He Feeding and Growth Portion of the Protozoan Life Cycle is Known as the Stage

Protozoa

William D. Taylor , Robert W. Sanders , in Ecology and Classification of North American Freshwater Invertebrates (Third Edition), 2010

A. Protozoa as Cells and Organisms

Large protozoa that have many nuclei, or large amitotic, polyploid nuclei may be best considered acellular rather than unicellular creatures. Nonetheless, some species have been studied extensively by cell biologists as model cells, and ecologists interested in protozoa can glean much useful information from their labors. This section will rely heavily on information from those few taxa. We will first describe some organelles that are important and widely distributed among protozoa and then discuss major groups of protozoa with respect to their more unique organelles. Lastly, we will revert to an overall view in discussing environmental physiology of protozoa. In all sections, we will emphasize those organelles that relate to feeding, locomotion, ecology, and morphology at the light-microscope level.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123748553000030

Protozoa

Nigel Horan , in Handbook of Water and Wastewater Microbiology, 2003

4 PROTOZOAL NUTRITION

Protozoa demonstrate a wide range of feeding strategies of which four types are represented by the protozoa found in wastewater treatment systems. Certain members of the Phytomasti-gophorea are primary producers and capable of photoautotrophic nutrition, in addition to the more usual chemoheterotrophic nutrition.

Heterotrophy among the flagellated protozoa contributes to the process of biochemical oxygen demand (BOD) removal, and uptake of soluble organic material occurs either by diffusion or active transport. Protozoa that obtain their organic material in such a way are known as saprozoic, and are forced to compete with the more efficient heterotrophic bacteria for the available BOD. Amoebae and ciliated protozoa are also capable of forming a food vacuole around a solid food particle (which include bacteria) by a process known as phagocytosis. The organic content of the particle may then be utilized after enzymic digestion within the vacuole, a process which takes from 1 to 24 hours. This is known as holozoic or phagotrophic nutrition, and does not involve direct competition with bacteria, which are incapable of particle ingestion.

The final nutritional mode practised by the protozoa is that of predation. These predators are mainly ciliates, some of which are capable of feeding on algae (and are thus herbivores), as well as other ciliate and flagellate protozoal forms.

All protozoa rely on phagocytosis for their energy and carbon for building cellular material (Fig. 4.2). This involves the enclosure of a solid food particle in a vacuole, which is covered with a membrane and in which digestion occurs. Dissolved nutrients are removed from the vacuole leaving the indigestible remains behind. These are removed from the cell by fusion of the vacuole with the cell surface membrane. The typical lifetime of a food vacuole is around 20 minutes, although this time reduces if the cell is not feeding.

Fig. 4.2. Degradation of a food particle by phagacytosis. (a) Food particle engulfed by pseudopodia and a vacuole formed; (b) enzymic digestion occurs within the vacuole and digestion products released to the cytoplasm; (c) undigested remains ejected from the body.

In addition to phagocytosis, there are other mechanisms by which a protozoan can obtain energy and cellular building blocks. Some protozoa participate in symbiotic relationships with photosynthetic organisms, whereas others are thought able to take up dissolved nutrients. It is doubtful, however, if this latter mechanism plays any role for the free-living protozoa outside of a laboratory culture.

Although phagocytosis is practised by all the protozoa there are a number of different feeding patterns which are exploited to capture the solids particle and these can be classified into three categories, namely: filter feeders, raptorial feeders and diffusion feeders. Filter feeding involves the creation of a feeding current, which is then passed through a device which acts to filter out the solids particles in the water. In the flagellates this is a collar of straight, rigid tentacles. For the ciliates the water is passed through an arrangement of parallel cilia. The clearance between the tentacles in the collar and the parallel ciliates, dictates the size of particle that is retained. This is typically between 0.3 and 1.5 μm and helps to explain why the presence of a healthy ciliate population in an activated sludge plant generates such a crystal clear effluent with a reduced number of faecal indicator bacteria (Table 4.3).

TABLE 4.3. The effects of ciliated protozoa on the effluent quality from a bench-scale activated sludge plant

Parameter	Without ciliates	With ciliates
BOD (mg/l)	53-70	7-24
COD (mg/l)	198-250	124-142
Organic nitrogen (mgN/l)	14-21	10
Suspended solids (mg/l)	86-118	6-34
OD6 20	0.95-1.42	0.23-0.34
Viable bacterial count (cfu/ml × 106)	106-160	1-9

(from Pike and Curds, 1971)

Copyright © 1971

Raptorial feeding is practised in small flagellates and amoebae, which use it to feed on bacteria. In this mode, water currents are driven against the cell using a hairy anterior flagellum. Particles which make contact with a lip-like structure on the protozoa are phagocytized (Fig. 4.2). As each particle is captured separately (compared to filter feeders which retain all particles of the correct size), this allows the protozoa some discrimination as to what is ingested. This may be based on prey size or type, such as algae or small flagellates. Protozoa are also able to discriminate between different bacterial species with preferred types being selected.

Diffusion feeding is practised by the sarcodines. The suctorians are common protozoa in activated sludge and they feed by diffusion, largely on other ciliates. The suctorians are attached to a floc particle by a stalk and they have bundles of tentacles supported with an internal cylinder of microtubules. Ciliates which touch these tentacles become attached and immobilized. The tentacles then penetrate the attached ciliate and draw the contents through the tentacle into the suctorian.

Within the latter two modes of nutrition, the protozoa display a certain degree of selective feeding. Larger forms of amoebae are carnivorous, eating mainly ciliates and flagellates, whereas the smaller amoebae feed primarily on bacteria. The predatory suctorians are found to feed almost exclusively on holotrichous and spiriotrichous ciliates, with hypotrichs, flagellates and amoebae rarely being captured. Peritrichous ciliates are primarily bacterial feeders, but have a limited number of bacterial species upon which they can feed. Certain bacterial species are capable of supporting growth for long periods, whereas others induce starvation after a short time. In addition, many bacteria, in particular the pigmented types, prove toxic to those ciliates which ingest them.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780124701007500054

PROTOZOA

W. Foissner , in Encyclopedia of Soils in the Environment, 2005

Introduction

Protozoa are unicellular, heterotrophic, eukaryotic organisms comprising four organization types: amebae, flagellates, ciliates, and parasitic sporozoans. About 1600 species, of which some are restricted to certain geographic regions, are known to live in terrestrial habitats; however, at least the same number is still undiscovered. Small body size and the ability to produce protective resting cysts are the main adaptations of protozoa to the peculiarities of the soil environment. Many soil protozoa feed, more or less selectively, on bacteria, while others are omnivorous or highly specialized fungal feeders. Protozoa (active and cystic) inhabit the soil in great numbers, that is, some 10   000–1   000   000 individuals per gram dry mass, and produce many generations annually. They significantly enhance the flow of nutrients and growth of plants and earthworms. Accordingly, they are important soil inhabitants, and studies on their dynamics and community structures thus provide a powerful means for assessing and monitoring changes in biotic and abiotic soil conditions. Unfortunately, methodological and taxonomical problems still limit the use of protozoa as bioindicators in terrestrial environments.

This article covers the diversity, ecology, and bioindicative value of soil protozoa. The knowledge on autotrophic soil protists, which mainly live on the soil surface because they depend on light, is still in its infancy. However, they play an important role, especially as a symbiotic partner of lichens in the crust soils of extreme regions, such as desert and high mountain areas.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B0123485304001624

Protozoa

Bland J. Finlay , Genoveva F. Esteban , in Encyclopedia of Biodiversity (Second Edition), 2013

Protozoa and Ecosystem Function

Protozoa are abundant. One gram of soil typically contains 103–107 naked amebae, 105 planktonic foraminiferans can often exist beneath 1   m² of oceanic water, and almost every milliliter of fresh water or sea-water on the planet supports at least 100 heterotrophic flagellates. When expressed in global terms, these numbers are very large, and an inevitable consequence of the persistence of such a large number of very small organisms is that migration rates will be relatively high. It follows that rates of speciation and extinction must be low, as will the consequent global number of species. It also follows that protozoa are unlikely to have biogeographies, and endemic species probably do not exist. The authors might expect that the local diversity of protozoa would account for a significant proportion of global diversity, even if at any moment in time much of this diversity is represented by rare or inactive individuals (e.g., cysts awaiting the arrival of suitable conditions). There is indeed good evidence for the global distribution of protozoan species, including the morphologically distinctive flagellate Rhynchomonas nasuta that has been found in most aquatic and terrestrial environments worldwide; marine foraminiferans and ciliates found living in slightly salty water of desert oases, hundreds of kilometers from marine coasts; the same radiolarian species living in high northern and southern oceanic latitudes; the same pond-dwelling ciliates living in Australia and northern Europe; and the cosmopolitan distribution of the same species of agglutinated foraminiferans in the deep-sea benthos. In general, protozoan morphospecies are ubiquitous and apparently cosmopolitan if the habitats to which they are adapted are distributed in different parts of the world (Finlay, 1998, 2002). In accordance with this, the global number of protozoan species is indeed relatively modest (Table 1), and the number of species that can be retrieved from a local area (e.g., a pond), in both active form and from a passive state is a significant proportion (usually at least 10% for various morphological-functional groups) of the global total. This fact may not be obvious from short-term ecological sampling programs because only a limited number of microbial niches are available at any moment in time.

Table 1. Estimates of global species richness of extant free-living protozoa ^a

			Marine	Nonmarine	Total
Ameboid protozoa	Slime molds	Dictyostelids	–	60	60
		Myxomycetes	–	550	550
	Rhizopod amebae	Naked	180	220	400
		Testate	–	200	200
	Foraminiferans	Planktonic	40	–	40
		Benthic, inshore	4000 b	–	4000
		Benthic, deep sea	250 b	–	250
	Actinopod amebae	Acantharians	150	–	150
		Radiolarians, solitary	750	–	750
		Radiolarians, colonial	50	–	50
		Heliozonas	–	120	120
Flagellated protozoa	Excluding heterotrophic dinoflagellates c	Marine plankton	420	–	420
		Marine benthos	330	–	330
		Freshwater and soil	–	350	350
	Heterotrophic dinoflagellates		900	110	1010 d
	Other mixotrophic flagellates		–	–	150 e
Ciliated protozoa			1400	1660	3060
Total					11890

a

Compiled from numerous published and unpublished sources. The more problematic estimates are highlighted.

b

There is considerable uncertainty attached to these estimates. The figure of 4000 is generally accepted as a working figure for extant species but is probably inflated by synonyms, especially those of shallow-water benthic species. There is no firm information for species richness of deep-sea benthic foraminiferans (Gooday et al., 1998). The estimate of 250 is approximately double the typical figure for local richness of species, most of which may be cosmopolitan, but there are probably many undescribed deep-sea soft-shelled foraminiferans that have in the past been ignored by geologists.

c

The total given here for heterotrophic flagellates is 1100 species. This includes some synonyms and mixotrophs. It is believed by some that the real global total is closer to 3000 species.

d

Assuming there are 1800 marine and 220 freshwater species, and that 50% of these are heterotrophs.

e

This estimate is simply derived by doubling some recent estimates. Note that these species may be only temporarily phagotrophic.

Protozoa and other microorganisms have other special properties. Microbial activities interact strongly with physical and chemical factors in the natural aquatic environment (e.g., light transmission or the concentrations of essential nutrients) to create a continuous turnover of microbial niches. These niches are quickly filled from the locally available diversity of rare and dormant microbes, and the activities of the latter create further reciprocal interactions. Therefore, the diversity of active protozoan species in a pond, at any moment in time, is the result of preceding reciprocal interactions involving many biological and nonbiological factors, and the biodiversity of protozoa and other microbes is an integral part of ecosystem functions such as carbon fixation and nutrient cycling (Finlay et al., 1997).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123847195001180

Protozoa

Alan Warren , ... Bland J. Finlay , in Thorp and Covich's Freshwater Invertebrates (Fourth Edition), 2016

Preservation

Wherever possible, protozoa should be observed in vivo to determine their behavior and certain features that may only be visible in live cells. Nevertheless, it may also be necessary to employ preservation methods, for example: (1) if it is not possible to observe the sample for a long period after collection; (2) to observe certain features not visible in live specimens; or (3) to maintain a reference collection of the organisms or permanent record of the sample. A useful general fixative is Lugol's Iodine, 1% volume/volume, or higher in saline or hard water (Taylor & Heynen, 1987). Mercuric chloride has been used extensively but should probably be discontinued for safety and environmental reasons. These fixatives do not lend themselves to the identification of ciliates, nor to the detection of chromatophores in small flagellates. Filtration methods may aid with both of these problems. The quantitative protargol method or QPS (Montagnes & Lynn, 1987a,b; Skibbe, 1994) produces permanent, quantitative, stained preparations for identification of ciliates and flagellates, although it requires that samples be fixed in a concentrated Bouin's fixative. Various types of silver-staining techniques, which highlight ciliary patterns, have been used in the identification of ciliates (Lee et al., 1985; Foissner, 1991). Other fixatives, such as glutaraldehyde and/or osmium tetroxide (OsO₄), are used if cells are to be examined by electron microscopy. A comprehensive account many of the main commonly used methods for the collection, isolation, cultivation, and preservation of protozoa is given in Lee & Soldo (1992).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123850287000020

Volume 4

Maria A. Efstratiou , in Encyclopedia of Environmental Health (Second Edition), 2019

Protozoa

Protozoa play important roles in environmental food web dynamics. They graze on bacteria thus regulating bacterial populations, they part-take in wastewater treatment processes, they maintain fertility in soil by releasing nutrients when they digest bacteria. Protozoa causing clinical diseases include the intestinal protozoa Giardia lamblia, Cryptosporidium sp. and Entamoeba histolytica. Giardia and Cryptosporidium assume a dormant cyst phase to survive under unfavorable conditions. Giardia cysts and Cryptosporidium oocysts have been detected in beach sand. Cryptosporidium oocysts are the more environmentally resistant. Both protozoa are responsible for outbreaks of waterborne diseases.

Opportunistic pathogens in this group, isolated from beach sand include, amongst others, free-living amoebae and Acanthamoeba sp.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780124095489109145

Biotic Characteristics of the Environment

I.L. Pepper , in Environmental and Pollution Science (Third Edition), 2019

5.2.5 Protozoa

Protozoa are unicellular, eukaryotic organisms that can be several mm in length, although most are much smaller. Most protozoa are heterotrophic and survive by consuming bacteria, yeast, fungi, and algae. There is evidence that they may also be involved, to some extent, in the decomposition of soil organic matter. Because of their large size and requirement for large numbers of smaller microbes as a food source, protozoa are found mainly in the top 15–20   cm of the soil. Protozoa are usually concentrated near root surfaces that have high densities of bacteria or other prey.

There are three major categories of protozoa: the flagellates, the amoebae, and the ciliates. The flagellates are the smallest of the protozoa and move by means of one to several flagella. Some flagellates (e.g., Euglena) contain chlorophyll, although most do not. The amoebae, also called rhizopods, move by protoplasmic flow, either with extensions called pseudopodia or by whole-body flow. Amoebae are usually the most numerous types of protozoan found in a given soil environment. Ciliates are protozoa that move by beating short cilia that cover the surface of the cell. The protozoan population of a soil is often correlated with the bacterial population, which is the protozoan's major food source. Numbers of protozoa can vary around 10 ⁴ per gram of soil (Takenouchi et al., 2016).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128147191000057

Biological HRPs in wastewater

Shuyu Jia , Xuxiang Zhang PhD , in High-Risk Pollutants in Wastewater, 2020

3.3.1 Biological characteristics of protozoa

Protozoa are the same as multicellular animals, with physiological functions including metabolism, exercise, reproduction, reaction to an external stimulus, and adaptability to the environment. Some common protozoa are distinguished from sizes, and protozoa individuals range in size from as little as 1   μm to several millimeters, or more (Singleton and Sainsbury, 2003). Moreover, all the protozoa have cell membranes, and the cell membranes of most protozoa are strong and elastic, so that protozoa could remain a certain shape. Generally, protozoa have one or more nuclei, which are various in shapes. However, there are also some protozoa, such as ameba, which have only one layer of the very thin plasma membrane and cannot maintain a fixed shape. Protozoa produce morphological differentiation in their cells and form organelles capable of performing various life activities and physiological functions. In terms of movement organelles, there are flagella, pseudopods, and cilia. Furthermore, some types of protozoa have myofilaments distributed in the cell membrane, which has the function of contraction and deformation.

There are three types of protozoa that are common in water treatment systems: (1) sarcopods, whose cytoplasm is flexible enough to form a pseudopod acting as an organelle for exercise and feeding; (2) flagellates, which have one or more flagella; (3) infusorians, which have cilia on the body or part of its surface acting as a tool for action or feeding. Some of the protozoa have two stages of the life cycle, alternating between proliferative stage (trophozoite) and dormant stage (cyst). When protozoa are in the stage of trophozoite, they can actively feed. As cysts, protozoa can survive in the harsh condition including extreme temperatures, harmful chemicals, and fewer nutrients, water or oxygen for a long time. The conversion from trophozoite to cyst is known as encystation, while the process of transforming from cyst to trophozoite is known as excystation.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128164488000034

Water microbiology

Miklas Scholz , in Wetland Systems to Control Urban Runoff, 2006

21.5 Protozoology of treatment processes

Protozoa are plentiful in constructed treatment wetlands, AS and other polluted mixed liquors (up to about 50 000 cells per ml). Protozoa species and their abundances can be related to water and wastewater treatment processes, and their corresponding water quality.

The spatial distribution of protozoa in a filter depends on the level of saprobity. It is possible to monitor the filter effluent quality by interpreting protozoa species and levels in various parts of the filter. The temporal succession of protozoa groups within polluted waters that become gradually cleaner is as follows: flagellates → free-swimming ciliates → crawling ciliates → attached ciliates (Scholz and Martin, 1998a,b).

Protozoa may be used as indicator organisms to predict treatment plant efficiencies in terms of BOD effluent concentrations (Scholz and Martin, 1998a,b). Under protozoa-free conditions, plants produce effluent of low quality with respect to BOD, permanganate value, organic nitrogen, suspended solids, viable bacteria, COD and optical density.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780444527349500244

RHIZOSPHERE

A.C. Kennedy , L.Z. de Luna , in Encyclopedia of Soils in the Environment, 2005

Microfauna (protozoa)

Protozoa are eukaryotic, unicellular organisms, most of which are microscopic in size, although some members may attain macroscopic dimensions. While the group exhibits differences in feeding behavior, all require a water film for metabolic activity. It is estimated that there are between 10⁴ and 10⁵ protozoa per gram of soil. Populations of protozoa are generally higher in rhizosphere soil (R) than bulk soil (S), with large numbers occurring in hotspots such as around dead plant roots. Protozoa feed on bacteria and fungi and thus contribute to the mineralization of N, leading to an increase in N uptake by plants. When rhizosphere protozoa prey on bacteria, up to 60% of the excess N and P is excreted in forms that can be readily utilized by plants. Plants may also benefit from the suppression of pathogenic bacteria and fungi by protozoa in the rhizosphere. Detrimental effects of protozoa include a suppression of Rhizobium populations in the rhizosphere, resulting in reduced root nodulation of Phaseolus vulgaris.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B0123485304001636

snydermucall.blogspot.com

Source: https://www.sciencedirect.com/topics/earth-and-planetary-sciences/protozoan