N,S cycling

Question 1

assimilative reactions - give example

Answer 1

nutrients are incorporated into the biomass of an organism - assimilatory NO3 reduction –> NH4, requires assimilatory nitrate reductase

Question 2

T/F - nitrate reductase is only single enzyme

Answer 2

false - nitrate reductaste can be assimilatory or dissimilatory

Question 3

dissimilative reactions

Answer 3

when compounds are reduces as terminal e acceptors in energy metabolism - dissimilatory NO3 reduction —>N2
requires dissimlatory nitrate reductase

Question 4

denitrification

Answer 4

dissimilatory reaction, oxidized N compounds is e acceptor in energy metabolism

Question 5

what is oxygen requirements of denitrifiers

Answer 5

most are facultative aerobes - prefer to use o2

Question 6

where do most denitrfication reactions happen

Answer 6

anoxic environments

Question 7

is e. coli a denitrify?

Answer 7

no - it can do the first step (nitrate to nitrite), but can’t do the rest

Question 8

what are all the steps of denitrificaitions

Answer 8

no3 –> no2 –> NO –> N2O –> N2

last 3 are gasses

Question 9

what are the practical imlications of N cycle rxns

Answer 9

n2 fixation
ammonifixation
nitrification
denitrification
agriculture practices

Question 10

n2 fixation

Answer 10

converts unusable n2 to combined N (eg. ammonia)

Question 11

ammonification pros and cons

Answer 11

releases NH4+ for subsequent use in new biomass [good]
NH4+ is most efficient form of inorganic N for incorporation
NH4 is cationic, thus held in soil (clay) [good]
some NH3 loss from soilt o atmosphere [bad]

Question 12

NH4+ positives

Answer 12

hangs out in soil surface, and when it rains, it won’t get washed down below root zone

Question 13

empirical formula for biomass

Answer 13

C106H263O110N16P

Question 14

true/false - atmosphere is a major reservoir for nitrogen

Answer 14

true, 80% nitrogen but this isn’t usable by most organisms

Question 15

n2 fixation

Answer 15

conducted by relatively few prokaryotes that use nitrogenase complex (enzyme)
vital to life
makes nitrogen more readily usable
N2 –> NH3 + H2

Question 16

what is the oxidation state of organic N, ammonia, nitrogen gas, and nitrate?

Answer 16

-3, -3, 0, +5

Question 17

what are the major steps in the biotic nitrogen cycle?

Answer 17

N2 fixation
mineralization
anammox
assimilation
nitrification
denitrification

Question 18

PICTURE

Answer 18

picture answer

Question 19

nitrification

Answer 19

NH4+ + 2H2O –> NO2- + 8H+ + 6e-
NO2- + 2H2O –> NO3- + 2H+ + 2e-
nitrosomonas
nitrobacter

Question 20

denitrification

Answer 20

NO3- –> N2

bacillus, parcoccus, pseudomonas

Question 21

types of nitrogen redox reactions listen by # of prokaryotes who perform the reaction (most to least)

Answer 21

n2 fixation > denitrification > nitrification > ammonification

Question 22

nitrogenase complex function and feature

Answer 22

n2 fixation
o2 sensitive and subject to strict regulatory control by combined N
N2 + 8H+ + 8e- –> 2NH3 + H2

Question 23

what is the site of reduction for dihydrogenase

Answer 23

FeMo-co

Question 24

examples of nitrogen-fixing microorganisms

Answer 24

symbiotic (mutualisms)
free-living aerobes
free-living anaerobes

Question 25

examples of symbiotic nitrogen-fixing microorganisms

Answer 25

legume-rhizobia symbioses - soybeans, clover, alfalfa with rhizobial bacterium, and actinorhizal plants like alder trees

Question 26

examples of free-living nitrogen-fixing aerobes

Answer 26

chemoorganotrophs including Azotobacter, klebsiella, methylcoccus, and other phototrophs: many cyanobacteria, chemolithotrophs: alcaligenes, some thiobacillus and others

Question 27

examples of free-living nitrogen-fixing anaerobes

Answer 27

chemoorganotrophs inlcuding clostridium, desulfovibrio and phototrophs including chromacium, thiocapsa, chlorobium, rhodospirillium, and chemolithotrophs - methanosarcina, methanococcus and other methanogens

Question 28

heterocyst

Answer 28

modified cells found in certain filamentous cyanobacteria | lack photostem II (and thus do not produce O2) but possess nitrogenase and can conduct N2

Question 29

symbiotic n2 fixation - steps in the formation of a root nodule in a legume infected by rhizobium

Answer 29

1. bacterium attaches to root hair 2. root hair curls around bacterium forming shepherd's crook 3. infection thread forms and bacteria replicates 4. infection thread extends into root cortex as root cells divide 5. infection thread branches, bacteria enter cell walls, lose their cell walls, and become n2-fixing bacteria 6. nodule consisting of plant cells is stimulated to grow by infecting bacteroids

Question 30

flavanoid

Answer 30

class of plant and fungus secondary metabolites

Question 31

how is root curling induced by rhizobium in n2 fixation

Answer 31

plant excretes flavanoids, attracting rhizobia, incuding nod factor synthesis bacterial signalling molecules (nod factors) control nodule formation (eg root cell formation)

Question 32

what is the major carbon compound metabolized by bacteria as they fix nitrogen?

Answer 32

C4 dicarboxylic acids (succinate, fumarate, malate)

Question 33

bacteroids

Answer 33

rhizobial cells transformed into swollen, misshapen branched shapes within the plant cell, possess nitrogenase activity, incapable of cell division

Question 34

symbiosome

Answer 34

single or small groups of bacteroids surrounded by portions of plant cell membrane n2 fixation begins after symbiosome formation

Question 35

leghemoglobin

Answer 35

o2-binding protien supplies o2 to bacteroid and protects nigtrogenase from o2 inactivation synthesis requires input from the plant and the bacterium Lb delivers bound O2 directly to bacterial ETS, protects nitrogenase complex from O2 damage

Question 36

how does the exchange of C and N compounds between bacteria and plants work?

Answer 36

C4-dicarbozylic acids are taken up by bacteroids in plant cytoplasm to enter into TCA cycle to make ATP, then the ATP and electrons that are generated are used by nitrogenase to convert nitrogen gas into ammonia (nitrogen fixation), ammonia is then used by bacteroids to make amino acids excess ammonia used by plants to make ammonium

Question 37

ammonification

Answer 37

RNH2 --> NH3 (NH4+) production of ammonia during the decomposition of organic nitrogen compounds conducted by wide range of aerobes, anaerobes

Question 38

what is ammonification like in oxic conditions?

Answer 38

some NH3 volatilization to atmosphere (favoured by dark, alkaline soil) assimilation by plants, microorganisms, production of new biomass NH4 subjected to nitrification

Question 39

what is ammonification like in anoxic conditions?

Answer 39

NH4+ tends to be stable and persist (exception anammox - anoxic ammonia oxidation; occurs in some ammonia rich habitats such as sewage)

Question 40

what environment conditions are good for nitrification?

Answer 40

well-drained, neutral-pH soils, aquatic environment

Question 41

what type of metabolism should a microbe have for nitrification?

Answer 41

aerobic, chemolithotrophic