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This research analyzes intracellular osmolyte accumulation in four Methanoculleus bourgensis strains (MAB1, MAB2, MAB3, BA1) exposed to stepwise ammonium and sodium chloride increases, compared with Methanoculleus bourgensis MS2T and Methanoculleus submarinus Nankai-1T. Several strains adapted to higher NH4+-N tolerance up to 25 g L−1, and Nε-acetyl-β-lysine was uniquely accumulated by M. bourgensis under increasing ammonium chloride, suggesting a mechanism for exceptional ammonia tolerance and revealing subspecies variation.",{"@graph":69,"@context":122},[70,84,105],{"@type":71,"itemListElement":72},"BreadcrumbList",[73,77,79,82],{"item":74,"name":75,"@type":76,"position":8},"https://docshare.wps.com","Home","ListItem",{"item":78,"name":9,"@type":76,"position":14},"https://docshare.wps.com/document/",{"item":80,"name":40,"@type":76,"position":81},"https://docshare.wps.com/document/research-report/",3,{"item":83,"name":65,"@type":76,"position":19},"https://docshare.wps.com/document/n-acetyl-lysine-or-glycine-betaine-as-compatible-solutes-in-response-to-increasing-ammonia-in-methanoculleus-sp-strains/455725/",{"url":83,"name":65,"@type":85,"image":86,"author":91,"headline":65,"publisher":94,"fileFormat":97,"inLanguage":63,"description":67,"dateModified":98,"datePublished":99,"encodingFormat":97,"isAccessibleForFree":100,"interactionStatistic":101},"DigitalDocument",{"url":87,"@type":88,"width":89,"height":90},"https://docshare.wps.com/thumbnails/n-acetyl-lysine-or-glycine-betaine-as-compatible-solutes-in-response-to-increasing-ammonia-in-methanoculleus-sp-strains/455725.png","ImageObject",300,407,{"name":92,"@type":93},"Valentina","Person",{"url":74,"name":95,"@type":96},"DocShare","Organization","application/pdf","2026-10-06","2026-09-30",true,{"@type":102,"interactionType":103,"userInteractionCount":19},"InteractionCounter",{"@type":104},"ViewAction",{"@type":106,"mainEntity":107},"FAQPage",[108,114,118],{"name":109,"@type":110,"acceptedAnswer":111},"What compatible solutes were tested in Methanoculleus strains under increasing ammonia?","Question",{"text":112,"@type":113},"The study focuses on intracellular osmolyte accumulation involving Nε-acetyl-β-lysine and glycine betaine as compatible solutes under increasing ammonium and ammonium chloride conditions.","Answer",{"name":115,"@type":110,"acceptedAnswer":116},"How did the strains respond to progressive increases in ammonium concentrations?",{"text":117,"@type":113},"All investigated strains grew up to 12 g L−1 NH4+-N, and gradual adaptation increased ammonium/ammonia tolerance in some strains up to 25 g L−1 NH4+-N.",{"name":119,"@type":110,"acceptedAnswer":120},"What is the key finding about Nε-acetyl-β-lysine and ammonia tolerance?",{"text":121,"@type":113},"M. bourgensis strains uniquely accumulated Nε-acetyl-β-lysine during increasing levels of ammonium chloride, indicating a potential biosynthetic mechanism underlying exceptional ammonium/ammonia tolerance and variation among subspecies.","https://schema.org",{"og:url":83,"og:type":124,"og:title":65,"og:site_name":95,"og:description":67},"article",{"robots":126,"canonical":83},"index,follow",{"doc_id":128,"site_id":62},455725,1790818545,{"code":4,"msg":5,"data":131},{"doc_id":128,"user_id":132,"nickname":92,"user_avatar":133,"doc_module":4,"category_id":39,"category_name":40,"doc_title":65,"doc_description":67,"doc_content":134,"file_id":135,"file_url":136,"file_type":137,"file_size":138,"view_count":19,"is_deleted":4,"is_public":8,"is_downloadable":8,"audit_status":8,"page_count":52,"language":139,"language_code":63,"site_id":62,"html_lang":63,"table_of_contents":140,"faqs":141,"seo_title":142,"seo_description":67,"update_tm":143,"read_time":144},13056703020460,"https://ap-avatar.wpscdn.com/avatar/be000253dac470eee5d?_k=1778207105932848923","FEMS Microbiology Letters, 2026, 373, fnaf143  \nDOI: 10.1093/femsle/fnaf143  \nAdvance access publication date: 24 December 2025 Research Article– Biotechnology & Synthetic Biology  \nNε -acetyl-β-lysine or glycine betaine as compatible solutes in response to increasing ammonia in Methanoculleus sp strains  \n *    \nAnna Schnürer , Maria Westerholm , Anders Broberg  \nDepartment of Molecular Sciences, Swedish University of Agricultural Sciences, Uppsala BioCenter, Box 7025, SE-750 07 Uppsala, Sweden  \n∗ Corresponding author. Anna Schnürer, Department of Molecular Sciences, BioCenter, Swedish University of Agricultural Sciences, SLU, Box 7015, 750 07 Uppsala, Sweden, E-mail: [anna.schnurer@slu.se](anna.schnurer@slu.se)  \nEditor: Michael Sauer  \nAbstract  \nMethanogens rely on compatible solutes to withstand osmotic stress, yet their responses to high ammonium concentrations, common in biogas digesters, remain poorly understood. In this study, intracellular osmolyte accumulation was examined in four Methanoculleus bourgensis strains (MAB1, MAB2, MAB3, and BA1), isolated from high-ammonia biogas digesters, under progressive increase in concentrations of ammonium and sodium chloride. Their responses were compared with those of the type strain Methanoculleus bourgensis MS2T and the halophilic Methanoculleus submarinus Nankai-1T . All investigated strain grew to 12 g l−1 NH4 + -N (0.3 mg l−1 NH3), and gradual adaptation increased ammonium/ammonia tolerance in some strains to 25 g l−1 NH4 + -N. Whereas the reference strains accumulated glycine betaine under both ammonium and sodium chloride stress, the M. bourgensis strains from high ammonia biogas systems uniquely accumulated Nε -acetyl-β-lysine during increasing levels of ammonium chloride. This β-amino acid derivative is known as a NaCl-induced osmoprotectant in methanogens, but it´s association with high ammonium/ammonia levels in pure cultures has not previously been demonstrated. Our findings identify Nε -acetyl-β-lysine biosynthesis as a potential mechanism underpinning the exceptional ammonium/ammonia tolerance of M. bourgensis, a taxon frequently dominating methane production in high-ammonia biogas systems, while also revealing notable variation in this trait among its subspecies.  \nKeywords: methanogen; ammonia stress; compatible solute; glycine betaine; Nε -acetyl-β-lysine; HR-MAS NMR  \nIntroduction  \nAnaerobic digestion (AD) is an established biological process used to treat a wide range of organic waste materials while simultaneously generating renewable energy in the form of biogas and producing a nutrient-rich digestate suitable for use as fertilizer (Kougias et al. 2018) . The degradation of organic matter during the AD proceed via four main interdependent steps, hydrolysis, acidogenesis, acetogenesis, and methanogenesis, performed by different groups of microorganisms (Schnürer 2016) .  \nWhen protein-rich substrates, such as food waste and animal manure are degraded, ammonium is released. Although, ammonium serves an essential nutrient for many microorganisms (Merrick et al. 1995) high concentrations can inhibit key populations. Elevated ammonium levels particularly inhibit acetate-utilizing (aceticlastic) methanogens, resulting in volatile acid accumulation and reduced methane production (Schnürer et al. 2008 , Duanet al. 2022 , Wang et al. 2022) . In aqueous solution, ammonium exists in two forms, unionized free ammonia (NH3) and the ammonium ion (NH4 +) . NH3 is generally considered more toxic as it freely diffuses across cell membranes. The proportion of NH3 vs NH4 + is increased with higher temperature and pH (CapsonTojo et al. 2020) . Once, inside the cells, NH3 is converted to NH4 + , disrupting intracellular pH homeostasis and increasing osmotic pressure, which can lead to excessive water influx, leading to cell  \nswelling and, potentially, lysis (Sprott et al. 1986 , Bremer et al. 2019,) .  \nAll microorganisms must maintain an intracellular osmotic pressure sligh","cbCaiqRAgnXjdnWJ","https://ap.wps.com/l/cbCaiqRAgnXjdnWJ","pdf",1422105,"English","# Abstract\n# Keywords\n# Introduction","[{\"question\":\"What compatible solutes were tested in Methanoculleus strains under increasing ammonia?\",\"answer\":\"The study focuses on intracellular osmolyte accumulation involving Nε-acetyl-β-lysine and glycine betaine as compatible solutes under increasing ammonium and ammonium chloride conditions.\"},{\"question\":\"How did the strains respond to progressive increases in ammonium concentrations?\",\"answer\":\"All investigated strains grew up to 12 g L−1 NH4+-N, and gradual adaptation increased ammonium/ammonia tolerance in some strains up to 25 g L−1 NH4+-N.\"},{\"question\":\"What is the key finding about Nε-acetyl-β-lysine and ammonia tolerance?\",\"answer\":\"M. bourgensis strains uniquely accumulated Nε-acetyl-β-lysine during increasing levels of ammonium chloride, indicating a potential biosynthetic mechanism underlying exceptional ammonium/ammonia tolerance and variation among subspecies.\"}]","Nε-acetyl-β-lysine or glycine betaine as compatible solutes in response to increasing ammonia in Methanoculleus sp strains | PDF",1790743992,25]