2-1 - Prokaryotic Cells _ Their Morphology.pdf

Topic 2 Microbial cells: Structure & Function 2-1: Prokaryotic Cells & Their Morphology Lecture Overview: • Differences between prokaryotic and eukaryotic cells. Different types of prokaryotic cell shapes and their names (& examples) • Textbook: Chapter 1 (I) Two Major Differences Between Prokar...

Topic 2 Microbial cells: Structure & Function 2-1: Prokaryotic Cells & Their Morphology Lecture Overview: • Differences between prokaryotic and eukaryotic cells. Different types of prokaryotic cell shapes and their names (& examples) • Textbook: Chapter 1 (I) Two Major Differences Between Prokaryotes and Eukaryotes In the simplest terms, the two major differences between prokaryotes and eukaryotes are: 1. Prokaryotes are generally much smaller in size: roughly equivalent to a mitochondrion 2. Eukaryotes contain numerous compartments (organelles) and prokaryotes generally lack organelles Example of cell sizes: Salmonella enterica within a human cell Image of a single human cell infected with Salmonella enterica serovar Typhi S. enterica shown in green/red. Cell boundaries can be inferred from bacteria. Note “hole” where nucleus is. This cell’s cytoplasm is over-run with bacteria (unusual for S. enterica infections) Scale bar, 10 μM Fowler and Galan, Cell Host & Microbe, 2018 Sizes of both cell types can vary significantly In the extreme example below, a prokaryotic cell (the bacterium Epulopiscium fishelsoni) is larger than a eukaryotic cell (a Paramecium protist) Epulopiscium fishelsoni (amongst the largest bacteria) are millions of times larger than Mycoplasma pneumoniae (the smallest known bacterium) These are extreme examples, most bacterial cells are ~0.5 μM to 10 μM in length. Textbook, Fig. 1.6 Cell size and cell growth Surface area to volume ratio affects how quickly cells exchange nutrients and waste with their environment For a given shape, small cells do this more quickly/efficiently Result is that small cells can generally grow (reproduce) more quickly Smaller size/less complexity also means less time/energy to replicate cell Textbook, Fig. 1.7 Cell structure overview: prokaryotic cells & eukaryotic cells The fundamental difference between prokaryotes and eukaryotes is the presence of membrane-bound compartments Eukaryotic cells contain multiple membrane-bound compartments, prokaryotic cells generally do not. Prokaryotic cells typically lack compartmentalization within cell membrane (we come back to this!) Asgard archaea an exception? We’ll come back to this Textbook, Fig. 1.4 Common morphologies of prokaryotes o Prokaryotic cells come in different shapes and sizes o Historically, morphology has been important for naming and identifying bacteria (still today, but to a lesser extent) o Shapes dictated by a number of factors (cell wall structure, cell growth/division mechanism, cell differentiation) Textbook Fig. 13.1 Textbook Fig. 1.8 Cocci: spheres Staphylococci Diplococci Streptococci (clusters of cocci) (pairs of cocci) (chains of cocci) Shen et al., Scientific Reports, 2016 Staphylococcus aureus Common component of human microbiota (often nasal). Opportunistic pathogen, often via wounds/cuts. CDC rendering of N. gonorrhoeae Neisseria gonorrhoeae Etiological agent of the common STD gonorrhea CDC rendering of S. pyogenes Streptococcus pyogenes The predominant “group A strep”. Can cause a range of diseases, including “strep throat”. Bacilli: rods Vibrio: comma shaped (bent rod) CDC rendering of S. enterica Salmonella enterica Common cause of “food poisoning” worldwide. Also cause more serious disease, such as typhoid fever. Vibrio cholerae Important human pathogen, especially in developing world, that causes profuse diarrhea and dehydration. Vibrio cholerae Subject of “contagious” -- an inspirational (but factually questionable) made for TV movie from the 1990s When some shrimp from Colombia, tainted with cholera, is served to some people on a plane bound for L.A., an outbreak ensues. And a doctor sets out to find the source and contain it before it turns into a epidemic. And if things weren't bad enough, a drug smuggler who was carrying some drugs on him contaminates the drugs, which are sold on the street. And to top things off, the doctor's husband, who is on a camping trip with their two children, is sick but did not show any symptoms until they were isolated from the rest of the world. Can she get to them in time? “What you can’t see CAN kill you” Helical CDC: Dr. Patricia Fields, Dr. Collette Fitzgerald Helicobacter pylori Commonly found in human stomach, often innocuous. Cause of vast majority of stomach ulcers, stomach cancers Spirochetes (long spirals) Jutras et al., PNAS, 2016 Borrelia burgdorferi Bacterial pathogen that causes Lyme disease, transmitted by ticks Appendaged/ Budding Holden et al., PNAS, 2014 Caulobacter crescentus Used as a model system to study bacterial cell cycle, asymmetric cell division Filamentous Picture: Sylvia Herter (genome.jgi.doe.gov) Chloroflexus aurantiacus Photosynthetic bacterium that does not produce O2. Studied to understand the evolutionary origins of photosynthesis Why different cell morphologies?? Cell Shape can affect many aspects of day-to-day life o Nutrient access/uptake (surface:volume ratio) o Motility o Attachment to surfaces o Formation of biofilms o Interactions with other microbes and/or eukaryotic host cells o More… Morphogenesis: change in shape Monomorphic: one shape; observed in most pure cultures of bacteria Pleomorphic: multiple different morphologies for same bacterium What causes different morphologies/changes of morphology? o Differentiation into different cell types or spore formation o Altered morphology in response to environmental cues o Altered morphology due to mutation Example: different morphologies at different stages of growth Arthrobacter crystallopoietes: - Grows as a rod during logarithmic (fast) growth. See panel b in image. - Becomes a coccus in stationary phase (slow/no growth). See panel a in image. Ward and Claus, J. Bacteriology, 1973