23. Vegetative reproduction. Budding. Multiply fission. The types of grown cycle. Asexual Reproduction of Actinomycetes.

Vegetative reproduction includes: Budding, Fragmentation and Binary fission.

Budding: In this case, a small protuberance, called bud, develops at one end of the cell. Genome replication follows, and one copy of the genome gets into the bud. Then the bud enlarges, eventually become a daughter cell and finally gets separated from the parent cell.

MULTIPLE FISSION: Some algae, some protozoans, and the true slime molds (Myxomycetes) regularly divide by multiple fission. In such cases the nucleus undergoes several mitotic divisions, producing a number of nuclei. After the nuclear divisions are complete, the cytoplasm separates, and each nucleus becomes encased in its own membrane to form an individual cell. 

Actinomycetes reproduce by producing chains of spores and their tips (via spores), while other filamentous species fragment into new cells. Hyphal growth is followed by fragmentation and release of spores. One form of reproduction is Hyphal growth, which is followed by fragmentation and release of spores. Another form of reproduction is Conidia, which is when spores produce asexually on aerial fillaments. Cell wall is rich in lipids including waxes and fatty acids, mycolic acid. Asexual reproduction occurs by fragmentation, conidia, sporangiospores and oidia. They are saprotrophs and may produce a chemical substance which inhibit the growth of other micro organisms and are called antibiotics. The term antibiotic was given by Waksman, who also extracted first antibiotic from Streptomyces griseus and named it streptomycin. He was given Nobel Prize for it.

23. Resting cell shape in prokaryotes. Cysts. Endospore. The structure and function.

При переходе к неблагоприятным условиям существования многие прокариоты образуют особые дифференцированные формы – покоящиеся клетки, основным назначением которых является обеспечение переживания вида в неблагоприятных условиях. Их общей морфологической особенностью являются утолщенные клеточные стенки, а также частое образование дополнительных поверхностных структур на фоне одновременной дегидратации и компактизации метаболического и генетического аппаратов. В результате этого покоящиеся клетки характеризуются чрезвычайно низким (фоновым) уровнем обмена веществ и энергии, но приобретают повышенную устойчивость к действию разнообразных повреждающих факторов: высоких и низких температур, кислотности среды, радиации и пр. При попадании же в благоприятные условия покоящиеся клетки прорастают с образованием активно метаболизирующих вегетативных клеток.

Cyst – bacterial cells that have lost mobility turned into resting forms. Cyst have two coats – intine and exine. Contain poly-beta-hydroxybutyric acid (Azotobacter). Cysts form osme methanotrophic and oligotrophic bacteria, Spirochetes, Rickettsia

Эндоспоры– это особый тип покоящихся клеток грамположительных

бактерий, формирующихся внутри цитоплазмы материнской клетки. В каждой бактериальной клетке формируется одна эндоспора. Эндоспоры обладают многослойными белковыми покровами, наружной и внутренней мембранами, кортексом. Кроме того, они устойчивы к высоким температурам и радиации, летальным в норме для вегетативных клеток.

Образование эндоспор– процесс, происходящий только в мире прокариотов. Этапы формирования эндоспоры на примере бактерий родов

Bacillus и Clostridium.

23. The stage of endospore formation. Germination of endospore.

Эндоспоры– это особый тип покоящихся клеток грамположительных

бактерий, формирующихся внутри цитоплазмы материнской клетки. В каждой бактериальной клетке формируется одна эндоспора. Эндоспоры обладают многослойными белковыми покровами, наружной и внутренней мембранами, кортексом. Кроме того, они устойчивы

к высоким температурам и радиации, летальным в норме для вегетативных клеток

Образование эндоспор– процесс, происходящий только в мире прокариотов. Этапы формирования эндоспоры на примере бактерий родов Bacillus и Clostridium

the formation of endospore 0 the first in this stage the cell which is going to formthe endospore, enlarges in this size and its chromatin material condences attain the shape of an axial filament reaching from one end to the another end of cell

1 Replication and formation of axial filament. there’s a change in the metabolic activity of the cell

2 Septation. the plasma membrane start invaginating towards the one end of the cell. this invagination grows centripetally and both the end unite to form a spore septum. septum formation ends by the formation of a small spore known as fore spore. the genetic material also get transported to this structure. resulting in the structure encircled by two membranes.

3 Mother cell membranes engulfs forespore. spore septum of both i.e. mother cell and fore spore grows around the protoplasm of fore spore by a process called engulfment. thus fore spore lies freely in the cytoplasm of mother cell.

mother cell chromosome is destroyed and a cortex, made up of peptidoglycan layer is placed between the two membranes surrounding the fore spore protoplast. This cortex will be important in providing heat resistance and maintaining dormancy to the spore

4 Mother cell chromosome destruction. cell wall of peptidoglycan is synthesized outside the plasma membrane of fore spore. this structure is called as spore wall. In this stage layers of coat proteins are deposited on the outer membrane

5 deposition of coat proteins. There’s deposition of peptidoglycan cortex between the spore wall and cell membrane. The protoplasm condenses and synthesize dipliconic acid which deposition occurs on cell membrane. There’s an increase in the concentration of Calcium, arginine and glutamic acid in the spore cytoplasm. Spore wall become multilayered.

6 Maturation. Completing development. The mother cell – now called sporangium – releases the mature spore

7 the mother cell releases spore. Spore are resistant to many environmental stresses, that would be kill vegetative cells. The nature of this resistance is due, in part to a spore’s having only 10-30% of a vegetative cell’s water content. Spores also contain small acid-soluble proteins that bind to and protect DNA from damage by UV light and various toxic chemicals.

Germination of endospore

Favorable growth conditions signal the process of endospore germination. Germination of a spore results in a break in the spore wall and the outgrowing of a new vegetative cell. The newly formed vegetative cell is capable of growth and reproduction. A single spore upon germination forms a single vegetative cell. Germination occurs in following steps: Activation: Even in the presence of favorable conditions, the spore will not germinate until its protective spore coat is not damaged. Conditions such as heat, acidity, abrasion or compounds containing free sulphydryl groups activate the spore to germinate.  Initiation: once activated, the spore will germinate provided the environment is suitable. Different signaling effectors exist for different species. Binding of effector stimulates autolytic enzymes that degrade the peptidoglycan of cortex. Water is absorbed and calcium dipicolinate is released.  Outgrowth: once the cortex and outer layers is degraded, a new vegetative cell consisting of spore protoplast and its wall emerges. This is followed by active biosynthetic activity and process terminates with cell division.