Experimental evidence of d-glutamate racemase activity in the uncultivated bacterium Candidatus Saccharimonas aalborgensis

IF 4.3 2区 生物学 Q2 MICROBIOLOGY
Marcos Peñalver, Alberto Paradela, César Palacios-Cuéllar, M. Graciela Pucciarelli, Francisco García-del Portillo
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Abstract

The Candidate Phyla Radiation (CPR) encompasses widespread uncultivated bacteria with reduced genomes and limited metabolic capacities. Most CPR bacteria lack the minimal set of enzymes required for peptidoglycan (PG) synthesis, leaving it unclear how these bacteria produce this essential envelope component. In this study, we analysed the distribution of d-amino acid racemases that produce the universal PG components d-glutamate (d-Glu) or d-alanine (d-Ala). We also examined moonlighting enzymes that synthesize d-Glu or d-Ala. Unlike other phyla in the domain Bacteria, CPR bacteria do not exhibit these moonlighting activities and have, at most, one gene encoding either a Glu or Ala racemase. One of these ‘orphan’ racemases is a predicted Glu racemase (MurICPR) from the CPR bacterium Candidatus Saccharimonas aalborgenesis. The expression of MurICPR restores the growth of a Salmonella d-Glu auxotroph lacking its endogenous racemase and results in the substitution of l-Ala by serine as the first residue in a fraction of the PG stem peptides. In vitro, MurICPR exclusively racemizes Glu as a substrate. Therefore, Ca. Saccharimonas aalborgensis may couple Glu racemization to serine and d-Glu incorporation into the stem peptide. Our findings provide the first insights into the synthesis of PG by an uncultivated environmental bacterium and illustrate how to experimentally test enzymatic activities from CPR bacteria related to PG metabolism.

Abstract Image

实验证明未培养的奥尔堡酵母菌具有 d-谷氨酸消旋酶活性
候选菌属辐射(CPR)包括大量未培养的细菌,它们的基因组缩小,代谢能力有限。大多数 CPR 细菌缺乏肽聚糖(PG)合成所需的最基本的酶,因此尚不清楚这些细菌如何生产这种重要的包膜成分。在这项研究中,我们分析了产生通用 PG 成分 d-谷氨酸(d-Glu)或 d-丙氨酸(d-Ala)的 d-氨基酸消旋酶的分布情况。与细菌领域的其他门类不同,CPR 细菌不表现出这些月光活性,最多只有一个编码 Glu 或 Ala 消旋酶的基因。这些 "孤儿 "消旋酶之一是来自 CPR 杆菌 Saccharimonas aalborgenesis 的一种预测的 Glu 消旋酶(MurICPR)。MurICPR 的表达可恢复缺乏内源消旋酶的沙门氏菌 d-Glu 辅助营养体的生长,并导致部分 PG 茎肽的第一个残基由丝氨酸取代 l-Ala。在体外,MurICPR 只将 Glu 作为底物进行消旋化。因此,Ca.因此,Ca. Saccharimonas aalborgensis 可能将 Glu 消旋化与丝氨酸和 d-Glu 结合到干肽中。我们的研究结果首次揭示了一种未培养的环境细菌合成 PG 的过程,并说明了如何通过实验检测与 PG 代谢有关的 CPR 细菌的酶活性。
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来源期刊
Environmental microbiology
Environmental microbiology 环境科学-微生物学
CiteScore
9.90
自引率
3.90%
发文量
427
审稿时长
2.3 months
期刊介绍: Environmental Microbiology provides a high profile vehicle for publication of the most innovative, original and rigorous research in the field. The scope of the Journal encompasses the diversity of current research on microbial processes in the environment, microbial communities, interactions and evolution and includes, but is not limited to, the following: the structure, activities and communal behaviour of microbial communities microbial community genetics and evolutionary processes microbial symbioses, microbial interactions and interactions with plants, animals and abiotic factors microbes in the tree of life, microbial diversification and evolution population biology and clonal structure microbial metabolic and structural diversity microbial physiology, growth and survival microbes and surfaces, adhesion and biofouling responses to environmental signals and stress factors modelling and theory development pollution microbiology extremophiles and life in extreme and unusual little-explored habitats element cycles and biogeochemical processes, primary and secondary production microbes in a changing world, microbially-influenced global changes evolution and diversity of archaeal and bacterial viruses new technological developments in microbial ecology and evolution, in particular for the study of activities of microbial communities, non-culturable microorganisms and emerging pathogens
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