Lesson 6 Prokaryotes: Part II February 17, 2015

Gram-Positive Bacteria Divided into two groups based on G + C content (%of GC in the DNA) – Firmicutes (low G + C ratio) Staphylococcus, Enterococcus, Streptococcus Endospore-forming bacteria – Clostridium and Bacillus Mycoplasma lacks a cell-wall – Actinobacteria (high G + C ratio) Highly pleomorphic Mycobacterium, Corynebacterium, Propionibacterium Streptomyces is the source of several antibiotics

Firmicutes

Order Clostridiales Clostridium – Endospore-producing – Obligate anaerobes – Causative agent of tetanus (tetani), botulism (botulinum), foodborne diarrhea (perfringens) – C. difficile normal part of intestinal microbiota Produces toxins

Figure Clostridium difficile. Endospore

Order Bacillales Bacillus – Endospore-producing rods – B. cereus and B. anthracis are human pathogens – B. thurigenesis infects insects. Used as insecticide Staphylococcus – Clusters of cocci – Halophilic and survive in low moisture environments – Produces enterotoxins. Targets intestines. – Causes food poisoning and Toxic Shock Syndrome

Figure Bacillus. This Bacillus cereus cell is shown emerging from the endospore. Endospore case

Figure Staphylococcus aureus. Aureus = golden Color may provide protection from Antimicrobial properties of the sun

Order Lactobacillales Generally aerotolerant anaerobes; lack an electron transport chain Produce lactic acid that restricts growth of other bacteria – Lactobacillus located in vagina, intestines, oral cavity – Streptococcus produce exotoxins that destroy phagocytic cells, connective tissue, fibrin – Enterococcus live in areas rich in nutrients but low in oxygen. Important in nosocomial infections – Listeria contaminates dairy products and deli meat. Survives within phagocytes and can grow in refrig. temps. Can cause stillbirth in pregnant women

Order Mycoplasmatales Lacks a cell wall; highly pleomorphic – Difficult to treat Very small size range (0.1–0.24 µm) – Primary source of laboratory contamination M. pneumoniae is the causative agent of pneumonia and M. ureaplasma are associated with urinary tract infections

Actinobacteria

Actinomyces Corynebacterium Frankia Gardnerella Mycobacterium Nocardia Propionibacterium Streptomyces

Mycobacterium Aerobic, non-endospore forming rods Cell wall is similar to gram negative but the LPS is replaced with mycolic acids (forms wax layer) – Resists drying – Disallows many antimicrobial drugs from entering Multi-drug Resistant Tuberculosis (efflux pumps) – Nutrients also enter slowly (slow growth of bacteria) Causative agents of tuberculosis (tuberculosis) and leprosy (leprae)

Propionibacteria Slow growing aerotolerant anaerobe rods Located within pores of the skin and uses sebum and fatty acids as food source – More sebum causes more growth – Destroys cells in pores allowing other bacteria to colonize the pores Produces propionic acid – Used to ferment swiss cheese

Streptomyces Largest group of the Actinobacteria Commonly found in soil – Produces geosmin (gaseous compound that gives soil its “musty” odor) Produce over two-thirds of the clinically used antibiotics – Neomycin, chloramphenicol, Amphotericin B – Streptomycin takes its name from this bacteria

Nonproteobacteria Gram-Negative Bacteria

Chlamydia and Chlamydophila Obligate intracellular pathogens Gram negative Chlamydia trachomatis – Trachoma – STI, urethritis. Most common STD in U.S. Chlamydophila pneumoniae – Prevalent in young adults Chlamydophila psittaci (zoonosis) – Psittacosis Very distinct developmental cycle

Developmental Cycle Beatty et. al., 1994

Nonproteobacteria Gram-Negatives Bacteroidetes – Anaerobic Bacteroides are found in the mouth and large intestine – Most common bacteria in the intestine (1 billion per gram of fecal matter) Cytophaga: degrade cellulose in soil Fusobacterium – Resides in the mouth – May be involved in dental diseases

Spirochaetes Move via axial filaments (corkscrew) Many are located in the oral cavity Treponema pallidium causes syphilis. – Spread by sexual contact or mother to fetus (congenital syphilis) Borrellia causes Lyme disease. Carried by ticks/lice

Microbial Diversity Microbiologists have described ~5000 bacterial species – PCR indicates up to 10,000 bacterial species per gram of soil Many bacteria have not been identified because they – Have not/can not be cultured – Need special nutrients – Are a part of complex food chains requiring the products of other bacteria