Biological Effects Of Greenhouse Gases And Climate Change 567

Figure 15.31 Effect of substrate concentration on competition. Maximum growth rate, mm, for species A and B are 0.2 and 0.12day_1, respectively, and KS values are 50 and 5.0 mg/L, respectively.

Figure 15.31 Effect of substrate concentration on competition. Maximum growth rate, mm, for species A and B are 0.2 and 0.12day_1, respectively, and KS values are 50 and 5.0 mg/L, respectively.

Bacteria, fungi, algae, and protozoans all have their parasites. Many of the parasites are viruses, which are obligate parasites. Vibrio cholerae is thought to be eliminated from river water following fecal contamination by the action of viral parasites. Bdellovibrio is a bacterium that is parasitic on bacteria. It attaches to larger gram-negative bacteria, causing cell lysis. E. coli has been found to be partially protected from Bdellovibrio by the presence of clay particles. Other bacteria produce extracellular enzymes that can lyse bacteria, algae, or protozoans, making their cell contents available for uptake.

It can sometimes be difficult to distinguish predation from parasitism among microbes. The distinction can be made if predation is limited to cases where the prey is actually ingested by the predator. Some protozoans prey on other protozoans. Didinium preys on Paramecium. Many protozoans prey on bacteria. When bacteria are under strong predation pressure, they may change their growth habits: for example, growing in an attached form instead of dispersed. Again, clay particles have been observed to reduce the vulnerability of some bacteria.

Even algae and fungi can prey on other organisms. Some dinoflagellates consume bacteria, other algae, and other dinoflagellates. Slime molds such as Dictyostelium prey on bacteria. The nematode-trapping fungi capture nematodes by adhesives or by "lassoing" them with constricting rings. When it attempts to swim through a ring, the ring swells, trapping the worm. Despite thrashing motions, the nematode cannot free itself. Eventually, the fungus hyphae grow into the body of the prey. Interestingly, the fungi do not produce the trapping structures in laboratory culture unless nematodes are also present in the culture.

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