Thermal regulation of membrane lipid fluidity by a two-component system in Bacillus subtilis

Fifty years of biophysics in Argentina

In 1972, a group of young Argentinean scientists nucleated in the so-called Membrane Club constituted the Biophysical Society of Argentina (SAB). Over the years, this Society has grown and embraced new areas of research and emerging technologies. In this commentary, we provide an overview of the early stages of biophysics development in Argentina and highlight some of the notable achievements made during the past five decades. The SAB Annual Meetings have been a platform for intense scientific discussions, and the Society has fostered numerous international connections, becoming a hallmark of SAB activities over these 50 years. Initially centered on membrane biophysics, SAB focus has since expanded to encompass diverse fields such as molecular, cellular, and systems biophysics.

Bacillus anthracis Responds to Targocil-Induced Envelope Damage through EdsRS Activation of Cardiolipin Synthesis

Bacillus anthracis is a spore-forming bacterium that causes devastating infections and has been used as a bioterror agent. This pathogen can survive hostile environments through the signaling activity of two-component systems, which couple environmental sensing with transcriptional activation to initiate a coordinated response to stress. In this work, we describe the identification of a two-component system, EdsRS, which mediates the B. anthracis response to the antimicrobial compound targocil. Targocil is a cell envelope-targeting compound that is toxic to B. anthracis at high concentrations. Exposure to targocil causes damage to the cellular barrier and activates EdsRS to induce expression of a previously uncharacterized cardiolipin synthase, which we have named ClsT. Both EdsRS and ClsT are required for protection against targocil-dependent damage. Induction of clsT by EdsRS during targocil treatment results in an increase in cardiolipin levels, which protects B. anthracis from envelope damage. Together, these results reveal that a two-component system signaling response to an envelope-targeting antimicrobial induces production of a phospholipid associated with stabilization of the membrane. Cardiolipin is then used to repair envelope damage and promote B. anthracis viability.IMPORTANCE Compromising the integrity of the bacterial cell barrier is a common action of antimicrobials. Targocil is an antimicrobial that is active against the bacterial envelope. We hypothesized that Bacillus anthracis, a potential weapon of bioterror, senses and responds to targocil to alleviate targocil-dependent cell damage. Here, we show that targocil treatment increases the permeability of the cellular envelope and is particularly toxic to B. anthracis spores during outgrowth. In vegetative cells, two-component system signaling through EdsRS is activated by targocil. This results in an increase in the production of cardiolipin via a cardiolipin synthase, ClsT, which restores the loss of barrier function, thereby reducing the effectiveness of targocil. By elucidating the B. anthracis response to targocil, we have uncovered an intrinsic mechanism that this pathogen employs to resist toxicity and have revealed therapeutic targets that are important for bacterial defense against structural damage.

RNA-seq analysis provides insights into cold stress responses of Xanthomonas citri pv. citri

Background

Xanthomonas citri pv. citri (Xcc) is a citrus canker causing Gram-negative bacteria. Currently, little is known about the biological and molecular responses of Xcc to low temperatures.

Results

Results depicted that low temperature significantly reduced growth and increased biofilm formation and unsaturated fatty acid (UFA) ratio in Xcc. At low temperature Xcc formed branching structured motility. Global transcriptome analysis revealed that low temperature modulates multiple signaling networks and essential cellular processes such as carbon, nitrogen and fatty acid metabolism in Xcc. Differential expression of genes associated with type IV pilus system and pathogenesis are important cellular adaptive responses of Xcc to cold stress.

Conclusions

Study provides clear insights into biological characteristics and genome-wide transcriptional analysis based molecular mechanism of Xcc in response to low temperature.

Liposome permeability probed by laser light scattering

We have developed a laboratory project in which students prepare liposomes, expose them to hyperosmotic and hypoosmotic solutions, and follow the resulting shrinking and swelling (respectively) with laser light scattering. Each light intensity transient can be fit to an exponential decline or rise, with the decay constant (k) and the amplitude (ΔV_max ) being indirectly related to the kinetics and thermodynamics (respectively) of transmembrane osmotic flux. Students vary the experimental system by changing the types and concentrations of osmolytes such as alcohols, amides, and salts. Students then compare how these changes alter the rate and extent of osmotic flux. This upper division biochemistry laboratory project is a challenging and rewarding one that exposes students to a biomolecule (lipid) and a spectroscopic technique (laser spectroscopy) that are not commonly used in the undergraduate laboratory setting. © 2019 International Union of Biochemistry and Molecular Biology, 47(3):239-246, 2019.

Stressing Escherichia coli to educate students about research: A CURE to investigate multiple levels of gene regulation

Course-based undergraduate research experiences (CUREs) have been shown to increase student retention and learning in the biological sciences. Most CURES cover only one aspect of gene regulation, such as transcriptional control. Here we present a new inquiry-based lab that engages understanding of gene expression from multiple perspectives. Students carry out a forward genetic screen to identify regulators of the stationary phase master regulator RpoS in the model organism Escherichia coli and then use a series of reporter fusions to determine if the regulation is at the level of transcription or the post-transcription level. This easy-to-implement course has been run both as a 9-week long project and a condensed 5-6 week version in three different schools and types of courses. A majority of the genes found in the screen are novel, thus giving students the opportunity to contribute to original findings to the field. Assessments of this CURE show student gains in learning in many knowledge areas. In addition, attitudinal surveys suggest the students are enthusiastic about the screen and their learning about gene regulation. In summary, this lab would be an appropriate addition to an intermediate or advanced level Molecular Biology, Genetics, or Microbiology curriculum. © 2017 by The International Union of Biochemistry and Molecular Biology, 45(5):449-458, 2017.

Role of fatty acids in Bacillus environmental adaptation

The large bacterial genus Bacillus is widely distributed in the environment and is able to colonize highly diverse niches. Some Bacillus species harbor pathogenic characteristics. The fatty acid (FA) composition is among the essential criteria used to define Bacillus species. Some elements of the FA pattern composition are common to Bacillus species, whereas others are specific and can be categorized in relation to the ecological niches of the species. Bacillus species are able to modify their FA patterns to adapt to a wide range of environmental changes, including changes in the growth medium, temperature, food processing conditions, and pH. Like many other Gram-positive bacteria, Bacillus strains display a well-defined FA synthesis II system that is equilibrated with a FA degradation pathway and regulated to efficiently respond to the needs of the cell. Like endogenous FAs, exogenous FAs may positively or negatively affect the survival of Bacillus vegetative cells and the spore germination ability in a given environment. Some of these exogenous FAs may provide a powerful strategy for preserving food against contamination by the Bacillus pathogenic strains responsible for foodborne illness.

Fatty acid profiles and desaturase-encoding genes are different in thermo- and psychrotolerant strains of the Bacillus cereus Group

BACKGROUND

The Bacillus cereus Group consists of closely-related bacteria, including pathogenic or harmless strains, and whose species can be positioned along the seven phylogenetic groups of Guinebretière et al. (I-VII). They exhibit different growth-temperature ranges, through thermotolerant to psychrotolerant thermotypes. Among these, B. cytotoxicus is an atypical thermotolerant and food-poisoning agent affiliated to group VII whose thermotolerance contrasts with the mesophilic and psychrotolerant thermotypes associated to the remaining groups I-VI. To understand the role of fatty acid (FA) composition in these variable thermotypes (i.e. growth behavior vs temperatures), we report specific features differentiating the FA pattern of B. cytotoxicus (group VII) from its counterparts (groups I-VI).

FINDINGS

The FA pattern of thermotolerant group VII (B. cytotoxicus) displayed several specific features. Most notably, we identified a high ratio of the branched-chain FAs iso-C15/iso-C13 (i15/i13) and the absence of the unsaturated FA (UFA) C16:1(5) consistent with the absence of ∆5 desaturase DesA. Conversely, phylogenetic groups II-VI were characterized by lower i15/i13 ratios and variable proportions of C16:1(5) depending on thermotype, and presence of the DesA desaturase. In mesophilic group I, thermotype seemed to be related to an atypically high amount of C16:1(10) that may involve ∆10 desaturase DesB.

CONCLUSION

The levels of i15/i13 ratio, C16:1(5) and C16:1(10) UFAs were related to growth temperature variations recorded between thermotypes and/or phylogenetic groups. These FA are likely to play a role in membrane fluidity and may account for the differences in temperature tolerance observed in B. cereus Group strains.

Thermosensing to adjust bacterial virulence in a fluctuating environment

The lifecycle of most microbial pathogens can be divided into two states: existence outside and inside their hosts. The sudden temperature upshift experienced upon entry from environmental or vector reservoirs into a warm-blooded host is one of the most crucial signals informing the pathogens to adjust virulence gene expression and their host-stress survival program. This article reviews the plethora of sophisticated strategies that bacteria have evolved to sense temperature, and outlines the molecular signal transduction mechanisms used to modulate synthesis of crucial virulence determinants. The molecular details of thermal control through conformational changes of DNA, RNA and proteins are summarized, complex and diverse thermosensing principles are introduced and their potential as drug targets or synthetic tools are discussed.