Recombinant Cronobacter sakazakii ATP synthase subunit b (atpF)

What is Cronobacter sakazakii ATP synthase subunit b and what is its role in bacterial metabolism?

ATP synthase subunit b (atpF) in Cronobacter sakazakii functions as a critical component of the F0 sector of ATP synthase, an essential enzyme complex that catalyzes ATP synthesis during oxidative phosphorylation. This protein consists of 156 amino acids and serves as a stator stalk that connects the F1 catalytic domain to the F0 membrane domain .

In bacterial metabolism, ATP synthase harnesses the energy of the proton motive force across the membrane to synthesize ATP from ADP and inorganic phosphate. Subunit b specifically contributes to the structural stability of the complex and anchors the catalytic portion to the membrane-embedded components, enabling the rotational mechanism necessary for ATP synthesis. This energy production is particularly crucial during various growth phases and environmental stress conditions that C. sakazakii encounters.

How is ATP synthase utilized in Cronobacter species classification?

ATP synthase genes play a significant role in Cronobacter species classification through multilocus sequence typing (MLST). While atpF itself is not directly used in the established MLST scheme, the related atpD gene (encoding ATP synthase β chain) is one of seven loci used for identification and discrimination of Cronobacter species .

The atpD gene fragment (390 bp) used in MLST analysis shows approximately 10.8% polymorphic sites and 12 different alleles across analyzed strains . The low ratio of non-synonymous to synonymous substitutions (dN/dS = 0.006) indicates strong purifying selection, confirming its suitability as a phylogenetic marker . This classification system has proven more robust than traditional biotyping schemes for identifying and discriminating between C. sakazakii and C. malonaticus strains.

How does ATP synthase expression in Cronobacter sakazakii respond to environmental stressors?

Transcriptomic analyses reveal that C. sakazakii undergoes extensive gene expression changes in response to environmental conditions. When C. sakazakii BAA-894 was grown in minimal medium (M9) compared to rich medium (LB), a total of 3,956 genes were differentially expressed, with 2,339 up-regulated and 1,617 down-regulated .

While the specific regulation of ATP synthase genes was not detailed in the studies, the global impact of amino acid deficiency suggests significant metabolic adaptation. Energy production pathways, including ATP synthase components, likely undergo regulation to optimize energy utilization under stress conditions. This adaptation mechanism is particularly relevant for understanding how C. sakazakii survives in various environments, including food processing facilities and during host infection.

What methodological approaches are most effective for studying ATP synthase function in Cronobacter sakazakii?

Several methodological approaches can be employed to study ATP synthase function in C. sakazakii:

Table 1: Methodological Approaches for ATP Synthase Research

Transcriptomic analysis has been successfully employed to study gene expression in C. sakazakii under different growth conditions , and this approach could be applied specifically to ATP synthase components to understand their regulation under various environmental conditions.

What is the relationship between ATP synthase and biofilm formation in Cronobacter sakazakii?

The relationship between ATP synthase and biofilm formation in C. sakazakii involves complex metabolic interconnections. While ATP synthase is not directly identified as a biofilm-related gene in current research, energy production genes such as cytochrome o ubiquinol oxidase protein CyoD have been implicated in biofilm formation .

ATP synthase likely plays a supportive role by providing the energy required for biofilm development and maintenance. Research has shown that when specific biofilm-related genes in C. sakazakii are mutated, biofilm formation is affected, with quantifiable changes in production . The energy demands during different stages of biofilm development (attachment, maturation, dispersal) may require regulated ATP synthase activity to support these processes.

What are the optimal storage and handling conditions for recombinant Cronobacter sakazakii ATP synthase subunit b?

For optimal preservation of recombinant C. sakazakii ATP synthase subunit b activity and integrity, researchers should follow these evidence-based storage and handling protocols:

• Store the protein at -20°C for regular use, or at -80°C for extended storage periods

• Use the supplied Tris-based buffer containing 50% glycerol, which is optimized for this specific protein

• Avoid repeated freeze-thaw cycles, as they can compromise protein structure and activity

• For ongoing experiments, maintain working aliquots at 4°C for up to one week

• Before experimental use, validate protein integrity using techniques such as SDS-PAGE, Western blotting, or activity assays

These conditions are designed to maintain structural integrity and functional activity. Researchers should validate stability in their specific experimental conditions, particularly if using specialized assay buffers or additives.

How can researchers verify the activity and integrity of recombinant ATP synthase preparations?

Verifying the activity and integrity of recombinant ATP synthase subunit b preparations requires multiple complementary approaches:

Protein integrity verification:

• SDS-PAGE to confirm molecular weight (expected ~16 kDa) and purity

• Western blotting with specific antibodies

• Mass spectrometry to verify sequence and identify any post-translational modifications

• Circular dichroism to assess secondary structure composition

Functional assays:

• ATP synthase reconstitution if studying the whole complex

• Binding assays to verify interactions with other ATP synthase subunits

• In vitro assembly studies to confirm proper complex formation

Structural integrity assessment:

• Thermal shift assays to determine protein stability

• Size exclusion chromatography to verify oligomerization state

• Limited proteolysis to probe for proper folding

These verification methods ensure that experimental results accurately reflect the protein's natural properties and functions within the ATP synthase complex.

What experimental controls should be included when studying Cronobacter sakazakii ATP synthase?

When designing experiments involving C. sakazakii ATP synthase, researchers should incorporate the following controls:

Table 2: Recommended Experimental Controls

These controls help distinguish specific effects related to ATP synthase function from experimental artifacts or non-specific effects, increasing the reliability and reproducibility of research findings.

How can ATP synthase genes be used for molecular typing and epidemiological studies of Cronobacter species?

ATP synthase genes, particularly atpD, have proven valuable for molecular typing and epidemiological studies of Cronobacter species. The established multilocus sequence typing (MLST) scheme incorporates atpD (ATP synthase β chain) as one of seven loci for strain discrimination .

Analysis of 60 C. sakazakii and 16 C. malonaticus strains identified 12 sequence types (STs) in C. sakazakii and 3 in C. malonaticus . Notably, ST4 contained 22/60 C. sakazakii strains with nearly equal numbers of clinical and infant formula isolates spanning from 1951 to 2008, while ST8 appeared particularly virulent with 7/8 strains being clinical isolates from four countries between 1977-2006 .

This MLST approach provides several advantages for epidemiological research:

• Higher discriminatory power than traditional biotyping

• Ability to track specific lineages across time and geography

• Identification of potentially hypervirulent sequence types

• A standardized framework for global surveillance

The established Cronobacter MLST database (http://pubmlst.org/cronobacter/) serves as a valuable resource for researchers conducting epidemiological investigations and outbreak analyses .

What role does ATP synthase play in the virulence and pathogenicity of Cronobacter sakazakii?

While ATP synthase primarily functions in energy metabolism rather than as a direct virulence factor, it plays a supportive role in pathogenicity by powering various virulence-associated processes. C. sakazakii has been associated with severe infant infections, particularly meningitis, and can cross the blood-brain barrier to affect the central nervous system .

ATP synthase likely supports these virulence mechanisms by providing energy for:

• Adhesion to and invasion of host cells

• Production and secretion of toxins and other virulence factors

• Resistance to host defense mechanisms

• Adaptation to the nutrient-limited environment within the host

This supportive role makes ATP synthase an indirect contributor to pathogenicity. Research has identified that C. sakazakii produces bioactive compounds that can modify host immune regulatory genes, affecting the expression of genes involved in pathogen recognition and kinase activity such as clec-60, clec-87, lys-7, akt-2, pkc-1, and jnk-1 . The energy requirements for producing these compounds likely depend on functional ATP synthase.

How does ATP synthase contribute to Cronobacter sakazakii survival under nutrient limitation?

Transcriptomic analyses reveal that C. sakazakii undergoes substantial gene expression changes in response to nutrient limitation. When grown in minimal medium (M9) compared to rich medium (LB), C. sakazakii BAA-894 showed differential expression of 3,956 genes . Under amino acid deficiency, genes relevant to exopolysaccharide biosynthesis were significantly up-regulated, while genes involved in flagellum formation and chemotaxis were down-regulated .

Although specific data on ATP synthase regulation is not detailed in the current research, the global metabolic reconfiguration suggests that energy production pathways are likely optimized to support survival under nutrient stress. This adaptation mechanism is crucial for C. sakazakii's persistence in environments with limited nutrients, such as during food processing, storage, or within certain host tissues.

The production of exopolysaccharides under nutrient limitation is particularly noteworthy, as this process requires significant energy input, suggesting a prioritization of ATP utilization toward protective mechanisms rather than motility under stress conditions.

What are promising research areas involving Cronobacter sakazakii ATP synthase as a potential antimicrobial target?

ATP synthase represents a promising antimicrobial target due to its essential role in bacterial energy metabolism. Several research directions could be explored:

• Structure-based drug design: Determining the unique structural features of C. sakazakii ATP synthase could facilitate the development of specific inhibitors that target this pathogen while minimizing effects on human ATP synthase.

• Natural products screening: Identifying natural compounds that specifically inhibit bacterial ATP synthase could provide lead molecules for antimicrobial development.

• Combination therapy approaches: Investigating synergistic effects between ATP synthase inhibitors and existing antibiotics could enhance antimicrobial efficacy.

• Membrane permeabilization strategies: Developing compounds that specifically increase proton permeability in C. sakazakii could uncouple ATP synthesis and deplete energy reserves.

• Nanoparticle delivery systems: Engineering nanoparticles to deliver ATP synthase inhibitors specifically to C. sakazakii could increase therapeutic efficacy while reducing off-target effects.

This research holds particular promise given the increasing concerns about antimicrobial resistance and the need for new therapeutic approaches against opportunistic pathogens like C. sakazakii.

How might comparative analyses of ATP synthase across Cronobacter species contribute to evolutionary studies?

Comparative analyses of ATP synthase across Cronobacter species could provide valuable insights into evolutionary relationships and adaptation mechanisms:

• Phylogenetic analysis: Constructing phylogenetic trees based on ATP synthase gene sequences could clarify evolutionary relationships within the Cronobacter genus and between Cronobacter and related genera.

• Selection pressure analysis: Examining the ratio of non-synonymous to synonymous substitutions in ATP synthase genes across species could identify regions under different selective pressures.

• Adaptive evolution: Investigating ATP synthase variations in Cronobacter species from different ecological niches could reveal adaptations to specific environmental conditions.

• Horizontal gene transfer: Analyzing ATP synthase gene sequences could identify potential instances of horizontal gene transfer and its role in Cronobacter evolution.

• Ancestral sequence reconstruction: Reconstructing ancestral ATP synthase sequences could provide insights into the evolutionary trajectory of energy metabolism in these bacteria.

These studies would complement existing MLST-based approaches and contribute to our broader understanding of bacterial evolution and adaptation mechanisms.