Proteobacteria

General features of Proteobacteria, alpha Proteobacteria
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1. Proteobacteria Prepared by Dharmesh N. Sherathia CCSIT, Junagadh (BKNMU) [email protected]

2. Features of P roteobacteria

3. The Proteobacteria are a major group (phylum) of  bacteria I nclude a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, and many other notable genera Proteobacteria are Gram-negative, with an outer membrane mainly composed of lipopolysaccharides move about using  flagella , but some are nonmotile or rely on bacterial gliding The last include the  myxobacteria

4. many different shapes, to reflect the enormous diversity of morphologies and physiologies observed within this bacterial phylum In 2002, the Proteobacteria consist of more than 460 genera and more than 1600 species, scattered over 5 major phylogenetic lines of descent known as the classes “ Alphaproteobacteria ,” “ Betaproteobacteria ,” “ Gammaproteobacteria ,” “ Deltaproteobacteria ” “ Epsilonproteobacteria .

5. H abitat O rganisms that can be found in different habitats ranging from plant roots (Rhizobium and Azospirillum ) inside the cells of a host ( rickettsias ) and as free living bacteria in the environment such as Methylobacteriaum species F ound in virtually any environment across the globe S ome of the species in the phyla can survive extreme environments with very little to no oxygen.  

6. D iversity of morphological and physiological types: besides rods and cocci , curved, spiral, ring-shaped, appendaged , filamentous and sheathed bacteria occur among this phylum Most Proteobacteria are mesophilicphilic,but some thermophilic (e.g., Thiomonas thermosulfata and Tepidomonas ) and psychrophilic (e.g., Polaromonas ) representatives have been described

7. A great number of Proteobacteria are motile by means of polar or peritrichous flagella, whereas the myxobacteria (belonging to the “ Deltaproteobacteria ”) display a gliding type of motility and show highly complex developmental lifestyles, whereby often remarkable multicellular and macroscopic structures (so-called “ fruiting bodies ”) are formed

8. Most of the known Proteobacteria are free-living ; some (such as the rhizobia) enter in symbiotic associations with specific leguminous plants , where they fix nitrogen in root or stem nodules Others live as intracellular endosymbionts of protozoa and invertebrates (mussels, insects and nematodes), whereas the rickettsiae are obligate intracellular parasites of humans or mammals

9. The extreme diversity of energy generating mechanisms is a unique biochemical characteristic of the Proteobacteria : some are chemoorganotrophs (e.g., Escherichia coli), others are chemolithotrophs (e.g., the sulfuroxidizing bacteria such as the thiobacilli and the ammonia-oxidizing bacteria such as Nitrosomonas ) or phototrophs ( e.g., the purple colored Chromatium , Rhodospirillum and many others)

10. Concerning their relationship towards oxygen, the Proteobacteria include strictly aerobic and anaerobic species as well as facultative aerobes and microaerophiles Denitrifiers are reported among the “ Alphaproteobacteria ,” “ Betaproteobacteria ,” “ Gammaproteobacteria ,” and the “ Epsilonproteobacteria .

11. Types of organisms Purple Phototrophic Bacteria Nitrifying Bacteria Sulphur and Iron Oxidising Bacteria Hydrogen Oxidising Bacteria Methanotrophs Acetic Acid Bacteria Bioluminescent and Related Bacteria

12. Classification 1987, Carl Woese established- ribosomal  RNA  ( rRNA ) sequences The Proteobacteria are divided into six sections , referred to by the Greek letters alpha through zeta alpha, beta, delta, epsilon sections are monophyletic. Alphaproteobacteria , Betaproteobacteria , Gammaproteobacteria , Deltaproteobacteria , Epsilonproteobacteria and Zetaproteobacteria

13. HISTORY 1987, Carl Woese established this grouping called it the "purple bacteria and their relatives“ great diversity of forms found in this group Proteobacteria are named after Proteus Greek god of the sea Capable of assuming many different shapes, and it is therefore not named after the genus Proteus

14. G reat biological importance, as they include the majority of the known Gram negatives of medical, veterinary, industrial and agricultural interest B ecause they play key roles in the carbon, sulfur and nitrogen cycles on our planet e.g rhizobium, green purple sulphur bacteria

15. Alpha proteobacteria

16. O ligotrophic proteobacteria - those capable of growing at low nutrient levels Some have unusual metabolic modes such as Methylotrophy ( Methylobacterium ), C hemolithotrophy ( Nitrobacter ) fix nitrogen ( Rhizobium ) Members of genera such as Rickettsia and Brucella are important pathogens Many genera are characterized by distinctive morphology such as prosthecae

17. A prostheca (pl., prosthecae ) is an extension of the cell, including the plasma membrane and cell wall, that is narrower than the mature cell A stalk is a nonliving appendage produced by the cell and extending from it . Budding is distinctly different from the binary fission normally used by bacteria .

18. The Purple Non sulfur Bacteria Noxygenic photosynthesis, possess bacteriochlorophylls a or b, All purple nonsulfur bacteria are – proteobacteria (exception Rhodocyclus ) Trap light energy and employ organic molecules as both electron and carbon sources( photoorganoheterotrophs )- Nonsulfur Bacteria( do not oxidize elemental sulfur to sulfate) During absence of light- devoid colour - grow like chemoorganotrophs

19. Representatives of Purple Nonsulfur Bacteria Figure 15.6

20. P revalent in the mud and water of lakes and ponds with abundant organic matter and low sulfide levels

21. Family: Rhodospirillaceae Rhodospirillum and Azospirillum Cyst formation is unique feature of this family Cyst is for P rotect cell from dessication L ess protective against UV and heat Made in response to nutrient limitations

22. Rickettsia and Coxiella These bacteria are rod-shaped, coccoid, or pleomorphic with typical gram-negative walls and no flagella . Although their size varies, they tend to be very small . For example, Rickettsia is 0.3 to 0.5 m in diameter and 0.8 to 2.0 m long; . All species are parasitic or mutualistic.

23. The parasitic forms grow in vertebrate erythrocytes, macrophages , and vascular endothelial cells. Often they also live in blood-sucking arthropods such as fleas, ticks, mites, or lice, which serve as vectors or primary hosts. This order contains many important pathogens. Rickettsia prowazekii and R. typhi are associated with typhus fever, and R. rickettsii , with Rocky Mountain spotted fever. Coxiella burnetii causes Q fever in humans.

24. Rickettsias are very different from most other They lack glycolytic pathways and do not use glucose as an energy source, but rather oxidize glutamate The rickettsial plasma membrane has carrier-mediated transport systems host cell nutrients and coenzymes are absorbed and directly used

25. The Caulobacteraceae and Hyphomicrobiaceae These bacteria can have at least one of three different features: a prostheca , a stalk , or reproduction by budding The genus Hyphomicrobium contains chemoheterotrophic , aerobic , budding bacteria that frequently attach to solid objects in freshwater , marine, and terrestrial environments A bout 0.5 to 1.0 by 1 to 3 m- vegetative cell size Prostheca 0.2 to 0.3 um in diameter, that grows to several u m in length Budding >>>>>>>>>>>>>>>>>>>>>>>> 

26. Bud is finally released as an oval- to pear-shaped swarmer cell,

27. Hyphomicrobiaceae

28. Distinct metabolism -> Sugars and most amino acids do not support abundant growth https://www.tandfonline.com/doi/pdf/10.1080/00021369.1982.10865468 Hyphomicrobium grows on ethanol and acetate and flourishes with one-carbon compounds such as methanol, formate , and formaldehyde facultative methylotroph and can derive both energy and carbon from reduced one carbon compounds Hyphomicrobium may comprise up to 25% of the total bacterial population in oligotrophic or nutrient-poor freshwater habitats.

29. Caulobacter Possess a prostheca and holdfast Material secreted at the end of the Caulobacter holdfast is the strongest biological adhesion molecule known-superglue F reshwater and marine habitats with low nutrient levels A dhere to bacteria, and got nutrient from them Here prostheca contain only cytoplasm of cell can enlarge 10 time larger than vegetative cells Caulobacter can survive in diluted medium by enlarging their size

30. Family: Rhizobiaceae O rder Rhizobiales of the - proteobacteria contains 11 families This includes the family Hyphomicrobiaceae Important family in this order is Rhizobiaceae which includes rhizobium and agrobacterium Cells often contain poly— hydroxybutyrate inclusions . They grow symbiotically within root nodule cells of legumes as nitrogen-fixing bacteroids Live with leguminous plant symbiotically within the nodule it fix atmospheric nitrogen

31. Agrobacterium is placed in the family Rhizobiaceae but differs from Rhizobium agrobacteria invade the crown , roots, and stems of many plants and transform plant cells into autonomously proliferating tumor cells Responsible genes are located on plasmid best-studied species is A. tumefaciens, which enters many broad-leaved plants through wounds and causes crown gall disease Presence of a large Ti (for t umor inducing) plasmid

32. Nitrifying Bacteria Nitrifiers may be rod-shaped , ellipsoidal, spherical, spirillar or lobate, and they may possess either polar or peritrichous flagella Nitrifying bacteria make important contributions to the nitrogen cycle

33. most of the proteobacteria that are capable of growth at very low levels of nutrients Some have unusual morphology, including protrusions such as stalks or buds known as prosthecae . also include agriculturally important bacteria capable of inducing nitrogen fixation in symbiosis with plants, and several plant and human pathogens

34. List of microbes included in alpha proteobacteria

35. Magnetococcus marinus ability to form a structure called a magnetosome a membrane encased single-magnetic-domain mineral crystals formed by biomineralisation allows the cells to orientate along the Earth’s geomagnetic field

36. Magnetotactic bacteria (or MTB) are a polyphyletic group of bacteria discovered by Richard P. Blakemore in 1975 The biological phenomenon of microorganisms tending to move in response to the environment's magnetic characteristics is known as magnetotaxis Blakemore realised that these microorganisms were following the direction of Earth's magnetic field, from south to north, and thus coined the term " magnetotactic “

37. The MTBs can be subdivided into two categories, according to whether they produce particles of  magnetite  (Fe 3 O 4 ) or of  greigite  (Fe 3 S 4 ) Many MTB are able to survive only in environments with very limited oxygen, and some can exist only in completely anaerobic environments

38. Some types of magnetotactic bacteria can produce magnetite even in  anaerobic  conditions, using  nitric oxide ,  nitrate , or  sulfate  as a final acceptor for  electrons . The greigite mineralising MTBs are usually strictly anaerobic It has been suggested MTB evolved in the early  Proterozoic   Era

39. order: Rickettsiales Most of those described survive only as  endosymbionts  of other cells Some are notable pathogens, including  Rickettsia , which causes a variety of diseases in humans S tudies support the  endosymbiotic theory  according to which  mitochondria  and related  organelles  developed from members of this group

40. owing largely to difficulties in cultivating them The Rickettsiales has a sister order the  Pelagibacterales

41. Order: Pelagibacterales Alphaproteobacteria  composed of free-living  bacteria It was first placed in the  Rickettsiales , but was later raised to the rank of  order , and then placed as sister order to the  Rickettsiales   P elagibacter ubique  and related species are  oligotrophs —scavengers—and feed on dissolved organic carbon and nitrogen

42. They are unable to fix carbon or nitrogen, but can perform the  TCA cycle  with  glyoxylate bypass  and are able to synthesise all amino-acids, except glycine It is non- photosynthetic Possesses  proteorhodopsin  (incl.  retinol  biosynthesis) for  ATP  production from light

43. Parvularcula bermudensis Parvularcula  isolates are  Gram-negative , strictly  aerobic ,  chemoheterotrophic , slightly  motile  short rods with a single  flagellum . Colonies on marine agar are very small (0·3–0·8 mm in diameter), yellowish-brown and very hard. They are  oxidase  positive and  catalase  negative.