Applied and Environmental Microbiology最新文献

{"title":"Microbial hauberks: composition and function of surface layer proteins in gammaproteobacterial methanotrophs.","authors":"Richard Hamilton, William Gebbie, Chynna Bowman, Alex Mantanona, Marina G Kalyuzhnaya","doi":"10.1128/aem.01364-24","DOIUrl":"10.1128/aem.01364-24","url":null,"abstract":"<p><p>Many species of proteobacterial methane-consuming bacteria (methanotrophs) form a hauberk-like envelope represented by a surface (S-) layer protein (SLP) matrix. While several proteins were predicted to be associated with the cell surface, the composition and function of the hauberk matrix remained elusive. Here, we report the identification of the genes encoding the hauberk-forming proteins in two gamma-proteobacterial (Type I) methanotrophs, <i>Methylotuvimicrobium buryatense</i> 5GB1 (EQU24_15540) and <i>Methylotuvimicrobium alcaliphilum</i> 20Z^R (MEALZ_0971 and MEALZ_0972). The proteins share 40% amino acid (AA) sequence identity with each other and are distantly related to the RsaA proteins from <i>Caulobacter crescentus</i> (20% AA sequence identity). Deletion of these genes resulted in loss of the characteristic hauberk pattern on the cell surface. A set of transcriptional fusions between the MEALZ_0971 and a superfolder green fluorescent protein (sfGFP) further confirmed its surface localization. The functional roles of the hauberk and cell-surface-associated proteins, including MEALZ_0971, MEALZ_0972, EQU24_15540, and a copper-induced CorA protein, were further investigated via gene expression studies and phenotypic tests. The hauberk core protein of <i>M. alcaliphilum</i> 20Z^R showed constitutive expression across 18 growth conditions with reduced growth at high salinity, high methanol, and metal-limited conditions, suggesting a role in cell-envelope stability and metal scavenging. Overall, understanding the genetics, composition, and cellular functions of S-layers contributes to our knowledge of methanotroph adaptation to environmental perturbations and opens a promising prospect for (nano)biotechnology applications.</p><p><strong>Importance: </strong>Understanding the genetics, composition, and cellular functions of the cell envelope proteins, such as S-layers, contributes to our knowledge of microbial cell biology and stress responses and molecular adaptations to environmental perturbations. In addition, this study opens a promising prospect for (nano)biotechnology applications of methane-derived self-assembling protein materials.</p>","PeriodicalId":8002,"journal":{"name":"Applied and Environmental Microbiology","volume":" ","pages":"e0136424"},"PeriodicalIF":3.9,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11784148/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142913240","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Variability in cadmium tolerance of closely related <i>Listeria monocytogenes</i> isolates originating from dairy processing environments.","authors":"Andrea Domen, Jenna Porter, Jared Johnson, James Molyneux, Lorraine McIntyre, Jovana Kovacevic, Joy Waite-Cusic","doi":"10.1128/aem.01281-24","DOIUrl":"10.1128/aem.01281-24","url":null,"abstract":"&lt;p&gt;&lt;p&gt;Increased tolerance to cadmium in &lt;i&gt;Listeria monocytogenes&lt;/i&gt; has been suggested to contribute to their persistence in natural and food production environments. This study investigated the phenotypic cadmium response of &lt;i&gt;L. monocytogenes&lt;/i&gt; strains with efflux pump &lt;i&gt;cadAC&lt;/i&gt; (variants 1-4) and related strains with &lt;i&gt;cadA1C1&lt;/i&gt;. Growth of &lt;i&gt;cadAC&lt;/i&gt; variant strains (&lt;i&gt;n&lt;/i&gt; = 5) in 0 µM-120 µM cadmium salts (CdCl&lt;sub&gt;2&lt;/sub&gt;, CdSO&lt;sub&gt;4&lt;/sub&gt;) in Mueller-Hinton broth (MHB) was evaluated. Additionally, 88 &lt;i&gt;L&lt;/i&gt;. &lt;i&gt;monocytogenes&lt;/i&gt; strains from dairy processing facilities were exposed to 43.8 µM CdCl&lt;sub&gt;2&lt;/sub&gt; in MHB, and their lag phase duration (LPD) was measured. Strains with &lt;i&gt;cadA1&lt;/i&gt; through &lt;i&gt;cadA3&lt;/i&gt; showed similar growth trends in the presence of cadmium, while the &lt;i&gt;cadA4&lt;/i&gt; variant (Scott A) had the highest CdCl&lt;sub&gt;2&lt;/sub&gt; minimum inhibitory concentration (175 µM). Growth varied between the two salts, with CdSO&lt;sub&gt;4&lt;/sub&gt; significantly increasing LPD (&lt;i&gt;P&lt;/i&gt; &lt; 0.05) compared to CdCl&lt;sub&gt;2&lt;/sub&gt;. In 43.8 µM CdCl&lt;sub&gt;2&lt;/sub&gt;, &lt;i&gt;cadA1&lt;/i&gt; strains displayed LPDs ranging from 0.99 ± 0.14 h to 6.44 ± 0.08 h, with no clear genomic differences explaining this variability. Strains without &lt;i&gt;cadA&lt;/i&gt; did not grow at 43.8 µM CdCl&lt;sub&gt;2&lt;/sub&gt; but exhibited low tolerance (10.9 µM CdCl&lt;sub&gt;2&lt;/sub&gt;), potentially due to non-specific soft metal ATPases (626 aa; 737 aa) and soft metal resistance proteins encoded by &lt;i&gt;czc&lt;/i&gt; genes (289 aa; 291 aa; 303 aa) within their chromosomes. These findings enhance our understanding of &lt;i&gt;L. monocytogenes&lt;/i&gt; cadmium tolerance and underscore the need for further research to explore the genetic and physiological factors underlying these trends.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Importance: &lt;/strong&gt;Mobile genetic elements in &lt;i&gt;Listeria monocytogenes&lt;/i&gt; contribute to its survival in natural and food processing environments. This study focused on how different genetic variants of the efflux pump gene &lt;i&gt;cadAC&lt;/i&gt; and group of closely related &lt;i&gt;cadA1C1&lt;/i&gt; strains respond to cadmium exposure. When exposed to two cadmium salts, cadmium chloride and cadmium sulfate, we observed varying growth patterns, with a significantly longer lag phase in cadmium sulfate compared to cadmium chloride. Strains with &lt;i&gt;cadA1&lt;/i&gt; to &lt;i&gt;cadA3&lt;/i&gt; had similar growth trends, whereas a strain with the &lt;i&gt;cadA4&lt;/i&gt; variant had the highest minimum inhibitory concentration value. Among 88 strains from dairy processing facilities, significant phenotypic differences were observed despite core genome similarities, indicating other underlying genetic and physiological factors contribute to cadmium tolerance. Since cadmium tolerance studies in &lt;i&gt;L. monocytogenes&lt;/i&gt; are limited, with rare phenotypic comparisons between closely related strains, our study makes an important observation and contribution to understanding of &lt;i&gt;L. monocytogenes&lt;/i&gt; tolerance to cadmium by providing phenotypic comparisons between numerous strains withi","PeriodicalId":8002,"journal":{"name":"Applied and Environmental Microbiology","volume":" ","pages":"e0128124"},"PeriodicalIF":3.9,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11784300/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142680690","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Microbiome composition and turnover in the face of complex lifecycles and bottlenecks: insights through the study of dung beetles.","authors":"Joshua A Jones, Irene Garcia Newton, Armin P Moczek","doi":"10.1128/aem.01278-24","DOIUrl":"10.1128/aem.01278-24","url":null,"abstract":"<p><p>Microbiome composition and function often change throughout a host's life cycle, reflecting shifts in the ecological niche of the host. The mechanisms that establish these relationships are therefore important dimensions of host ecology and evolution; yet, their nature remains poorly understood. Here, we sought to investigate the microbial communities associated with the complex life cycle of the dung beetle <i>Onthophagus taurus</i> and the relative contributions of host life stage, sex, and environment in determining microbiome assembly. We find that <i>O. taurus</i> plays host to a diverse microbiota that undergo drastic community shifts throughout host development, influenced by host life stage, environmental microbiota, and, to a lesser degree, sex. Contrary to predictions, we found that egg and pupal stages-despite the absence of a digestive tract or defined microbe-storing organs-do not constrain microbial maintenance, while host-constructed environments, such as a maternally derived fecal pellet or the pupal chamber constructed by late larvae, may still serve as complementary microbial refugia for select taxa. Lastly, we identify a small community of putative core microbiota likely to shape host development and fitness. Our results provide important insights into mechanisms employed by solitary organisms to assemble, maintain, and adjust beneficial microbiota to confront life-stage-specific needs and challenges.</p><p><strong>Importance: </strong>As the influence of symbionts on host ecology, evolution, and development has become more apparent so has the importance of understanding how hosts facilitate the reliable maintenance of their interactions with these symbionts. A growing body of work has thus begun to identify diverse behaviors and physiological mechanisms underpinning the selective colonization of beneficial symbionts across a range of host taxa. Yet, how organisms with complex life cycles, such as holometabolous insects, establish and maintain key symbionts remains poorly understood. This is particularly interesting considering the drastic transformations of both internal and external host morphology, and the ecological niche shifts in diet and environment, that are the hallmark of metamorphosis. This work investigates the dynamic changes of the microbiota associated with the complex life cycle and host-constructed environments of the bull-headed dung beetle, <i>Onthophagus taurus</i>, a useful model for understanding how organisms may maintain and modulate their microbiota across development.</p>","PeriodicalId":8002,"journal":{"name":"Applied and Environmental Microbiology","volume":" ","pages":"e0127824"},"PeriodicalIF":3.9,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11784073/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142863170","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Structural and mechanism-based engineering of sulfotransferase CHST15 for the efficient synthesis of chondroitin sulfate E.","authors":"Zhonghua Wang, Wei Song, Wanqing Wei, Hejia Qi, Weiwei Meng, Jia Liu, Xiaomin Li, Cong Gao, Liming Liu, Guipeng Hu, Yiwen Zhou, Jing Wu","doi":"10.1128/aem.01573-24","DOIUrl":"10.1128/aem.01573-24","url":null,"abstract":"<p><p>Natural chondroitin sulfate (CS), extracted from animal cartilage, is widely used in the pharmaceuticals and foods. However, contamination with animal-derived heteropolysaccharides presents significant challenges, including potential immune responses. To address this, we developed a green and efficient method for synthesizing chondroitin sulfate E (CSE) via enzymatic synthesis, identifying <i>Ec</i>CHST15, a sulfotransferase that catalyzes the conversion of chondroitin sulfate A (CSA) to CSE. We investigated the novel catalytic mechanism of CHST15 through quantum mechanical (QM) calculations and experimental validation, confirming its alignment with the SN2 reaction mechanism. Subsequently, we enhanced the catalytic efficiency of CHST15 using protein engineering, improving the catalytic efficiency from 18.1% in the wild type (WT) to 62.5% in the M7 mutant-a 3.5-fold increase. Finally, we constructed a six-enzyme cascade whole-cell catalyst, achieving a 72.2% conversion of 15 g/L CSA to produce CSE within 24 h. These findings offer a promising strategy for the industrial production of CSE.IMPORTANCECurrent methods for obtaining chondroitin sulfate (CS) primarily rely on tissue extraction and chemical synthesis. However, these approaches are hindered by contamination risks from animal-derived heteropolysaccharides and the technical challenges inherent in complex chemical synthesis, limiting the scalability of industrial CS production. To address this, we developed a green and efficient enzymatic biosynthesis method for chondroitin sulfate E (CSE). By identifying and engineering the sulfotransferase CHST15 from <i>Erpetoichthys calabaricus</i>, we created a mutant (<i>Ec</i>CHST15^M7) with a 3.5-fold increase in catalytic efficiency toward chondroitin sulfate A (CSA) compared to the wild-type enzyme. Additionally, we constructed a six-enzyme cascade whole-cell biocatalyst, achieving a 72.2% conversion rate from CSA to CSE. This study opens new avenues for the industrial-scale production of CSE through sustainable enzymatic processes.</p>","PeriodicalId":8002,"journal":{"name":"Applied and Environmental Microbiology","volume":" ","pages":"e0157324"},"PeriodicalIF":3.9,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11784081/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142765697","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"<i>Wolbachia</i> strain <i>w</i>MelM disrupts egg retention by <i>Aedes aegypti</i> females prevented from ovipositing.","authors":"Perran A Ross, Ella Yeatman, Mel S Berran, Xinyue Gu, Ary A Hoffmann, Belinda van Heerwaarden","doi":"10.1128/aem.01491-24","DOIUrl":"10.1128/aem.01491-24","url":null,"abstract":"<p><p><i>Aedes aegypti</i> mosquitoes are well adapted to dry climates and can retain their eggs for extended periods in the absence of suitable habitat. <i>Wolbachia</i> strains transferred from other insects to mosquitoes can be released to combat dengue transmission by blocking virus replication and spreading through populations, but host fitness costs imposed by <i>Wolbachia</i>, particularly under some environments, can impede spread. We, therefore, assessed the impact of two <i>Wolbachia</i> strains being released for dengue control (<i>w</i>AlbB and <i>w</i>MelM) on fecundity and egg viability following extended egg retention (up to 24 days) under laboratory conditions. Egg viability following retention decreased to a greater extent in females carrying <i>w</i>MelM compared to uninfected or <i>w</i>AlbB females. Fertility fully recovered in uninfected females following a second blood meal after laying retained eggs, while <i>w</i>MelM females experienced only partial recovery. Effects of <i>w</i>MelM on egg retention were similar regardless of whether females were crossed to uninfected or <i>w</i>MelM males, suggesting that fitness costs were triggered by <i>Wolbachia</i> presence in females. The fecundity and hatch proportions of eggs of <i>w</i>MelM females declined with age, regardless of whether females used stored sperm or were recently inseminated. Costs of some <i>Wolbachia</i> strains during egg retention may affect the invasion and persistence of <i>Wolbachia</i> in release sites where larval habitats are scarce and/or intermittent.IMPORTANCE<i>Wolbachia</i> mosquito releases are expanding around the world with substantial impacts on dengue transmission. Releases have succeeded in many locations, but the establishment of <i>Wolbachia</i> has been challenging in some environments, and the factors contributing to this outcome remain unresolved. Here, we explore the effects of <i>Wolbachia</i> on a novel trait, egg retention, which is likely to be important for the persistence of mosquito populations in locations with intermittent rainfall. We find substantial impacts of the <i>Wolbachia</i> strain <i>w</i>MelM on the quality of retained eggs but not the <i>w</i>AlbB strain. This cost is driven by the <i>Wolbachia</i> infection status of the female and can partially recover following a second blood meal. The results of our study may help to explain the difficulty in establishing <i>Wolbachia</i> strains at some field release sites and emphasize the need to characterize <i>Wolbachia</i> phenotypes across a variety of traits and strains.</p>","PeriodicalId":8002,"journal":{"name":"Applied and Environmental Microbiology","volume":" ","pages":"e0149124"},"PeriodicalIF":3.9,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11784415/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142765706","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Untrimmed ITS2 metabarcode sequences cause artificially reduced abundances of specific fungal taxa.","authors":"Kathleen E Kyle, Jonathan L Klassen","doi":"10.1128/aem.01537-24","DOIUrl":"10.1128/aem.01537-24","url":null,"abstract":"<p><p>Advances in DNA metabarcoding have greatly expanded our knowledge of microbial communities in recent years. Pipelines and parameters have been tested extensively for bacterial metabarcoding using the 16S rRNA gene and best practices are largely established. For fungal metabarcoding using the internal transcribed spacer (ITS) gene, however, only a few studies have considered how such pipelines and parameters can affect community prediction. Here, we report a novel bias uncovered during ITS region 2 (ITS2) sequencing of <i>Trichoderma</i>-infected ant fungus gardens and confirmed this bias using mock communities. Abnormally low forward read quality caused <i>Trichoderma</i> ITS2 reads to be computationally filtered before and during read pair merging, thus almost entirely eliminating <i>Trichoderma</i> amplicon sequence variants from the resulting fungal community profiles. Sliding window quality trimming before filtering allowed most of these reads to pass filtering and merge successfully, producing community profiles that now correlated with visual signs of <i>Trichoderma</i> infection and matched the composition of the mock communities. Applying such sliding window trimming to a previously generated environmental ITS2 data set increased the detected fungal diversity and again overcame read quality biases against <i>Trichoderma</i> to detect it in nearly every sample instead and often at high relative abundances. This analysis additionally identified a similar, but distinct, bias against a second fungal genus <i>Meyerozyma</i>. The prevalence of such quality biases against other fungal ITS sequences is unknown but may be widespread. We, therefore, advocate for the routine use of sliding window quality trimming as a best practice in ITS2 metabarcoding analysis.</p><p><strong>Importance: </strong>Metabarcode sequencing produces DNA abundance profiles that are presumed to reflect the actual microbial composition of their corresponding input samples. However, this assumption is not always tested, and taxon-specific biases are often not apparent, especially for low-abundance taxa in complex communities. Here, we identified internal transcribed spacer region 2 (ITS2) read quality aberrations that caused dramatic reductions in the relative abundances of specific taxa in multiple data sets characterizing ant fungus gardens. Such taxon-specific biases in read quality may be widespread in other environments and for other fungal taxa, thereby causing incorrect descriptions of these mycobiomes.</p>","PeriodicalId":8002,"journal":{"name":"Applied and Environmental Microbiology","volume":" ","pages":"e0153724"},"PeriodicalIF":3.9,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11784184/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142891490","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Correction for Tothero et al., \"<i>Leptothrix ochracea</i> genomes reveal potential for mixotrophic growth on Fe(II) and organic carbon\".","authors":"Gracee K Tothero, Rene L Hoover, Ibrahim F Farag, Daniel I Kaplan, Pamela Weisenhorn, David Emerson, Clara S Chan","doi":"10.1128/aem.02044-24","DOIUrl":"10.1128/aem.02044-24","url":null,"abstract":"","PeriodicalId":8002,"journal":{"name":"Applied and Environmental Microbiology","volume":" ","pages":"e0204424"},"PeriodicalIF":3.9,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11784243/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142724994","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"<i>Wohlfahrtiimonas chitiniclastica</i>: current insights and complementary review from Chinese cases.","authors":"Qin Yuan, Cheng Peng, Xin-Lin Sun, Zi-Chun Nie, Yi-Wen Zhang, Ying-Ye Miao","doi":"10.1128/aem.00965-24","DOIUrl":"10.1128/aem.00965-24","url":null,"abstract":"<p><p><i>Wohlfahrtiimonas chitiniclastica</i> is an emerging zoonotic pathogen associated with bacteremia, myiasis, and soft tissue infections. It is insufficiently identified and underestimated due to reasons, such as shortcomings of the traditional identification techniques and language barriers in local case reports from different regions. In this review, we summarize the currently available literature. In particular, we added previously overlooked cases from Chinese and other medical communities. The clinical characteristics, identification, and treatment of <i>W. chitiniclastica</i> are discussed. This work provides a complete review of the previous work including cases from human, animal, and other sources.</p>","PeriodicalId":8002,"journal":{"name":"Applied and Environmental Microbiology","volume":" ","pages":"e0096524"},"PeriodicalIF":3.9,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11784361/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142724991","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ferruginous hemeprotein HhuH facilitates the cadmium adsorption and chromium reduction in <i>Stenotrophomonas</i> sp. SY1.","authors":"Zijie Zhou, Hongbo Yu, Jiahui Liu, Lin Zhu, Gejiao Wang, Kaixiang Shi","doi":"10.1128/aem.02097-24","DOIUrl":"10.1128/aem.02097-24","url":null,"abstract":"<p><p>Cadmium (Cd) and chromium (Cr) are frequently encountered toxicants, while iron (Fe) plays a crucial role in bacterial survival under conditions of heavy metal stress. However, intracellular Fe ion depletion by heavy metals leads to a state of Fe starvation. Therefore, it is imperative to investigate the mechanism through which bacteria maintain a balance between heavy metal detoxification and Fe homeostasis. This study demonstrates Cd(II) immobilization and Cr(VI) reduction abilities of <i>Stenotrophomonas</i> sp. SY1, while proteomics reveals the upregulation of heme metabolism in response to Cd(II) and Cr(VI) exposure. The expression of the heme-uptake system in <i>Escherichia coli</i> can enhance Cd(II) immobilization and facilitate Cr(VI) reduction. The ferruginous hemeprotein HhuH exhibits the ability to chelate Cd(II) and reduce Cr(VI). The presence of Cd(II) and Cr(VI) in strain SY1 initially led to Fe starvation. Subsequently, the hemeprotein HhuH facilitated Cd(II) adsorption and Cr(VI) reduction, thereby restoring normal cellular Fe homeostasis. Our findings explain the hemeprotein-mediated mechanism for Cd(II) adsorption and Cr(VI) reduction, providing further insights into the correlation between heavy metal and Fe metabolism.IMPORTANCEIron (Fe) is an indispensable trace element for many organisms, and virtually, all bacteria require Fe as a cofactor in enzymes to facilitate redox reactions involved in fundamental cellular processes during periods of heavy metal stress. Understanding bacterial response to Fe in heavy metal contamination is essential. Therefore, our study elucidates Cd(II) adsorption and Cr(VI) reduction processes mediated by the Fe-bearing hemeprotein HhuH. It is a unique trifunctional protein capable of chelating Cd(II) and reducing Cr(VI), demonstrating significant potential in the environmental remediation of heavy metals.</p>","PeriodicalId":8002,"journal":{"name":"Applied and Environmental Microbiology","volume":" ","pages":"e0209724"},"PeriodicalIF":3.9,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11784086/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142765710","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The phospho-ferrozine assay: a tool to study bacterial redox-active metabolites produced at the plant root.","authors":"David Giacalone, Emilly Schutt, Darcy L McRose","doi":"10.1128/aem.02194-24","DOIUrl":"10.1128/aem.02194-24","url":null,"abstract":"<p><p>Soil microbial communities are pivotal to plant health and nutrient acquisition. It is becoming increasingly clear that many interactions, both among and between microbes and plants, are governed by small bioactive molecules or \"secondary metabolites\" that can aid in communication, competition, and nutrient uptake. Yet, secondary metabolite biogeography - who makes what, where, and why-is in its infancy. Further, secondary metabolite biosynthesis genes are often silent or weakly expressed under standard laboratory conditions, making it incredibly difficult to study these small molecules. To begin to address these dual challenges, we focused on redox-active metabolites (RAMs), a specific class of small molecules, and took advantage of recent findings that many RAMs aid in acquiring phosphorus and that their production is frequently stimulated by stress for this macronutrient. We developed a screen for RAM-producing bacteria that leverages phosphorus limitation to stimulate metabolite biosynthesis and uses a colorimetric (ferrozine) iron-reduction assay to identify redox activity. We isolated 557 root-associated bacteria from grasses collected at sites across the United States (Santa Rita Experimental Range [AZ], Konza Prairie Biological Station [KS], and Harvard Forest [MA]) and from commercial tomato plants and screened them for RAM production. We identified 128 soil isolates of at least 19 genera across Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes that produced RAMs under phosphorus stress. Our work reveals that the production of RAMs under phosphorus stress is common across diverse soil bacteria and provides an approach to screen for these small molecules rapidly.IMPORTANCEBy secreting secondary metabolites, bacteria at the plant root can defend against diseases and help acquire essential nutrients. However, the genes that synthesize secondary metabolites are typically inactive or are weakly expressed under standard laboratory conditions. This fact makes it difficult to study these small molecules and hinders the discovery of novel small molecules that may play crucial roles in agricultural and biomedical settings. Here, we focus on redox-active metabolites (RAMs), a class of secondary metabolites that can help bacteria solubilize phosphorus and are often produced when phosphorus is limited. We developed a screen that rapidly identifies RAM-producing bacteria by utilizing a colorimetric iron-reduction assay in combination with phosphorus limitation to stimulate biosynthesis. The screen reveals that RAM-producing bacteria are far more prevalent in soil than previously appreciated and that this approach can be used to identify RAM producers.</p>","PeriodicalId":8002,"journal":{"name":"Applied and Environmental Microbiology","volume":" ","pages":"e0219424"},"PeriodicalIF":3.9,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11784245/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142833769","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}