_Hydrogenomonas_ bacteria can be used for at least part of the
astronauts’ diet. The washed bacteria have a mild taste and are being
studied for their total energy content, protein and lipid digestibility,
and vitamin content. Carbon and nitrogen balances, and respiratory
quotient are to be determined in animals fed the bacteria as their sole
food source. No toxic constituents have been discovered. Sonicated and
cooked bacteria, when fed to white rats as 12 percent of the solids of a
nutritionally balanced diet, were eaten readily and produced no ill
effects. Net utilization of the protein appears to be somewhat lower
than casein and about the same as legume proteins.
The composition of _Hydrogenomonas eutropha_ is shown in table XI. The
composition of the bacteria varies with the age and growth phase of the
cells and with the medium and gas available. It is possible to modify
the growth conditions to grow the type of bacteria desired for nutritive
purposes.
_Hydrogenomonas_ cells contain about 75 percent water. Of the dry
weight, about 74 percent is protein, calculated as 6.25 times the
nitrogen content. Table XI shows the amino acid composition to be
comparable with other bacterial proteins, except for higher tryptophan
and methionine values.
Table XI—_Analysis of_ Hydrogenomonas eutropha _Cells Grown in
Continuous Culture_ [From [ref.194]]
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Constituent Percent by weight
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Moisture 74.55
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Fat .44
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Ash 1.73
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Nitrogen 3.02 (wet)
-------------------
11.87 (dry)
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Protein (N × 6.25) 18.90 (wet)
-------------------
74.26 (dry)
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Amino acids (dry weight)⁸
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Alanine 4.47
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Arginine 3.41
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Aspartic acid 4.32
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Cystine .08
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Glutamic acid 7.67
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Glycine 2.76
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Histidine .95
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Isoleucine 2.17
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Leucine 4.04
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Lysine 2.65
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Methionine 1.14
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Phenylalanine 2.20
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Proline 2.06
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Serine 1.80
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Threonine 2.15
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Tryptophan .78
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Tyrosine 1.79
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Valine 3.03
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⁸ Trace amounts of the following were also found: methionine
sulfoxide, citrulline, alpha-amino-n-butyric acid, homocitrulline,
glucosamine, galactosamine, methionine sulfoximine, ethionine, and
ethanolamine.
The lipid content of rapidly growing cells is normally quite low (0.45
to 2.3 percent crude ether extractable lipids). The most important lipid
is poly-beta-hydroxybutyric acid, which is stored under the growing
conditions of insufficient nitrogen or oxygen supply (refs. [ref.187]
and [ref.191]). Under these conditions, this unusual polymer constitutes
up to 80 percent of the dry weight. While the monomer itself,
beta-hydroxybutyric acid, is rapidly and efficiently used in cell
metabolism, the nutritive value of the polymer is yet to be determined.
The fatty acids found include lauric, myristic, palmitic, palmitoleic,
heptadecaenoic, C17 saturated(?), stearic, linoleic, and linolenic(?)
([ref.195]).