Journal of Microbiology

Review

MAPK Cascades in Plant Microbiota Structure and Functioning: Thijs Van Gerrewey, Hoo Sun Chung; J. Microbiol. 2024;62(3):231-248. Published online April 8, 2024; DOI: https://doi.org/10.1007/s12275-024-00114-3

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Abstract: Mitogen-activated protein kinase (MAPK) cascades are highly conserved signaling modules that coordinate diverse biological processes such as plant innate immunity and development. Recently, MAPK cascades have emerged as pivotal regulators of the plant holobiont, infuencing the assembly of normal plant microbiota, essential for maintaining optimal plant growth and health. In this review, we provide an overview of current knowledge on MAPK cascades, from upstream perception of microbial stimuli to downstream host responses. Synthesizing recent fndings, we explore the intricate connections between MAPK signaling and the assembly and functioning of plant microbiota. Additionally, the role of MAPK activation in orchestrating dynamic changes in root exudation to shape microbiota composition is discussed. Finally, our review concludes by emphasizing the necessity for more sophisticated techniques to accurately decipher the role of MAPK signaling in establishing the plant holobiont relationship.

Journal Article

Pat- and Pta-mediated protein acetylation is required for horizontallyacquired virulence gene expression in Salmonella Typhimurium: Hyojeong Koo , Eunna Choi , Shinae Park , Eun-Jin Lee , Jung-Shin Lee; J. Microbiol. 2022;60(8):823-831. Published online May 27, 2022; DOI: https://doi.org/10.1007/s12275-022-2095-y

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Abstract: Salmonella Typhimurium is a Gram-negative facultative pathogen that causes a range of diseases, from mild gastroenteritis to severe systemic infection in a variety of animal hosts. S. Typhimurium regulates virulence gene expression by a silencing mechanism using nucleoid-associated proteins such as Histone-like Nucleoid Structuring protein (H-NS) silencing. We hypothesize that the posttranslational modification, specifically protein acetylation, of proteins in gene silencing systems could affect the pathogenic gene expression of S. Typhimurium. Therefore, we created acetylation-deficient mutant by deleting two genes, pat and pta, which are involved in the protein acetylation pathway. We observed that the pat and pta deletion attenuates mouse virulence and also decreases Salmonella’s replication within macrophages. In addition, the Δpat Δpta strain showed a decreased expression of the horizontally-acquired virulence genes, mgtC, pagC, and ugtL, which are highly expressed in low Mg2+. The decreased virulence gene expression is possibly due to higher H-NS occupancy to those promoters because the pat and pta deletion increases H-NS occupancy whereas the same mutation decreases occupancy of RNA polymerase. Our results suggest that Pat- and Pta-mediated protein acetylation system promotes the expression of virulence genes by regulating the binding affinity of H-NS in S. Typhimurium.

Review

Aequoribacter fuscus gen. nov., sp. nov., a new member of the family Halieaceae, isolated from coastal seawater: Shan-Hui Li , Jaeho Song , Ilnam Kang , Juchan Hwang , Jang-Cheon Cho; J. Microbiol. 2020;58(6):463-471. Published online May 27, 2020; DOI: https://doi.org/10.1007/s12275-020-0206-1

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Abstract: A Gram-stain-negative, rod-shaped, obligately aerobic, nonflagellated, and chemoheterotrophic bacterium, designated IMCC3088T, was isolated from coastal seawater of the Yellow Sea. The 16S rRNA gene sequence analysis indicated that this strain belonged to the family Halieaceae which shared the highest sequence similarities with Luminiphilus syltensis NOR5-1BT (94.5%) and Halioglobus pacificus S1-72T (94.5%), followed by 92.3–94.3% sequence similarities with other species within the aforementioned family. Phylogenetic analyses demonstrated that strain IMCC3088T was robustly clustered with Luminiphilus syltensis NOR5-1BT within the family Halieaceae. However, average amino acid identity (AAI), percentages of conserved proteins (POCP), average nucleotide identity (ANI), and alignment fraction (AF) between strain IMCC3088T and Luminiphilus syltensis NOR5-1BT were 54.5%, 47.7%, 68.0%, and 16.5%, respectively, suggesting that they belonged to different genera. Whole-genome sequencing of strain IMCC3088T revealed a 3.1 Mbp genome size with a DNA G + C content of 51.7 mol%. The genome encoded diverse metabolic pathways including sulfur oxidation, phenol degradation, and proteorhodopsin phototrophy. Mono-unsaturated fatty acids were found to be the predominant cellular fatty acid components in the strain. Phosphatidylethanolamine, phosphatidylglycerol, and diphosphatidylglycerol were the primarily identified polar lipids, and ubiquinone-8 was identified as a major respiratory quinone. The taxonomic data collected herein suggested that strain IMCC3088T represented a novel genus and species of the family Halieaceae, for which the name Aequoribacter fuscus gen. nov., sp. nov. is proposed with the type strain (= KACC 15529T = NBRC 108213T).

Journal Article

Rhizocompartments and environmental factors affect microbial composition and variation in native plants: Myung-Suk Kang , Moonsuk Hur , Soo-Je Park; J. Microbiol. 2019;57(7):550-561. Published online June 27, 2019; DOI: https://doi.org/10.1007/s12275-019-8646-1

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Abstract: Molecular analysis based on large-scale sequencing of the plant microbiota has revealed complex relationships between plants and microbial communities, and environmental factors such as soil type can influence these relationships. However, most studies on root-associated microbial communities have focused on model plants such as Arabidopsis, rice or crops. Herein, we examined the microbiota of rhizocompartments of two native plants, Sedum takesimense Nakai and Campanula takesimana Nakai, using archaeal and bacterial 16S rRNA gene amplicon profiling, and assessed relationships between environmental factors and microbial community composition. We identified 390 bacterial genera, including known plant-associated genera such as Pseudomonas, Flavobacterium, Bradyrhizobium and Rhizobium, and uncharacterized clades such as DA101 that might be important in root-associated microbial communities in bulk soil. Unexpectedly, Nitrososphaera clade members were abundant, indicating functional association with roots. Soil texture/type has a greater impact on microbial community composition in rhizocompartments than chemical factors. Our results provide fundamental knowledge on microbial diversity, community and correlations with environmental factors, and expand our understanding of the microbiota in rhizocompartments of native plants.

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