Microbiology II: Complex Microorganisms

[Music] some microorganisms are extremely complex in their internal organization and possess many different kinds of organelles and multiple structures of the same kind among the most complex of these forms are the two groups known as the flagellates and the ciliate both of which show by their rapid locomotion that they have specialized structures for movement we've already seen that the amoeboid microorganisms are relatively simple in their organization even though they're only one unit but there is not a great deal of duplication of parts or multiplication of parts within the single cell there is however some apparent evolutionary relationship between amoeboid forms and the flagellates because there are soil organisms that have both pseudopodia and flagella and even in the slime molds there are stages which are amoeboid and other stages which are flagellated these specialized locomotor structures of flagella and cilia are keys to the organization of the very complex microorganism the unit known as a flagellum is a long whip-like appendage which may or may not appear to be attached to granules in the cytoplasm and which extends out considerable distance away from the body of the of the cell itself now a single one of these units is known as a flagellum they may be of varying length they may move rapidly or slowly and in some cases there may be a great many flagella covering the surface of the body of the animal in general a cilium on the other hand is usually quite a bit shorter and is more whisker-like in its appearance and movement an example of how complex the organization of some of these structures may be in a ciliate can be shown by this diagram of a slice through just the outer layer of a single paramecium here you can see that the outer surface is covered by a complexly organized pelican or non-living wall with spaces present in it and that each of the cilia is also covered with this layer from anterior to posterior the cilia appear to be in pairs in the depression of the pellicle each psyllium appears to have a number of fibers running down the center of it which connect with fibers running underneath the pellicle and which are probably involved in the coordination of the movements of the cilia between each pair of cilia is a flask-shaped structure known as a trichocyst they are capsules which explode and send materials outside the cell now all of this lies in the thin layer of ectoplasm of a paramecium interestingly enough if we make much larger magnifications of a single flagellum we find that it too has a pellicle layer on the outside cytoplasm in a cylinder in it and a number of fibers present which uh we'll discuss in their organization very shortly now this concept of locomotor units in multiple patterns so that a single cell has a great many of such structures introduces us to a very important general idea about trends in the history and evolution of organism we find that wherever structures tend to duplicate and duplication or reproduction is characteristic of living units and living organisms then some of these duplicated units become different from the others they become specialized to do different things and their structures change let's follow a pattern of how such a sequence works duplication of parts at any level is one of the characteristics of living thing at its most basic level one chromosome becomes two chromosomes or the dna molecule of a chromosome replicates itself and forms two dna molecules and the protein around the dna also is duplicated one unit by a process of replication may become two or three or four or a great many units now as soon as this happens in an organism specialization of some of these units occurs and the result is a much greater complexity and variety of the organism and we can see this even in microorganisms particularly in the flagellates and ciliates where the basic locomotor unit appears to be a center or perhaps a granule with fibers this when multiplied within the cell becomes flagella and cilia and perhaps many other derived organelles that are of a special sort that we don't find perhaps in other than microorganisms at the cellular level you see the same pattern happening one cell becomes two and four and if this remains as a multicellular organism then these different cells become specialized some become muscle and some become nerve and some become connective tissue cells so that whatever the unit may be if it increases in numbers this increase in numbers is almost always followed by specialization and the complexity of the flagellates and ciliates is apparently due to this process of multiplication of units multiplication of structures that is along with differentiation of them into somewhat modified forms we still have living examples of some fairly simple types of flagellates a common soil form called neglaria shows a flagellate with just one simple flagellum and yet it's definitely an animal-like cell it has no chlorophyll among the other animal type flagellates there's one group that covers quite a wide range in organization and this is the group of forms known as the trypanosomes and their relatives the tropanosomes are commonly parasites in vertebrates including man and in some plant organisms too or relatives of them here we have a problem of size the trypanosomes are really not very big and if you refer back to our familiar paramecium about two-tenths of a millimeter in length 200 microns our scale models show one of the green flagellates euglena about this size in proportion and an ordinary trypanosome perhaps something like this you'll notice that we already here have a modification in the form of the flagellum it extends out along the margins of the body covered by a layer of plasma membrane and cytoplasm as a kind of fin-like projection and this whole structure is known as an undulating membrane one of the trypanosomes at least in its life history goes through a series of stages which show us a variety of forms even with a single flagellum the tropanosome form itself which shows the nucleus here and the basal granule and then the long undulating membrane may become modified by the position of the membrane and granule with respect to the nucleus and this is known as a chrysidia form and there are some flagellates in which this is the adult form in the life cycle still another modification is that in which the flagellum and its granule are at one end and no undulating membrane is present and this is known as leptomonad form lifemania is an organism in which the structures of this locomotor unit are present but do not project beyond the cell beyond the plasma membrane and there's actually no free flagellum and no membrane and in the course of its life history a trypanosome may run through all of these forms showing variations on the theme of even a single flagellum the trypanosomes that are important to man or those that produce african sleeping sickness primarily forms which infect man and vertebrates and are transmitted by a biting fly the sexy fly here the life history of the parasite has two hosts the organism is picked up from the bloodstream by the setsi fly drawn into the digestive system where it undergoes changes in form in its life cycle and then when that infected fly bites another possible host the tropanosomes are injected into the new host and this parasite host pattern then applies to a complex cycle of events even in a single celled microorganism of course there are some other flagellates that are much more complex than the trypanasomes one of these includes the series of flagellates that live in the intestine of the termite this is a relationship that has been mentioned of symbiosis living together in this case a living together of mutual benefit no injury is done to either partner and benefit to both have you ever wondered how it happened that a termite could eat wood practically no other multicellular organism can do so and get nourishment the pattern works like this the termite chews up and ingests the wood or cellulose then in its digestive tract the flagellates ingest the wood and break it down and change it into glucose this supplies the flagellate with its nourishment and energy and the extra glucose is given off from its plasma membrane absorbed by the termite and is the source of nourishment for the termite so both organisms benefit in this rather unusual relation the flagellates in the termite gut represent probably among the most complex of the flagellate group where there are dozens or hundreds of flagella covering the whole surface of the body if we move to the even more complicated group of ciliates with modified structures of this locomotor type one that is easy to see and common is a ciliate called opalina which occurs in the large intestine of ordinary frog here you see the ciliar unit multiplied as though it were a coat of fur over the whole surface of the body and you'll notice also another example of multiplication of units opalina has not just one nucleus it has literally hundreds of nuclei if we turn to a more familiar ciliate our friend paramecium that we have seen before in other connections and look at living specimens under the microscope we find that we can see a number of detailed structures in the body of the paramecium but most detail and most of the structures will show best if these specimens are killed and stained and prepared for detailed examination we can see some of the techniques that have been developed for the study of such internal structure and paramecia in the laboratories of dr tracy sonoburn at indiana university where many many different kinds and races of paramecia have been collected and are studied in detail if the animal is first killed and then stained and made to adhere to a cover slip and the cover slip is mounted on a slide upside down and then observed under oil immersion which gives an enlargement of about a thousand times we can begin to see some of the details of this complex multiple structure to begin with let's take the nuclear organization the nuclear organization turns out to consist of two units at least at least one micronucleus and one macronucleus some varieties of paramecia have many micronuclei now let's follow this just a little further the number of chromosomes in a single micronucleus of paramecium is between 80 and 100 for the diploid set in pairs depending on the kind of paramecium and the strain if we examine the macronucleus we find that it contains about 500 complete diploid sets of chromosomes now here is an example not only of difference in function of two parts of two kinds of nuclei but also multiplication of structures within one of them the macronucleus the macronucleus is essential for the ordinary physiological activity of the paramecium if it's removed the animal stops growing and very quickly dies the micronuclei on the other hand are involved in sexual reproduction and at no other time in the life cycle of the animal now let's turn to the cytoplasm where again we find examples of repeated units that have become specialized for different functions particularly let's turn our attention to the outer layer the ectoplasm and pellicle one way to study this in detail is to deposit silver in the outer portions of the paramecium and in a sense let it take a picture of itself if this is done we see a pattern when it's examined under high magnification of what is known as the silver line system in which only the bases of the granules or of the cilia appear and in this photograph each one of the dots represents the base of a single psyllium there are about 50 rows of cilia in a paramecium and about 80 cilia per row giving us something like 4 000 of the units multiplied over the surface of the body as a matter of fact the basic unit itself as we saw in the diagram on the blackboard was a unit consisting of more complex structures of two cilia and certain patterns and folds in the pellicle and part of the ectoplasm this unit which is repeated many times over the surface becomes highly specialized in the region of the mouth opening and gullet the structures are modified into quite different patterns than over the surface of the body the openings of the two vacuoles through the pellicle again have specialized modifications of this same ectoplasmic unit that is derived probably from the sillier structure the opening through which waste products are expelled shows again a different modification and there are many other now one of the best ways we can study the details of such a small organism is of course with the electron microscope and this requires embedding a paramecium or many paramecia in material which will harden as a plastic and then slicing it into sections so thin that about 500 000 of them would make only slightly more than a centimeter in thickness examination of these thin sections shows us many more details of the structure of these organelles in a complex ciliate for example let's consider the pattern of organization of a cilium itself in this electron microscope photograph of a section through a ciliate called euplotes we see cross-sections of a number of cilia we can also see some of the fibrils in the cytoplasm which may be involved in coordination and various other structures mitochondria which are present in all cells a paramecium has about 500 mitochondria and one of the interesting things about this locomotor unit the psyllium or the flagellum is that as far as we can tell the pattern of structure seems to be the same in all organisms perhaps with the exception of the bacteria this is a fiber or cilium or a flagellum consisting of a ring of nine fibers with two in the center now this is the number that is believed to be constant for all organisms here in the drawing you can see the ring of fiber or in the photograph the ring of fibers and the two in the center in the case of the bacteria we're not so certain of this organization in this electron microscope photograph a single flagellum appears to be a single fiber here a greatly enlarged example of that flagellum shows that the fiber is coiled and to get some idea of the magnification involved here this whole photograph it represents only one micron in width on the other hand there are photographs of bacteria which show a compound structure to the flagellum so we're not really sure just what the organization of the bacterial flagellum actually is but in all of the flagellates and ciliates in all the flagellated plant cells and animal cells the tails of sperm the flagella of sperm or even in these photographs of ciliated epithelium from the trachea of man the basic structure of all of these seems to be as in this euglena flagellum a ring of fibers probably nine with two in the center now this is a very good example of how similarities and organization run through all the plant and animal kingdoms and tend to indicate relationship there are some ciliates even more complex than paramecium here is another one showing many variations on these locomotor structures and the macronucleus and micronucleus in this particular one you can see a row of fused cilia forming a still more specialized unit a membrane now one group of cilia bearing organisms known as the suctoria possess cilia during the early part of their life cycle and are free swimming and then they settle down and attach themselves to various surfaces one example of a sectorian is tocopheria here is an ordinary photograph of such an organism and you'll notice that it is surrounded by a cluster of tentacles hollow tentacles that it uses in feeding we're not certain whether these structures too are derived from the ciliary unit or not it's attached by a stalk to a disc which adheres to some surface tocopheria feeds by capturing other animal cells attaching the hollow tentacles and drawing cytoplasm into food vacuoles in the body of the suctorian the complexity of organization here is illustrated by this electron microscope picture of the basal disk that attaches or adheres the suctorian to a surface and by this photograph of a greatly enlarged tentacle showing that it consists of various layers and has complex structure in addition to the presence of cilia during the early stages of its life cycle a photograph of toccophria showing its macronucleus shows the same characteristic we mentioned for paramecium and other ciliates the macronucleus contains many many complete diploid sets of chromosomes represented by each one of these dots the contractile vacuole of tocopheria illustrates another modification in structure because the pore through which this vacuole empties as is the case with paramecium is not just haphazard but it has structure and fibers and in this electron microscope picture you can see it open and the contents emptying to the outside here you see it closed and the fibers have drawn together and shut off the opening now all of these illustrations a very complex organization in ciliates and flagellates have led some biologists to say maybe we ought not to call them single cells in certain ways they're just as complicated as a multicellular organism perhaps they're non-cellular at any rate we know that these represent specializations that have developed within the unit of the organism and this is an indication of their long specialized evolutionary history which is just as long as ours [Music] you