Bacteria: The Low G + C Gram Positives Chapter 23 Bacteria: The Low G + C Gram Positives

Low G + C Gram-Positive The phylum Firmicutes divided into 3 classes Mollicutes Clostridia Bacilli

Figure 23.1

Class Mollicutes (The Mycoplasmas) Lack cell walls and are pleomorphic cannot synthesize peptidoglycan precursors penicillin resistant sterols may stabilize plasma membrane most nonmotile; some have gliding motility smallest bacteria capable of self-reproduction

Table 23.1

Figure 23.3

Growth of Mycoplasmas

Figure 23.4

More about Mycoplasma Genomes less than 1000 genes one of the smallest found in procaryotes

Metabolism of Mycoplasmas Chemoorganotrophs some produce ATP by glycolysis and lactic acid fermentation some catabolize amino acids and urea some have functional pentose phosphate pathway none have complete TCA cycle deficient in a number of biosynthetic pathways

Important pathogens Mycoplasma mycoides – bovine pleuropneumonia in cattle Mycoplasma gallisepticum – chronic respiratory disease in chickens Mycoplasma hyopneumoniae – pneumonia in swine Mycoplasma pneumoniae – primary atypical pneumonia in humans Ureaplasma urealyticum – premature birth, neonatal meningitis and pneumonia spiroplasmas – pathogenic in insects, ticks, and a variety of plants

Bacillus and Clostridium Production of endospores is a hallmark of the key genera Bacillus and Clostridium. Gram-positive Bacteria are major agents for the degradation of organic matter in soil, and a few species are pathogenic.

Endospores Have a complex structure containing a coat, cortex, and inner spore membrane surrounding the protoplast Dipicolinic acid is present Heat resistant dormant and viable for long periods of time

Figure 23.6

Class Clostridia

Genus Clostridium Fermentative metabolism ferment amino acids using Stickland reaction oxidation of one amino acid using another as electron acceptor

Important species of Clostridium C. botulinum – food spoilage (especially canned foods); botulism C. tetani – tetanus C. perfringens – gas gangrene C. acetobutylicum – manufacture of butanol

Figure 23.7

Figure 23.8

Class Bacilli Large variety of gram-positive organisms Contains two orders, Bacillales and Lactobacillales , 17 families and over 70 genera

Bacillus subtilis Used as model organism for cellular differentiation, division and other processes Its genome was one of first to be sequenced has families of genes expanded by gene duplication 10 integrated prophages or remnants of prophages Various species produce antibiotics

Other important species of Bacillus B. cereus – food poisoning B. anthracis – anthrax B. thuringiensis and B. sphaericus – used as insecticide parasporal body – solid protein crystal that contains toxin

Figure 23.9

endospore parasporal body Figure 23.10 (a) An electron micrograph of B. sphaericus sporulating. The parasporal body is just beneath the endospore. Bar=400nm. Figure 23.10 (a)

Genus Thermoactinomyces Historically classified as actinomycete More recently, phylogenetic analysis places it with low G+C microbes in order Bacillales, family Thermoactinomycetaceae Commonly found in high temperature environments such as composts

Figure 23.11

FamilyStaphylococcaceae Facultatively anaerobic, nonmotile, gram-positive cocci Usually form irregular clusters Normally associated with warm blooded animals in skin, skin glands and mucous membranes

Figure 23.13

Pathogenic Staphylococcus Staphylococcus epidermidis common skin resident sometimes responsible for endocarditis and for infections of patients with lowered resistance e.g., wound infections, surgical infections, and urinary tract infections

Antibiotic Resistant Staphylococci Resistance to methicillin Methicillin-Resistant Staphylococcus aureus (MRSA) obtained from genetic elements received from other organisms Resistance to vancomycin, the “drug of last resort”

Staphylococcus aureus Produces the virulence factor coagulase causes blood plasma to clot Produces a-hemolysin toxin which lyses cells major cause of food poisoning recently >1,000 school children in Texas had staphylococcal food poisoning caused by eating improperly handled chicken Found on nasal membranes and skin, and in gastrointestinal and urinary tracts

Order Lactobacillales Also called lactic acid bacteria Morphologically diverse nonsporing usually nonmotile Ferment sugars for energy lack cytochromes fastidious contains several important genera

Order Lactobacillales Largest genus - Lactobacillus grow optimally in slightly acidic conditions (pH 4.5 to 6.4) carry out either homolactic fermentation (via glycolytic pathway) or heterolactic fermentation (via pentose phosphate pathway)

Genus Lactobacillus Widely distributed in nature on plant surfaces in dairy products, meat, water, sewage, beer, fruits, and other materials normal flora of mouth, intestinal tract, and vagina usually not pathogenic

Figure 23.14

Importance of lactobacilli Fermented vegetable products (sauerkraut, pickles, and silage) Fermented beverages (beer, wine, juices) Sour dough bread Swiss cheese and other hard cheeses yogurt Sausages spoilage of beer, milk, and meat

Streptococci Lancefield grouping system – based on polysaccharide and techoic acid antigens in cell wall or between cell wall and plasma membrane nonmotile facultative and strict anaerobes homolactic fermentation

a-hemolysis b-hemolysis Table 23.5 incomplete lysis of red blood cells seen as greenish zone around colony on blood agar b-hemolysis complete lysis of red blood cells seen as clear zone around colony on blood agar

Figure 23.17

Enterococci and lactococci

Figure 23.18

Important streptococci, enterococci, and lactococci Streptococcus pyogenes – streptococcal sore throat, acute glomerulonephritis, and rheumatic fever Streptococcus pneumoniae – lobar pneumonia and otitis media Streptococcus mutans – dental caries Enterococcus faecalis – opportunistic pathogen (urinary tract infections and endocarditis) Lactococcus lactis – production of buttermilk and cheese