Team:Valencia/cultures

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Cultures:

Chassis growth and metabolism

Here we aim to experiment with the chemical conditions of growth media for our chassis organisms, in order to assess the best conditions for maximum growth and best metabolic response of their biomachine functions.

Growth media experimental array:

Original media for our chassis:

• BG11: Classical medium for freshwater cyanobacteria, without organic carbon neither nitrogen sources, rich in micronutrients for the development of photosynthetic apparatus.





• TCBS: Thio-Citrate-Bile-Salts, selective medium for Vibrionacean gamma-proteobacteria, rich in organic nitrogen sources such as peptone, and sucrose as carbon source. Ox bile and other reagents prevent the growth of enteric bacteria.

Media to test:

• COMPO (commercial plant fertilizer diluted in water)
• BG11
• BG11+NaCl (200,250,300mM): Salt is an essential component for the growth of A. fischeri, and necessary to activate the cscB transporter protein.
• BG11+NaCl(200,250,300mM)+20g/l Sucrose: A basal quantity of sucrose can be useful to start off growth of A. fischeri, and can be interesting in terms of osmotic response of cscB sucrose export.
• TCBS
• Marine broth/agar: Basic medium for heterotrophic marine bacteria, such as A. fischeri
• Marine broth/agar + micronutrients: Could be a solution to sustain both autotrophic and heterotrophic cultures, in salty conditions to induce sucrose export.
• BG11+NaCl250mM+20gl Sucrose+10g/l Peptone+5g/l Yeast extract: Includes not only carbon but also nitrogen sources to help A. fischeri grow, besides BG11 micronutrients for cyanobacterial development.

Conditions: Swirling broth/agar plates for each medium
Chassis to test: S. elongatus WT, S. elongatus cscB, S. elongatus cscB + psbA-cI-luxI construct, Aliivibrio fischeri.

Basic coculture:

Once found the ideal medium where to grow both cscB S. elongatus with A. fischeri, we’d set an array of coculture dispositions:

• Mixed populations: Agar plates and broth
• Biphasic broth (membrane separated): 0.45microns pore (minimal to retain cells, full exchange of molecules including AHL), dialysis semipermeable membrane (only sucrose, water, ion and gas exchange; no AHL).

Analyze in each case (for chassis, medium, and disposition) a temporal series for:

• Growth curves using a photometer at different wavelengths of optical densities
• For S. elongatus cscB:


• Export of sucrose (saccharase and Fehling’s reagent, analysis in colorimeter; or clinical glucometer) with IPTG induction at different salt stress and growth phases.
• Night production of AHL in the transformed strain at different sucrose export rates and growth phases (analysis by co-elution in HPLC). Residence time of AHL in the liquid medium and degradation half-life (24h light controls).



• For A. fischeri:


• Consumption rate of sucrose (saccharase and Fehling’s reagent, analysis in colorimeter; or clinical glucometer) at different growth phases.
• Luminescence of A. fischeri (in a luminometer) at different conditions of initial sucrose concentrations, growth phase and external inputs of AHL (synthesized by our transformed E. coli).
• Qualitative luminescence test under ‘natural’ conditions: “Marine Snow Experiment”, placing a colony growing on a small lump of agar, in a sea water solution, emulating a marine snow particle colonized by A. fischeri. Mechanical stimulation is known to trigger bioluminescence in this kind of aggregates at the marine environment, which we imitate by shaking.

[Further developments: As an idea for improving our system’s biosafety, we could induce auxotrophic artificial symbiosis knockouts in S. elongatus and A. fischeri, by extraction of genes responsible for the synthesis of determined aminoacids, where each partner synthesizes the one that the other lacks. This reduces the chances of contamination of the natural environment, as hardly ever organisms from both culture modules could escape simultaneously and be able to stay together to survive].

[Further developments: We realized our photosynthetic sucrose exporter bioreactor can have a wide spectrum utility by itself, when connected to a diffusion membrane system. Mechanical standardization of the S. elongatus cscB module as a Powercell (Brown-Stanford 2011 iGEM), would have application as a solar-powered energy donor to feed other heterotrophic cultures from any kind of biotechnological industry, which normally use Saccharromyces cerevisiae or E. coli, which grow well with sucrose as a carbon source].

Results:

Key:

• + = Grown
• - = Not grown

(Note: 2 replicates were done to assure the result obtained.)

Growth of cscB S. elongatus:

• BG11 broth: ++
• BG11 agar: --
• COMPO broth: -+
• COMPO agar: ++
• BG11+200mM NaCl broth: +-
• BG11+250mM NaCl broth: ++
• BG11+300mM NaCl broth: +-
• BG11+250mM NaCl agar: --
• BG11+250mM NaCl+20g/l Sucrose+10g/l Peptone+5g/l Yeast extract broth: --
• BG11+250mM NaCl+20g/l Sucrose+10g/l Peptone+5g/l Yeast extract agar: --

Growth curve of S. elongatus cscB (growing on BG11+250mM NaCl – pH 8.9) and S. elongatus WT, growing on BG11 – pH 7.4, linear regression on OD750 (wavelenght wich Chlorophyl A takes up light) and OD630 (wavelenght which measure celular density) from spectrophotometric readings:

(fig 1, 2)

Fig 1: At ʎ=750 nm, to measurements Chlorophyl A concentration
conteined in bacterial membrane, S. elongatus showed higher values due
to their population, bigger than S. elongatus WT. We got the expected results,
because Chlorophyl A concentration increase when bacterial population grow.



Fig 2 : At ʎ=630nm, we wanted to measure population density, and
S. elongatus WT exhibited lower growth than S. elongatus cscB, because
cscB strain grew faster than WT strain. Furthermore WT strain died at second day.

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