Problem 4 - Biology: The Dynamic Science

Question

At the health center, a fecal sample was taken from a feverish student. Organisms with corkscrewlike flagella and no endomembranes but with cell walls that lack peptidoglycan were isolated as the cause for the illness. These organisms probably belong to the group: a. chlamydias. b. spirochetes. c. Euryarchaeota. d. Cyanobacteria. e. Archaea

Step-by-Step Solution

Answer

The organisms likely belong to the group b. spirochetes.

Step 1: Identify Key Characteristics

Note the key characteristics described: organisms have corkscrewlike flagella, no endomembranes, a cell wall without peptidoglycan, and are associated with illness.

Step 2: Eliminate Unfit Options

Eliminate the options that do not match the characteristics. Chlamydias lack flagella and have a life cycle involving host cells. Euryarchaeota and other Archaea lack peptidoglycan but are not known for corkscrewlike flagella. Cyanobacteria have endomembranes and peptidoglycan.

Step 3: Identify the Correct Group

Match the characteristics with the correct option. Spirochetes are known for their corkscrewlike flagella, are pathogenic, and their cell walls do not contain peptidoglycan, fitting the description perfectly.

Key Concepts

Spirochetes

Spirochetes are a distinctive group of bacteria known for their unique shape and motility. These microorganisms are characterized by their long, spiral, and flexible form that resembles a corkscrew, which is facilitated by the presence of axial filaments or periplasmic flagella. These flagella are located in the space between the outer sheath and the cell wall, allowing them to move in a twisting motion. This distinctive movement enables them to burrow through viscous environments, such as the mucous membranes of their hosts.

In the context of illnesses, certain spirochetes are the causative agents behind diseases such as Lyme disease, caused by Borrelia burgdorferi, and syphilis, caused by Treponema pallidum. Their ability to invade and persist within host tissues can be directly attributed to their motility and cell structure. Moreover, their cell walls lack peptidoglycan, a component commonly found in many other bacteria, making them more elusive to certain immune responses or antibiotic treatments.

Cell Wall Composition

The composition of a bacterial cell wall is a critical factor in its ability to survive in various environments and affects how organisms are classified. The most well-known division is between Gram-positive and Gram-negative bacteria, determined by the Gram stain test, which is based on the composition of their cell walls.

Gram-positive bacteria have a thick layer of peptidoglycan that traps the crystal violet stain, appearing purple under a microscope. Contrastingly, Gram-negative bacteria have a thinner layer of peptidoglycan and an outer membrane containing lipopolysaccharides that do not retain the crystal violet stain; instead, they appear pink after a counterstain is applied. Spirochetes, in particular, possess a distinctive cell wall without peptidoglycan, placing them outside the typical Gram classification and enabling them to evade certain antimicrobial defenses.

Microbial Pathogenicity

Microbial pathogenicity refers to the ability of microorganisms, such as bacteria, viruses, fungi, and parasites, to cause disease in a host. The pathogenicity of microorganisms is influenced by various factors including their virulence factors, such as toxins, adhesion factors, evasion strategies, and invasiveness.

For bacteria like spirochetes, motility mechanisms like the corkscrew-like flagella are essential for invasiveness, allowing them to penetrate host tissues. The absence of peptidoglycan in their cell walls also plays a role in their ability to evade the host's immune system. Microorganisms have complex interactions with their hosts, and a detailed understanding of their pathogenic mechanisms helps in developing effective treatments and preventive measures for the diseases they cause. Consequently, studying microbial pathogenicity is vital for the fields of microbiology, immunology, and public health.