<named-content content-type="genus-species">Escherichia coli</named-content> K-12 Lacks a High-Affinity Assimilatory Cysteine Importer

ABSTRACT The most direct route by which microbes might assimilate sulfur would be by importing cysteine. However, alone among the amino acids, cysteine does not have well-characterized importers. We determined that Escherichia coli can rapidly import cysteine, but in our experiments, it did so prima...

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Autores principales:	Yidan Zhou, James A. Imlay
Formato:	article
Lenguaje:	EN
Publicado:	American Society for Microbiology 2020
Materias:	LIV system YhaO amino acid uptake Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/665f49a2ade74b7c867f40cac42a35fb
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spelling	oai:doaj.org-article:665f49a2ade74b7c867f40cac42a35fb2021-11-15T15:56:46Z<named-content content-type="genus-species">Escherichia coli</named-content> K-12 Lacks a High-Affinity Assimilatory Cysteine Importer10.1128/mBio.01073-202150-7511https://doaj.org/article/665f49a2ade74b7c867f40cac42a35fb2020-06-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.01073-20https://doaj.org/toc/2150-7511ABSTRACT The most direct route by which microbes might assimilate sulfur would be by importing cysteine. However, alone among the amino acids, cysteine does not have well-characterized importers. We determined that Escherichia coli can rapidly import cysteine, but in our experiments, it did so primarily through the LIV ATP-driven system that is dedicated to branched-chain amino acids. The affinity of this system for cysteine is far lower than for Leu, Ile, and Val, and so in their presence, cysteine is excluded. Thus, this transport is unlikely to be relevant in natural environments. Growth studies, transcriptomics, and transport assays failed to detect any high-affinity importer that is dedicated to cysteine assimilation. Enteric bacteria do not contain the putative cysteine importer that was identified in Campylobacter jejuni. This situation is surprising, because E. coli deploys ion- and/or ATP-driven transporters that import cystine, the oxidized form of cysteine, with high affinity and specificity. We conjecture that in oxic environments, molecular oxygen oxidizes environmental cysteine to cystine, which E. coli imports. In anoxic environments where cysteine is stable, the cell chooses to assimilate hydrogen sulfide instead. Calculations suggest that this alternative is almost as economical, and it avoids the toxic effects that can result when excess cysteine enters the cell. IMPORTANCE This investigation discovered that Escherichia coli lacks a transporter dedicated to the assimilation of cysteine, an outcome that is in striking contrast to the many transporters devoted to the other 19 amino acids. We ascribe the lack of a high-affinity cysteine importer to two considerations. First, the chemical reactivity of this amino acid is unique, and its poorly controlled import can have adverse consequences for the cell. Second, our analysis suggests that the economics of biosynthesis depend sharply upon whether the cell is respiring or fermenting. In the anoxic habitats in which cysteine might be found, the value of import versus biosynthesis is strongly reduced compared to that in oxic habitats. These studies may explain why bacteria choose to synthesize rather than to import other useful biomolecules as well.Yidan ZhouJames A. ImlayAmerican Society for MicrobiologyarticleLIV systemYhaOamino acid uptakeMicrobiologyQR1-502ENmBio, Vol 11, Iss 3 (2020)
institution	DOAJ
collection	DOAJ
language	EN
topic	LIV system YhaO amino acid uptake Microbiology QR1-502
spellingShingle	LIV system YhaO amino acid uptake Microbiology QR1-502 Yidan Zhou James A. Imlay <named-content content-type="genus-species">Escherichia coli</named-content> K-12 Lacks a High-Affinity Assimilatory Cysteine Importer
description	ABSTRACT The most direct route by which microbes might assimilate sulfur would be by importing cysteine. However, alone among the amino acids, cysteine does not have well-characterized importers. We determined that Escherichia coli can rapidly import cysteine, but in our experiments, it did so primarily through the LIV ATP-driven system that is dedicated to branched-chain amino acids. The affinity of this system for cysteine is far lower than for Leu, Ile, and Val, and so in their presence, cysteine is excluded. Thus, this transport is unlikely to be relevant in natural environments. Growth studies, transcriptomics, and transport assays failed to detect any high-affinity importer that is dedicated to cysteine assimilation. Enteric bacteria do not contain the putative cysteine importer that was identified in Campylobacter jejuni. This situation is surprising, because E. coli deploys ion- and/or ATP-driven transporters that import cystine, the oxidized form of cysteine, with high affinity and specificity. We conjecture that in oxic environments, molecular oxygen oxidizes environmental cysteine to cystine, which E. coli imports. In anoxic environments where cysteine is stable, the cell chooses to assimilate hydrogen sulfide instead. Calculations suggest that this alternative is almost as economical, and it avoids the toxic effects that can result when excess cysteine enters the cell. IMPORTANCE This investigation discovered that Escherichia coli lacks a transporter dedicated to the assimilation of cysteine, an outcome that is in striking contrast to the many transporters devoted to the other 19 amino acids. We ascribe the lack of a high-affinity cysteine importer to two considerations. First, the chemical reactivity of this amino acid is unique, and its poorly controlled import can have adverse consequences for the cell. Second, our analysis suggests that the economics of biosynthesis depend sharply upon whether the cell is respiring or fermenting. In the anoxic habitats in which cysteine might be found, the value of import versus biosynthesis is strongly reduced compared to that in oxic habitats. These studies may explain why bacteria choose to synthesize rather than to import other useful biomolecules as well.
format	article
author	Yidan Zhou James A. Imlay
author_facet	Yidan Zhou James A. Imlay
author_sort	Yidan Zhou
title	<named-content content-type="genus-species">Escherichia coli</named-content> K-12 Lacks a High-Affinity Assimilatory Cysteine Importer
title_short	<named-content content-type="genus-species">Escherichia coli</named-content> K-12 Lacks a High-Affinity Assimilatory Cysteine Importer
title_full	<named-content content-type="genus-species">Escherichia coli</named-content> K-12 Lacks a High-Affinity Assimilatory Cysteine Importer
title_fullStr	<named-content content-type="genus-species">Escherichia coli</named-content> K-12 Lacks a High-Affinity Assimilatory Cysteine Importer
title_full_unstemmed	<named-content content-type="genus-species">Escherichia coli</named-content> K-12 Lacks a High-Affinity Assimilatory Cysteine Importer
title_sort	<named-content content-type="genus-species">escherichia coli</named-content> k-12 lacks a high-affinity assimilatory cysteine importer
publisher	American Society for Microbiology
publishDate	2020
url	https://doaj.org/article/665f49a2ade74b7c867f40cac42a35fb
work_keys_str_mv	AT yidanzhou namedcontentcontenttypegenusspeciesescherichiacolinamedcontentk12lacksahighaffinityassimilatorycysteineimporter AT jamesaimlay namedcontentcontenttypegenusspeciesescherichiacolinamedcontentk12lacksahighaffinityassimilatorycysteineimporter
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<named-content content-type="genus-species">Escherichia coli</named-content> K-12 Lacks a High-Affinity Assimilatory Cysteine Importer

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