Bacteria: The Deinococci and Nonproteobacteria Gram Negatives Chapter 21 Bacteria: The Deinococci and Nonproteobacteria Gram Negatives

Life on Earth evolved along three major lines, called domains, all derived from a common ancestor. Each domain contains several phyla. The domains, Bacteria and Archaea, remained prokaryotic, whereas the third, Eukarya, evolved into the modern eukaryotic cell.

Aquificae and Thermotogae Thermophiles that grow at temperatures above 85° C -Aquificae and Thermotogae Figure 21.1

Phylum Aquificae Thought to be deepest (oldest) branch of Bacteria Contains one class, one order, and five genera two best studied genera are Aquifex and Hydrogenobacter

Genus Aquifex Thermophile with a growth optimum of 85°C and a maximum of 95°C Microaerophilic Chemolithoautotroph -uses hydrogen, thiosulfite, and sulfur as electron donor -uses oxygen as electron acceptor -genome ~1/3 size of E. coli

Phylum Thermotogae Second deepest branch of Bacteria Contains one class, one order, and six genera best studied genus is Thermotoga

Genus Thermotoga Gram-negative rods Thermophiles have outer sheathlike envelope that can balloon out from ends of cell Thermophiles optimum 80°C; maximum 90°C grow in active geothermal areas terrestrial solfataric springs

Thermotoga… Chemoheterotrophs e.g., Thermatoga maritima have functional glycolytic pathway can grow anaerobically on carbohydrates and proteins digests e.g., Thermatoga maritima ~24% of coding sequences are similar to archaeal genes

Figure 21.2

Deinococcus-Thermus

Genus Deinococcus Deinococcus is best studied Spherical or rod-shaped associated in pairs or tetrads stain gram-positive but do not have typical gram-positive cell wall layered outer membrane similar to gram-negatives L-ornithine in peptidoglycan lacks teichoic acid

Figure 21.3

Deinococcus… Mesophilic Mesophilc, aerobic, produce acid Extraordinarily resistant to desiccation and radiation can survive 3-5 million rad (100 rad lethal to humans) Isolated from ground meat, feces, air, fresh water, and other sources, but natural habitat unknown

Deinococcus…… Genome consists of two circular chromosomes, a megaplasmid, and a small plasmid radiation resistance due to ability to repair genome when it is severely damaged Rapidly repairs fragmented DNA within 12-24 hours when exposed to radiation D. radiodurans shown to have an efficient DNA repair system

Photosynthetic Bacteria Three groups of photosynthetic bacteria the purple bacteria the green bacteria the cyanobacteria differ from the purple and green bacteria by carrying out oxygenic photosynthesis have two photosystems use water as an electron donor and generate oxygen during photosynthesis

Bloom of Purple Sulfur Bacteria, Sulfide Spring, Madison, WI Alga Bloom of Purple Sulfur Bacteria, Sulfide Spring, Madison, WI

differences in absorption spectra correlates with ecological distribution absorption spectra of 5 photosynthetic bacteria showing the differences in absorption maxima and the contributions of various accessory pigments Figure 21.4

Taxonomy of Photosynthetic Bacteria Phylum Chloroflexi – green nonsulfur bacteria Phylum Chlorobi – green sulfur bacteria Phylum Cyanobacteria Phylum proteobacteria purple bacteria purple sulfur bacteria purple non-sufur bacteria phylum Firmicutes – heliobacteria There appears to have been considerable horizontal transfer of photosynthetic genes between the 5 phyla. About 50 genes related to photosynthesis are common to all 5 phyla.

Purple sulfur bacteria: Note the sulfur granules deposited inside the cells Green sulfur bacteria: Note the sulfur granules deposited outside the cells

Halophilic Purple bacteria Chlorosomes from green bacteria Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Purple bacteria Halophilic Purple bacteria Chlorosomes from green bacteria

Phylum Chlorobi Green sulfur bacteria Morphologically diverse rods, cocci, or vibrios; single cells, chains, or clusters

Chlorobi… Have chlorosomes ellipsoidal vesicles attached to plasma membrane contain accessory photosynthetic pigments most efficient light harvesting complexes found in nature

Chlorosomes –Green Sulfur & Green Non-sulfur

Chlorobi… Lack flagella; nonmotile Some have gas vesicles used to adjust depth of cell for adequate light and H2S Obligately anaerobic photolithoautotrophs use H2S, elemental sulfur and H2 as electron sources elemental sulfur deposited outside cell

Figure 21.5

Phylum Chloroflexi Green nonsulfur bacteria Contains photosynthetic and nonphotosynthetic members e.g., genus Chloroflexus – photosynthetic e.g., genus Herpetosiphon - nonphotosynthetic

Genus Chloroflexus Thermophilic Metabolism often isolated form neutral to alkaline hot springs grow in form of orange-reddish mats Metabolism anoxygenic photosynthesis does not use water as electron donor photoheterotroph can grow aerobically as a chemoheterotroph

Chloronema sp. on stratified Michigan Lake Chloroflexus sp.

Phylum Cyanobacteria Largest, most diverse group of photosynthetic bacteria Most obligate photolithoautotrophs; some can grow slowly in dark as chemoheterotrophs One current classification system divides group into 62 species and 24 genera

Photosynthesis in cyanobacteria Resembles that of eucaryotes have chlorophyll a prochlorophytes have chlorophyll a and b have photosystem I and II oxygenic photosynthesis

Photosynthesis in cyanobacteria… Use phycobiliproteins as accessory pigments phycobilisomes, which line thylakoid membranes, contain phycocyanin and phycoerythrin prochlorophytes lack phycobilins use Calvin cycle to fix CO2

Cyanobacterial Thylakoids and Phycobilisomes Figure 21.6

typical gram- negative contains cell phyco- wall bilin pigments site Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. typical gram- negative cell wall contains phyco- bilin pigments site of photo- synthesis nitrogen storage polymer Schematic drawing of a vegetative cyanobacterial cell. The insert shows an enlarged view of the envelope with its outer membrane and peptidoglycan. Figure 21.7 (a)

Thin section of Synechocystis during division Thin section of Synechocystis during division. Thylakoid membranes house photosynthetic pigments and ETC components. Phycobilisomes line the thylakoid membranes and contain phycobilin pigments, especially phycocyanin. Carboxysomes contain ribulose 1,5-bisphosphate carboxylase, which is an important enzyme of the Calvin Cycle. Figure 21.7b

Oxygenic Photosynthetic Bacteria Figure 21.8

Heterocysts Specialized cells used for nitrogen fixation produced when organism is nitrogen deprived differentiate from individual cells in filament involves reorganization of photosynthetic membranes thick heterocyst wall prevents O2 diffusion into heterocyst which would inactivate nitrogenase, enzyme responsible for nitrogen fixation

Heterocysts and Akinetes Figure 21.9

Prochlorophytes Cyanobacteria in genera Prochloron, Prochlorococcus, and Prochlorothrix distinguished by presence of chlorophyll a and b and lack of phycobilins are the only procaryotes to possess chlorophyll b makes them candidates as ancestors of endosymbionts that give rise to chloroplasts

Prochloron Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 21.10

Ecology of cyanobacteria Tolerant of environmental extremes thermophilic species can grow at temperatures up to 75°C often are primary colonizers Can cause blooms in nutrient-rich ponds and lakes some produce toxins Often form symbiotic relationships e.g., are phototrophic partner in most lichens e.g., symbionts with protozoa and fungi e.g., nitrogen-fixing species form associations with plants

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 21.11

Phylum Chlamydiae

Genus Chlamydia Gram-negative bacteria cell walls lack muramic acid and peptidoglycan have very small genomes Obligate intracellular parasites with unique developmental cycle involving formation of elementary body (EB) and reticulate body (RB) or initial body found mostly in mammals and birds some recently isolated from spiders, clams, and freshwater invertebrates

Figure 21.13b

Chlamydial metabolism Appear to be energy parasites, obtaining ATP from host do have genes for substrate-level phosphorylation, electron transport, and oxidative phosphorylation Reticulate bodies have biosynthetic capabilities when supplied precursors from host; can synthesize some amino acids Elementary bodies seem to be dormant forms

Important pathogens C. trachomatis C. psittaci C. pneumoniae infects humans and mice causes trachoma, nongonococcal urethritis, and other diseases in humans C. psittaci infects humans and many other animals causes psittacosis in humans C. pneumoniae common cause of human pneumonia

Phylum Spirochaetes Gram-negative bacteria with distinctive structure and motility slender, long with flexible helical shape creeping (crawling) motility due to a structure called an axial filament Chemoheterotrophs Ecologically diverse

Figure 21.14

axial filament = complex of axial fibrils (periplasmic flagella) Figure 21.15 (a1) and (a2)

Figure 21.15 (b)

Figure 21.15 (c) and (d)

Spirochete Motility current thought: axial fibrils rotate, causing corkscrew-shaped outer sheath to rotate and move cell through surrounding liquid Figure 21.16

Symbiotic Associations Broad range of organisms Found in a variety of locations, for example hindguts of termites digestive tracts of mollusks and mammals oral cavities of animals

Spirochete-Protozoan Associations Figure 21.17