104 4 Taxonomy, Physiology, and Ecology of Aquatic Microorganisms
Fig. 4.28 Bacteriophages and their hosts (All items in the table reproduced with permission; Anonymous 2010 d)
13 TECTIVIRIDAE
Structure
Non enveloped, icosahedral virion with a pseudo T=25 symmetry.
Virion size is about 66 nm with apical spikes of 20 nm. The
capsid encloses an inner membrane vesicle within which the
genomic DNAis coiled.
Linear, dsDNA genome of about 15 kb flanked by inverted
repeats. Encodes for 30 ORFs. Replication is proteinprimed.
Host
A wide range of bacteria including Alicyclobacillus, Bacillus,
Enterobacteria, Pseudomonas, Thermus.4.1.8.1 Crustaceans (Including Rotifers)
Microscopic crustaceans like tiny lobsters are found in
sewage works where they feed on bacteria and algae.
Some of the species encountered are Cyclops spp.,
Paracyclops spp., and Oaphia spp.
Rotifers, small microscopic animals of the class
Rotifera, are found in water in great abundance. They
are usually less than 1 mm, most usually in the range
of 500 mm in length. Three orders are known:
Seisonidae is marine, while the other two, Bdelloidea
and Monongononta, are freshwater and found in reser
voirs, streams, and sewage treatment plants.
Rotifers may be sessile or planktonic, although they
can swim with their cilia; their usual locomotive
method is by crawling. They are common in structures
with large exposed surfaces such as in trickling filters
sewage treatment plants. They are found in oligotrpic
waters, i.e., waters low in organic matter, for example
in sewage effluents and reservoirs after protozoa have
died off, and thus are indicators of posteutrophication
waters. Indeed, they have been used as indicators of
water quality. Various species are identified with dif
ferent levels of water quality. Brachionus angularis,
Trichocerca cylindrica, Polyurthra euryptera,
Pompholyx sulcata, Rotaria rotatoria, Filinia long
iseta have been designated as indicators of heavy pol
lution (eutrophic) while Ascomorpha ovalis,
Asplanchna herricki, Synchaeta grandis, Ploesoma
hudsoni, Anuraeopsis fissa, Monostyla bulla, and M.
hamata are indicators of fresh and clean waters (olig
otrophic). A variety of rotifers including Brachionus,
Keratella spec, are inhabitants of moderately clean
(mesotrophic) waters (Saksena 2006 ).
Rotifers have been also been used to detect the
oocysts of Cryptosporidium, in water samples. The
fluorescent insitu hybridization (FISH) technique
(see Sect. 4.1.3.3.2d) applied to rotifers has enabled
the detection of biological contamination of surface
water through an assessment of the dispersive stages
of the parasite (see Table 4.1 9 ).
Other crustaceans found in water are Daphnia,
Cyclops, Synchaeta.4.1.8.2 Nematodes
Nematodes are invertebrate roundworms that inhabit
marine, freshwater, and terrestrial environments.
They comprise the phylum Nematoda (or Nemata)
which includes parasites of plants and of animals,