M 31: Sulfur Cycling and Microbial Diversity

Flashcards covering the fundamentals of the sulfur cycle, microbial metabolic diversity, specific sulfur-metabolizing organisms, and clinical diagnostic media for enteric pathogens.

Sulfur cycle

The process of sulfur cycling involving both reduction and oxidation, distributed across the phylogenetic tree in both Archaea and Bacteria.

Gene loss

A mechanism for creating diversity within phylogenetic groups where an organism loses an ancestral metabolic trait, such as anoxygenic phototrophy.

Convergent evolution

The independent evolution of similar traits (like wings in bats and birds) that are not encoded by homologous genes, occurring separately despite having the same function.

Horizontal gene transfer (HGT)

The acquisition of traits or genes from a non-ancestor or distantly related lineage, rather than being passed down vertically.

Chemolithotrophs

Organisms that obtain their chemical energy and electrons from inorganic compounds.

Chemoorganotrophs

Organisms that obtain their electron donors and energy from organic compounds.

Anaerobic respiration

A respiratory process using a terminal electron acceptor other than oxygen, which typically yields less energy than the $O_2 / H_2O$ redox pair.

Facultative

The ability of an organism to switch to an alternative electron acceptor, such as nitrate or sulfate, when its preferred acceptor is unavailable.

Sulfidic environments

Natural or built environments rich in sulfide, such as salt marshes, sewers, and wastewater treatment plants.

Obligate anaerobe

An organism that does not have the ability to respire with $O_2$, either because it lost the necessary genes or never possessed them.

Assimilative process

The incorporation of inorganic nutrients into a cell's biomass for biosynthesis, a process that consumes $ATP$ and reducing power.

Dissimulative process

A respiratory process for the conservation of energy where electron acceptors are reduced and the resulting products are excreted as waste rather than becoming part of the biomass.

Sulfate

$SO_4^{2-}$; an oxidized sulfur compound with an oxidation state of $+6$.

Sulfide

The most reduced form of sulfur, such as $H_2S$ or $HS^-$, with an oxidation state of $-2$.

DMSO

Dimethyl sulfoxide; an important abundant sulfur compound found in oceans and marine products like algae.

Sulfate reduction

The reduction of $SO_4^{2-}$ to $H_2S$, a process that requires the transfer of $8$ electrons.

Beggiatoa

A filamentous sulfur-oxidizing bacterium commonly found where sulfide-rich muds meet oxygenated water.

Thiomargarita

The largest known bacteria, which contains a large vacuole filled with nitrate and stores elemental sulfur in intercellular granules.

Carboxysomes

Non-membrane bound structures within some autotrophic sulfur-oxidizing bacteria where the Calvin cycle occurs.

Mixotrophs

Organisms that can use a variety of different carbon and energy sources, such as using both organic and inorganic compounds.

Hydrothermal vents

Deep-sea geothermal features where the environment is full of reduced compounds like sulfide, hydrogen, and iron, supporting life through chemosynthesis.

Riftia

Giant tube worms found at hydrothermal vents that lack a mouth and anus, relying on symbiotic bacteria in an organ called a trophosome.

Trophosome

A specialized gut organ in tube worms filled with symbiotic bacteria that use sulfide and $CO_2$ to support the host worm.

Alvinella

Small tube worms that are among the most heat-tolerant organisms on the planet, growing at temperatures around $80$ \text{ } ^\circ C.

Hektoen Enteric (HE) agar

A selective and differential medium used in clinical microbiology to distinguish Salmonella (which forms black colonies) from Shigella (which forms green colonies).

Ferric ammonium citrate

A component in HE agar that reacts with produced sulfide to create a black precipitate, indicating thiosulfate reduction.