1.1 Physical mutagenesis
1.1.1 Ultraviolet irradiation
Ultraviolet irradiation is one of the commonly used physical mutagenesis methods and is an extraordinary method of inducing microbial mutations. Useful tool. The maximum absorption peak of purine and pyrimidine in DNA and RNA is at 260nm, so ultraviolet radiation at 260nm is the most effective lethal agent. There are many explanations for the effect of ultraviolet radiation, but the more certain effect is to make DNA molecules form pyrimidine dimers [1]. The formation of dimers will hinder normal pairing between bases, so it may lead to mutations or even death [2].
Ultraviolet irradiation mutagenesis is simple, economical and can be achieved under general laboratory conditions, and the probability of positive mutations is high. This method is mostly used for mutagenesis of yeast strains.
1.1.2 Ionizing radiation
γ-rays are one of the most widely used ionizing rays in ionizing biology. They have high energy and can produce ionization. They can be used directly or Indirectly alters DNA structure. The direct effect is to oxidize the base of deoxyribose, or the chemical bond between deoxyribose and the sugar-phosphate. Its indirect effect is to cause water or organic molecules to generate free radicals, which can undergo chemical changes with solute molecules in cells, leading to DNA component deletion and damage [2].
In addition to γ-rays, ionizing radiation also includes X-rays, β-rays and fast neutrons. Ionizing radiation has certain limitations, high operational requirements, and certain risks. It is usually used in mutation breeding processes where other mutagens cannot be used.
1.1.3 Ion implantation
Ion implantation is a high-tech technology that emerged in the early 1980s and is mainly used to modify the surface of metal materials. It has been gradually used in crop breeding since 1986, and this technology has been gradually introduced in microbial breeding in recent years [3].
During ion implantation, biomolecules absorb energy and cause complex physical and chemical changes. The intermediates of these changes are various types of active free radicals. These free radicals can cause damage to other normal biological molecules, cause chromosome mutations in cells, DNA chain breaks, and plasmid DNA breaks. Since the ion implantation range is controllable, with the development of micro-beam technology and precise positioning technology, positioning mutagenesis will become possible [4].
Ion implantation method for microbial mutation breeding is difficult to achieve under general laboratory conditions and is currently relatively rarely used.
1.1.4 Laser
Laser is a kind of light quantum flow, also known as light particles. Laser radiation can directly or indirectly affect organisms through the combined application of light, heat, pressure and electromagnetic field effects, causing cell chromosome distortion effects, activation or inactivation of enzymes, and changes in cell division and cell metabolic activities. Once light quanta acts on any substance in the cell contents, it may cause variations in the cellular and genetic characteristics of biological organisms. Different types of laser irradiate biological organisms and exhibit different cytological and genetic changes [5].
As a breeding method, laser has the advantages of simple operation and safe use. In recent years, laser has made a lot of progress in microbial breeding.
1.1.5 Microwave
Microwave radiation is a kind of low-energy electromagnetic radiation. The frequency range with strong biological effects is 300MHz~300GHz, and it has thermal and non-thermal effects on living organisms. Its thermal effect means that it can cause the local temperature of organisms to rise. Thus causing physiological and biochemical reactions; non-thermal effects refer to the fact that under the action of microwaves, organisms will produce various physiological and biochemical reactions that are not related to temperature. Under the combined effect of these two effects, organisms will produce a series of mutation effects [6].
Thus, microwaves have also been used in mutation breeding in many fields, such as crop breeding, animal breeding, and industrial microbial breeding, and have achieved certain results.
1.1.6 Space Breeding
Space breeding, also called space mutation breeding, is the use of high-altitude balloons, returnable satellites, spacecraft and other spacecraft to mutate crop seeds, tissues, organs or Living individuals are carried into space, use the special environment of space to mutate biological genes, and then return to the ground for selective breeding and new crop breeding techniques to develop new varieties and new materials.
Space environmental factors mainly include microgravity, space radiation, and other mutagenic factors such as alternating magnetic fields, ultra-vacuum environments, etc. The interaction of these factors causes genetic damage to biological systems, causing organisms to undergo mutations, chromosome aberrations, and cell inactivation. , developmental abnormalities, etc.
Aerospace breeding is special than other breeding methods. It is an organic combination of aerospace technology and microbial breeding technology. It has high technical content and high cost. It is difficult for individual researchers or general research units to achieve it. It can only be combined with aerospace technology. The combination is done by the state.
1.1.7 Atmospheric and Room Temperature Plasma Mutation Breeding
Atmospheric and Room Temperature Plasma (ARTP), referred to as ARTP, refers to the ability to generate a temperature of 25 under atmospheric pressure. A plasma jet with a high concentration of active particles (including helium atoms, oxygen atoms, nitrogen atoms, OH radicals, etc. in excited states) between -40 °C. As a new physical method, ARTP technology has broad application prospects in the field of microbial mutation breeding.
An appropriate dose of active particles in the plasma acts on microorganisms, which can change the structure and permeability of the microbial cell wall/membrane and cause genetic damage. After the genetic material of the strain is damaged, the microorganism initiates the SOS repair mechanism. , which induces the production of DNA polymerases IV and V, which do not have the proofreading function of 3ˊ exonuclease, so even if unpaired bases appear at the damaged site of the DNA chain, replication can still proceed. Allowing mismatches in this situation increases the chance of survival. The damage caused by ARTP to genetic material is highly diverse; and SOS-induced repair itself is a fault-tolerant repair. Therefore, the damage caused by the diversity of ARTP may be contained in the DNA chain during the repair process. When microorganisms perform replication and repair, their Possible mismatches that may bring about diversity.
ARTP is used in microbial mutation breeding. It is low-cost and easy to operate. It does not require ancillary equipment such as ion or electron acceleration, vacuum and refrigeration required by many physical mutagenesis equipment (such as ion beam injection, etc.); ARTP is suitable for The damage mechanism of genetic material is diverse, with a high positive mutation rate and diverse mutation properties. It is effective on fungi, bacteria, algae, etc.; ARTP has no pollution to the environment and ensures the personal safety of the operator. No matter what kind of gas is used for discharge, None of them produce harmful gases.