The bacterial stress response enables

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

to survive adverse and fluctuating conditions in their immediate surroundings. 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. 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 Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

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. These systems can include immediate responses such as chaperones, as well as slower responses like

transcriptional regulation 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 alt ...

to control protein production, latency, and others. Stress response systems can play an important role in the

virulence Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ca ...

pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...

ic 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. 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

eukaryote Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

s 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.

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 acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

nucleic acid Nucleic acids are biopolymers, macromolecules, essential to all known forms of life. They are composed of nucleotides, which are the monomers made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main cl ...

s, and

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...

s. Another type of stressor could be the absence of a favorable

electron acceptor An electron acceptor is a chemical entity that accepts electrons transferred to it from another compound. It is an oxidizing agent that, by virtue of its accepting electrons, is itself reduced in the process. Electron acceptors are sometimes mista ...

for

cellular respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...

. 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. Other types of stressors include

oxidants An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxi ...

, nutrient deprivation, hypo/hyper- osmolarity, extreme pH, extreme temperature, and antimicrobial substances. 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. Another major stress response system is

. 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 Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...

. The concentration of different

RNA transcript Transcription is the process of copying a segment of DNA into RNA. The segments of DNA transcribed into RNA molecules that can encode proteins are said to produce messenger RNA (mRNA). Other segments of DNA are copied into RNA molecules calle ...

s is then altered to favor the production of those that will produce proteins that will mitigate the effects of the stimulus. However, this system may be limited by the

translational Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...

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

ribosome Ribosomes ( ) are macromolecular machines, found within all cells, that perform biological protein synthesis (mRNA translation). Ribosomes link amino acids together in the order specified by the codons of messenger RNA (mRNA) molecules to ...

s. A stress response that can occur under conditions that are non-advantageous, but also non-lethal, is the creation of a

biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...

. In this response, bacterial cells can secrete

extracellular polymeric substance Extracellular polymeric substances (EPSs) are natural polymers of high molecular weight secreted by microorganisms into their environment. EPSs establish the functional and structural integrity of biofilms, and are considered the fundamental comp ...

s to form a film that can provide support to the bacterial colony, such as by improving their ability to adhere to a surface. Another common stress response is latency. In a latent states, a cell will slow down its

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

and become virtually dormant. This makes the cell much less affected by stressors such as antibacterial agents, starvation,

hypoxia Hypoxia means a lower than normal level of oxygen, and may refer to: Reduced or insufficient oxygen * Hypoxia (environmental), abnormally low oxygen content of the specific environment * Hypoxia (medical), abnormally low level of oxygen in the tis ...

, and acidity. Some bacteria are able to enter a latent state and remain there for up to years before returning to an active state. A cell can also shift from production of unsaturated

fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, fr ...

s 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 Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

can also be changed in response to a stressor. In bacteria some other important stress response systems are: * Heat shock response, controlled by the

sigma factor A sigma factor (σ factor or specificity 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 ho ...

sigma 32 * Envelope stress response, controlled mainly by the sigma factor sigma E and the Cpx

two-component system In the field of molecular biology, a two-component regulatory system serves as a basic stimulus-response coupling mechanism to allow organisms to sense and respond to changes in many different environmental conditions. Two-component systems t ...

Cold shock Cold shock response is a series of neurogenic cardio-respiratory responses caused by sudden immersion in cold water. In cold water immersions, such as by falling through thin ice, cold shock response is perhaps the most common cause of death. Als ...

response, which governs expression of RNA chaperones and ribosomal factors * (p )ppGpp-dependent stringent response, which reduces the cellular protein synthesis capacity and controls further global responses upon nutritional downshift

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

protease A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the ...

s are rapidly induced to protect against the denaturation of proteins within the bacteria. 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.

Envelope Stress Response

The two-component signal transduction (2CST) system allows the bacterial cell to sense stress within the system. A

histidine kinase Histidine kinases (HK) are multifunctional, and in non-animal kingdoms, typically transmembrane, proteins of the transferase class of enzymes that play a role in signal transduction across the cellular membrane. The vast majority of HKs are homod ...

that can be found in the cell's inner membrane detects the stress. The histidine kinase detects stress due to the

autophosphorylation Autophosphorylation is a type of post-translational modification of proteins. It is generally defined as the phosphorylation of the kinase by itself. In eukaryotes, this process occurs by the addition of a phosphate group to serine, threonine or ...

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 In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The fu ...

. 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.{{Cite web, date=2018-10-22, title=Bacterial Stress Responses, url=https://www.news-medical.net/life-sciences/Bacterial-Stress-Responses.aspx, access-date=2021-05-05, website=News-Medical.net, language=en

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 A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

that occurs as well. This means that the cells will prematurely go onto the interphase stage of

mitosis In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is mainta ...

. There will also be an organization of the

nucleoid The nucleoid (meaning ''nucleus-like'') is an irregularly shaped region within the prokaryotic cell that contains all or most of the genetic material. The chromosome of a prokaryote is circular, and its length is very large compared to the cell dim ...

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

References