A microbiologist discovers a new infectious agent. In an effort to identify the type of agent, the microbiologist exposes the agent to the following: i. RNAse ii. DNAse iii. Protease iv. Heat v. Acid After the different treatments, the microbiologist determines that the agent is destroyed by treatments (i), (iv), or (v). This result leads the scientist to conclude that the agent likely is a(n) .

Viroid.

Explanation:

Microorganisms are those organisms that are very tiny in size and imperceptible to the naked eye. Thus, they are only visible under the microscope. They have a very basic biological organization, a significant proportion of them have only a single cell. Examples are bacteria, archaea (both prokaryotes), protozoa, microscopic fungi and microscopic algae (eukaryotes).

i. RNAases are enzymes of the endonuclease family that catalyze the breaking of ribonucleic acid (RNA) strands by a hydrolytic mechanism. It is present in almost all organisms, from bacteria and archaea to eukaryotes.

ii. DNAases are enzymes that catalyze the cleavage of phosphodiester bonds in deoxyribonucleic acid (DNA). If the enzyme catalyzes the cleavage of the terminal phosphodiester bond it is called exodeoxyribonuclease, whereas if it is an internal bond it is called endodeoxyribonuclease. As the RNAses, they are present in many microorganisms.

iii. Proteases are enzymes that break the peptide bonds found between amino acids of proteins. Proteins are polymers that are found also in almost all microorganisms and perform vital functions such as structural, DNA replication, reproduction, etc.

iv. All microorganisms are affected by heat at a certain degree. The heat causes denaturation of proteins and breaks the cellular membrane.

v. Acids are chemical compounds that release hydrogen ions (H+) in large quantities. They are characterized by being corrosive and they dissociate completely in an aqueous solution. Microorganisms are also susceptible to acids because they denature proteins and affect cell membranes.

If the agent is destroyed by RNAse, heat and acids, it is a viroid.

Viroids are infectious agents that have an extracellular cycle in which they are metabolic inactive, and an intracellular cycle in which they cause infections, like viruses do. However, unlike viruses, viroids have no proteins or lipids and consist of a short, circular RNA strand which does not encode proteins. So they are affected by RNAses but not DNAases. In addition, they have no proteins because they lack a capside and they are not translated into proteins. But like all microorganisms, they are affected by heat and acids (except for some cases of extremophilic bacteria that can withstand high temperatures and/or high levels of acidity).