Journal of Microbiology

Volume 62(11); November 2024

Review

Extensive Genomic Rearrangement of Catalase-Less Cyanobloom-Forming Microcystis aeruginosa in Freshwater Ecosystems.: Minkyung Kim, Jaejoon Jung, Wonjae Kim, Yerim Park, Che Ok Jeon, Woojun Park; J. Microbiol. 2024;62(11):933-950. Published online October 8, 2024; DOI: https://doi.org/10.1007/s12275-024-00172-7

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Abstract: Many of the world's freshwater ecosystems suffer from cyanobacteria-mediated blooms and their toxins. However, a mechanistic understanding of why and how Microcystis aeruginosa dominates over other freshwater cyanobacteria during warmer summers is lacking. This paper utilizes comparative genomics with other cyanobacteria and literature reviews to predict the gene functions and genomic architectures of M. aeruginosa based on complete genomes. The primary aim is to understand this species' survival and competitive strategies in warmer freshwater environments. M. aeruginosa strains exhibiting a high proportion of insertion sequences (~ 11%) possess genomic structures with low synteny across different strains. This indicates the occurrence of extensive genomic rearrangements and the presence of many possible diverse genotypes that result in greater population heterogeneities than those in other cyanobacteria in order to increase survivability during rapidly changing and threatening environmental challenges. Catalase-less M. aeruginosa strains are even vulnerable to low light intensity in freshwater environments with strong ultraviolet radiation. However, they can continuously grow with the help of various defense genes (e.g., egtBD, cruA, and mysABCD) and associated bacteria. The strong defense strategies against biological threats (e.g., antagonistic bacteria, protozoa, and cyanophages) are attributed to dense exopolysaccharide (EPS)-mediated aggregate formation with efficient buoyancy and the secondary metabolites of M. aeruginosa cells. Our review with extensive genome analysis suggests that the ecological vulnerability of M. aeruginosa cells can be overcome by diverse genotypes, secondary defense metabolites, reinforced EPS, and associated bacteria.

Journal Articles

Genomic Characterization and Comparative Analysis of Streptococcus zhangguiae sp. nov. Isolated from the Respiratory Tract of Marmota Himalayana.: Caixin Yang, Jiajia Ma, Huimin Zhou, Jing Yang, Ji Pu, Shan Lu, Dong Jin, Liyun Liu, Kui Dong, Jianguo Xu; J. Microbiol. 2024;62(11):951-963. Published online November 4, 2024; DOI: https://doi.org/10.1007/s12275-024-00177-2

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Abstract: Two Gram-stain-positive, oxidase-negative, non-motile, facultative anaerobic, α-hemolytic, coccus-shaped bacteria (zg-86^T and zg-70) were isolated from the respiratory tracts of marmots (Marmota Himalayana) on the Qinghai-Tibet Plateau of China. Phylogenetic analysis of the 16S rRNA gene and 545 core genes revealed that these two strains belong to the Streptococcus genus. These strains were most closely related to Streptococcus respiraculi HTS25^T, Streptococcus cuniculi CCUG 65085^T, and Streptococcus marmotae HTS5^T. The average nucleotide identity (ANI) and digital DNA‒DNA hybridization (dDDH) were below the threshold for species delineation. The predominant cellular fatty acids (CFAs) in this novel species were C_16:0, C_18:0, and C_18:1ω9c, whereas the primary polar lipids were phosphatidylglycerol (PG), phosphatidylethanolamine (PE) and an unknown phosphoglycolipid (PGL). The optimal growth conditions for the strains were 37 °C, pH 7.0, and 0.5% (w/v) NaCl on brain-heart infusion (BHI) agar supplemented with 5% defibrinated sheep blood. Comparative genomics analyses revealed the potential pathogenicity of strain zg-86^T through comparisons with suis subclade strains in terms of virulence factors, pathogen-host interactions (PHIs) and mobile genetic factors (MGEs). Based on the phenotypic characteristics and phylogenetic analyses, we propose that these two isolates represent novel species in the genus Streptococcus, for which the names Streptococcus zhangguiae sp. nov. (the type strain zg-86^T=GDMCC 1.1758^T=JCM 34273^T) is proposed.

The Impact of Makgeolli Consumption on Gut Microbiota: An Enterotype-Based Preliminary Study.: Gyungcheon Kim, Seongok Kim, Hayan Jung, Seohyun Kang, Gwoncheol Park, Hakdong Shin; J. Microbiol. 2024;62(11):965-972. Published online October 16, 2024; DOI: https://doi.org/10.1007/s12275-024-00176-3

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Abstract: Makgeolli, a traditional Korean liquor, contains components such as lactic acid bacteria and dietary fiber, which can induce changes in the gut microbiome. Since variations in microbiome responses may exist between enterotypes-classifications based on the dominant bacterial populations in the gut-we hypothesized that the consumption of makgeolli leads to enterotype-dependent differences in gut microbial structures among healthy participants. This study aimed to determine the effect of makgeolli consumption on gut microbial structures by stratifying all participants into two enterotype groups: Bacteroides-dominant type (B-type, n = 7) and Prevotella-dominant type (P-type, n = 4). The B-type showed an increase in alpha diversity, while no significant difference was observed in the P-type following makgeolli consumption. The composition of gut microbiota significantly changed in the B-type, whereas no noticeable alteration was observed in the P-type after makgeolli consumption. Notably, Prevotella exhibited the most significant changes only in the P-type. In line with the increased abundance of Prevotella, the genes associated with carbohydrate metabolism, including pentose/glucuronate interconversions, fructose/mannose metabolism, starch/sucrose metabolism and amino sugar/nucleotide sugar metabolism were significantly enriched following makgeolli consumption in the P-type. These findings suggest that makgeolli consumption induces enterotype-dependent alterations in gut microbial composition and metabolic pathways, highlighting the potential for personalized dietary interventions.

Description of Streptococcus dentalis sp. nov., Streptococcus gingivalis sp. nov., and Streptococcus lingualis sp. nov., Isolated from Human Oral Cavities.: Beom-Jin Goo, Young-Sik Choi, Do-Hun Gim, Su-Won Jeong, Jee-Won Choi, Hojun Sung, Jae-Yun Lee, Jin-Woo Bae; J. Microbiol. 2024;62(11):973-983. Published online November 12, 2024; DOI: https://doi.org/10.1007/s12275-024-00178-1

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Abstract: We isolated three novel strains, S1^T, S2^T, and S5^T, from human oral cavities and identified them as distinct novel species. All these strains are facultatively anaerobic, Gram-stain-positive, and non-flagellated bacteria. Their optimal growth conditions for these strains were observed in Columbia broth (CB) at 37 °C, pH 7.0, and in the absence of NaCl. Phylogenetic analyses, employing the 16S rRNA gene and whole-genome sequencing, confirmed that all three strains belong to the genus Streptococcus. The 16S rRNA gene sequences of strains S1^T, S2^T, and S5^T showed the highest similarities to Streptococcus parasanguinis, 98.57%, 99.05%, and 99.05%, respectively, and the orthologous average nucleotide identity (OrthoANI) values between the three strains and S. parasanguinis were 93.82%, 93.67%, and 94.04%, respectively. The pairwise OrthoANI values between the novel strains were 94.37% (S1^T-S2^T), 95.03% (S2^T-S5^T), and 94.71% (S1^T-S5^T). All strains had C_20:1 ω9c and summed feature 8 (C_18:1 ω7c and/or C_18:1 ω6c) as major cellular fatty acids. Additionally, diphosphatidylglycerol (DPG) and hydroxyphosphatidylethanolamine (OH-PE) were identified as major polar lipids. Menaquinone was undetected in all strains. The results from the phylogenetic, phenotypic, chemotaxonomic, and genotypic analyses collectively indicated that strains S1^T, S2^T, and S5^T represent three distinct novel species within the genus Streptococcus, and we propose the names Streptococcus dentalis sp. nov. for strain S1^T (= KCTC 21234^T = JCM 36526^T), Streptococcus gingivalis sp. nov. for strain S2^T (= KCTC 21235^T = JCM 36527^T), and Streptococcus lingualis sp. nov. for strain S5^T (= KCTC 21236^T = JCM 36528^T).

Rhodobacteraceae are Prevalent and Ecologically Crucial Bacterial Members in Marine Biofloc Aquaculture.: Meora Rajeev, Jang-Cheon Cho; J. Microbiol. 2024;62(11):985-997. Published online November 15, 2024; DOI: https://doi.org/10.1007/s12275-024-00187-0

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Abstract: Bioflocs are microbial aggregates primarily composed of heterotrophic bacteria that play essential ecological roles in maintaining animal health, gut microbiota, and water quality in biofloc aquaculture systems. Despite the global adoption of biofloc aquaculture for shrimp and fish cultivation, our understanding of biofloc microbiota-particularly the dominant bacterial members and their ecological functions-remains limited. In this study, we employed integrated metataxonomic and metagenomic approaches to demonstrate that the family Rhodobacteraceae of Alphaproteobacteria consistently dominates the biofloc microbiota and plays essential ecological roles. We first analyzed a comprehensive metataxonomic dataset consisting of 200 16S rRNA gene amplicons collected across three Asian countries: South Korea, China, and Vietnam. Taxonomic investigation identified Rhodobacteraceae as the dominant and consistent bacterial members across the datasets. The predominance of this taxon was further validated through metagenomics approaches, including read taxonomy and read recruitment analyses. To explore the ecological roles of Rhodobacteraceae, we applied genome-centric metagenomics, reconstructing 45 metagenome-assembled genomes. Functional annotation of these genomes revealed that dominant Rhodobacteraceae genera, such as Marivita, Ruegeria, Dinoroseobacter, and Aliiroseovarius, are involved in vital ecological processes, including complex carbohydrate degradation, aerobic denitrification, assimilatory nitrate reduction, ammonium assimilation, and sulfur oxidation. Overall, our study reveals that the common practice of carbohydrate addition in biofloc aquaculture systems fosters the growth of specific heterotrophic bacterial communities, particularly Rhodobacteraceae. These bacteria contribute to maintaining water quality by removing toxic nitrogen and sulfur compounds and enhance animal health by colonizing gut microbiota and exerting probiotic effects.

H-NS is a Transcriptional Repressor of the CRISPR-Cas System in Acinetobacter baumannii ATCC 19606.: Kyeongmin Kim, Md Maidul Islam, Seunghyeok Bang, Jeongah Kim, Chung-Young Lee, Je Chul Lee, Minsang Shin; J. Microbiol. 2024;62(11):999-1012. Published online November 11, 2024; DOI: https://doi.org/10.1007/s12275-024-00182-5

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Abstract: Acinetobacter baumannii is a multidrug-resistant opportunistic pathogen primarily associated with hospital-acquired infections. The bacterium can gain multidrug resistance through several mechanisms, including horizontal gene transfer. A CRISPR-Cas system including several Cas genes could restrict the horizontal gene transfer. However, the molecular mechanism of CRISPR- Cas transcriptional regulation remains unclear. We identified a type I-F CRISPR-Cas system in A. baumannii ATCC 19606^T standard strain based on sequence analysis. We focused on the transcriptional regulation of Cas3, a key protein of the CRISPR-Cas system. We performed a DNA affinity chromatography-pulldown assay to identify transcriptional regulators of the Cas3 promoter. We identified several putative transcriptional factors, such as H-NS, integration host factor, and HU, that can bind to the promoter region of Cas3. We characterized AbH-NS using size exclusion chromatography and cross-linking experiments and demonstrated that the Cas3 promoter can be regulated by AbH-NS in a concentration-dependent manner via an in vitro transcription assay. CRISPR-Cas expression levels in wild-type and hns mutant strains in the early stationary phase were examined by qPCR and β-galactosidase assay. We found that H-NS can act as a repressor of Cas3. Our transformation efficiency results indicated that the hns mutation decreased the transformation efficiency, while the Cas3 mutation increased it. We report the existence and characterization of the CRISPR-Cas system in A. baumannii 19606^T and demonstrate that AbH-NS is a transcriptional repressor of CRISPR-Cas-related genes in A. baumannii.

The Salmonella enterica EnvE is an Outer Membrane Lipoprotein and Its Gene Expression Leads to Transcriptional Repression of the Virulence Gene msgA.: Sinyeon Kim, Yong Heon Lee; J. Microbiol. 2024;62(11):1013-1022. Published online November 15, 2024; DOI: https://doi.org/10.1007/s12275-024-00183-4

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Abstract: The envE gene of Salmonella enterica serovar Typhimurium is encoded within Salmonella Pathogenicity Island-11 (SPI-11) and is located immediately upstream of the virulence gene msgA (macrophage survival gene A) in the same transcriptional orientation. To date, the characteristics and roles of envE remain largely unexplored. In this study, we show that EnvE, a predicted lipoprotein, is localized on the outer membrane using sucrose gradient ultracentrifugation. Under oxidative stress conditions, envE transcription is suppressed, while msgA transcription is induced, indicating an inverse correlation between the mRNA levels of the two neighboring genes. Importantly, inactivation of envE leads to constitutive transcription of msgA regardless of the presence of oxidative stress. Moreover, trans-complementation of the envE mutant with a plasmid-borne envE fails to prevent the induction of msgA transcription, suggesting that envE functions as a cis-regulatory element rather than a trans-acting factor. We further show that both inactivation and complementation of envE confer wild-type levels of resistance to oxidative stress by ensuring the expression of msgA. Our data suggest that the S. enterica envE gene encodes an outer membrane lipoprotein, and its transcription represses msgA expression in a cis-acting manner, probably by transcriptional interference, although the exact molecular details are yet unclear.

Investigation of Bottleneck Enzyme Through Flux Balance Analysis to Improve Glycolic Acid Production in Escherichia coli.: Jungyeon Kim, Ye-Bin Kim, Ju-Young Kim, Min-Ju Seo, Soo-Jin Yeom, Bong Hyun Sung; J. Microbiol. 2024;62(11):1023-1033. Published online October 28, 2024; DOI: https://doi.org/10.1007/s12275-024-00175-4

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Abstract: Amid rising environmental concerns, attempts have been made to produce glycolic acid (GA) using microbial processes with renewable carbon resources instead of using chemicals. The Dahms pathway for GA production uses xylose as a substrate and consists of relatively simple enzymatic steps. However, employing it leads to a decrease in cell growth and GA productivity. Systematically identifying and addressing metabolic bottlenecks in the Dahms pathway are essential for efficient glycolic acid (GA) production have not yet been performed. Through metabolic flux balance analysis, we found that insufficient aldehyde dehydrogenase (AldA) activity lowers GA production and negatively affects cell growth due to reduced energy production. Thus, we discovered a novel AldA isolated from Buttiauxella agrestis (BaAldA) demonstrated a 1.69-fold lower K_M and a 1.49-fold higher turnover rate (k_cat/K_M) than AldA from Escherichia coli (EcAldA). GA production in E. coli harboring BaAldA was 1.59 times higher than in the original strain. Fed-batch fermentation of E. coli harboring BaAldA produced 22.70 g/L GA with a yield of 0.497 g/g_xylose (98.2% of the theoretical maximum yield in the Dahms pathway), showing a higher final yield for GA than previously reported in E. coli. Our novel BaAldA enzyme shows great potential for the production of GA using microorganisms or enzymes. Furthermore, our approach to identifying metabolic bottlenecks using flux balance analysis could be utilized to enhance the microbial production of various desirable products in future studies.

Characterization and Comparative Genomic Analysis of vB_BceM_CEP1: A Novel Temperate Bacteriophage Infecting Burkholderia cepacia Complex.: Momen Askoura, Eslam K Fahmy, Safya E Esmaeel, Wael A H Hegazy, Aliaa Abdelghafar; J. Microbiol. 2024;62(11):1035-1055. Published online November 18, 2024; DOI: https://doi.org/10.1007/s12275-024-00185-2

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Abstract: The increasing prevalence of multidrug-resistant bacteria imminently threatens public health and jeopardizes nearly all aspects of modern medicine. The Burkholderia cepacia complex (Bcc) comprises Burkholderia cepacia and the related species of Gram-negative bacteria. Members of the Bcc group are opportunistic pathogens responsible for various chronic illnesses, including cystic fibrosis and chronic granulomatous disease. Phage therapy is emerging as a potential solution to combat the antimicrobial resistance crisis. In this study, a temperate phage vB_BceM_CEP1 was isolated from sewage and fully characterized. Transmission electron microscopy indicated that vB_BceM_CEP1 belongs to the family Peduoviridae. The isolated phage demonstrated enhanced environmental stability and antibiofilm potential. One-step growth analysis revealed a latent period of 30 min and an average burst size of 139 plaque-forming units per cell. The genome of vB_BceM_CEP1 consists of 32,486 bp with a GC content of 62.05%. A total of 40 open reading frames were annotated in the phage genome, and none of the predicted genes was annotated as tRNA. Notably, genes associated with antibiotic resistance, host virulence factors, and toxins were absent from the vB_BceM_CEP1 genome. Based on its unique phenotype and phylogeny, the isolated phage vB_BceM_CEP1 is classified as a new temperate phage with lytic activity. The findings of this study enhance our understanding of the diversity of Bcc phages.

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