Bacterial stress response

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The bacterial stress response enables bacteria to survive adverse and fluctuating conditions in their immediate surroundings. [1] Various bacterial mechanisms recognize different environmental changes and mount an appropriate response. A bacterial cell can react simultaneously to a wide variety of stresses and the various stress response systems interact with each other by a complex of global regulatory networks. [2]

Contents

Bacteria can survive under diverse environmental conditions and in order to overcome these adverse and changing conditions, bacteria must sense the changes and mount appropriate responses in gene expression and protein activity. The stress response in bacteria involves a complex network of elements that counteracts the external stimulus. Bacteria can react simultaneously to a variety of stresses and the various stress response systems interact (cross-talk) with each other. A complex network of global regulatory systems leads to a coordinated and effective response. These regulatory systems govern the expression of more effectors that maintain stability of the cellular equilibrium under the various conditions. [3] These systems can include immediate responses such as chaperones, as well as slower responses like transcriptional regulation to control protein production, latency, and others. [4] [5]

Stress response systems can play an important role in the virulence of pathogenic organisms. Their stress response systems, such as entering into a latent state, can allow them to survive the stressful conditions inside of the host or other surroundings. [5]

There are regulatory systems that respond to changes in temperature, pH, nutrients, salts, and oxidation. The response level is based on the amount of change that occurs in the environment. The response is highest when changes occur under stress conditions, in this case the control networks are called stress response systems. These systems are very similar within prokaryotes and some of the systems, specifically the heat shock response, are conserved in eukaryotes and archaea. While the systems are extremely similar, the conditions under which they are activated differ greatly from organism to organism. The systems that activate the response to environmental change have many control elements. These control elements can be specific to one gene or they can control a large group of genes. When control elements control a large group of genes it is called a regulon. A regulon is a group of genes that are all regulated by the same control pattern. A stimulon is all the genes who express responses to the same condition. The control elements also regulate the expression of genes during various environmental conditions including starvation, sporulation and others. [6]

Types of Stressors

A stressor that can induce a stress response in bacteria can be any condition outside of the ideal conditions for survival. The stressors that inflict harm to the cell are the ones that illicit the strongest responses. One such stressor is exposure to reactive oxygen species and reactive chlorine species chemicals that are used as disinfectants. Included in this category is sodium hypochlorite(NaOCl), or household bleach. These chemicals inflict extensive cellular damage to different systems such as the bacterial membrane, denaturation of proteins, and interference with biomolecules such as amino acids, nucleic acids, and lipids. [4] Another type of stressor could be the absence of an favorable electron acceptor for cellular respiration. The shift from a more favorable energy production to a less favorable one, such as nitrate, has been shown in a study to change cell morphology and composition of the cellular membrane. [7] Other types of stressors include oxidants, nutrient deprivation, hypo/hyper-osmolarity, extreme pH, extreme temperature, and antimicrobial substances. [4] [8] This list of stressors is not comprehensive, as stressors by definition can be anything and everything that may not be favorable to a cell.

Types of Responses

An initial stress response systems that will likely go into effect against situations that are damaging to the bacterial cell is chaperones. Chaperones are proteins that are responsible for keeping other proteins in their proper conformations by binding to them. Without the chaperones as a first line of defense, other stress response systems would not be able to react quickly enough to stop proteins from denaturing in time. While a protein is denaturing, it will produce intermediate conformations of itself, and these intermediates are what activate chaperone proteins. [4] Another major stress response system is transcriptional regulation. Many transcriptional regulation systems are well defined, while others are less understood, but they can be activated by different pathways and stimuli, and is a general response to most stimuli. What this involves is proteins binding to promoter regions of DNA to regulate which sections are transcribed into RNA. The concentration of different RNA transcripts is then altered to favor the production of those that will produce proteins that will mitigate the effects of the stimulus. [4] However, this system may be limited by the translational ability of the cell. The transcriptional changes can only be effective if ribosomal speed to translate mRNA to protein is quick enough. This can be a bottleneck in the capability of bacteria to react to stressors quick enough, and some stressors, such as oxidative stress, can inhibit the function of ribosomes. [8]

A stress response that can occur under conditions that are non-advantageous, but also non-lethal, is the creation of a biofilm. In this response, bacterial cells can secrete extracellular polymeric substances to form a film that can provide support to the bacterial colony, such as by improving their ability to adhere to a surface. [4] Another common stress response is latency. In a latent states, a cell will slow down its metabolism and become virtually dormant. This makes the cell much less affected by stressors such as antibacterial agents, starvation, hypoxia, and acidity. Some bacteria are able to enter a latent state and remain there for up to years before returning to an active state. [5] A cell can also shift from production of unsaturated fatty acids to saturated fatty acids to decrease the fluidity of the cellular membrane. If the stressor is a molecule, this will make it more difficult for it to get into the cell. Overall cellular morphology can also be changed in response to a stressor. [7]

In bacteria some other important stress response systems are:

Heat Shock Response

The heat-shock response in bacteria helps to stop any damage to the cellular processes in high temperature conditions. In response to high temperatures, heat-shock proteins, including chaperones and proteases are rapidly induced to protect against the denaturation of proteins within the bacteria. [9] These chaperones help facilitate the folding of proteins within the cell to protect against rising temperatures. In most bacterial strains, sigma factor-32 (32) is responsible for regulating the heat-shock response. Sigma factor-32 is encoded by the rpoH gene and sits upstream of heat-shock genes. [10]

Envelope Stress Response

The two-component signal transduction (2CST) system allows the bacterial cell to sense stress within the system. A histidine kinase that can be found in the cell's inner membrane detects the stress. The histidine kinase detects stress due to the  autophosphorylation that initially occurs upon detection. Once the stress is detected, the system moves to a cytoplasmic response regulator. This is due to the cell being in a phosphate group, but this new response regulator will start to act like a transcription factor. This means that it will start to change what is expressed when looking at the genes. This is especially true when looking at the Cpx proteins which help to prevent the protein from folding the wrong way or not at all. Cpx proteins also help to ensure that there will be no other damage when looking at other cellular processes. [11]

Cold Shock Response

When bacteria is in an area of very low and cold temperature, they will have a five hour long phase that will cause them not to grow at all. The way the bacteria tries to adapt is by creating child shock proteins that will be transcription factors that will be upregulated during the five hour phase. Once this five hour period ends, the bacteria will start to grow again, but it will be at a very slow rate. These proteins will help for the bacteria to continue to grow and survive at the lower temperatures. A protein called CspA was originally found in E. coli and is known to be one of the first cold shock proteins discovered and is known to be a single-stranded RNA. This aids in the processes of transcription and translation, there can be condensation of the chromosome that occurs as well. This means that the cells will prematurely go onto the interphase stage of mitosis. There will also be an organization of the nucleoid which is when the intracellular and extracellular factors in the cell. And lastly, there is an enhancement when it comes to the survival of bacteria which helps the cell to get the food and nutrients it needs to survive [11]

See also

Related Research Articles

Heat shock proteins (HSP) are a family of proteins that are produced by cells in response to exposure to stressful conditions. They were first described in relation to heat shock, but are now known to also be expressed during other stresses including exposure to cold, UV light and during wound healing or tissue remodeling. Many members of this group perform chaperone functions by stabilizing new proteins to ensure correct folding or by helping to refold proteins that were damaged by the cell stress. This increase in expression is transcriptionally regulated. The dramatic upregulation of the heat shock proteins is a key part of the heat shock response and is induced primarily by heat shock factor (HSF). HSPs are found in virtually all living organisms, from bacteria to humans.

In molecular biology and genetics, transcriptional regulation is the means by which a cell regulates the conversion of DNA to RNA (transcription), thereby orchestrating gene activity. A single gene can be regulated in a range of ways, from altering the number of copies of RNA that are transcribed, to the temporal control of when the gene is transcribed. This control allows the cell or organism to respond to a variety of intra- and extracellular signals and thus mount a response. Some examples of this include producing the mRNA that encode enzymes to adapt to a change in a food source, producing the gene products involved in cell cycle specific activities, and producing the gene products responsible for cellular differentiation in multicellular eukaryotes, as studied in evolutionary developmental biology.

A sigma factor is a protein needed for initiation of transcription in bacteria. It is a bacterial transcription initiation factor that enables specific binding of RNA polymerase (RNAP) to gene promoters. It is homologous to archaeal transcription factor B and to eukaryotic factor TFIIB. The specific sigma factor used to initiate transcription of a given gene will vary, depending on the gene and on the environmental signals needed to initiate transcription of that gene. Selection of promoters by RNA polymerase is dependent on the sigma factor that associates with it. They are also found in plant chloroplasts as a part of the bacteria-like plastid-encoded polymerase (PEP).

Heat shock response

The heat shock response (HSR) is a cell stress response that increases the number of molecular chaperones to combat the negative effects on proteins caused by stressors such as increased temperatures, oxidative stress, and heavy metals. In a normal cell, proteostasis must be maintained because proteins are the main functional units of the cell. Many proteins take on a defined configuration in a process known as protein folding in order to perform their biological functions. If these structures are altered, critical processes could be affected, leading to cell damage or death. The heat shock response can be employed under stress to induce the expression of heat shock proteins (HSP), many of which are molecular chaperones, that help prevent or reverse protein misfolding and provide an environment for proper folding.

The gene rpoS encodes the sigma factor sigma-38, a 37.8 kD protein in Escherichia coli. Sigma factors are proteins that regulate transcription in bacteria. Sigma factors can be activated in response to different environmental conditions. rpoS is transcribed in late exponential phase, and RpoS is the primary regulator of stationary phase genes. RpoS is a central regulator of the general stress response and operates in both a retroactive and a proactive manner: it not only allows the cell to survive environmental challenges, but it also prepares the cell for subsequent stresses (cross-protection). The transcriptional regulator CsgD is central to biofilm formation, controlling the expression of the curli structural and export proteins, and the diguanylate cyclase, adrA, which indirectly activates cellulose production. The rpoS gene most likely originated in the gammaproteobacteria.

In molecular genetics, a regulon is a group of genes that are regulated as a unit, generally controlled by the same regulatory gene that expresses a protein acting as a repressor or activator. This terminology is generally, although not exclusively, used in reference to prokaryotes, whose genomes are often organized into operons; the genes contained within a regulon are usually organized into more than one operon at disparate locations on the chromosome. Applied to eukaryotes, the term refers to any group of non-contiguous genes controlled by the same regulatory gene.

Anti-sigma factors

In the regulation of gene expression in prokaryotes, anti-sigma factors bind to sigma factors and inhibit transcriptional activity. Anti-sigma factors have been found in a number of bacteria, including Escherichia coli and Salmonella, and in the T4 bacteriophage. Anti-sigma factors are antagonists to the sigma factors, which regulate numerous cell processes including flagellar production, stress response, transport and cellular growth. For example, anti-sigma factor 70 Rsd in E. coli is present in the stationary phase and blocks the activity of sigma factor 70 which in essence initiates gene transcription. This allows the sigma S factor to associate with RNA polymerase and direct the expression of the stationary genes. Although binding of Rsd to σ70 has been shown and numerous structural studies on Rsd have been performed, the detailed mechanism of action is still unknown.

Heat shock factor Transcription factor

In molecular biology, heat shock factors (HSF), are the transcription factors that regulate the expression of the heat shock proteins. A typical example is the heat shock factor of Drosophila melanogaster.

HSF1 Protein-coding gene in the species Homo sapiens

Heat shock factor 1 (HSF1) is a protein that in humans is encoded by the HSF1 gene. HSF1 is highly conserved in eukaryotes and is the primary mediator of transcriptional responses to proteotoxic stress with important roles in non-stress regulation such as development and metabolism.

Cold shock response is a series of neurogenic cardio-respiratory responses caused by sudden immersion in cold water.

FourU thermometer

FourU thermometers are a class of non-coding RNA thermometers found in Salmonella. They are named 'FourU' due to the four highly conserved uridine nucleotides found directly opposite the Shine-Dalgarno sequence on hairpin II (pictured). RNA thermometers such as FourU control regulation of temperature via heat shock proteins in many prokaryotes. FourU thermometers are relatively small RNA molecules, only 57 nucleotides in length, and have a simple two-hairpin structure.

Bacterial small RNAs (sRNA) are small RNAs produced by bacteria; they are 50- to 500-nucleotide non-coding RNA molecules, highly structured and containing several stem-loops. Numerous sRNAs have been identified using both computational analysis and laboratory-based techniques such as Northern blotting, microarrays and RNA-Seq in a number of bacterial species including Escherichia coli, the model pathogen Salmonella, the nitrogen-fixing alphaproteobacterium Sinorhizobium meliloti, marine cyanobacteria, Francisella tularensis, Streptococcus pyogenes, the pathogen Staphylococcus aureus, and the plant pathogen Xanthomonas oryzae pathovar oryzae. Bacterial sRNAs affect how genes are expressed within bacterial cells via interaction with mRNA or protein, and thus can affect a variety of bacterial functions like metabolism, virulence, environmental stress response, and structure.

The Selman A. Waksman Award in Microbiology is awarded by the U.S. National Academy of Sciences "in recognition of excellence in the field of microbiology." Named after Selman Waksman, it was first awarded in 1968. A $5000 prize is included in the honor.

Proteostasis is the dynamic regulation of a balanced, functional proteome. The proteostasis network includes competing and integrated biological pathways within cells that control the biogenesis, folding, trafficking, and degradation of proteins present within and outside the cell. Loss of proteostasis is central to understanding the cause of diseases associated with excessive protein misfolding and degradation leading to loss-of-function phenotypes, as well as aggregation-associated degenerative disorders. Therapeutic restoration of proteostasis may treat or resolve these pathologies. Cellular proteostasis is key to ensuring successful development, healthy aging, resistance to environmental stresses, and to minimize homeostatic perturbations from pathogens such as viruses. Cellular mechanisms for maintaining proteostasis include regulated protein translation, chaperone assisted protein folding, and protein degradation pathways. Adjusting each of these mechanisms based on the need for specific proteins is essential to maintain all cellular functions relying on a correctly folded proteome.

RNA thermometer Temperature-dependent RNA structure

An RNA thermometer is a temperature-sensitive non-coding RNA molecule which regulates gene expression. RNA thermometers often regulate genes required during either a heat shock or cold shock response, but have been implicated in other regulatory roles such as in pathogenicity and starvation.

The integrated stress response is a cellular stress response conserved in eukaryotic cells that downregulates protein synthesis and upregulates specific genes in response to internal or environmental stresses.

Oxidation response is stimulated by a disturbance in the balance between the production of reactive oxygen species and antioxidant responses, known as oxidative stress. Active species of oxygen naturally occur in aerobic cells and have both intracellular and extracellular sources. These species, if not controlled, damage all components of the cell, including proteins, lipids and DNA. Hence cells need to maintain a strong defense against the damage. The following table gives an idea of the antioxidant defense system in bacterial system.

Universal stress protein

The universal stress protein (USP) domain is a superfamily of conserved genes which can be found in bacteria, archaea, fungi, protozoa and plants. Proteins containing the domain are induced by many environmental stressors such as nutrient starvation, drought, extreme temperatures, high salinity, and the presence of uncouplers, antibiotics and metals.

Chaperones, also called molecular chaperones, are proteins that assist other proteins in assuming their three-dimensional fold, which is necessary for protein function. However, the fold of a protein is sensitive to environmental conditions, such as temperature and pH, and thus chaperones are needed to keep proteins in their functional fold across various environmental conditions. Chaperones are an integral part of a cell's protein quality control network by assisting in protein folding and are ubiquitous across diverse biological taxa. Since protein folding, and therefore protein function, is susceptible to environmental conditions, chaperones could represent an important cellular aspect of biodiversity and environmental tolerance by organisms living in hazardous conditions. Chaperones also affect the evolution of proteins in general, as many proteins fundamentally require chaperones to fold or are naturally prone to misfolding, and therefore mitigates protein aggregation.

GrpE

GrpE is a bacterial nucleotide exchange factor that is important for regulation of protein folding machinery, as well as the heat shock response. It is a heat-inducible protein and during stress it prevents unfolded proteins from accumulating in the cytoplasm. Accumulation of unfolded proteins in the cytoplasm can lead to cell death.

References

  1. ↑ Ron EZ (2012). "Bacterial Stress Response". In Rosenberg E, DeLong EF, Lory S, Stackebrandt E, Thomson F (eds.). Prokaryotes: a handbook on the biology of bacteria (4th ed.). Berlin: Springer. pp. 589–603. ISBN   978-3-642-30140-7.
  2. ↑ Requena JM (2012). Stress Response in Microbiology. Caister Academic Press. ISBN   978-1-908230-04-1.
  3. ↑ Filloux AA, ed. (2012). Bacterial Regulatory Networks. Caister Academic Press. ISBN   978-1-908230-03-4.
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  5. 1 2 3 Havis S, Rangel J, Mali S, Bodunrin A, Housammy Z, Zimmerer R, et al. (March 2019). "A color-based competition assay for studying bacterial stress responses in Micrococcus luteus". FEMS Microbiology Letters. 366 (5). doi:10.1093/femsle/fnz054. PMID   30865770.
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  9. ↑ Maleki, Farajollah; Khosravi, Afra; Nasser, Ahmad; Taghinejad, Hamid; Azizian, Mitra (March 2016). "Bacterial Heat Shock Protein Activity". Journal of Clinical and Diagnostic Research : JCDR. 10 (3): BE01–BE03. doi:10.7860/JCDR/2016/14568.7444. ISSN   2249-782X. PMC   4843247 . PMID   27134861.
  10. ↑ Yura, T.; Nagai, H.; Mori, H. (1993). "Regulation of the heat-shock response in bacteria". Annual Review of Microbiology. 47: 321–350. doi:10.1146/annurev.mi.47.100193.001541. ISSN   0066-4227. PMID   7504905.
  11. 1 2 "Bacterial Stress Responses". News-Medical.net. 2018-10-22. Retrieved 2021-05-05.
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