Bacterial Taxonomy, Genetics, and Pathogens

Vocabulary flashcards covering biological classification, molecular methods of species definition, bacterial strains, and key human and plant pathogens discussed in the lecture.

Domain

The top level of biological taxonomy consisting of three groups of living things, with every organism belonging to exactly one group.

Taxonomy

A classification system used to organize all living organisms into structured, hierarchical groups from domain down to species.

Binomial nomenclature

The practice of using two names—the capitalized genus name and the lowercase species name in italics (or underlined if handwritten)—to generate a unique scientific name for an organism.

Biological species concept

A concept that defines a species as groups of organisms that can mate and produce fertile offspring together.

Phenetic methods

Early taxonomic techniques used to define bacterial species based on observable phenotypes, such as cell morphology, Gram reaction, and lactose fermentation.

Carl Wojs and George Fox

Microbiologists who in the 1980s recognized prokaryotes as two distinct groups (Domain Bacteria and Domain Archaea) and proposed sequencing the small ribosomal subunit to define species.

Small ribosomal RNA sequence species threshold

The requirement that two organisms must share at least $97\%$ nucleotide identity in their small ribosomal RNA sequence to be classified as the same species.

Chromosomal DNA identity species threshold

The requirement that two organisms must share at least $95\%$ DNA identity across their whole genome to be considered the same species.

Morphovars

Bacterial strains or subspecies that display distinguishable variations in morphology, shape, or physical characteristics, such as rough and smooth colony types.

Serovars

Bacterial strains differentiated by antibodies in serum that recognize specific, distinct molecular structures such as variations in lipopolysaccharide endotoxin.

Obligate intracellular pathogens

Parasitic microorganisms, such as members of the genus Rickettsia, that must invade a host cell in order to reproduce.

Rickettsia typhus

A bacterial pathogen transmitted by flea bites that causes endemic typhus (scrub typhus), characterized by a dangerously high fever, skin rash, and an untreated mortality rate of approximately $5\%$.

Rickettsia praliceki

A bacterial pathogen transmitted by body lice that causes epidemic typhus, linked to conditions lacking basic hygiene and having an untreated mortality rate of at least $40\%$.

Rickettsia rickettsi

A pathogen spread by dog ticks that causes Rocky Mountain spotted fever, carrying an untreated mortality rate as high as $85\%$ and a treated mortality rate of up to $5\%$.

Diazotrophs

Soil bacteria—including Rhizobium, Bradyrhizobium, Nitrobacter, and Nitrosomonas—capable of nitrogen fixation to convert elemental nitrogen ($N_2$) into biologically available forms.

Crown gall disease

A plant disease caused by Agrobacterium tumefaciens characterized by the formation of galls, or plant tumors.

Ti plasmid

The tumor-inducing plasmid of Agrobacterium tumefaciens that transfers genes encoding auxins and opines into a plant host chromosome.

T pilus

A specialized pilus utilized by Agrobacterium tumefaciens to attach to plant cells and transfer a fragment of its Ti plasmid into the host nucleus.

Auxins

Plant growth hormones synthesized via genes introduced by the Ti plasmid that induce uncontrolled cell division and tumor formation.

Opines

Unusual amino acids encoded by Ti plasmid genes that cannot be metabolized by most organisms, serving as an exclusive nutrient source for Agrobacterium tumefaciens.

Bt toxin

A bacterial insecticide gene engineered into major crops (such as corn and soybeans) that kills plant pests upon ingestion while remaining harmless to humans.

Bordetella pertussis

The bacterium responsible for whooping cough (pertussis), which causes severe coughing fits by producing pertussis toxin.

Catarrhal stage

The initial stage of pertussis that mimics a common cold with mild symptoms like a runny nose and slight cough.

Paroxysmal stage

The second stage of pertussis characterized by persistent coughing paroxysms, whooping gasps for air, oxygen deprivation risk, and a duration of $8$ to $12$ weeks.

Convalescence stage

The final stage of whooping cough in which the patient is recovering and feeling improved, even if the pathogen has not been completely cleared.

Pertussis toxin

A bacterial toxin that stops the movement of respiratory epithelial cilia, leading to mucus accumulation and violent coughing spells.

DTP vaccine

A combination vaccine formulated in various types (such as DTaP and Tdap) to confer protection against three bacterial diseases, including pertussis.