Lecture VIII Protistans

surface waters teem with microscopic protists

In some near-shore areas, gigantic protists from underwater forests

Protists are particularly abundant in tidal habitats

Morphologies and lifestyles found among protists. Protists are abundant in a wide variety of aquatic habitats. In marine environments, they are found in open ocean as well as in near-shore intertidal habitats (Freeman 2002)

Source: Freeman (2002)

Eugleazoa includes both photosynthetic and heterotrophic flagellates. Most are autotrophic, but the lineage includes

Trypanosoma

Euglena

Alvoelata are unicellular, and bear a cavity called and “alveoli”. Diverse in body form.

Apicompla

dinoflagellates

Ciliates

Stramenopilan are a diverse lineage of heterotrophs and phothynthetic forms (algae). The name refers to fine hairs on the flagella of members of this lineage

water molds

diatoms

brown algae

Rhodophyta are red algae – unlike other eukaryotic algae, they lack flagella at any stage in their life history. They are the most abundant algae in tropical coastal areas

Dulce, a large, edible red algae

Green Algae and Plants evolved from a common photoautotrophic ancestor. Over 7000 species, mostly fresh water.

Volvox colonies

Sea lettuce

Desmid

Choanoflagellida Flagellate protists. Possible ancestor to Sponges – to Animals.

Source Solomon et al 2002

Lecture Themes

structure and function; ecurring evolutionary themes and unifying features

the origin of mitochondria and chloroplasts

Impact of Protists on Human Health and Welfare

“The key to understanding the protists is to recognize that a series of important innovations occurred, often repeatedly, as eukaryoites diversified.” (Freeman 2002)

Size and Structure of Eukaryotic Cells compartmentalization and differentiation makes large size possible.

Problem: transport and exchange limitations with increasing size

Solution: compartmentalization

Example: Paramecium

Eukayotic compartments; nucleus, peroxisomes, mitochondria, chloroplasts, central vacuole, golgi, rough ER, smooth ER

Paramecium, a predaceous protist that feeds on prokaryotes and other protists

Nutritional and Metabolic Diversity in Protists Ingestive Lifestyles: Predation and Scavengers

Absorbtive Lifestyles; Decomposers and Parasites

Photosynthetic Lifestyles; Producers, many of which are symbionts

Photosynthetic unicellular dinoflagellates

Giardia, a unicellular human parasite

giant kelp

Paramecium

Predation and Scavenging Parasitism

pseudopodia engulf food Ciliary currents sweepd food into gullet

host parasite

the parasite is a red algae – with nonpigmented cells

host symbionts

Green cells are dinoflagellates inside a heliozoan

Red: chlorophyll a and phycobilins

Brown: chlorophyll a and chlorophyll c

Green: chlorophyll a and chlorophyll b

Photosynthetic pigmentsSymbiosis

Many photosynthetic groups of algae are distinguished by the accessory pigments they contain, in addition to chlorophyll a. Each of these accessory pigments interecpts different wavelengths of light

Apicomplexans-most apicomplexans are parasitic

Ciliates -many predators and herbivores-some parasite/basorbers (eg cattle guts, fish gills)-some feed via symbiotic photosynthesizers

Dinoflagellates-half or so are photosynthetic, many others are parasitic

Feeding diversity in protists, like electron donor and electron acceptor diversity in prokaryotes, no doubt drove phylogenetic diversification

Consider the diversity of feeding modes in the lineage Alveolata

Locomotion and Structures for Support and Protection

Pseudopodia

flagella

cilia

Structure of microtubules in cilia and flagella

Modes of Locomotion in Protists

2 single microtubules (red) surrounded by

nine paired microtubules (yellow)

A ciliatedProtist

An Amoeboid Protist

Interrelated cytoskeletal functions

-maintain cell shape

-provide for cell movement

-serve as tracks for motor proteins

reference: chapter 4 in textbook

A ciliated protist

Paramecium can swim in either direction relative to its long axis by beating its cilia in rhythmic, coordinated fashion that progresses from one end of the cell to the other.

Amoeba extends a pseudopodium toward a Pandorina colony. At right, the amoeba surrounds colony before engulfing it

Proposed mechanism of psuedopodial movement

Source: Hickman et al 2001 Actin subunits in endoplasm are bound to regulatory proteins to prevent assembly

On stimulation, hydrostatic force carries subunits to hyaline cap where lipids in membrane free actin subunits from regulatory proteins

subunits quickly assemble into filament sand on intearction with actin-binding protein, form gel-like ectoplasm

calcium ions at trailing edge activate actin-severing proteins, loosening network enough to that myosin molecules can pull on it

External Structures for Support and Protection

Amoeba; shell made of cemented sand grains

Radiolarians; glassy skeletons allow light penetration for photosynthetic endosymbionts

Diatoms

foraminiferan with protein-hardened, calcium carbonate tests

diatoms have glass-like silicon containg sructures

Dinoflagelates surrounded by cellulose plates

Sources: Purves et al (2002), Freeman (2002)

White Cliffs of Dover are limestone composed almost entirely of protistan fossil shells, including forams and coccolithophores (an alga)

Multicellularity

Clamydomonas Gonum Pandorina Volvox

Multicellular Green Alga (Coleochaete orbiculairs)

Morphological continuum in Volvocales from unicellular to multicelluar.

True multicellarity is defined functionally

Differentiation of cell function (specialization, division of labor)

Differential gene expression

Multicellularity has evolved independently multiple times in Protistan lineages

Multicelluarity confers advantages by allowing for increased size, specialization, and complexity

The initial evolution towards multicellularity begins with differentiation of gamete-producing cells, the consequence of the uniquely eukaryotic reduction division process; meiosis

Source: Freeman 2002

Life cycle of a diploid species in which the multicellular organism is diploid

Life cycle of a diploid species in which the multicellular organism is haploid

Life cycle of a diploid species in which there is an alternation of generations of multicelluar form – 1n gametophye and 2n sporophyte

Reproduction, Life Cycles and Alternation of Generations

Meiosis and Sexual reproduction were important Protistan innovations

The three basic eukaryotic life cycles are shown here – all occur among Protists, and other variations on these as well

http://megasun.bch.umontreal.ca/protists/chlamy/introduction.html

http://www.ucmp.berkeley.edu/greenalgae/greenalgae.html

Life Cycle of Chlamydomonas Inset shows mature cells before reproduction

Stages of Sexual and Asexual Lifc Cycles

Mature cell is haplid

Mature cell reproduces asexaully; is resorbs its flagella and then divides twice by mitosis

Daughter cells devlop flagella and cell walls, then emrge as swimming zoospores from wall of parcnt cell. Zoospores grow to mature haploic cells, completing asexual lfie cycle.

Sexual reproduction is triggered by shrotage of nturients,dryong of the pond, or some other stress. Within the wall of the parent cell, mitosis produces many haploid gametes.

After their release, gametes from opposiste mating types (desginated + and -) pair off and cling together. Fusion (syngamy) of the gametes froms a diploid zygote.

Zygote secrests a durable coat that protects cell against harsh conditions

When zygote breaks from dormancy, meiosisi produces four haploid individuals (two of each mating type that emerge from the coat and grow into mature cells.

Life cycle of Laminaryia: an example of alternation of generations

Sporophytes of this seasweed are usually found in water just below the line of the lowest tides, attached to the rocks by branching holdfasts

In early spring, at end of the main growing season, cells on the surface of the blade develop into sporangia

sporangia produce zoosporres by meiosis

Zoospores are all structurally alike, but about half of them are capable of developing into a male gametophyte and half into a femlel gametophye. Gametophytes look nothing like the sporophytes, being short, branched filaments that grow on the surface of subtidal rocks

Male gametohytes release sperm, and female gametophytes produce eggs, which remain attached tot eh gametophyte. Eggs secrete a chemical signal that attracts sperm of the same species, thereby increasing the probability of gametic union in the ocean.

Sperm fertilize the eggs

The zygotes grow into new sprorophytes, starting life attached to the remains of the old female gametophyte

Gametophytes (n)

Sporophytes (2n)

Lines of evidence indicating mitochondria and chloroplasts arose as prokaryotic symbionts

-membranous enzymes and transport systems

-replication process

-genome

-protein translation machinery, including ribosomes, t-rna

-similarities of mitochondrial and chloroplast ribosomes to prokaryote ribosomes

Endosymbiotic Theory

2.5 um 80 um

Margulis webpage www.bio.umass.edu/faculty/biog/margulis.html

Lynn Margulis

U. Mass., Distinguished Professor and Member of the National Academy of Science – developed endosymbiotic theory

Proteobacteria Cyanobacteria

Phylogenetic analyses using small subunit RNA

Ribosomes are comprised of one small and one large subunit. The single rRNA molecule of the small subunit

Ribosomes are

Gene for small subunit r-RNA is present in all organism –good gene for determining deep branching in tree of life

Sequence comparisons show that closest prokaryote relatieves of mitochondria are altpha proteobacteria.

Sequence comparisons of plastids from various photosynthetic eukaryotes cluster with prokaryotic cyanobacteria (photosyntheitc machinery and metabolic pathways are shared as well.

Protists and Human Health:

Plasmodium and Malaria

http://www.malaria.org/lifecycle.html

P. falciparum is the most widespread and dangerous of the four: untreated it can lead to fatal cerebral malaria.

Infected Red Blood Cells

The distribution of malaria varies greatly from country to country and within the countries themselves. In 1990, 75% of all recorded cases outside of Africa were concentrated in nine countries

Infected mosquito bites and infects person; sporozoites and enter liver cells After several days, undergo multiple divisions to become merozoites (specialized spore) that uses apical complex to penetrate RBC

Merozoites reproduce asexually in RBC’s and lyse cells at 48 or 72 hr intervals (species specific); coordinated lysing of cells causes periodic chills and fever.

Some merozoite infect new RBC’s, some divide to form gametocytes; gametocytes that infect a biting female mosquite compete the life cycle in her body.

Gametocytes form gametes and fertilization occurs in mosquito digestive tract; zygote is the only dipolid stage in the life cycle

Oocyst develops in wall of mosquito gut. Thousands of sporozoites develop in the oocyst and then migrate to mosquites salivary gland

Merozite

Apex

Red blood cell0.5 um

Plasmodium Infection InterpretationStrain Rate

cp26 Low

cp29 LowHLA-B53 binds to these proteins. Immune resonse is effective

cp26 and cp29 strains together

HighImmune response fails when these strains infect the same person

cp27 Highcp28 Average

HLA-B53 does not bind to these proteins. Immune response is not as effective

Co-evolutonary Arm Race

Strong association between HLA-B53 allele and protection against malaria found in West Africa

HLA-B53 in infected liver cells bind to particular sporozoite protein and display protein-protein complex before they produce merozoites

Recognition breaks down in people co-infected by certain strains

NS leads to iimmune system adaptations for protection – and to pathogen adaptations to overcome them

HUMAN IMMUNE-DEFENSE AGAINST PLASMODIUM

Source: Freeman 2002

extra slides

Chlamydomonas Genome Project and the Origins of Green Plants

http://megasun.bch.umontreal.ca/protists/chlamy/introduction.html

http://www.ucmp.berkeley.edu/greenalgae/greenalgae.html

Postulated global eukaryote phylogeny based on presence or (ancestral) absence of mitochondria, and shape of mitochondrial cristae. Chlamydomonas belongs to the flattened clade.

Postulated phylogenetic position of Chlamydomonas, inferred from molecular and morphological data. Branch lengths are arbitrary and do not

reflect phylogenetic distance.

Extra Slides

Life Cycle of a cellular slime mold (Dictyostelium)

Encysted zoospores land on a substrate and germinate, growing into the tufted byody of hypae

Several days later, organism begins to form sexual structures

meosito produces eggs in oogonia

on separate brances fo the same or different idndividuals, meiosis produces several haploid sperm nuclie contained within compartments called antheridial hyphae

hypae grow like hooks around the oogonium and depsoit their nuclei through fertiliaation tubes that lead to eggs. The resulting zygotres )oospores) may degvelop resistant walls but are also protected within the walls of the old oogonia

dormant perido followd, duuring which oogonium wall usually disintegrates

Zygotes germinate and form short hyphae tipped by zoosporangia, and the cycle is completed

Ends of hyphae form tubular zoosporangia

Each zoosporangium produces about 30 biflaagellated zoosppres asexually

Life Cycle of a cellular slime mold (Dictyostelium)