Bioremediation of wastewater Flashcards
The water cycle: stress points
- precipitation
- groundwater
- runoff
- transpiration (? - arrow to tree)
- evaporation
(Shiklomanov, 1993)
Distribution of Earth’s water
1. Total global water
2. Freshwater
3. Surface water and other freshwater
- Oceans = 96.5%
saline lakes = 0.07%
saline ground-water = 0.93%
freshwater = 2.5% - glaciers and ice caps = 68.6%
groundwater = 30.1%
surface water and other freshwater = 1.3% - ice and snow = 73.1%
lakes = 20.1%
soil moisture = 3.52%
swamps and marshes = 2.53%
rivers = 0.46%
biological water = 0.22%
atmospheric water = 0.22%
Nitrogen cycle: stress points
- legumes - nitrogen-fixing bacteria in root modules
- wastage - N20
- urine runoff
- Nitrates (NO3-) runoff
Nitrogen cycle: stress points
1. Fixed Nitrogen entering STWs (Sewage Treatment Works) wasted by…
2. Insufficient crop rotation with…
3. Excessive nitrate and ammonium pollution by…
4. Carbon emissions of…
- denitrification which also releases N2O (greenhouse gas)
- legumes
- agricultural runoff
- ammonia manufacture
Haber-Bosch process (ammonia synthesis)
1. The equation for the Haber-Bosch process (ammonia synthesis)?
2. equation for steam reforming from natural gas? primary method to produce what?
3. coal gasification?
4. Energy consumption?
5. example of what used to be “green”?
- N2 + 3H2 → 2NH3
- CH4 + 2H2O → CO2 + 4H2
primary method to produce hydrogen for the Haber-Bosch process - C + 2H2O → 2H2+ CO2
- energy-intensive, accounting for 1-2% of global energy consumption, 3% of global carbon emissions and 3-5% of natural gas consumption
- Vermork hydroelectric, Norway production in Europe used to be “green”
Phosphorus cycle: stress cycle
1. compared with the other macronutrients (carbon, sulphur, and nitrogen: C, S and N), what does the biogeochemical cycle of Phosphorus (P) lack?
- What has this led to? and what is the consequence of this for modern agriculture?
- how long are high grade Pi rock reserves projected to last?
- global distribution of rock phosphate is uneven with?
- an estimated what of extracted Pi is lost due to what? and what is this detrimental for?
- lacks a gaseous atmospheric component to assist with cyclic replenishment of soils (e.g. for N: lightning, biological N-fixation, and the Haber-Bosch process)
- led to P cycle being described as “broken”.
T/F modern agriculture largely depends on non-renewable inorganic Phosphate (Pi)-based fertilisers derived from geological sources - only 50 to 150 years as mined products already show diminished Pi content and greater levels of heavy metal contamination
- most reserves present in just a handful of countries; Morocco and Western Sahara alone hold over 70% of total global reserves
- an estimated 80% of extracted Pi is being lost due to runoff, which in addition to Pi present in sewage discharges is detrimental for the environment
Atmospheric flux does exist but its not?
gaseous in the P-cycle
Dynamic changes of what phosphorus cycle from when to when?
dynamic changes of the Chinese phosphorus cycle from 1600 to 2016
what are some naturally occurring sources (of phosphorus)?
atmospheric phosphorus and inland and marine waters
anthropogenic sources (of Phosphorus)?
mining, chemical production, agriculture, animal husbandry, and human consumption
and phosphorus from trade
(Demay et al., 2023)
1. where did half of global agricultural soil phosphorus fertility derive from?
2. what does the figure in the paper provide?
3. imports have…?
4. what percentage dependency does domestic production have on mineral inputs?
5. what will future problems with mineral supply impact?
- mined mineral sources
- Structural Model of P-fluxes for any given country
- higher natural component reflecting the output from developing world
- domestic production has up to 50% dependency on mineral inputs
- food and feeds
What are the two problems with Phosphate fertilizer application?
and what is one solution?
- soluble phosphates get rapidly locked into the soil as less soluble forms (released slowly - but not all crop plants can access this)
- soluble Phosphates get applied in excess because of this but a lot is wasted in runoff
one solution: slow-release Phosphate fertilizer
What can be used as slow-release fertilizer?
Algal Polyphosphates
Is manure or sewage slow-release fertiliser?
organic manure consists largely of orthophosphate (Pi). particularly piggery manure + to a lesser extent dairy where phytate (10% of total Pi) = present along with pyrophosphate (6%) and PolyP (3%)
application of sewage sludge to agricultural soil -> contamination w/ toxic heavy metals (e.g. Cd, Cu, Zn, Ni + Pb), and toxic organic compounds + pathogens, imposing health and environmental risks
(Slocombe et al., 2020)
What is PolyP?
Where is it found/not found?
Structure and were specifically found?
PolyPs of biological origin are unbranched linear polymers of inorganic phosphate (Pi) linked by phospho-anhydride bonds and of variable chain lengths, ranging from 10s to 100s. tend to accumulate in vacuoles, or acidocalcisomes as granules
found in bacteria, fungi, and lower plants, such as algae and the mosses
absent from higher plants - although they produce organic phosphate (Po) in form of phytate (inositol hexakisphosphate) there is no evidence they produce PolyP
PolyP = very ordered structure in granules found in the vacuoles and cell walls
What can PolyP be used for?
- PolyP in form of triphosphate (TPP) - act as slow-release P-fertilizer = desirable and favours utilisation by crops and delays leaching into agricultural runoff
- Algal biomass = practical for return-to-soil, not requiring tilling or exhibiting N-volatilization or fugitive methane emissions like manures, sludge, or digestate
- Algal PolyP has potential in feeds: taken up in mammalian gut cell lines, so there could be option of using biomass for feeds
Searching for circular economic solutions
sewage pollution crisis in UK waterways ->
Poly Phosphate granules in algae can act as a slow-release fertilizer ->Phosphate absorbed from wastewater by algae can be returned to agricultural land
Microalgae have been long studied for…?
What does this mean?
sustainable wastewater treatment and have added advantage of accumulating polyphosphate granules (PolyP)
means they could be used to return Pi back to soil in slow-release form and help to close the P-cycle
What is the wastewater crisis?
wastewater and agricultural runoff pollution
what percentage of wastewater and faecal sludge is disposed of without treatment globally?
80%
on average, what percentage of high-income countries treat their domestic and industrial wastewater?
70%
in the UK, what is the estimate of nutrient losses to surface waters?
980 kt N year-1 of total dissolved N and 16 kt P year-1 of total dissolved phosphorus
STPs
Sewage Treatment Plants
STWs
Sewage Treatment Works
Current status of STPs
what have large centralized STWs introduced?
on site energy generation via anaerobic digestion of sewage sludge (to provide methane) to reduce net greenhouse gas (GHG) emissions
Current status of STPs
What is nutrient control prioritised over?
so what happens to nutrients?
recovery and reuse
comparatively little progress has been made to achieve similar efficiencies in the N and P cycles at STWs
nutrients are wasted
current status of STPs
how do STWs currently remove organic matter?
using heterotrophic bacteria but rely on nitrification/denitrification to remove N compounds, a process that is energy intensive and wastefully returns N2 (and greenhouses gases, e.g. N2O) to the atmosphere
current status of STPs
what is the estimated N2O emission rate at STWs?
4.9 tonnes of CO2-e per tonne of N removed
Current status of STPs
The process
C, N, and P taken up by bacteria are removed from wastewaters as surplus activated sludge and sent to anaerobic digesters (AD) for biogas production, where C uptake is valorized as biomethane and the N and P are released either as reactive inorganic species (ammonium and Pi) into aqueous phase (digestate liquor that returns to the head of the treatment works) or as biomass in a solid phase (digestate cake that is preferable spread on land).
complementary processes recovering both N and P from digestate liquors as struvite precipitates (NH4MgPO4*6H2O) have been implemented at industrial scale but are limited by costs associated with Mg salts and alkali needed to optimize the precipitation
Current status of STPs
1. how is P control at small STWs often achieved?
2. what is used at large STWs?
how is P removal by PAO bacteria achieved?
what is this process limited by?
- by chemical precipitation but this impedes reuse
- Enhanced Biological Phosphorus Removal (EBPR) is used with heterotrophic bacteria, called PolyP-accumulating organisms (PAO) are enriched within the activated sludge process with extended aeration
- P removal by PAO bacteria is achieved via aerobic, in-cell accumulation of large quantities of Poly-P
- this process is limited by organic C, so an expensive acetate supplement is needed
How to improve conventional wastewater processing
Processing steps for (A) conventional STW combining…
and (B) proposed substitution of these steps with…
(A) combining denitrification treatments downstream of primary sedimentation
(B) with a microalgae/bacteria consortium
How to improve conventional wastewater processing
undesirable products
- important greenhouse gases (e.g. CO2, N2O)
- energetically wasteful steps
- costly/non-renewable inputs (e.g. supplements: organic C) or wasteful outputs (e.g. N2, NO3-)
How to improve conventional wastewater processing
Some products were…
…beneficial or that can be potentially renewable, along with biogas, biofuels, and value products
How to improve conventional wastewater processing
what does downstream anaerobic digestions processes result in?
the production of methane and fertilizers
How to improve conventional wastewater processing
nutrient control and recovery from sewage is achieved via…
what does this offer?
…algal uptake, which offers a significant benefit over bacteria in that algae accumulate both N and P
How to improve conventional wastewater processing
what do the microalgae perform under some environmental/operational conditions?
perform “luxury P uptake”, defined as the uptake of P beyond that required for growth and storage of phosphate within the biomass as PolyP (>1% P dry weight)
How to improve conventional wastewater processing
how long do algae preserve their PolyP granules?
what about bacteria?
algae preserve their PolyP granules for several days, whereas bacteria tend to rapidly re-release their stored P making any scaled-up PolyP storage and processing through to fertilizer far more difficult
How to improve conventional wastewater processing
Process
standard preliminary treatment (screens, grit, sand removal, etc.) and primary clarification
-> followed by anaerobic digestion (e.g. Upflow Anaerobic Sludge Blanket - UASB reactors) + aerobic stabilisation, where a microalgae/bacterial consortium benefits from algal oxygen production + nutrient uptake in symbiosis w/ bacterial stabilisation of organic carbon compounds (e.g. HRAP)
-> resulting algal biomass can be used to enhance biogas production in existing AD digesters or applied directly as a slow-release fertilizer
(Craggs et al., 2015) (Sutherland & Ralph, 2020 (New Zealand))
HRAPs algal system for wastewater (sewage) remediation
1. what does HRAP stand for?
Example location?
- what are CAPs?
Sedimentation of? production of? what conditions?
Oxygen from what, helps what? - what is AHPs?
what can harvested algal biomass be used as? - Maturation ponds - what do algae do here?
- Rock Filter - what is this step?
- HRAPs: High-Rate Algal Ponds
New Zealand has led research into HRAPs for wastewater - CAPs: Covered Anaerobic Ponds
Sedimentation of solids. Production of biomethane. Anaerobic conditions.
Oxygen from photosynthesis helps aerobic bacteria to breakdown organic C (measured as BOD - Biological Oxygen Demand) - AHPs: Algal Harvest Ponds
Harvested algal biomass can be used as fertilizer due to high NPK values - Algae “polish” the effluent by removing nutrients (NP) down to the regulatory levels for effluent discharge
- Final removal of suspended solids prior to discharge
(Craggs et al., 2015)
Recent improvements to HRAPs for wastewater: flow
- what damaged one in Christchurch?
- where was it redesigned and rebuilt, and from what?
- what is the floor of the pond, and what was expected to happen to it?
- what was the pond depth? how is increasing depth of pond beneficial?
- what were the sides made from, and what does it protect and allow?
- what did improvements aim for?
- what was semi-circular baffles replaced with at the ends of the ponds? what does the serpentine shape improve?
- what was placed downstream of the HRAP to minimize wave action?
- earthquake
- at Cambridge from disused sedimentation pond
- sediment - expected to self-seal (low-cost solution)
- pond depth 40 cm - increasing depth of pond increases amount of wastewater that can be dealt with and reduces costs
- sides were made from textiles to protect the banks and allow mosses etc. to grow to provide further protection
- improvements aimed to improve flow uniformity, eliminate eddies, prevent scouring of the bottom of the pond (earthen base) and increase turbulent flows down the length of the channel
- replaced with teardrop shape at the ends of the pond - the serpentine shape overall improves turbulent flows (and aesthetics)
- paddle was placed downstream of the HRAP corner to minimize wave action
(Craggs, 2015) (Sutherland & Ralph, 2020 (New Zealand))
Recent improvements to HRAPs for wastewater: CO2 supply
- what is CO2 added in?
- what does CO2 increase?
- what does CO2 do to pH?
- optimally provided every…?
- what limits growth rate in summertime (New Zealand), so what was there an incentive for, and what was used?
- position of sumps…? CO2 injection sump size?
- small bubble size…?
- CO2 source…?
- what does using CO2 from biogas-powered generator exhaust require?
- CO2 as a control of predators?
- CO2 is added in a sump (deep trough below base of pond to improve CO2 dissolution as it bubble up)
- CO2 increases biomass productivity (photosynthetic efficiency)
- keeps the pH lower which prevents ammonia outgassing (when pH>9) and reduces bacteria:algae ratio
- 30 min or by pH-stat to maintain pH at 6.5-8
- CO2-provision limits growth rate, - there was an incentive to increase CO2 provision
- position of sumps is important: mid-channel reduced wind-wave action down the length of the channels, created additional mixing points to reduce laminar flow
CO2 injection sump (1.0 m wide and 1.5 m deep below the pond bottom) spanned the HRAP channel width - small bubble size is important: biogas CO2 was sparged into the bottom of the sump through six fine bubble diffuser tubes at variable flow rate
- CO2 source is relevant: biogas directly from AD was passed into the sump to remove CO2 contaminating the methane. A hood on the water surface of the CO2 sump will collect the scrubbed biogas for energy use
- Using CO2 from the biogas-powered generator exhaust requires expensive heat exchangers to cool the generator exhaust gas before using a blower and pipeline to transfer it to the HRAP site
- CO2 can control predators: nighttime CO2 asphyxiation of predatory zooplankton appears to be an effective control
(Craggs, 2015) (Sutherland & Ralph, 2020 (New Zealand))
Recent improvements to HRAPs for wastewater: algal biomass harvester
- first developed?
- at large scale, algae are harvested by?
- what is the optimal shape?
- what reduced costs in recent ponds?
- situated next to what and why?
- gravity-bases harvesting?
- first developed in the 1950s
- sedimentation
- inverted pyramid
- most recent pond employed dugout ponds rather than the concrete structure - reduced costs
- situated next to the CAP (AD) so the algal biomass could be directed there for generating biomethane
- gravity-based harvesting is slow however, can be accelerated by chemical flocculants
Alternatives to the HRAP system
1. in future, new STWs can be developed/retrofitted in places where…?
2. for instance?
3. what question is asked for these?
- space is not at a premium
- freshwater algae can be cultivated in floating modules adjacent to coastal cities for sewage treatment on the sea
- are these storm proof?
Often the challenge is retrofitting existing STWs
1. what is needed for large STWs?
2. where especially is this problem? and why?
3. what challenge is faced?
4. what must future development do?
5. what are constantly being examined?
6. example location?
- space
- especially in UK (highly populated)
- challenge is intensification: how to boost algal productivity with a restricted footprint
- future development must intensify by increasing biomass growth rates and Phosphate uptake
- new cultivation methods are constantly being examined
- Retrofit project at Summit Lake, IN, USA (Algae wheel)
Summary of wastewater remediation by HRAPs - advantages
- natural process, optimized after decades of research (1950s to present)
- future proof: combines solar UV and algal oxygen and microbial/algal detoxification
- performance is enhanced by siting next to CO2 sources
- possible to reduce costs to enable scale-up
- valorization of algal products can help with costs
Summary of wastewater remediation by HRAPs - disadvantages
- bigger the pond, less the biomass productivity and nutrient removal rates per area (less efficient mixing of culture)
- footprint is large, even if you go for many small ponds instead of one big one
- season variation in yield, latitude is a factor
- nutrient removal and synthesis of PolyPhosphate requires some improvement
- Nitrous oxide (N2O) emissions - species dependent
- Low-cost biomass harvesting still an issue
- Low take-up: stakeholders are not interested
What species for microalgae remediation?
1. what type of algae?
2. what is it dominated by?
3. others include?
4. what systems are they prominent in?
5. algal diversity in wastewater treatment?
6. microalgae are vulnerable to?
7. dominance turnover rate occurred…?
8. what can maintain consortium stability?
9. what might microalgal functional groups be more important for?
10. what is functional redundancy?
- freshwater green algae
- often dominated by non-motile, green algae from the group Chlorococcales, with genera Desmodesmus/Scenedesmus, Micratinium, Microcystis, Mucidosphaerium, and Pediastrum often reported.
- Chlamydomonas, Chlorella, Euglena
- in nature, these species are prominent constituents of microalgal communities in shallow, disturbed and highly enriched systems
- algae diversity is often low in wastewater treatment HRAPs: typically, 1-5 species dominating the community
- microalgae are vulnerable to shifts in dominance and community structure
- dominance turnover rate occurred rapidly (<1 week), suggesting that HRAP microalgae were sensitive to environmental change: light, temperature or nutrients, or predation by zooplankton grazers
- recycling some harvested microalgal biomass from the HRAP effluent back into the HRAP can maintain consortium stability
- microalgal functional groups may be more important for maintaining the integrity of wastewater treatment in HRAPs than individual species, suggesting high functional redundancy
- functional redundancy is the ecological theory that the environment selects for life forms of species that share similar roles in ecosystem functionality, rather than specific taxa
Main species for algae remediation
Micractinium
Pediastrum
Mucidosphaerium
Scenedesmus
Microcystis
- What else is in the HRAP?
- how do they effect HRAPs?
- what did grazing pressure also result in?
- what do many grazers preferentially feeding on? and what does this result in?
- what did the shift towards larger, colonial species result in, in HRAPs?
- grazers
- once established, zooplankton can quickly reduce the performance of the HRAPs, through the consumption of the microalgal biomass
- grazing pressure result in a change in the microalgal community, with smaller, more edible species, such as Ankistrodesmus sp. and Monoraphidium sp. being replaced by larger, colonial species, such as Mucidosphaerium sp, and Pediastrum sp.
- many grazers preferentially feeding on smaller microalgal and cyanobacterial species, resulting in microalgal community shifts
- In the HRAPs, shifts in the microalgal community towards larger, colonial species, resulted in improved gravity-based harvest-ability
What else is in the HRAP - grazers examples?
Rotifer
Water fleas
Copepods
Chlamydomonas fact sheet
- Chlamydomonas reinhardtii is a single-celled green alga with two long identical flagellae (‘tails’)
- belongs to the green algae (Chlorophyta) a broad group
- they tend to be green in colour because of pigments chlorophyll a and b
- because of this close connection to plants (and how easy it is to grow in the laboratory), Chlamydomonas reinhardtii has become a model lab organism
- has been called ‘green yeast’
- Chlamydomonas reinhardtii has specialised cell structure called an eyespot, which appears as an orange oval in the cell. The eyespot allows the cell to detect direction and intensity of light and move towards it
- this allows Chlamydomonas reinhardtii to seek out light for photosynthesis
- eyespot is special part of chloroplast containing pigment granules
- genetic analysis is facilitated by the existence of 2 mating types, analogous to yeast, and the advanced stages of genome sequence annotation (Salomé and Merchant, 2019)
- There are extensive collections of point and insertional mutants and gene modification by CRISPR-cas has also been reported (Guzmán-Zapata et al., 2019;Shin et al., 2019) thereby facilitating testing of gene function.
Chlamydomonas model algae species
- ideal for researching phosphate homeostasis
- PTA & PTB transporters import phosphate
- PolyP accumulates in the acidocalcisome
- ATP from the chloroplast is used to acidify the acidocalcisome and to make PolyP
- VTC is the PolyP polymerase
Synthesis and turnover of PolyP
1. where is the VTC complex (PolyP polymerase) located?
2. what does VTC complex or acidocalcisomes appear to be responsible for?
3. what does electron microscopy (TEMs) in microalgae suggest?
4. in yeast, what does synthesis and translocation by VTC into the organelle ensure?
5. what is the acidity of acidocalcisome lumen controlled by?
- at the vacuole
- responsible for PolyP synthesis in yeast (Hothorn et al., 2009) and Chlamydomonas
- Electron microscopy (TEMs) in microalgae suggest that complex at the membrane of this organelle generates strands of PolyP that are injected into the organelle (Shebanova et al., 2017)
- that PolyP is targeted exclusively to this organelle, given that it appears to be toxic in the cytosol
- the proton-pump activity of the membrane-bound H+-PPase and the V-type ATPase, where the acidic lumen facilitates cation import by proton-exchangers
Storage in acidocalcisomes
1. where are PolyP stored in both eukaryotes and prokaryotes?
2. what 5 non-exclusive features have been defined for eukaryotic organelles?
3. what do they also have the capacity to store?
4. in Chlamydomonas and Trypanosomes, where are the organelles generated?
5. Under N-stress in Chlamydomonas, what do acidocalcisomes generate and what do they appear to do?
6. What is one role of PolyP at the cell wall?
- membrane-bound organelles called acidocalcisomes
- i) presence of single PolyP granule; ii) an acidic lumen; iii) a characteristic complement of trans-membrane transporters (H+-PPase and V-type ATPase; metal cation exchangers); iv) a trans-membrane complex responsible for PolyP synthesis (e.g. VTC); v) a distinctive membrane ultrastructure under TEM which presumably relates to its individual protein/lipid composition
- Ca-storage (e.g. in Chlamydomonas sp., where Pi uptake was shown to be Ca-dependent (Siderius et al., 1996) + is important for coccolithophore formation in marine Haptophyte algae
- at the trans-face of the Golgi (Goodenough et al., 2019)
- a single PolyP granule + appear to fuse with autophagous vacuoles
- PolyP is likely to be trafficked to the cell wall by this route, where it has a role in retention of some of the periplasmic proteins
Stress and PolyP accumulation
1. what occurs at nutrient-replete (filled/well supplied) conditions (light-limited)?
2. under active growth, what must Pi be assimilated in the form of?
3. what can the synthesis of PolyP under replete conditions compete with, and why?
- many microalgae do not accumulate extensive PolyP reserves, in the absence of prior stresses
- in the form of phospholipids and nucleic acids in preparation for cell division
- growth and cell division, due to the energetics of Pi-uptake and PolyP synthesis
Stress and PolyP accumulation
Under nutrient limitation
1. what occurs as nutrients are consumed?
2. what phase does this happen in?
3. In Chlamydomonas and other microalgae, what can this stressor drive?
4. when is this accumulation observed and what is it triggered by?
5. with provided P supply is adequate, where do PolyP granules accumulate?
- as nutrients consumed, growth is restricted
- “stationary phase”
- can drive PolyP accumulation as part of the “luxury-phosphate” response
- observed in stationary phase and is also triggered by experimental depletion of N, S, Zn, or alterations in pH
- provided P supply is adequate, PolyP granules accumulate in acidocalcisomes
Stress and PolyP accumulation
1. P”over-plus” hyper-accumulation of PolyP or “overplus” requires what?
2. what is presumably a strategic adaptation in the face of fluctuating supplies?
3. Why is this phenomenon important?
- a period of starvation before resupply of Pi
- priming for hyper-accumulation, through induction of PolyP synthesis and P-uptake
- for P-remediation purposes, because it implies that uptake can be accelerated through genetic or physiological means (“conditioning”)
sequestration of heavy metals
1. what do PolyP/acidocalcisomes sequester?
2. what can microalgae therefore be used for?
3. what are negative charges balanced by?
- enzyme co-factor cations (Ca2+, Mg2+, Fe3+, Zn2+, Mn2+) and toxic metals (Al3+, Cu2+, Cd2+ etc.) in a range of organisms
- both P recovery for agriculture and removal of heavy metals which can be found in sewage, mine-workings etc.
- Ca2+ and Mg2+ ions and sometimes heavy metals in the acidocalcisome
(Pilátová et al., 2022) (Moudříková et al., 2017) (Goodenough et al., 2019)
Nitrogenous storage in many algae
what has been identified recently?
separate nitrogenous granules containing guanine have been identified in Chlamydomonas acidocalcisomes (Moudříková et al., 2017) and distinct granule forms have been visualised in these organelles (Goodenough et al., 2019)
What species for microalgae remediation?
all green algae and freshwater used
most form colonies - most have this in common
Phosphate Starvation Response (PSR)
1. what does it do?
2. what are changes in gene expression driven by?
3. increase in…
by repression of…
4. induction of…
5. increased capacity for…
increase in…
- conserve phosphate and continue uptake
- PSR1 (a Myb-type transcription factor)
- phosphate transporter protein capacity & affinity: (10-fold increase in the Vmax with a shift in Km from 10 µM to 0.1-0.3 µM)
PTA1, 3 genes and elevation of PTB 2-5, 8 genes
- peri-plasmic phosphatase activity (PHOX genes) to release phosphate from external organic sources
- PolyP synthesis
increase in gene expression of the VTC genes (PolyP polymerase) and VCX genes (vacuolar Ca-importer)
Phosphate Starvation Response (PSR)
1. P-Sparing Measures?
2. Protective measures?
3. photoinhibition?
- replacement of phospholipids with sulfolipids. Reducing copies of DNA in the chloroplast
- shifting reduced carbon into oil and carbohydrate instead of growth creating a sink for surplus photosynthetic energy
- reducing photosynthetic gene expression to avoid light stress
- what is PSR1?
- short conserved amino acid sequences bind the what?
- adjacent conserved amino acids bind?
- a myb-type transcription factor
- conserved DNA binding site (LUX)
- the DNA consensus
Testing a theory: can overexpression of PSR1 in algae improve phosphate uptake?
PSR1-venus protein fusion was over-expressed in Chlamydomonas
the venus marker is like GFP, it enables over-expression to be detected
was the overexpressed PSR1-venus protein going to the right place?
Overexpressed PSR1-venus in Chlamydomonas located to the nucleus
PSR1 overexpression accelerates P uptake
Overexpression of PSR1-venus caused a transient hyper-accumulation of PolyPhosphate
PSR1-venus over-expression targets genes that are affected by phosphate stress
(Slocombe et al., 2023)
Model for P-stress perception mechanism
1. Internal P levels detected by…
- external P levels detected by…
- other nutrient stresses (e.g. Fe-stress) could be detected by…
- PSR1 and other transcription factors can integrate…
- what can this model explain?
- a signal transduction cascade based on Inositol Phosphate kinases (yeast and algae) and the SPX proteins which block PSR1
- a Calcium-mediated signal transduction cascade in some algae (poorly understood)
- distinct signalling pathways
- the information by regulating overlapping sets of genes
- why some phosphate-regulated genes behave in different ways when the PSR1 gene is over-expressed
(Thiriet-Rupert et al., 2021)
Another stressor?
cadmium stress
PSR1 (P-starvation): a Myb
bHLH (Cre05.g241636) (Fe-starvation)
bHLH: a basic Helix-loop-helix transcription factor)
Stressor (Cadmium)
The regulatory networks overlap with Cadmium stress
Chlamydomonas
green yeast: can be grown on agar plates like yeast
can be mutated (ultra-violet light) and then screened by simple tests
Example:
mutated colonies plated on different media to look for growth differences
then sprayed with substrates such as BCIP which give a blue dye when the phosphate is removed by a Phosphatase
a mutant can be detected that fails to shut down a Phosphatase gene when Phosphite (PHI) is supplied
Summary
algae can be used to remediate waste nutrients from wastewater and then returned to the soil as fertiliser
this is a circular economy
Chlamydomonas a “green yeast” algae can be studied to improve Phosphate uptake in algal remediation
