Bacillariophyta—the diatoms

Bacillariophyta—the diatoms
•thick bivalved ornate cell wall made of
silica (glass),
•Nucleate(1), vacuoles present,
•pigments contained within chloroplasts,
chloroplasts brownish (chlorophyll a plus
accessory carotenoids),
•food stored as oils,
•single celled (elongate or round) although
sometimes joined side-by-side or end-toend
as filaments
Some essential terminology
fr—frustule, cn—central nodule, r—raphe,
p—punctae, s—striae, c--costa
Valve view, girdle view
Pennate and centric forms

Diatom in valve view, What does the word diatom mean?
Central area
raphe stria
Central nodule
Striae are composed of punctae (pores), what do you think their function is?
Terminal
nodule

The new valve is always a hypovalve—producing smaller and smaller cells
Size range increases each generation
http://images.google.ca/imgres?imgurl=http://www.jochemnet.de/fiu/bot4404/Dia_division2.jpg&imgrefurl=http://www.jochemnet.de
/fiu/bot4404/BOT4404_19.html&h=424&w=400&sz=28&hl=en&start=5&tbnid=Ao72SPPZ1BjQBM:&tbnh=126&tbnw=119&prev=/imag
es%3Fq%3Dreproduction%2Bdiatoms%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DG

Centric diatoms are oogamous, with flagellated
sperm.Pennate diatoms are isogamous, with
ameboid gametes
The smallest cells become sexual and release isogamous gametes
What type of sexual life cycle is this?
http://www.mie.utoronto.ca/labs/lcdlab/biopic/fig/27.19.jpg

Some examples of pennate diatoms
generally raphed—capable of movement on substrate (1-20 µm s)
solitary and benthic (in streams or wave washed shores of lakes) or epiphytic
Gyrosigma
Frustules raphed, valves sigmoid, raphe sigmoid with external proximal raphe ends recurved in opposite directions
form one another. central area round to elliptical.
A genus of benthic species, often in lakes and reservoirs.
Around 100 microns long

Synedra: long straight needle-like cells, araphid, cells appear rectangular in girdle view, punctae (pores)
arrange in rows (striae) axial area, fairly broad, common benthic species.
About 100 microns long

Some pennate forms are colonial and live in the plankton
Fragilaria:cells joined at the valve face to form ribbon-like colonies,
Fragilaria colony cells joined side-by-side in
girdle view, generally planktonic
Valve view (on the left)
Each cell 50-70 microns

Asterionella: elongate cells which are
joined at the base to form stellate
colonies, (seen in valve view) basal pole
of the cell typically wider than the apical
pole
Fairly large for planktonic diatoms, each
cell 50-70 microns
Commonly found in dense blooms during
May, prior to the onset of thermal
stratification

Examples of centric diatoms
Non-raphed and non-motile
Cyclotella: and Stephanodiscus
•Solitary forms (non-colonial)
•Usually abundant in spring & fall plankton
20 µm

10 µm
Melosira
•a colonial (filamentous)form
•valve surfaces joined end to
end
In the phytoplankton of lakes in the spring, but sink rapidly into the hypolimnion during the summer
months, Some species grow attached to rocks in streams

Achnanthes: heterovalvular, one valve with and one without a raphe, flexed in girdle view, either solitary or in
chains joined at the valvular surface, attached to substrate either by mucilage pad or by a stalk at the valve
apex, valves ellipitical with rounded or protracted apices, striation and central area variable.
http://craticula.ncl.ac.uk/EADiatomKey/html/Achnanthes.html
Sometimes the striation and central areas of the raphed and
rapheless valve can be different

Achnanthes longipes: alternation between a motile, solitary phase and a stalked sessile phase
Under what conditions would this life cycle be advantageous?
When inoculated into fresh media, the cells are at first motile (I), then become sessile and produce a stalk
that anchors them to the substratum (II). This stalk continues to be synthesized as the cell is pushed away
from the substratum (III), and eventually mitosis occurs producing a row of cells stacked one upon the
other (IV). These cells eventually detach from one another (I) and begin the cycle again.
http://www.bio.mtu.edu/the_wall/integrated_microscopy/a_longipes_general.html

Epiphytic pennate diatoms

Ecology of diatoms
•Extremely important primary producers in lake and ocean phytoplankton, and
in the benthic algal communities of lakes and streams (20-25% of global PP).
•Resistant to attack (predators pathogens) silica resistant to most enzymes.
•Pennate (raphed) diatoms well adapted to life on hard substrates
•Many pennate diatoms alternate between solitary and filamentous life styles,
which suits them well for life in unstable environments.
•Colonial centric forms adapted for life in the plankton of cold lakes and
oceans—siliceous frustules sink rapidly, unless they have special shape
adaptations.
•Diatoms often form dense blooms in silica rich cold waters, mainly spring and
fall, when the water column is well-mixed.
•Diatoms are very tolerant of low light conditions
•Most diatom species have narrow limits of tolerance and preference for
chemical conditions in the water example, pH, alkalinity, salinity, Ca, P, N,
organic matter, pollutants of various kinds, as well as temperature.
•This, together with the fact that diatoms are so abundant and preserve well in
sediment cores, makes diatoms very useful as indicators in paleolimnology.

Chrysophyta--Golden brown algae
Cells small to medium (>10 microns)
Nucleus (1),
chloroplasts (2)brown to golden brown
(chlorophyll a plus carotenoids),
food stored mainly as oils and
carbohydrates
Unicellular or colonial, some species
with flagellae (usually 2)
Cell wall—often absent, sometimes
present as a lorica (cellulose)
simple unicellular naked flagellate

flagellate colonial form, a gelatinous matrix may be present but lorica absent--Uroglena
Uroglena

50 microns
large branched colonies, flagellate
cells within a lorica—Dinobryon
Important mixotrophic species in the
plankton of lakes—consume bacteria

Ecology of Chrysophytes
Common in the plankton of lakes especially during the colder parts of the year
May occasionally form blooms that colour the water brown and give taste and
odour problems—Eg Ochromonas
Some species also found in cold steams and springs.
Acid lakes and bogs, support a diverse Chrysophyte community, most important
primary producers in such systems.

Pyrrophyta--Dinoflagellates
•Cells fairly large (>25 microns)
•Nucleate (1),
•Cellulose wall often present
•Cells with grooves (sulci) within which
flagellae lie
•Chloroplasts, 2 or more small disc
shaped, brown to golden brown
(chlorophyll a, c, plus carotenoids),
•Food stored as starch and oils
•Cells often emitting bioluminescence
•Cells very motile (~ 5-10 mm/sec)
•Often live as “mixotrophs” --ingest
bacteria--phagocytosis

Ceratium
cells armoured, with a sculptured cellulose
wall often consisting of several plates,
perforated with pores, and with deep
transverse and longitudinal grooves
large (>100 microns) with lobe like
extensions “horns”
> 100 microns long
In the plankton of lakes and ponds

Gonyaulax—causes red tides, shellfish poisoning in estuaries
Cells about 25-30 microns

Ecology of dinoflagellates
Can be very important primary producers in both lakes and oceans
Many dinoflagellates occur as symbionts inside animals eg corals or sponges
Can cause toxic blooms, eg red tides, usually in estuaries—shellfish poisoning
Very motile can usually maintain their position in the water column if they remain
near the thermocline where turbulence is not too great
Can produce bioluminescence in response to disturbance of the water column or
predators.
Many species are heterotrophic and mainly live by ingesting bacteria (phagocytosis),
many such species have little chlorophyll.

Pfiesteria—a toxic dinoflagellate that
forms lesions on fish skin
Found in coastal rivers and estuaries
mainly along the US east coast
Pfiesteria piscicida
Complex life-cycle with free living and
parasitic ameboid phases—can produce
toxins that are harmful to fish and possibly
humans.
Estuarine Associated Syndrome
Symptoms include: headache, dizziness, skin rashes,
nausea, muscle cramps, and short-term memory loss.
However, not all Pfiesteria organisms are toxic