Department of Microbiology, University of Georgia, Athens, Georgia 30602.
Appl Environ Microbiol. 1987 Oct;53(10):2373-8. doi: 10.1128/aem.53.10.2373-2378.1987.
In this study we found that autotrophic methanococci similar to Methanococcus maripaludis obtained up to 57% of their cellular carbon from exogenous amino acids. About 85% of the incorporation was into protein. Primarily nonpolar and basic amino acids and glycine were incorporated; only small amounts of acidic and some polar amino acids were taken up. An additional 10% of the incorporation was into the nucleic acid fraction. Because little CO(2) was formed from the C-amino acids, little metabolism of the amino acids occurred. Therefore the growth stimulation by amino acids was probably due to the sparing of anabolic energy requirements. Of the amino acids incorporated, only alanine was also a sole nitrogen source for these methanococci. In contrast, Methanococcus vannielii and "Methanococcus aeolicus" are autotrophic methanococci which did not incorporate amino acids and did not utilize alanine as a sole nitrogen source. Although glutamine served as a sole nitrogen source for the autotrophic methanococci and Methanococcus voltae, a heterotrophic methanococcus, growth was due to chemical deamination in the medium. M. voltae requires leucine and isoleucine for growth. However, these amino acids were not significant nitrogen sources, and alanine was not a sole nitrogen source for the growth of M. voltae. The branched-chain amino acids were not extensively metabolized by M. voltae. Pantoyl lactone and pantoic acid were readily incorporated by M. voltae. The intact vitamin pantothenate was neither stimulatory to growth nor incorporated. In conclusion, although amino acids and vitamins are nutritionally important to both autotrophic and heterotrophic methanococci, generally they are not subject to extensive catabolism.
在这项研究中，我们发现类似于 Methanococcus maripaludis 的自养甲烷球菌可以从外源性氨基酸中获得高达 57%的细胞碳。约 85%的掺入量进入蛋白质。主要是极性和碱性氨基酸以及甘氨酸被掺入；只有少量的酸性和一些极性氨基酸被吸收。另外 10%的掺入量进入核酸部分。由于从 C-氨基酸形成的 CO2 很少，因此氨基酸的代谢很少发生。因此，氨基酸的生长刺激作用可能是由于节省了合成代谢的能量需求。在所掺入的氨基酸中，只有丙氨酸也是这些甲烷球菌的唯一氮源。相比之下，Methanococcus vannielii 和 "Methanococcus aeolicus" 是自养甲烷球菌，它们不掺入氨基酸，也不将丙氨酸用作唯一氮源。虽然谷氨酰胺是自养甲烷球菌和异养甲烷球菌 Methanococcus voltae 的唯一氮源，但生长是由于培养基中的化学脱氨作用。M. voltae 需要亮氨酸和异亮氨酸才能生长。然而，这些氨基酸不是重要的氮源，并且丙氨酸不是 M. voltae 生长的唯一氮源。分枝链氨基酸未被 M. voltae 广泛代谢。泛酰内酯和泛酸很容易被 M. voltae 吸收。完整的维生素泛酸既不能刺激生长也不能被吸收。总之，尽管氨基酸和维生素对自养和异养甲烷球菌都具有重要的营养意义，但它们通常不会受到广泛的代谢作用。
