MICROBES AND PARASITES

The Effects of Microbes and Parasites on the Environment

The Effects of Microbes and Parasites on the Environment

Introduction

Microbes are a large, diverse group of organisms that exist as single cells or as colonies (clusters of cells of the same species) that are able to grow, generate energy, and reproduce independently of other cells. Microbes may be eukaryotic or prokaryotic. The eukaryotic microbes include algae, fungi, slime molds, and protozoa, and the prokaryotic microbes are the bacteria, archaebacteria, and cyanobacteria. (Because viruses cannot metabolize and reproduce without hijacking the metabolic processes of a host cell, viruses are not true cells. Thus, debate exists about whether viruses are living organisms and thus technically “microbes.”) (Surve, 2011, 20)

Microbes colonize virtually all terrestrial and aquatic habitats on Earth, from polar glaciers to deep-ocean hydrothermal vents. Microbes contain the greatest species diversity of any group of organisms on Earth. Bacteria have particularly high species diversity, and their tremendous metabolic flexibility allows them to inhabit the extremely unfavorable environments of deep sea hydrothermal vents, polar ice, and deep buried sediments.

The first organisms to evolve on Earth, microbes have played a key role in altering the gaseous makeup of the Earth's atmosphere, and in the evolution of higher life forms. For example, early in the history of life, enormous colonies of aquatic cyanobacteria grew as pincushion-shaped organisms termed stromatolites. Over hundreds of millions of years, oxygen emitted by stromatolites as a by-product of their prolific photosynthesis progressively oxygenated the atmosphere. Scientists believe that the cyanobacteria-mediated oxygenation of the atmosphere facilitated the evolution of new organisms that rely upon oxygen. Soil fungi may have also facilitated the evolution of higher life forms. Root imprints of the earliest land plants fossilized in sedimentary rock show evidence of fungal symbionts present in root cortical cells. This suggests that the movement of plants onto land was aided by a mutualism with mycorrhizal fungi, specialized fungal microbes that today colonize the roots of most terrestrial vascular plants to aid in nutrient uptake.

Discussion & Analyses

People most commonly associate microbes (“germs”) with human illness, and indeed microbes act as pathogens or parasites on a great number of humans and other animals. The effects of microbial colonization of animal tissue, however, may be positive, negative, or neutral. Hair follicles are inhabited by an array of bacteria, yeasts, and filamentous fungi. Various pathogenic bacteria cause diseases such as Stapholococcus and Streptococcus infections, diphtheria, Legionnaires' disease, tuberculosis, and sexually-transmitted diseases. The bacterium Yersinia pestis, transmitted to humans through bites from fleas that have fed on infected rodents, caused the bubonic plague, which killed 25 million people around the world over five years during the Middle Ages. Protozoan diseases such as leishmaniasis, African sleeping sickness, malaria, and amoebic dysentery cause serious illness and death to millions of people worldwide each year. The same bacteria that can cause illness when present in the mammalian stomach, however, are essential for nutrient transformation and uptake in the large intestine.

By no means are all microbes ...