Lecture 2 - the global impact of microbes 2 Flashcards
what are the challenges facing the human population in the 21st century?
-climate change
-energy production
-food security and sustainability
- man made damage to the environment
what is climate change?
consequences of increases in gases that trap heat that would otherwise escape into space the resultant natural cooling of the earth.
what are the main protagonists?
-CO2, methane (CH4), N2O
-Resulting in significant and rapid changes to both marine and terrestrial environments
how is microbial activity important in climate change?
Reduction of these gases
Fix CO2
Increasing CO2, CH4 and N2O emission as consequence of their metabolism
Impact of these changes on microbial populations not widely considered
what are the 3 types of organisms on earth that fix CO2 using oxygenic photosynthesis to generate biomass?
These are plants, algae and photosynthetic bacteria known as cyanobacteria
what are cyanobacteria?
-Pigmented for optimal light absorption
-Found in freshwater and marine environments as part of the phytoplankton
-Responsible for up to 50% of global C02 fixation
-Cyanobacteria are photo autotrophs fixing carbondioxide in 2 stages.
what are the 2 parts of CO2 fixation?
-generation or energy and assimilated of CO2 through the Calvin cycle
how does the carbon fixation process work?
This is done via photexcitation of chlorophyll that is found concentrated in specialized regions in the bacteria known as thykalod bodies.
The energy captured by the chlorophyll in a redox reaction that results in the splitting of water to produce molecular oxygen, electrons and protons.
The electrons are transferred within the cell membrane and are used to reduce NADP to NADPH, while the protons are retained, resulting in the development of a proton motif force that is necessary to drive ATP synthesis
Both NADPH and ATP are required for the assimilation of C02
what does enzyme RuBisCO bind to
Enzyme RuBisCO (Ribulose-1,5-bisphosphate carboxylase) binds the C02 in specialized micro compartments called carboxysomes in which C02 is concentrated
what is the impact of climate change on oceans?
Optimal absorption of light – achieved by by inflating and deflating gas vesicles in the cytoplasm
Rising temperatures-
Affect water salinity (melting of arctic shelf)
Winds/temperature
-Stratification, mixing and water circulation
-Optimal absorbance of light in infrared spectrum (725-1025nm)
-May increase/decrease phytoplankton growth
Increase in surface runoff of nutrients
Fe, NO3- ,PO4 in commercial fertilizer’s
Likely to influence composition, location and existence of these important marine based carbon-fixing microbial communities
what organism is evidence of climate change
Cyanobacteria blooms which are Huge mat like structures of organisms – reflect rapid growth.Availability of nutrients/sunlight/heat/loss of stratification
what are the concerns about cyanobacteria blooms?
2 major concerns:
Biochemical Oxygen Debt
Oxygen depletion
O2 usage associated with C02 fixation
resulting from decomposition of dying cyanobacterial blooms
Dead material limits light penetration
Impact on aquatic life
By-products of growth
Capacity to release metabolites produce affect taste and quality water
produce toxins – health implications
what is the dead zone in the Gulf of Mexico?
Unbalanced blooms of this type has significant impact.
For example, Every summer drainage from Missisippi basin releases high concentrations of organic carbon and nitrogen from farmland into the river, causing blooms and crashes of cynaobacterial growth leading to hypoxia in the water and death of thousands of fish.
So, whilst these bacteria play a key role in carbon capture, this demonstrates how such cycles are finely balanced and how our actions we are destroying the equilibrium.
what are other microbial fixers of CO2?
Facultative anaerobic purple bacteria-
fix C02 using the Calvin cycle. Energy derived from light and oxidation of inorganic compounds rather than O2
Lithoautotrophs-
Largely fix C02 under anaerobic conditions generating their energy through the oxidation of compounds such as hydrogen sulphide
Both use RuBisCo – like homologues to capture CO2.
What are lithotrophs?
-Lithotrophs in contrast to photosynthetic bacteria fix carbondioxide by deriving the energy needed to drive this cycle through the oxidation of inorganic minerals alone.
In the case of some organisms, oxidation of sulphur compunds results in the production of strong acids that can corrode masonary and concrete causing significant structural damage to buildings – hence why these organisms have been nick named the rock eaters
Other examples of bacteria that fix Co2 include green sulphur phototrophs, however these organisms like C02 fixing members of the archea use pathways other than the calvin cycle for CO2 assimilation
how is carbon cycling a chained event?
Cycling of carbon within the environment is a chained event. Although C02 is fixed to generate glucose which is then used as building block of the majority of organic material, its subsequent breakdown will results in the release of CO2.
In nature, the majority of organic material decay and destruction is performed by microbes
how do CO2 fixing organisms play a central role in oceanic food webs
So whilst the majority of C02 is fixed by plants, algae and bacteria, the biomass built up by these primary fixers are subsequently consumed by primary grazers, which in the oceans include the small crustacea of the phytoplankton. These organisms oxidised the fixed carbon to generate energy via respiration, releasing C02 back into the atmosphere or assimilate this material during central metabolism into other complex molecules.
Small crustacean are then consumed by predators and more of the fixed carbon is used for respiration or in the development of complex structures. Unlike the carbon fixers, which are known as autotrophs, these consumers of organic material for the generation of energy are known as heterorganotrophs.
However, the death and subsequent decomposition of all forms of life releases organic material which ultimately results in the release of this captured carbon in the form of CO2.
what is the role of marine environment as a carbon sink?
In this context, the marine environment has played a crucial role as a carbon sink, absorbing more C02 than it releases
This is because the sea not only provides a suitable environment for Co2 by photosynthetic bacteria, it also can absorb C02 directly, and as a consequence of its depth many animals whch die decompose at depths at which complete oxidation of carbon compounds by aerobic bacteria is limited.
Over millions of years compression of this carbon from such organic material has resulted in the production of hydrocarbons that we recognized as fossil fuels today
how are the mechanisms of CO2 release into the environment?
So, the fossil fuels burnt today is actually realeasing carbon that was captured from the environment millions of years ago, leading to a huge in balance in this cycle
However, this is not the only issue.
Increasing global temperatures are causing the unfreezing of carbon trapped in permafrost regions of the world such as the Russian tundra. Consequently, microbes that previously is also enhancing microbial decomposition of carbon based material in the soil. Includes aerobic and anaerobic destruction of carbon-based material that results in the release of CO2.
what is the role of symbiosis in digestion in the termite gut?
Production of methane not limited to mammals. Insects such as termites also produce C02 and Ch4 during their digestion of their Main food source – wood.
Termites are interesting though as the – wood digesting bacteria – are found within the eukaryotic protist Mixotricha paradoxa –that is located within the gut of the termite.
This protist contains several bacterial endosymbionts which digest the lignin in the wood to generate acetate that can be ultilised by absorbed by termite. H2 and Co2 generated during this conversion are then used by methanogens to make methane
how can the use of microbes be used to help Clean out planet?
Well it has been long recognized that microbes have an amazing metabolic capacity that has allowed them to adapt use a huge range of complex carbohydrates as sources of energy.
It was the dutch microbiologist Van Niel who hypothesized that ‘every molecule that exists in nature can by used as a source of carbon or energy by micro-organisms’
how do contaminated sites provide opportunities for microbial enrichment?
eg is the Deep Horizon Oil Spill in Gulf of Mexico in 2010
-Resulted in release of over 4.9 million barrels of oil
-Impact on local ecology was massive
-Enriched for microbes that can catabolise compounds found in oil.
what about man made plastics?
But what about manmade plastics which were once considered to be non-biodegradable?
One of the most prevalant man made plastics in the environment today
polyethylene tetrepthalate or PET which is a polymer of polyethlene esters which has been made since the 1970s and is commonly used in the production of plastic bottles.
We are increasingly aware of its contamination of the environment, following destruction and fragmentation of this material.
Previously throught to be impossible to biodegrade, some hope was provided in 2016 when Sosuke Toshida and colleagues from Japan reported the isolation of a bacterium from a the soil of a bottle recycling plant that was able to degrade PET.
Using genomic sequencing he showed that the bacterium encoded an hydrolase enzyme which showed similarity in structure to hydrolase enzymes found in the guts of mammals that break down complex carbohydrates from our diet. By cloning this gene and expressing this enzyme has a recombinant protein he was able to confirm this activity.
He subsequently showed that the bacterium had a second enzyme was present that broke down the PET monomer releasing compounds that could eventually enter the TCA cycle to produce energy.
Such reports have envigorated this area of research and encouraged others to use similar approaches to look for organisms that can detoxify other poisons that contaminate our environment.
It also strongly underlines the flexibility and adaptability of microbial life
how are biofuels made?
Biofuels are defined as fuels produced from biological material. Currently, this mainly describes bioethanol production which results from the fermentation of plant based sugars by microbes.
Whilst burning of biofuels does not reduce the total amount of C02 released during combustion its release is considered to be carbon neutral as the carbon released is only equivalen that fixed by the plants used in the fermentation process … so this is not releasing it from ancient sources as occurs when fossil fuels are used
Still produce CO2 but carbon neutral
carbon fixed by plants = carbon used as fuel
what are the advantages of bioethanol production?
-Renewable source of energy
-Carbon neutral
-Can be used alone or can be mixed with other liquid fuels
what are the disadvantages of bioethanol production?
-Plate vs Energy debate-In order to use plant material for this process, it must be grown
-Use of land and loss of foodstuff in production
-Production requires an input of energy
-Bioethanol can be damaging in non compatible fuel systems
1970 Brazil began commercial production of bioethanol from sugar cane
Now >46% of world supply
14.5 billion litres per year
what are feedstocks for ethanol production?
Easiest; Sugar crops: sucrose, Beet and cane
Harder ;
Starch crops
Grain: maize (corn), barley, wheat, rice, etc
Roots and tubers: cassava, potatoes
Problem: require energy-consuming hydrolysis processes
Hardest
Lignocellulosic material
Switchgrass, Miscanthus
Willow, Poplar
Require even greater processing
And energy input!
what is the industrial process of the production of ethanol?
This shows the different manufacturing processes required using the 3 different plant substrate demonstrating that whilst sugar cane can be used directly that both corn and substrates with high content of complex carbohydrates require additional steps that require time, energy input and additional equipment, highlighting why cost of production with these substrates is currently high.
how can this be used for genetic engineering
Re-engineered microbes - to express enzymes involved in simultaneous saccharification and fermentation of lignocellosic material
This development in consolidated bioprocessing may have important implications for the cellulosic ethanol industry
what are the changing faces of carbon emissions?
Whilst burning of fossil fuels remains a major cause of C02 emissions, there has also been a global increase in the release of carbon as a consequence of biological activity. In particular, the thawing of the permafrost in places like Siberia, offers opportunities through the release of C02 or methane as a consequence of microbial degradation. In addition, changes to farming practices around food security is significanty leading to higher levels of methane in the environment.
As you can see from this figure sources of green house gases produced from biological sources far outstrip those from burning of fossil fuels.
So I hope you can see that microbes are playing a key role in carbon return to the atmosphere and global warming however this is very much being influenced by mans activities
what is in the mammalian gut?
Enzymes that allow breakdown of many complex carbohydrates frequently absent
Harvest of energy depends on symbiotic relationship with gut microbes
Primary degraders
Secondary fermentation, by–products of which include CO2 and H2
One of the endpoints of microbial activity is methane (CH4)
