25

Many cyanobacteria are capable of fixing N, converting atmospheric N into nitrate or ammonia. In habitats like Artic regions where N is a limiting element, they can contribute up to 80% of annual N input.

Question 26

Nitrogen fixation in cyanobacteria - in rice paddy fields?

Answer 26

Anabaena and Nostoc species. Long filamentous algae.

Question 27

What else is the ecology of cyanobacteria?

Answer 27

Also widely distributed in terrestrial, marine and freshwater environments - more tolerant of extremes than eukaryotic algae (e.g. hot springs, saline lakes, desert soils), develop freshwater lake blooms, can be symbionts. Important metabolic products (e.g. potent neurotoxins and toxic blooms, geosmin in water).

Question 28

Cyanobacteria as extremophiles?

Answer 28

Their metabolism and lifestyle is very flexible, survive extremely high & low temperatures (-2 degC to 70 degC). Impressive ability to colonise infertile substrates e.g. volcanic ash, desert sand & rocks.

Question 29

Cyanobacteria symbiosis with plants?

Answer 29

Cyanobacteria form symbiotic associations with a wide range of eukaryotic hosts including plants, fungi, sponges, ascidians and protists. E.g. gunnera plant - in singleton park.

Question 30

What else are cyanobacteria symbiotic with?

Answer 30

Fungi in lichens

Question 31

Cyanobacteria as marine symbionts?

Answer 31

Abundant in coral reefs, common hosts: sponges & ascidians. Also a factor preventing recovery from coral reef phase shifts. Cyanobacteria help build reefs, form a major component of epiphytic, epilithic, and endolithic communities as well as of microbial mats. Provide nitrogen through nitrogen fixation.

Question 32

Cyanobacteria in microbial mats and biofilms?

Answer 32

They can form an important part of microbial mats or biofilms in terrestrial and aquatic ecosystems, along with bacteria and archaea. Can see them on pipes, in gardens, boggy areas etc. Given away by the colour - blue green is cyanobacteria.

Question 33

What is there in cyanobacteria?

Answer 33

Impressive morphological diversity. Unicellular, colonies or filamentous with specialised cells. Range from 0.5 to 100um in diameter, five morphological groups. Less diverse in form than eukaryotic algae but rich in chemical diversity

Question 34

What are the chroococcales?

Answer 34

Unicellular, divide by binary fission; includes prochlorophytes (unique, unicellular)

Question 35

What are the Pleurocapsales?

Answer 35

Unicellular, dividing by multiple fission (colonial)

Question 36

What are the Oscillatoriales?

Answer 36

Filamentous nonheterocystous

Question 37

What are the Nostocales?

Answer 37

Filamentous, divide on single axis, can differentiate

Question 38

What are the Stigonematales?

Answer 38

Filamentous, divide in multiple planes, forming branching filaments

Question 39

What is Synechocystis Sp. PCC 6803?

Answer 39

Unicellular spherical cells. Binary fission, found in freshwater.

Question 40

Why is Synechocystis Sp. PCC 6803 so important?

Answer 40

Model cyanobacterium, first photosynthetic organism to have its entire genome sequenced - 1996. Autotrophic and heterotrophic growth. Gene expression regulated by a circadian clock - predicts light - dark

Question 41

What is Synechococcuss?

Answer 41

Unicellular, prokaryotic autotrophic picoplankton. Discovered in the sea in 1979!. Abundant in the world's oceans. Also many freshwater strains. Main source of primary production in oligotrophic, pelagic marine waters. Major primary producers on a global scale.

Question 42

What are the size of Nanoeukaryotes, Picoeukaryotes, Picoprokaryotes?

Answer 42

2-20um, 0.2-2um, 0.2-2um

Question 43

What are the picoplankton?

Answer 43

Prochlorococcus and synechococcus are not the only picoplankton. New picoplanktonic eukaryotic algal class: Bolidophyceae.

Question 44

What are prochlorococcus?

Answer 44

Component of the picoplankton : picoprokaryotes. Discovered recently in 1988. Smallest & most abundant photosynthetic organism on earth. Major importance in the ocean. Different ecotypes. Unusual chlorophylls - divinyl chlorophyll-a and b.

Question 45

Where is the global abundance of prochlorococcus and synechococcus?

Answer 45

Quantitatively the most important organisms on earth. >25% of net primary production in the oceans

Question 46

What is Trichodesmium (sea sawdust)?

Answer 46

Filamentous cyanobacteria. Trichodesmium sp. is non-heterocystous cyanobacteria. Widespread in tropical & subtropical seas. Fixes N2 without heterocysts i.e. occurs aerobically. Gas vesicles regulate buoyancy in the water column

Question 47

What is Spirulina (Arthrospira platensis)?

Answer 47

Freshwater, well known species, occurs naturally in tropical and subtropical lakes with high pH. Large commercial production. 65-71% protein.

Question 48

What is Nostacales: Anabaena and Nostoc?

Answer 48

Colonial filamentous - hair like trichomes. Terrestrial or freshwater species. Forms loose clumps on soil, gravel and paved surfaces, among mosses and between cobbles. Can survive in extreme conditions: Polar & arid areas.

Question 49

What cyanobacteria are toxic?

Answer 49

Some freshwater species are toxic and can cause major problems in lakes and reservoirs. Anabaena flosaquae - 'anatoxin'. Microcystis - 'microcystin'. Aphanizomenon flosaquae - 'saxitoxin'. Recent discovery - widespread across cyanobacteria - BMAA (Beta-N-methylamino-L-alanine)

Question 50

What is different in the different toxic species?

Answer 50

Different toxin molecules.

Question 51

What are toxic blooms of cyanobacteria in baltic sea: microcystins - hepatotoxic?

Answer 51

Filamentous cyanobacteria: Nodularia spumigena. Occurs every year late summer: phosphate in the surface water, temperature and weather conditions are important factors

Question 52

What is BMAA?

Answer 52

A more recently discovered neurotoxin, Beta-methylamino-L-alanine or 2-Amino-3-(methylamino)propanoic acid. Widespread in terrestrial, but also marine cyanobacteria. BMAA can cause neurodegenerative disease like Alzheimer's and possibly motor neurone disease.

Question 53

What are some cyanobacterial anticancer drug candidates?

Answer 53

Malyngamide 2, Dolastatin 10, Cylindrospermopsin, synthetic analogue of crytptophycin

Question 54

What is Malynamide 2?

Answer 54

Natural product isolated from the cyanobacterium Lyngbya majuscula that has shown potent anticancer activity in preclinical studies. A clinical trial was conducted to investigate its safety and efficacy for the treatment of solid tumours, but the results have not yet been published.

Question 55

What is Dolastatin 10?

Answer 55

Natural product, isolated from the cyanobacterium Symploca, that has shown potential anticancer activity. It has been investigated in several clinical trials for the treatment of various types of cancer, including breast, lung, and melanoma

Question 56

What is Cylindrospermopsin?

Answer 56

A toxic natural product, produced by various cyanobacteria that has been investigated for its potential as an anticancer agent. Several preclinical studies have shown that it has potent anticancer activity against various types of cancer cells, but clinical trials have not yet been conducted

Question 57

What is Cryptophycin?

Answer 57

Synthetic analogue of cryptophycin isolated from terrestrial cyanobacteria progressed to Phase 2 clinical trials for the treatment of patients with platinum-resitant ovarian cancer.

Question 58

Cyanobacteria and biotechnology?

Answer 58

Have minimal nutritional requirements. Higher photosynthetic efficiency in terms of sunligh conversion into biomass and growth rates than all other photosynthetic organisms. Cyanobacteria have been used as food sources and biofertilisers for centuries. Through N2 fixation they improve the fertility of rice-fields and many soils. They produce a broad spectrum of high value compounds.