Synechococcus PCC 7002 - bicarbonato

8/17/2019 Synechococcus PCC 7002 - bicarbonato

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Effects of Sodium

Bicarbonate on Biomassand Carbohydrate

Production in Synechococcus PCC

7002

Carlos Eduardo

de Farias Silva

Fellowship granted by CNPq –

Brazilian Ministry of Education

Carlos Eduardo de Farias Silva*a, Barbara Grisa,

Eleonora Sforzaa, Nicoletta La Roccab, Alberto

Bertuccoa a Dept of Industrial Engineering, University of

Padova, Italy.b Dept of Biology, University of Padova, Italy.



Introduction Microalgae and

cyanobacteria:

Photosyntheticmicroorganisms

Biomass production;

Nutraceutical compounds;

Natural colorants;

Pharmaceutical compounds.

BIOFUELS

Biodiesel (lipids) ;

Biogas; Biohydrogen;

Bioethanol (carbohydrates).

eukaryotic

prokaryotic

Introduction

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Nutrients are needed for cultivation (C,N,P)



Introduction

Costs of CO2 supply are related to technological aspects ofcapturing, compressing, transportating, temporary storing and

loss of gas (Chi et al., 2011), and can reach up to 50% ofbiomass production costs (Chisti, 2013). Bicarbonate salts canbe used instead of CO2.

Bicarbonate solubility (> 90 g/Lat 25°C), makes it attractiveand more efficient than CO2 incarbon management andenergy consumption.

Not all microalgal species are

capable to grow in highconcentrations of bicarbonate(Substrate Inhibition – OsmoticImbalance). Cyanobacteria aregood candidates.

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Aim of the work

General:

To exploit sodium bicarbonate to grow thecyanobacterium Synechococcus PCC 7002.

Specific:

To study

Biomass Productivity;

Carbohydrates Accumulation;

Kinetic of bicarbonate absorption and cell growth.

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−



Species:

Material and Methods

Synechococcus PCC 7002

Sodium Bicarbonate

Concentrations

5.5 and 88 g/L.

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Operating Conditions: 100 µE m-2 s-1;

Basal A medium (Bernstein et al.,

2014);

Temperature at 28°C;

pH 8.5;

250 working-volume glass bottles.

Analysis: Cell concentration by optical density

at 750 nm;

Dry Weight by gravimetry;

Carbohydrates by Antrhone Method

(Morris, 1948);

Nitrate, Bicarbonate and Phosphate

(APHA, 1992).



Synechococcus PCC 7002

Growth Curves and Rates

Results: Cultivation

Substrate Inhibition

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Sodium Bicarbonate Concentration g/L

22 g/L88 g/L

44 g/L

5.5 g/L

11 g/L

Osmotic Stress



Biomass Production

Sodium Bicarbonate Concentration g.L-1

Bicarbonate Sodium

Concentration (g L-1)

Productivity

(g L-1 day-1)

Days to reach

stationary phase

5.5 0.44 3.6

11 0.48 3.7

22

1.12

3.3

44 0.91 6.6

88 0.62 9.8

Higher Productivity

Using bicarbonate is an efficient approach to produce biomasswith this cyanobacterium.

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Probably, loss of cabon asCO2



Bicarbonate Wasted

Considerable lost of cabonas CO2

()

∗

− +

− 2+

(pK1 = 3.6, pK2 = 6.3 pK3 = 10.3)

CO2-Bicarbonate-Carbonate Equilibrium

The automatic pH control (by adding acid) shifts theequilibrium to the left and a quantity of bicarbonate is lostas CO2.

The bicarbonate lost was more visible in the experimentat 88 g/L since a typical Yield Yc/x is 0.5.



Carbohydrate Production

It is known that Synechococcus

sp. can accumulate up to 50%(% DCW) of carbohydrates with

CO2 as a carbon source(Mollers et al., 2014),


Bicarbonate Sodium Concentration g/L

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Using bicarbonate is an efficient approach but not enough toproduce high amounts of carbohydrates.



Model of Substrate Consumption andSynechococcus Growth

Kinetic Model

=

(Bicarbonate Consumption)

(1)

= µ

(Growth)

(2)

µ = µ .

(3)

Mass Balance6.9 g sodium bicarbonate →

1 g biomass


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Substrate Inhibition Model(Haldane Equation):

µ = 2.74 −

= 3.44 /

= 28.5 /

= 1.50 −

= 6.73 /

= 21.7 /

Bicarbonate Absorption Cell growth

Bicarbonate Absorption Rate

Cell growth Rate



Source: Gris et al., 2014. Development of a process for an efficient exploitation of CO2 captured from fluegases as liquid bicarbonates for Chlorella protothecoides cultivation. I & EC research.

Large Scale Perspective

In situ production of bicarbonate and direct distribution in thecultivation system.

In this work, the experiments were carried out in batch conditions. Incontinuous mode of operation, a lower concentration of sodiumbicarbonate could be necessary, thus reducing inhibition effects.



Conclusions

This cyanobacterium produced high quantity of

biomass reaching 6 g/L, with a maximumproductivity of 1.12 g/(L day);

Synechococcus PCC 7002 was able to absorbe

high amounts of sodium bicarbonate, growing inconcentrations between 5.5 – 88 g/L;

A kinetic model based on substrate inhibition wasable to predict the kinetic constants ofbicarbonate absorption and cell growth whensodium bicarbonate is used.

Probably, the carbon source was still limiting.

As regards carbohydrate content, this method ofcarbon exploitation is not enough efficient toaccumulate high contents of carbohydrates;

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But, above 22 g/L substrate inhibition started.



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Synechococcus PCC 7002 - bicarbonato

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