Microbial and higher plant biomass selection for closed ecological systems

ActaAstronautica Vol.27,pp.219 - 230, 1992 Printed in GreatBritain

0094-5765/92 $5.00+0.00 Pergamon Press Ltd

MICROBIAL AND HIGHER PLANT BIOMASS SELECTION FOR CLOSED ECOLOGICAL SYSTEMS. Christian TAMPONNET and Roger A. BINOT Life Support and Habitability Section,European Space Research and Technology Centre, European Space Agency, Keplerlaan 1, Postbus 299, 2200AG Noordwijk, The Netherlands

ABSTRACT A selection of higher plants and microbial strains is presented with its rationale in order to progressively regenerate food from waste in future space and planetary missions. KEYWORDS Closed Ecological System, Higher Plant, Life Support, Microorganism, Selection

INTRODUCTION In order to achieve the long-term goal of autonomy in manned space operations, or to participate effectively in cooperative international missions, Europe needs to develop the technologies required for advanced life support systems in which virtually all resources are recycled, i.e. the technologies to establish and maintain a stable closed ecological system containing man as one important element. Since food cannot be recycled by physico-chemical means, this element at least must be biological, and it is anticipated that the other, currently physico-chemical, elements in the system will be progressively substituted by biological techniques. In parallel with the development of a Micro Ecological Life Support System Alternative (MELISSA, Mergeay et al., 1988) based on an anaerobic fermentation compartment and an anoxygenic photobeterotrophic compartment producing an edible biomass (RhodospirUlura rubrum, Rhodobacter capsulata ), which partially short-circuits the total oxidation of waste into carbon dioxide and water, and on a photouutotrnphic compartment (Spirulina platensis ) reducing carbon dioxide into carbohydrates and then producing mainly proteins, ESA will initiate the study of a higher plant ccgnpartment to nearly completely provide the crew with sufficient food. Food for use by the crew must be of high quality, nourishing, not contaminated, and constitutes a balanced diet. Indeed, ff Rhodospirillum rubrum, Rhodobacter capsulata, and Spirulina platensis and selected micro-algae can easily provide the daily average protein intake to the crew, they fall very short for the coverage of the carbohydrates intake. So, the addition of another compartment which could provide the carbohydrates, lipids, proteins (if we do not want to only rely on a microbial source) and the essential amino acids of the human diet, is necessary. Such a higher plant compartment should contain diffc~.nt plant strains chosen for:. (1) their high growth and edible hiomass yields using light as energy source, CO2 as carbon source, nitrogen, phophorous and sulfur being provided by the microbiological loop in the adeq~_~ cbemical form, - (2) their complementarity in food production according to the nutritional needs for a human crew member on a long duration s~ace mission, - (3) their biological compatibility (i.e. their ability to grow one beside each other). -

To begin with, the nutritional needs for a human crew member on a long duration space mission have to be © ~ defined because they are the cornerstone on which all this work is built. Then, thelnupcmtzn of the nutritional needs to be provided through regenerative means as a function of the length and type of space missions will have to be established and according to these conswaints, categories of plants will have to be selected which moreover will differ one from each other by two marc prerequisites: - theae pimus ~ provide ornot the protein intake of the human diet. these .i~. ts w/ll ~ w ~ pl .an~aty base. (partial gravity, cosmic rays and particles) or under space nasslon conmuons tnuerogawty, cosrmc r~vs and particles). 219 -

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9th IAA Man in Space Symposium

NUTRITIONAL NEEDS FOR A HUMAN CREW MEMBER ON LONG DURATION SPACE MISSIONS. Long duration space navels have physiological impacts on man (muscular atrophy, loss of minerals, modification of body's electrolytes, changes in body's mass). Such problems can be partially solved with a specific physiological training programme and also with an adapted nutritional scenario. According to data registered during previous space missions (Apollo, Soyouz, Skylab, Mir,etc) a typical daily diet should be as follow:

Table 1. Space Recommanded Energy Allowance Recommanded Energy Allowance

I (12.6MJ) ~

Table 2. Space Recommanded Daily Allowance (SRDA) of food macronutrients Normal Day 375-415 8 100-120 8 90-135 ~

Carbohydrates (50-55%) Lipids (30-35%) Proteins (12-18%)

EVA Day 435-480 8 115-135 8 105-155

1.5 1

Drinkin8 Water (50%)

1.75

Table 3. SRDA of Essential Amino Acids

Ineu

lieu

10.Sg ILys

10.8g

IPhe

II.lg

ITrp

11.1~ IMct II.l~ IThr ]O.5g IWl

10.2g I

11-°~ I

Table 4. SRDA of Food Vitamins

,drosoluble Vitamins ( g ~ 3 A~orbic Acid

l~dfloxine R

(C)

Biotine (H) Choline Cyanocobalamin ( B ~ Folic Acid Nicotinic Acid (PP) Pantothcnic Acid (Bs)

(B6)

avine

(B 2)

fs~)

1.8-3.1 12

0.1-0.2 0.5-1.5

a~iaminc

Liposo!uble Vitamins

(ms)

.5-1.8

0:003 0.4 7-8 4-7

Cholecalciferol

.0I-.025

(D3) (A) (E)

Retinol

Tocopherols Vitamine K

.002-2.5 13-780 0.15

Note that these data correspond to an average 70 kg man and have to adapted via modelling software for each crew member according to sex, size,weight, basal metabolism, and food habits (in so far as these food habits are not harmful to theirhealth).W h e n applicable,the lower value indicates the minimum necessary to maintain constant the body level, and the upper value the quantity above which adverse side effectscould appear.

Table 5: S R D A of food Minerals

Macro Minerals Ca C1

[ 1200-1500 ] 4000-7000

Micro Minerals Cu Cr F

2-3 0.05-2.5 10-40

ii1,|

(mg) ] K ] M8

(m~) Fe I Mn

3500-3900 350

Na P

II00-i300 1200-1500

10 0.07-0.15 2.5-5

Mo Se Zn

0.15-0.5 0,05-0.2

15

9th IAA Man in Space Symposium

221

BACTERIAL BIOMASS PRODUCTION. Food production from microorganisms is the first topic to consider because of the high growth rate, the high harvesting index, and the early involvement of microorganisms in the waste ~.atmant and regeneration procedmv,s. Mica~m'nnim~t ~ nmmin source Indeed, such microorganisms are well-known sources of proteins so-called Single-Cell Proteins (SCP). The main problem resides in the accompanying nucleic acids production. According to the Protein Advisory Group (1975) the total nucleic acids intake from all sources must not exceed 4 g per day, and only half of it could come from "unconventional" sources. This lead us to conclude that the maximal daily intake of selected microbial biomass is around 50 g of dry weight per clay covering only 30-40 % of the protein Space Recommanded Daily Allowance (SRDA, see table 6 below).

Table 6. Nucleic acids composition in various organisms I

Bacteria Nucleic Acids (Percenmgeof dry weight)

Mi~isms

10- 20

Yeasts 5- 10

Micro-ai~ 2-5

Hi~her Plants 1-2

as linid source

Many microorganisms do nattwallyor under some form of slress produce and even excrete edible oils (Ratledge and Boulton, 1985) e.g. linolenic acid from Chlorella, glycerol from Dunaliella.

Microofnnisms as carbohydrate source Under nitrogen deprivation, many microalgae and photosynthetic microorganisms over-produce carbohydrates instead of proteins, e.g. glycogen accumulation in Spirulina or Anabaena, paramylum storage in Euglena, etc (Ernst and Bogcr, 1985, Cornet and Dubertret, 1991). Finally, microorganisms can be easily envisioned as potential but partial sources of proteins. Further developments are necessary before microorganisms can be considered as acceptable .so~ce of carbohYdrat,es. At least, partial co.~letion of dail.y intakes of spec.ifiCvitamins and mmerats can be obtained through the absorption of some particular m l ~ s m s (see table 7 ). Following the actual study of pure cultures of Spirulina and photorbodochromogens, mixed Cultures are envisioned (e.g. Spirniina and Dunaliella) in order to increase the stability and the efficiency of continuous cultures.

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Table 7. Nutrient composition of microbial and "fresh raw products

Energy (gear100g) Protein ~/100 g) Carbohydrate (g/10og) Lipid (gtl00S) Water ~10o g) Harvestin~ Ratio (~)

Spirulina 60.9 10.8 1.95 1.1 85.0 100

Lettuce 14 1 2.1 0.2 95.8 .........85

Spinach 29 2.9 3.6 0.3 91.5 70

Tomato 24 0.9 4.3 0.7 93.0 45

Essential Amino Acids (m~) Isoleucine Leucine Lysine Methionine Phenylalaaine Threonine Trpytophan Valine

670 950 505 275 480 575 170 720

75 70 75 28 78 53 8 62

145 225 175 90 240 120 39 160

2l 33 33 20 38 22 7 23

Hydrosoluble Vitamins (m~) Ascorbic Acid C B]otine H Choline F~oanocobalamin B12 Acid Nicotinic Acid PP Pantothenic Acid B5 P~i."doxine B 6 Riboflavine B2 Thiamine B1

1.5 0.006

3.9

0.03 0.008 1.75 0.17

0 0.055 0.185 0.046 0.04 0.03 0.046

0.05

0.67 0.83

28 0.007 0 0.195 0.7 0.07 0.2 0.19 0.08 i

18 0.0015 0 0.010 0.6 0.25 0.05 0.05 0.06 i

Liposoluble Vitamins (m~) Choleealcfferol 1)3 Retinol A Tocopherols E ~tamine K

0 26 2.9

0.52

2.35 0.00035

0.44 0.008

Maerominerals (mg) Calcium Chlorine Mat,nesium Phosphorus Potassium Sodium

14.5 180

19

100

7

9

80

11

20 160 9

50 560 79

23 205 8

Microminerals (mg) Chromium Copper Fluorine Iodine Iron

M~dybdenum s e enium

0.028

:IU

0.5 0.22

0.13 0.01 0.012 2.7 0.026 0.0017 0.53

0.077 0.024 0.003 0.5 0.001 0.11

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Table 8. Nutrient corn 3osition of hi~ r plant raw products Rice Wheat meal ! Potatoes Soybeans Energy (~aV10o~) Protein (gloo g) Carbohydrate (~0o10 Lipid (fj10o0) Water ~loo 0 Harvesun~ Ratio 0t) Essential Amino Acids (m~) Isoleucine

I~ucine

Lysine Methionils: Phenylalanine Threonine Tryptophan Valine Hydrosoluble

354.3 8.4 77.7 1.1 12.0

353.3 12.7 70.0 2.5 13.0

45

40 ¸

370 730 320 325 710 295 90 510

N Choline FC~oanocobalamin Bl2 lic Acid Nicotinic Acid PP Pantothenic Acid B5 P~i."doxine B6 Riboflavine B2 Thiamine Bl Liposoluble Vitamins (m~) Cholecalciferol D3 Retinol A Tocopherols E Vitamine K Macrominerals (rag)

435 670 275 375 865 29O ' 125 470

~

77.7 2.1 17.1 0.I 79.8 8O 92

105 113 46 58 83 22

113

157.2 13.0 11.0 6.8 67.5 50 570 925 775 275 1050 515 155 575

29

H

0 0.029 1.5 0.55 0.17 0.04 0.13

0 0.052 4.4 1.1 0.39 0.12 0.66

0 0.025 1.5 0.2 0.39 0.04 0.I

0 0 0.46

0 0 1.16

0 0 0.013

0 1.65 0 O.175 0.435

Sunflower seeds 621.6 19.3 24.1 49.8 5.3 33 1140 1660 935 945 1835 1350 350 1350 0 0 0.235 4.5 0.7 0.8 0.25 0.11 0 41.6

Chlorine

Magnesium Phosphorus

t~,tassium Sodium Microminerals

28 127 85 8

113 386 435 3

20 53 407 3

194

354 705 690 3

(rag)

Chromium

~opper

uorine Iodine Iron !Molybdenum Selenium Zinc ,HH,

0.2 0.19 0.0018 0.1 0.015 0.02 1.3

0.93 0.053 0.0041 4.3 0.036 0.063 3.4

0.311 0.045 0.004 0.6 0.003 0.01 0.58

1.73 3.55

6.77 5.06

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9th 1AA Man in Space Symposium

HIGHER PLANT BIOMASS PRODUC"rlON The main purpose of this study is to show the feasibility of satisfying the human nutritional requirements described above, through combinations of the products of microorganisms and crops which could be cultivated under closed and controlled environments. The crops envisioned in this study have been selected upon either their ability to be cultured under such conditions, or their nutritional qualities ( see table 8): source of Carbohydrates ( rice,wheat, potatoes), source of Proteins (soybeans), source of Lipids (sunflower), source of "fresh" food (tomatoes,.lettuce, spinach). Indeed, model diets have been proposed from the simple combinations of these crops (Wade, 1989) and completely fulfil the nutritional requirements with the addition of some vitamins, minerals and essential amino-acids.

DIFFERENT POSSIBLE FOOD SCENARIOS Once the complete nutritional requirements are established, one has m define which part of them has to be fulfilled through regenerative means according to the different possible space mission scenarios and to the different sources of food available. Then, a trade-off is absolutely necessary to select the ideal (if any) diet components according to the physical-chemical conditions encountered and scenarios have to be obtained. Trade-off for the nhomsvnthetic organisms for food nroduction For such a trade-off, we have selected two main groups of raw materials: - higher plants (crops), - micro-algae and cyanophyceae. Trade-offcdteria have been divided into four classes: - Operating criteria, Safety and Reliability, - Food characteristics, - Impact on Life Support sub-systems. -

Two types of mission are considered in this ~ , le-off because of the difference in their physicalchemical conditions:

Space missions, - Planetary missions (see table 9). -

In space mission conditions, the use of higher plants as source of food suffers major drawbacks, mainly in operating criteria and therefore prevents us, according to todays knowledges, from utilising them despite their very good food characteristrics. On the contrary, Cyanophyceae and micro-algae are very good candidates as far as food production is concerned, but their relatively even food characteristics made us to only consider them as partial contributors to the daily diet; as a matter of fact, there is now no possibility to cover more than 25-30% (w/w dry weight) of the diet. In planetary mission conditions, significant improvements are noted for the operating criteria of higher plants production compared to the space mission conditions, but they still cannot reach the food production rates and other advantages of micro-algae and cyanophyceae. Nevertheless, higher plant production will be foreseen in planetary mission conditions according to the following rationale: - resupply is more expensive and should be avoided, food habits are difficult to change for long duration missions, - the presence of plants has a major psychological impact on crew. -

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TABLE 9

: QUALITATIVE ASSESSNENT OF PHOTOSYNTHETIC ORBANISN$ FOR FOOD PRODUCTION

(I) [CONOITIONS

IOPTION HigherPlants '

J f

~-Operating criteria ~Abilitytooperate inmicro-gravity Adaptability to crew activity Adaptability to crew size

Continuousoperation lEasinessof automation Easinessfor sanitation Growth rate Volume/area productivity

SPACE

IRANGEOF ISELECTEO I VALUES i VALUE (AI 1

s

1 J

PLANETARY

I(BI I (c,

I O0

,,.OHT J.o0 (B, Ic,

% OF TOTAL (01):

IPoorJGoodJ IPoorpodl I NO IYes I [Poorl6ood !

3 3 2 2

JPoorJ~ I

3

ILow ).tgh I

,

50 5 5 5 5 S 5 20

10 20 5 15 10 10 30 33

SUB~-TOTALS:

9.9

6 12 Z 6 6 8 12 52

15.6

t

Safety~Reliability criteria Buffering of environmental conditions Feasibility for hold on Tolerance to contaminants Vegetative reproduction

~ OF TOTAL (02): Poor 6ood No jYes Poor Good No Yes

2 1 2 2

25

10

10

2

25 40

10 16 38

SUB-TOTALS:

Food characteristics Diversity Food habits Food value of biomass Food value of edible fraction Suitability for Human diet of edtble fraction - Source of proteins - Source of carbon hydrates

C02 buffering capacity Harvest index / reduced waste generation Light utilisation Thermal load

10 6 lO 8

34

5.7

5.1

~ OF TOTAL (03): Low Poor Low Low Poor

High Good High; High 6ood

S 5 2 4 S

!Poor Good Poor C,ood

3 5

S 15 15 20 20

5 15 6

16 20 6

15 83

SUB-TOTALS:

Impact on other Life Support Sub-Systems

Z5 30 25 20

5 15 15 20 20

5 15 6 16 20

10 15

15

6

83

24.9

24,9

g OF TOTAL (D4): PoorlGood Low ;High Poor C~)ocl High Low

25 25 25 25

2 2 1 1

30

SUB-TOTALS:

TOTALS TO SHEET ..: SCORING (A) 1 = ALTERNATIVEMEETSCRITERIA LEAST

10 10 5 5

(X)

25 25 25 25 7.5

J

5"ALTERNAT[VEMEETSCR]TERIA BEST

lO

10 10 10

30

7.5

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9th IAA Man in Space Symposium

TABLE 9

: QUALITATIVE ASSESSMENT OF PHOTOSYNTHETIC ORGANISMS FOR FOOD

PRODUCTION

(ii)

F I CONOITIONS

2 SPACE

l 7-----I

O•-PTION

Eucaryotic Microalgae

II

I

VALUES1 5 JVALUE (A)

{WEIGHT (A~B)

(B) I

IOperating criteria

100

IWEIGHTi 5 B, i fc)

(C)

% OF TOTAL (OI): PoorlGo~5 PoorIGeod 5 P~rlGo~ 4

50 5 5 5 5 5 5 20

3 4

Poor]Good 3 Low IHigh 4 !LowIHigh4

50 5 4 3 4 3

4 16

L-

I0 20 S ts i

I0 16 3 iz

i0 tO 30

5 8 ;>4

i

L_ ..... y ...............

89

SUB-TOTALS:

i

26.7

......... '

I

Buffering of environmental conditions Feasibility for hold on Tolerance to contaminants Vegetative reproduction

,B

'0 I

3

I0 25

15

I I

5

40

40

I

Poor ~ocl No Yes

4 4

Poor Good No Yes

Diversity Food habits Food value of biemass Food value of edible fraction Suitability for Humandiet of edible fraction Source of proteins Source of carbon hydrates

8

--I! f............ I

!

]Poor Good I

LOW HighI LOW High Poor Good IPoor G°°dI Poor Good

2O 24

I

20

20

I

!

p ......

:I

15 15 20 20

2 3 2

l

IO

3 2

15

]

:79

I 119 L .......

15 20 20

6 ;2 8

! i I

6 B

!0 15

~ 6

F i

12.9

43

]25' F----+

I z~!

4 3 2

I 25 25

2

TOTALS TO SHEET .. :

I SCORING (A) i = ALTERNATIVEMEETSCRITERIALEAST

I

j

~

i ~

15

I 2s I

IO i0

!

to

25

I

I

'~

L ......

;

13.7

L

(~)

.......... -r---

2o! i~

55

iSUB-TOTALS:

1!~9, I

i

[. . . . . . . . :

[-T5-

I

CO2 buffering capacity IPoor Good Harvest index I reduced waste generation Low HighI 'Light utilisation PoorlBoodI Thermal load _~gh Low

i

÷- ....................

/

%OF TOTAL (D4)

....

.......

2 3 6 12 8

43

UB-TOTALS:

Impact on other Life Support Sub-Systems

J

1 30

% OF TOTAL (D3): I

'LowIHighi

.....

i-

25 30

L2 ,' ;

SUB-TOTALS:

Food characteristics

I

23,y i

15

% OF TOTAL (D2):

Safety/Reliability criteria

100

3G

]

No IYes Poorl~od

. . . . . T ....... :

(c,o.l I ~ I(A~B! (cx0o!

IRANGEOF ISELECTED

I

Ability to operate in micro-gravity Adaptability to crew activity Adaptability to crew size Continuous operation Easiness of automation Easiness for sanitation Growth rate Volume/area productivity

PLANETARY

.......

6B.

7

1

5 = ALTERNATIVEMEETSCRITERIABEST

i ............

I 62.2

I

!

9th IAA Man in Space Symposium

:

TABLE 9

227

QUALITATIVE ASSESSMENTOF PHOTOSYNTHETICORBANISMSFOR FOOD PRODUCTION (nx)

[

CONDITIONS

OPTION

Cyanophyceae

Operating criteria

Abiltty to operate In micro-gravity Adaptability to crew activity Adaptability to crew size Continuous operation Easiness of automation Easiness for sanitation Growth rate Volume/area productivity

SPACE

RAN6E OF SELECTEDJ X (CxOn) V~LUES5 VALUE VEIBHT (A~B) 100 (B) (C)

(A,j

Buffering of enviromental conditions Feasibility for hold on Tolerance to contaminants Vegetative reproduction

Poor ~ Poor Good Poor Good No Yes Poor Good Poor 6ood Low Htgh Low High

5 S 4 4 4 4 4 4

50 5 5 5 5 5 5 20

Diversity Food habits Food value of biomass Food value of edible fraction Suitability for Human diet of edible fraction - Source of proteins - Source of carbon hydrates

C02 buffering capacity Harvest index / reduced waste generation Ltght u t t l tsat Ion Thermal load

(CxOn)

X

WEIGHT EASE) (B)

[C)

10 20 5 15 lO 10 30

10 16 4 12 8 8 24

1oo

27.3

82

24.6

OF TOTAL (02}: Poor Good No Yes Poor Good No Yea

4 4 3 5

25 10 25 40

20 8 15 40 83

25 30 25 20 12.4

20 24 1S 20 79

11.8

OF TOTAL (03): Low High IPoorl 6ood

2 2.

ILo. High

4

Low High Poor 6ood

4 3

S 15 15 20 26

Poor 6ood Poor 6ood

4 2

10 IS

SUB-TOTALS:

Impact on other Life Support Sub-System

50 S 4 4 4 4 4 16 91

SUB-TOTALS:

Food characteristics

]

% OF TOTAL (Ol):

SUB-TOTALS:

Safety/Reliability criteria

PLANETARY

2 6 12 16 12 8 6 62

5 15 15 20 20

18.6

2 6 12

16 12

62

18.6

I( OF TOTAL (D4): Poor Soo~ Low High Poor Ioood High!Low

5 4 2 2

25 25 25 25

SUB-TOTALS:

TOTALS TO SHEET ..: SCOAING (A) 1 - ALTERNATIVEMEETSCRITERIA LEAST

25 20 10 10 B5

(~)

25 25 25 25 16.3

J

S - ALTERNATIVEMEETSCRITERIA BEST

25 20 10 10 B5

16.3

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9th IAA Man in Space Symposium

First scenario: Production of some microbial food and ext~erimental studies on higher plants vroduction, applicable in the Stmce Station. EMSI.ere As a first step and for early use (already in Space Station), the production of microbial edible biomass can be envisioned such as Spirulina. A partial completion of the protein, vitamins, essential fatty acids and minerals requirements can be obtained. The limited amount of higher plants (essentially the ones with an important vegetative part such as lettuces, spinaches, ) produced by the experimental set up can be included into the diet but does not significantly td~'ect its balance.

Proteins Lipids FibresI Carbohydrates]Vitamins

FibresI Carbohydrates ]Vitamins ~

Stored Food

--]ProducedFood First

Scenario

Figure 1. Completion of the daily diet in the first scenario Second scenario: Production of some microbial food and fresh food. applicable mainly on planet missions and with some restrictions on lon~-duration st~ace missions The next step, which will comply with longer space missions, will be to provide daily fresh products to the crew (lettuce, spinach), to authorise a greater variability in meal compostion, and to bring the daily fibre intake (yet to be established even on Earth; indeed, it is known to prevent some typed of cancer but also interfere with the absorption of some minerals). Of course, energetics, proteins, carbohydrates and lipids requirements will be provided by a combination of microbial biomass and of supplies stored on board or resuplied from the Earth.

Proteins Lipids FibresI CarbohydratesIVitamins ~ ~ ~ ~

~:~StoredFood D

Second

Produced Food

Scenario

Figure 2.Completion of the daily diet in the second scenario

Third scenario: Most of food is mroduced and is onlv aoolicable, uo to now. m nlanetarv missions The final step, according to todays knowledge, will be the total completion of the daily needs in energy and macronutrients and the nearly total completion of the daily needs in vitamins, minerals, and essential amino- and fatty acids. In that case, stored nutrients would only be used as a backup, in case of urgency, and to diversify the meal composition (mainly through animal products).

9th IAA Man in Space Symposium

Proteins Lipids Fibres I Carbohydrates I Vitamins

;

~

~ ~;Salts F-] ProducedFood

.

.

.

.

.

l

i

l

i

Third Scenario Figure 3. Completion of the daily diet in the third scenario

CONCLUSIONS Now, food is totally resupplied from Earth. U.S. shuttle missions have food on board and Mir missions are continuously resupplied from Earth through Progress Modules. In a foreseen future, food production in space through regenerative means must be envisioned to permit long-duration space missions. The choice of biological materials from which food will be obtained is a primary priority and has to be carefully assessed. Indeed, volume and mass limitations are important constraints and then oblige us to essentially rely on photosynthetic biomass. Food production in closed systems will require mineral nutrients from waste regeneration systems.

tion

fff Light

£~ht

Figure 4. Global scheme of Food production using microbial and higher plant biomass

As such waste transformers are of microbial origin, the edible part of their biomass has to be taken into account (production of SCP). Indeed, waste mainly consists in organic molecules which.are usually degraded into minerals, CO2, H20. On an energetic ~.oint of view, such a oe..gf.~lation is a loss of ene.r~y which has to be prevented as far as possible by the use of the edthle part of the microbial biomass. This is an easy way to limit enthalpic and entropic energy losses. With the same rationale, the non-edible part of the biomass coming from the photoautotrophs (higher plants, Cyanophycose, micro-algae) can be partly converted into edible bionutss (e.g. microbial conversion of cellulose into glucose). All these possibilities have been summarised on a global scheme (see Figure 4). Finally, the optimal combination of the different microbial and higher plant strains will be the major breakthrough in food production but will remain dependent upon the mission charactedstic~ either space or planetary conditions.

229

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REFERENCES Comet J.-F. and G. Dubertret (1991). The Cyanobactcrium Spirulina in the photosynthetic compartment of the MELISSA artificial ecosystem. In: Workshop on artificial ecological systems, pp. 91-97. Mergeay M., W. Verstraet¢, G. Dubertret, M. Lefort-Tran, C. Chipaux, and R.A. Binot (1988). MELISSA, a microorganism-based model for CELSS development. In: Proc 3rd European Symposium on Space Thermal control and Life Support Systems, fT. Guyenne, Ed.), pp. 6568. Ernst A. and P. Boger P. (1985). Glycogen accumulation and the induction of nitrogenase activity in the heterocyst forming cyanobaeterium Anabaena variabilis. J. Gen Microbiol 131:3147-3153. Ratledge C.and C. Boulton (1985). Fats and oils. In: Comprehensive Biotechnology, (MooYoung, Ed.), Vol. 1, pp.983-1003. Wade R.C. (1989). Nutritional models for a controlled ecological life support system: linear mathematical modeling. NASA Contractor Report 4229. 125p.