Recombinant Bacillus amyloliquefaciens Glycerol-3-phosphate acyltransferase (plsY)
Description
Fundamental Characteristics of Recombinant Bacillus amyloliquefaciens PlsY
Recombinant Bacillus amyloliquefaciens Glycerol-3-phosphate acyltransferase (PlsY) refers to the artificially produced form of the PlsY enzyme derived from the Gram-positive bacterium Bacillus amyloliquefaciens. This enzyme belongs to a unique class of acyltransferases that catalyzes the first and committed step in bacterial phospholipid biosynthesis. The significance of PlsY lies in its essential role in bacterial membrane formation, making it an attractive target for antimicrobial development.
Bacillus amyloliquefaciens has emerged as a versatile microorganism with significant applications across various fields due to its status as a generally recognized as safe (GRAS) organism . This bacterium naturally produces numerous enzymes including α-amylase, protease, lipase, cellulase, and many others, demonstrating its robust capacity for protein production . The inherent genetic background of B. amyloliquefaciens, combined with well-developed gene manipulation tools, enables effective reconstruction of its cellular metabolism for optimized recombinant protein expression .
What distinguishes PlsY from other acyltransferases is its unique substrate specificity and catalytic mechanism. While conventional acyltransferases utilize acyl-CoA or acyl-carrier protein as acyl donors, PlsY specifically employs acylphosphate, representing a biochemically distinct pathway . This unique characteristic, coupled with PlsY's absence in eukaryotes, underscores its potential as a target for selective antibacterial agents.
Table 1: Conserved Motifs in Bacterial PlsY and Their Functions
| Motif | Key Residues | Function | Effect of Mutation |
|---|---|---|---|
| Motif 1 | Serine, Arginine | Catalytic activity | Loss of enzymatic function |
| Motif 2 | Multiple Glycines | Glycerol-3-phosphate binding | Increased Km for G3P binding |
| Motif 3 | Histidine, Asparagine, Glutamate | Structural integrity and catalytic activity | Compromised enzyme structure and reduced activity |
Catalytic Mechanism and Biochemical Properties
The catalytic mechanism of PlsY represents a departure from conventional acyltransferases, employing what researchers describe as 'substrate-assisted catalysis' . This distinctive mechanism does not require a proteinaceous catalytic base to complete the acylation reaction, unlike other acyltransferases . Instead, the substrates themselves participate directly in facilitating the catalytic transfer of the acyl group.
In the PlsY-catalyzed reaction, the enzyme transfers an acyl group from acylphosphate to the 1-position of glycerol-3-phosphate, forming lysophosphatidic acid. This reaction constitutes the committed step in bacterial phospholipid biosynthesis and is essential for bacterial survival . The most widely distributed biosynthetic pathway for initiating phosphatidic acid formation in bacterial membrane phospholipid biosynthesis involves the conversion of acyl-acyl carrier protein to acylphosphate by PlsX, followed by the PlsY-mediated transfer of the acyl group to glycerol-3-phosphate .
Biochemical studies have revealed several important properties of PlsY enzymes:
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Substrate Specificity: PlsY demonstrates high specificity for acylphosphate as the acyl donor, distinguishing it from eukaryotic glycerol-3-phosphate acyltransferases that utilize acyl-CoA .
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Inhibition Patterns: Research has shown that PlsY is noncompetitively inhibited by palmitoyl-CoA, providing insights into potential regulatory mechanisms and inhibitor design strategies .
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Structural Rigidity: Crystal structures have uncovered that PlsY possesses a relatively inflexible active site, which has implications for its catalytic efficiency and substrate recognition .
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Membrane Integration: PlsY's function is intimately connected to its membrane localization, with evidence suggesting potential substrate channeling mechanisms for acquiring acylphosphate from the membrane environment .
These biochemical characteristics highlight the specialized nature of PlsY in bacterial phospholipid biosynthesis and emphasize its potential as a distinct antimicrobial target.
Recombinant Expression Strategies in Bacillus amyloliquefaciens
The recombinant expression of PlsY in Bacillus amyloliquefaciens presents both opportunities and challenges. As a membrane-integral protein with multiple transmembrane segments, its expression, proper folding, and functional integration require specialized approaches. B. amyloliquefaciens offers several advantages as an expression host, including its GRAS status, rapid growth characteristics, and amenability to high-density fermentation .
Genomic and comparative transcriptome analyses have identified critical modular systems in B. amyloliquefaciens that significantly impact heterologous protein production. These key modules include:
When these three modules were engineered in combination, researchers observed a remarkable 39.6% increase in heterologous protein production compared to the control strain . These findings provide valuable strategies for optimizing the recombinant expression of membrane proteins like PlsY in B. amyloliquefaciens.
Table 2: Modular Engineering Strategies for Enhanced Protein Production in B. amyloliquefaciens
| Engineering Module | Target | Modification Strategy | Protein Yield Improvement |
|---|---|---|---|
| Module I (Sporulation) | sigF gene | Gene deletion | 25.3% increase |
| Modules I + II (Sporulation and Proteases) | sigF gene and extracellular proteases | Combined gene deletions | 36.1% increase |
| Modules I + II + III (Comprehensive) | Multiple targets | Integrated approach | 39.6% increase |
Purification and Characterization Methods
The purification and characterization of recombinant membrane proteins like PlsY require specialized techniques that address the challenges associated with their hydrophobic nature and membrane integration. Effective purification strategies typically involve a multi-step approach:
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Membrane Isolation: The initial step involves selective isolation of bacterial membranes containing the recombinant PlsY through differential centrifugation and washing procedures.
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Detergent Solubilization: Appropriate detergents must be carefully selected to solubilize PlsY from the membrane while maintaining its structural integrity and enzymatic activity.
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Chromatographic Separation: Affinity chromatography, often utilizing histidine tags or other fusion tags, facilitates selective purification of the recombinant enzyme.
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Quality Assessment: Purified PlsY can be analyzed through SDS-PAGE to confirm size and purity, similar to the analysis methods used for other recombinant proteins like Tn5 transposase .
For functional characterization, researchers have developed enzymatic assays to assess PlsY activity. These assays typically measure the transfer of acyl groups from acylphosphate to glycerol-3-phosphate. High-throughput enzymatic assays developed for PlsY have proven valuable for virtual and experimental screening of potential inhibitors .
Structural characterization through crystallography has provided critical insights into PlsY's conformation and active site. The crystal structure of PlsY at 1.48 Å resolution revealed its seven-transmembrane helix fold, while additional substrate- and product-bound structures uncovered the atomic details of its active site . These structural analyses are essential for understanding the enzyme's function and developing targeted inhibitors.
Biotechnological Applications and Antimicrobial Potential
Recombinant B. amyloliquefaciens PlsY offers significant biotechnological applications and therapeutic potential. Its unique characteristics position it as both a valuable research tool and a promising antimicrobial target.
As a research tool, recombinant PlsY facilitates detailed investigation of bacterial phospholipid biosynthesis pathways. The availability of pure, active enzyme enables mechanistic studies, substrate specificity analyses, and development of high-throughput screening assays for inhibitor discovery . Furthermore, structural studies of recombinant PlsY provide valuable insights into the architectural basis of its function, guiding rational design approaches for inhibitor development.
The antimicrobial potential of PlsY stems from several key attributes:
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Essential Function: PlsY catalyzes the committed and essential step in bacterial phospholipid biosynthesis, making it indispensable for bacterial survival .
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Taxonomic Restriction: PlsY exists exclusively in bacteria and lacks eukaryotic homologs, providing an opportunity for selective targeting without affecting host enzymes .
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Unique Mechanism: The enzyme's distinct catalytic mechanism and substrate specificity differentiate it from other acyltransferases, offering potential for developing highly specific inhibitors .
Previous research has identified several PlsY inhibitors, including acyl-sulfamates, as potential antimicrobials against pathogenic bacteria . The structural data and high-throughput enzymatic assays developed for PlsY provide valuable tools for virtual and experimental screening of additional inhibitor candidates .
Challenges and Future Directions
Despite its promising applications, research on recombinant B. amyloliquefaciens PlsY faces several challenges. As a membrane-integral protein, its expression and purification present inherent difficulties that can affect yield and activity. Additionally, assessing enzymatic activity requires specialized assays that accommodate its membrane-bound nature and unique substrate requirements.
Future research directions may include:
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Optimization of expression systems through further genetic engineering of B. amyloliquefaciens to enhance PlsY production yields and stability.
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Development of improved purification protocols specifically tailored to maintain the structural integrity and activity of membrane-bound PlsY.
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High-resolution structural determination of B. amyloliquefaciens PlsY to identify species-specific features that might inform inhibitor design.
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Comprehensive screening of compound libraries to identify novel PlsY inhibitors with antimicrobial potential.
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Investigation of PlsY's role in bacterial adaptation to environmental stresses and antibiotic resistance mechanisms.
The unique properties of PlsY and the versatility of B. amyloliquefaciens as an expression host converge to create significant opportunities for both fundamental research and applied biotechnology. As antimicrobial resistance continues to present global health challenges, novel targets like PlsY offer promising avenues for developing next-generation antimicrobials with reduced risk of cross-resistance to existing drugs.
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Target Background
This recombinant Bacillus amyloliquefaciens Glycerol-3-phosphate acyltransferase (PlsY) catalyzes the transfer of an acyl group from acyl-phosphate (acyl-PO4) to glycerol-3-phosphate (G3P), yielding lysophosphatidic acid (LPA). The enzyme utilizes acyl-phosphate as the fatty acyl donor, but not acyl-CoA or acyl-ACP.
KEGG: bay:RBAM_017880
Q&A
How does plsY differ from PlsX in the phospholipid synthesis pathway?
While both plsY and PlsX participate in the phospholipid synthesis pathway, they serve different but complementary functions. PlsX is an acyl-acyl carrier protein phosphate acyltransferase that works upstream of plsY in many Gram-positive bacteria. PlsX converts acyl-ACP to acyl-phosphate, which then serves as the acyl donor for plsY to catalyze the acylation of glycerol-3-phosphate.
In B. subtilis, PlsX has been identified as a component of the cell-division machinery through its interaction with FtsA . PlsX localizes at potential division sites independently of FtsA and FtsZ, suggesting it may play a role in coordinating membrane synthesis with cell division . Given the genetic similarity between Bacillus species, B. amyloliquefaciens plsY likely exhibits comparable localization patterns and interactions, though specific studies would be needed to confirm this.
What expression systems are most effective for recombinant production of B. amyloliquefaciens plsY?
For recombinant expression of B. amyloliquefaciens proteins, several effective systems have been documented. Based on research with similar proteins in B. amyloliquefaciens, the following expression methodologies can be applied to plsY:
Homologous Expression in B. amyloliquefaciens:
Research on alkaline protease (AprE) expression in B. amyloliquefaciens provides a useful template. Methylated plasmids can be used to transform competent B. amyloliquefaciens cells, with cultivation in LB medium (37°C, 220 rpm for 6-8 hours) followed by inoculation into fermentation medium containing appropriate antibiotics (e.g., 50 mg/L kanamycin) and incubation at 37°C for extended periods (approximately 60 hours) .
Transformation Methods:
For B. amyloliquefaciens, electrotransformation protocols similar to those used for transposon mutagenesis can be adapted. This involves growing the culture in neutral complex medium (NCM), diluting 25-fold with fresh NCM supplemented with glycine, and harvesting cells at appropriate optical density (OD600~0.8) for electroporation .
How can genetic engineering approaches enhance the stability and activity of recombinant B. amyloliquefaciens plsY?
Enhancing recombinant B. amyloliquefaciens plsY stability and activity requires a multi-modular engineering approach focusing on key cellular processes that affect protein production and function. Based on research with other recombinant proteins in B. amyloliquefaciens, the following strategies can be implemented:
Sporulation Control:
Modifying sporulation genes can significantly impact recombinant protein production. For instance, deletion of sigF (a sporulation transcription factor) increased alkaline protease (AprE) yield by 25.3% in B. amyloliquefaciens . Similar modifications could potentially enhance plsY production by reducing cellular resources allocated to sporulation.
Extracellular Protease Modification:
Research has demonstrated that combining sporulation control with mutation of extracellular proteases can synergistically increase recombinant protein production by up to 36.1% . When expressing membrane-associated proteins like plsY, reducing proteolytic degradation may be particularly beneficial for maintaining functional enzyme levels.
Polysaccharide Synthesis Regulation:
Extracellular polysaccharide synthesis consumes significant cellular resources. Modification of this module may redirect metabolic resources toward recombinant protein production, as observed in the AprE expression system .
What are the optimal conditions for assaying B. amyloliquefaciens plsY activity in vitro?
The optimal conditions for assaying B. amyloliquefaciens plsY activity in vitro should be established through systematic evaluation of buffer conditions, substrate concentrations, temperature, and pH. While specific data for B. amyloliquefaciens plsY is not provided in the search results, general protocols can be adapted from related research:
Proposed Assay Protocol:
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Buffer System: Phosphate buffer (50-100 mM, pH 7.0-7.5) with added divalent cations (5-10 mM Mg2+)
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Substrate Preparation: Glycerol-3-phosphate (1-5 mM) and acyl-ACP or acyl-phosphate (0.1-1 mM)
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Temperature Range: Initial screening at 25°C, 30°C, 37°C, and 42°C
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Reaction Monitoring: HPLC or TLC analysis of lysophosphatidic acid formation
Activity Validation:
Confirmation of enzyme activity should include both positive controls (using characterized acyltransferases) and negative controls (heat-inactivated enzyme). Kinetic parameters should be determined under optimized conditions to establish reference values for wild-type and engineered variants.
How does plsY localization correlate with cell division in B. amyloliquefaciens?
The spatial and temporal localization of phospholipid synthesis enzymes relative to the cell division machinery provides important insights into coordinated membrane biogenesis. In B. subtilis, the related enzyme PlsX has been shown to localize at potential division sites independently of the core division proteins FtsA and FtsZ, indicating a possible role in marking future division sites .
Based on these findings, several hypotheses can be formulated regarding B. amyloliquefaciens plsY:
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plsY may localize at potential division sites to coordinate phospholipid synthesis with septum formation
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Localization patterns may be influenced by cell cycle progression and DNA replication status
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Interaction with cytoskeletal elements may stabilize plsY at specific cellular locations
To test these hypotheses, fluorescent protein tagging of plsY combined with time-lapse microscopy would allow visualization of its dynamic localization. Co-localization studies with FtsZ, FtsA, and DNA would reveal temporal relationships between membrane synthesis, cell division, and genome replication.
What strategies can be employed to overcome expression challenges for membrane-associated plsY?
Expressing membrane-associated proteins like plsY presents unique challenges compared to soluble proteins. The following strategies can be employed to optimize expression and functionality:
Expression Host Selection:
B. amyloliquefaciens is recognized as a generally recognized as safe (GRAS) microorganism with excellent potential for heterologous protein production . For expression of its own plsY, using optimized B. amyloliquefaciens strains with reduced protease activity and controlled sporulation offers advantages for proper membrane integration.
Fusion Tag Approaches:
Strategic fusion tags can enhance membrane protein solubility and facilitate purification. A modular approach testing various N-terminal and C-terminal tags should be evaluated, with subsequent tag removal if necessary for activity assays.
Induction Conditions:
Temperature, inducer concentration, and growth phase significantly impact membrane protein expression. The following table outlines a systematic approach to optimizing these parameters:
| Parameter | Range to Test | Monitoring Method | Expected Outcome |
|---|---|---|---|
| Temperature | 18°C, 25°C, 30°C, 37°C | Western blot, activity assay | Lower temperatures often favor proper folding |
| Media composition | LB, TB, Minimal media | Growth curve, yield quantification | Rich media may increase yield but reduce specific activity |
| Induction time | Early log, mid-log, late log | Time-course sampling, activity/yield ratio | Mid-log often balances growth with expression capacity |
| Inducer concentration | 0.1 mM - 1.0 mM IPTG or equivalent | Dose-response analysis | Optimal concentration balances expression with toxicity |
How can transposon mutagenesis be utilized to study plsY function in B. amyloliquefaciens?
Transposon mutagenesis provides a powerful approach for generating random mutations to study gene function and create diverse phenotypes. For B. amyloliquefaciens plsY research, the following methodology can be adapted from existing protocols:
Mutagenesis Protocol:
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Utilize a TnYLB-1 transposon derivative carried in a thermosensitive shuttle plasmid such as pMarA
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Electrotransform the plasmid into B. amyloliquefaciens using established protocols
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Select for transposon integration using appropriate antibiotics (e.g., kanamycin resistance)
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Screen the mutant library for phenotypes of interest
Screening Strategies:
To identify mutations affecting plsY function or regulation, several phenotypic screens can be implemented:
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Altered membrane composition (assessed by lipid profiling)
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Changes in cell morphology or division patterns
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Modified growth rates under varying conditions
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Altered sensitivity to membrane-targeting antibiotics
Transposon insertion sites can be mapped through whole genome sequencing or targeted PCR approaches to identify genetic elements influencing plsY function.
How should researchers interpret discrepancies in plsY functional data between in vitro and in vivo studies?
Discrepancies between in vitro biochemical assays and in vivo functional studies of plsY are common and warrant careful analysis. When confronted with such inconsistencies, researchers should consider:
Potential Factors Contributing to Discrepancies:
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Membrane environment effects on enzyme activity and substrate accessibility
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Interaction with protein partners present only in the cellular context
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Regulatory mechanisms active in vivo but absent in reconstituted systems
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Differences in substrate concentrations between assay conditions and cellular environment
Recommended Analytical Approach:
The following analytical framework can help reconcile inconsistent results:
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Validate both in vitro and in vivo experimental systems through appropriate controls
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Bridge the gap with intermediate approaches (e.g., membrane vesicles, spheroplasts)
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Use genetic complementation to confirm functional relationships
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Employ quantitative proteomic and lipidomic analyses to assess cellular impacts
Successful interpretation requires triangulation across multiple experimental methods and recognition of the limitations inherent in each approach.
What statistical approaches are most appropriate for analyzing plsY mutant phenotypes?
Experimental Design Considerations:
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All fermentation experiments should be performed in triplicate at minimum
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Include appropriate wild-type and vector-only controls
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Block potential confounding variables (temperature fluctuations, media batch effects)
Statistical Analysis Framework:
| Data Type | Recommended Test | Assumptions | Application Example |
|---|---|---|---|
| Growth rates | Repeated-measures ANOVA | Normal distribution, sphericity | Comparing growth curves of multiple mutants over time |
| Enzyme activity | Student's t-test or one-way ANOVA | Normal distribution, equal variance | Comparing enzymatic activity between wild-type and mutant plsY |
| Lipid profiles | Multivariate analysis (PCA, cluster analysis) | Linear relationships for PCA | Identifying patterns in membrane composition changes |
| Localization data | Chi-square test | Independent observations | Analyzing distribution patterns of fluorescent plsY fusions |
For all statistical analyses, appropriate multiple testing corrections should be applied when comparing numerous mutants or conditions simultaneously.
How might systems biology approaches advance our understanding of plsY's role in B. amyloliquefaciens metabolism?
Systems biology offers powerful approaches to contextualize plsY function within the broader metabolic network of B. amyloliquefaciens. Future research directions might include:
Integrative Omics Approaches:
Combining transcriptomics, proteomics, and lipidomics can reveal how plsY expression and activity correlate with global cellular responses. Previous research has employed comparative transcriptome analysis to investigate critical modules affecting recombinant protein production in B. amyloliquefaciens . Similar approaches could identify regulatory networks controlling plsY expression and interactions with other metabolic pathways.
Metabolic Flux Analysis:
Isotope labeling experiments can trace carbon flow through glycerolipid biosynthesis pathways, quantifying the contribution of plsY to membrane biogenesis under various conditions. This approach would be particularly valuable for understanding how plsY activity relates to cell growth rates and division cycles.
Synthetic Biology Applications:
Engineering plsY expression and activity could enable production of modified membrane lipids or serve as a tool for controlling cell division. The potential for creating synthetic cellular modules builds on established approaches for multi-modular engineering of B. amyloliquefaciens .
What role might plsY play in coordinating membrane synthesis with cell division in B. amyloliquefaciens?
Research on the related enzyme PlsX in B. subtilis provides compelling evidence that phospholipid synthesis enzymes play crucial roles in coordinating membrane biogenesis with cell division. Future research on B. amyloliquefaciens plsY should explore:
Protein-Protein Interactions:
Comprehensive interaction analysis similar to that performed for PlsX could reveal whether plsY interacts with components of the cell division machinery such as FtsA or FtsZ. These interactions may provide a molecular basis for spatial and temporal coordination of membrane synthesis with septum formation.
Localization Dynamics:
Advanced imaging techniques can track plsY localization throughout the cell cycle. Evidence from B. subtilis suggests that the Z-ring stabilizes the association of phospholipid synthesis enzymes at the septum and pole . Similar mechanisms may exist for plsY in B. amyloliquefaciens.
Effects of plsY Mutations on Cell Division:
Investigating how plsY inactivation affects Z-ring formation and septum development could provide insights into its role in cell division. In B. subtilis, PlsX inactivation leads to aberrant Z-ring formation , suggesting these enzymes are needed for proper cell division beyond their catalytic roles in lipid synthesis.
