تعالی بسمه

Spores

Clostridium perfringens

Spores

Vegetative cells

The Bacterial Endospore

Bacterial spores

A few species of bacteria have the ability to produce highly resistant structures known as endospores (or simply spores).

These resist a range of hazardous environments, and protect against heat, radiation, and desiccation.

Endospores form within (hence endo-) special vegetative cells known as sporangia (singular sporangium).

Historical Developement & Importance

– Spore which can germinate have been found from structures 7200 year old temples have been found and recently from GI tract of a bee preserved in amber (1 million years old)

– 100's of species mainly of the genera Bacillus (aerobic rods, facultative anaerobes), and Clostridium (anaerobic rods); Few others include Sporosarcina (aerobic cocci), Desulfotomaculum (anaerobic rods, sulfate-reducers)

Historical Developement & Importance

Food industries (canning, milk etc) heat treat products to reduce microbial spoilage & kill pathogens;)

Mainly found in soils --> vegetables --> meat where spores germinate to produce toxins

Mainly found in soils --> infect wounds (problem with farm associated workers)

Some strains were being developed for biological warfare eg B. anthracis (anthrax)

Some strains produce important biopesticides (biotechnology) eg B. thuringiensis var. israelensis produces toxic proteins against mosquito & blackfly larvae.

Some sporeformers are pathogens of animals, usually due to the production of powerful toxins.

Bacillus anthracis causes anthrax, a disease of domestic animals (cattle, sheep, etc.) which may be transmitted to humans.

Clostridium botulinum causes botulism, a form of food poisoning.

Clostridium tetani is the agent of tetanus.

spores

• Endospore within the cells

• Exospore external to the cells

Location and shape of endospres within the vegetative cell

• Terminal (Clostridium tetani)

• Subterminal (Clostridium botulinum )

• Central (Bacillus cereus)

Spore shapes may be

round

oval

• There are various types of endospore formation in bacteria

• Round • Ellipsoidal • Oval • Cylindrical • Kidney shaped • Banana shaped•

Clostridium tetani•Clostridium botulinum

Bacterial endospores. Phase microscopy of sporulating bacteria demonstrates the refractility of endospores, as well as characteristic spore shapes and locations within the mother cell.      

formation of endospores

• Under conditions of starvation, – especially the lack of carbon and nitrogen

sources, – a single endospores form within some of the

bacteria.

• The process is called sporulation

The developmental cycle of the Endospore.

Early stages of endospore formation

First the DNA replicates and a cytoplasmic membrane septum forms at one end of the cell. A second layer of cytoplasmic membrane then forms around one of the DNA molecules (the one that will become part of the endospore) to form a forespore.

Middle stages of endospore formation

Both of these membrane layers then synthesize peptidoglycan in the space between them to form the first protective coat, the cortex.

Completion of endospore formation

Calcium dipocolinate is also incorporated into the forming endospore. A spore coat composed of a keratin-like protein then forms around the cortex. Sometimes an outer membrane composed of lipid and protein and called an exosporium is also seen Finally, the remainder of the bacterium is degraded and the endospore is released.

Stage Morphological event Biochemical event

1 Vegatative cell

2 Chromatin filament Exoenzyme

Antibiotic

3 Spore septum Alanine dehydrogenase

4 Spore protoplast

Alkaline phosphatase

Glucose dehydrogenase

Aconitase

Heat-resistant catalase

5

Cortex formation

(refractility)

Ribosidase

Adenosine deaminase

Dipicolinic acid

6 Coat formation Cysteine incorporation

Chemical resistance

7 Maturation Alanine racemase

Heat resistance

Morphologic and biochemical event in Bacillus subtilis

Structure of spore

Bacillus cereus

The Spread of Microorganisms

• SporeBacillus thuringeinsis

4- cortex4- cortex

The endosporeThe endospore

1-exosporium1-exosporium

2- coat2- coat

5- Inner 5- Inner membranemembrane

3- outer 3- outer membranemembrane

Structure of spore

يا • مركزي مواد : Protoplast – Coreهستهدارد سيتوپالسم كمي ومقدار اي هسته

وجود بعلت حرارت درمقابل مقاومتCalcium Dipicolinate dehydrated مي

باشد.داخلي • غشاء : innen membraneغشاء

داخلي آورد مي بوجود + بعدا را سيتوپالسميسيتوپالسمي پرده از اليه اين قسمت ترين

. گيرد مي منشاء مادر ياخته•Spore Cortex و كه بوده اسپور دیواره همان

شده تشکیل بیرونی و داخلی الیه دو از بینمرحله دراين باشد مي تر ضخيم ها اليه همه

Dipicolonic acid در كلسيم زيادي ومقداروكلسيم ماده اين دارد وجود اسپور مركز

مي باعث حرارت مقابل در را اسپور مقاومتشود.

Bacillus megaterium

Structure of spore

مانند Spore wallديواره – Cell wallاسپور ( شامل ( و باشد مي مثبت گرم هاي باكتري

peptidoglycan عرضی ( طبيعي های پل کهکمتر باشد آن است) مي ،.

يا • خارجي خارج :Spore Coatپوستهو خارجی پروتئين ( Polypeptideاز دیواره

دارد دوسولفوره اتصال كه كراتين شبيه ( باشد مي سيستن زيادي مقدار وداراي

. است شده تشكيل اليه چهار دوتا واز• exosporium :اليه مي Lipoproteinيك

راحتي به مواد كه است نازكي اليه و باشددر اليه اين و بشوند توانند نمي وارد آن از

مانند دارد وجود باكتريها از بعضيBacillus cereus

Bacillus megaterium

Lysine biosynthetic pathway

Resistant to harsh environments

-Heat (owing to high concentration of calcium dipicolinic acid)– UV radiation (increased cysteine amino acids)– Dessication– Disinfectants (impermeable cell coat)– Mechanical stress

Survival strategy when nutrients are limiting

Mechanism of heat ressistance

Physical (sporecoat): Ressistance to staining demonstrates imperability & therefore ressistant to dehydration & effects of toxins (multilayered thick peptidoglycan)

Chemical (core): Low water content (15% instead of 80% found in cells) makes proteins & nucleic acids more ressistant. CDPA complexes with proteins & other labile components & makes them more ressistant. Medium lacking calcium or mutant strains that do not form CDPA produce less "tolerant" spores

Heat ressistance Endospore-forming cell Time required to kill a

suspension in boiling water (100 C)

•  B. Anthracis 1-2 min (not very heat ressistant)

•  C. botulinum 2-6 hours • C. tetani  1-3 hours • E. coli & S. aureus • (non-endospore formers) 30 minutes at 70 C

The heat resistance of endospores is due to a variety of factors

• Calcium-dipicolinate, abundant within the endospore, may stabilize and protect the endospore's DNA.

• Specialized DNA-binding proteins saturate the endospore's DNA and protect it from heat, drying, chemicals, and radiation.

• The cortex may osmotically remove water from the interior of the endospore and the dehydration that results is thought to be very important in the endospore's resistance to heat and radiation.

• Finally, DNA repair enzymes contained within the endospore are able to repair damaged DNA during germination

Generation of active vegetative cell

–Activation

–Germination

–Outgrowth

Generation of active vegetative cell

– Activation• Reversible process• Prepares for germination• Often heat-induced process or by

chemical treat– L-alanine is the most common– Several amino acids, nocleoside and

glucose

Generation of active vegetative cell

– Germination• End of dormant• Irreversible process• In early stage

– Loss of refractility– Swelling of the cortex– Appearance of fine nuclear fibrils

• Breaks out of spore coatLost of resistance Increase in the sulfhydryl levelRelease spore componentIncrease metabolic activity

• Not inhibit by antibiotic that perturb protein and nucleic acid synthesis

Generation of active vegetative cell

– Outgrowth• Active growth – vegetative state

–Sopre core membrane develops into the cell wall

–Active biosynthetic activity» Inhibit by antibiotic that inhibit cell

wall, protein , or nucleic acid synthesis

ذيل مراحل زدن جوانه وقت درگردد مي :پديدار

بود • متشعشع + قبال كه هاگمي دست از را خاصيت اينخاصيت حال عين ودر دهد

رنگها برابر در ناپذيري نفوذ. شود مي گرفته آن از

غشاءهاي • نقاط از يكي درمي ايجاد شكافي هاگي،

باسيلي نوع آنجا واز شودواز آورد مي سربدر ميكروب

. شود مي خارج خود پوستهمعمولي • شكل مرحله اين در

مي هويدا ميكروب، وعاديهاگ دوره ترتيب وبدين شود

پايان- زدن جوانه گذاري. است پذيرفته

• Most endospore cannot germinate immediately– After they have rest for several days– After heated briefly (5 min, at 60 C).

If proper nutrient are present

spore takes in water and swells

spore coat cracks

vegetative cell grow

Differences Between Endospores And Vegetative Cells

1. Endospores Are Dormant (For At Least 100 Years)

2. Endospores Are Unable To Multiply.

3. Endospores Do Not Degrade Components To Generate Energy

4. Endospores Do Not Synthesize Cell Components

Property Vegetative cells Endospores

Surface coatsTypical Gram-positive peptido-glycan cell wall polymer

Thick spore coat, cortex, and peptidoglycan core wall

Microscopic appearance

Nonrefractile Refractile

Calcium dipicolinic acid

Absent Present in core

Cytoplasmic water activity

High Very low

Enzymatic activity Present Absent

Macromolecular synthesis

Present Absent

Heat resistance Low High

Resistance to chemicals and acids

Low High

Radiation resistance Low High

Sensitivity to lysozyme Sensitive Resistant

Sensitivity to dyes and staining

Sensitive (will take up stain)Resistant(need special techniques to stain)

Endospore stain of Bacillus megaterium

Note red endospores inside colorless streptobacillus

Spore Stain

• Purpose

A differential stain used to detect the presence or location of spores in bacterial cells. Only a few genera produce spores such as Bacillus and Clostridium Note the endospore within the rod gives the

bacterium a "tennis racquet" shape

Spore Stain • Principle

Spores have a touch outer covering made of the protein keratin and are resistant to heat and chemicals. The keratin also resists staining, so extreme measures must be taken to stain the spore. A primary stain of malachite green is forced into the spore by steaming the bacterial emulsion. Malachite green is water soluble and has a low affinity for cell material, so vegetative cells and spore mother cells may be decolorized with water and counterstained with safranin.

exospores

• Cells of the methane-oxidizing genus Methylosinus form exospores i.e. spores external to the vegetative cells, by budding at one end of the cell

• These are desiccation and heat resistant, but unlike endospores they do not contain DPA.

• Endospores– produced within the cell, the cell wall does not

contribute to the spore coat– eg Bacillus and Clostridium species

• Actinomycete exospores– produced by division of a filamentous cell, the

cell wall is modified to form the spore coat

– eg Actinomyces and Streptomyces species

Functions of spores

• Endospores– survival and dispersal, very resistant to

extreme environmental conditions– only one spore is produced per cell therefore

not significant in reproduction

• Exospores– survival and dispersal, moderately resistant to

extreme environmental conditions– many spores produced per cell therefore very

significant in reproduction

Actinomycete exospores

• Formation– borne on filamentous cells of actinomycete bacteria– produced on specialised aerial filaments called

sporophores each producing numerous spores– formed in response to nutrient depletion

• Morphology– very variable arrangement of spores on the aerial

filament– can be used in classification and identification

Properties of actinomycete exospores

Resistance to drying– very high, easily spread in dry conditions

• Resistance to heat– low, easily destroyed by exposure to heat

• Chemical and radiation resistance– low, easily destroyed by chemical and

physical agents

•The end

Spore

مي • كم درمحيط فسفر ويا نيتروژن كربن، ميزان زمانيكهومقاوم خاموش فرم سمت به مشخص باكتريهاي شود

. را حالتي چنين تشكيل روند پيشمي محيط Sporeبهرا endosporesويا اسپور كه مادر سلولي نامند مي

كرده . Sporangiumاحاطه اسپور تشكيل نامند ميهوازي بي هوازي،كلسترديومهاي هاي باسيل به محدود

از مي actinomyceteو Sarcinaeوتعدادي محدودوتشكيل. بوده مثبت گرم ها ارگانيسم اين تمام شود

مي كلفت ديواره يك تشكيل توانايي به وابسته اسپورباشد.

Spore

شبيه • باكتريها و exosporeاسپور actinomyceteقارچهاعالي، گياهان هاي دانه چنين وهم cryptobioticمشخص

متابوليكي فعاليت داراي آنها مرحله دراين كه باشند ميفعال حالت به مرحله ازاين قادرند ولي باشند نمي

+ نسبتا وقارچهاي متحرك غير هاي ودانه اسپور برگردند،مي كار به اطراف به آنها بخش براي كه وگياهان بزرگ

ماندن. زنده برعكسجهت باكتريها اسپور روندحرارت،خشكي، مانند سخت شرايط تحت ميكروارگانيسم

. چه اگر كند مي كمك اشعه و شيميايي مواد سرما،انگيخته رابر دراسپور توجه بيشترين گرما به مقاومت

آنها زندگي + احتماال اسپور اصلي اكولوژي نقش ولي است . نمونه از زنده هاي باسيل باشد مي خشك شرايط رادر

از بيش كه شده 30خاكيهايي جدا اند شده داري نگه سالاست.

Spore

ايجاد • باعث آنها زيرا باشند مي مهم پزشكي شناسي باكتري در اسپورهامي مقاوم سلولهاي استريل مواد درتوليد وهمچنين شده بيماريها از تعدادي

باشند.•Endospore formations (sporulation process )متابوليت • كاهش كه درزماني + غالبا اسپور تشكيل شد گفته كه همانطور

. باعث كه موادغذايي كمبود مكانيسم افتد مي اتفاق دارد وجود اساسياسپورالسيون . sporulationشروع اعتقاد ولي باشد مي ناشناخته شود مي

( ) ( عالمت ( سيگنال مولكولي درسطح يك كه است براين دانشمندان عموميسلولي داخلي شود guanine nucletideكمبود مي مرحله اين شروع باعث

مي مهار را گوانيدين كه موادي بوسيله سنتز كه آزمايش بوسيله نظريه اينو نيتروژن كربن، كافي درحضورمقدار حتي زمانيكه و شد مشاهده ساختندتغييرات . يافت ادامه شدن اسپور روند اين نوكلوتيد مهارگوانيدين با فسفر

افتد مي اتفاق شدن اسپور جهت مختلفي مراحلي زيادي وشيميايي فيزيكياز عبارتند ترتيب به كه

•Stage 1

•Stage 1 . از برداري رونوشت اتفاق باشد DNAاولين ميواحدهاي فرم از باكتري كروموزوم دوره اين طي در

بنام اي رشته ساختمان به تبديل axial filamentپيچيده . هاي ازگونه بعضي از مرحله اين درطي گردد مي

Bacillus . اين نقش شود مي ترشح خارج به بيوتيك آنتي . بعضي باشد مي نامشخص اسپور توليد در ها بيوتيك آنتيكه آنزيمهايي افزايش مانند مشخص درآنزيمهاي تغييرات

ديده دوره اين طي در كنند مي دخالت انرژي درتوليد ( ) . كافي ميزان كافي سطح است ادامه ATPشده جهت

. مانند آنزيمهايي باشد مي نياز مورد مرحله SerineاينProtease مي رها ازباكتري دوره اين طي در همچنين

. است نامشخص اسپور درتوليد آن نقش كه شود

گوانوزين • از بااليي Phosphorylated guanosineغلظتاما است شده ديده ازاسپوراسيون خاصي مراحل طي در

. است مشخص نا اسپور درتوليد آن دخالت چگونگي•Stage II : درشكل تغييرات اولين كه است اي مرحله اين

. سيتوپالسم غشاء فرورفتن افتد مي اتفاق باكتريهاغشاء ) Septumوتشكيل طرفين( از يكي درنزديكي ديواره

. ( مي( باعث اتفاق اين افتد مي اتفاق سلول قطب يك سلولباكتري كه مساوي Sporongiumشود غير دوقسمت به

را بزرگتر سلول كه شود وكوچكتري mother cellتقسيماست foresporeرا اسپور وپيش گويند مي اسپور پيش را

به درنهايت . endosporeكه شدن تقسيم گردد مي تبديلSporajium مولكول كه شود مي باعث به DNAهمچنين

. شود تقسيم اسپور وپيش مادر دوسلول

•Stage III . سلول غشاءديوارة مرحله اين درطيدربر دومي غشايي اليه رادريك اسپور پيش مادر

سيتوپالسم خود داخل اسپور وپيش گيرد مي . پيش بابودن آن ونتيجه گيرد مي قرار سلول

آزاد پرتوپالست بصورت سيتوپالسم اسپوردربلعيدن روند شود مادرمشخصمي به درسلول

آنزيم زيرا باشد مي گيري اندازه قابل راحتي . اين نقش ولي يابد مي ظهور فسفاتاز آلكالين

در .sporulationآنزيم باشد مي نامشخص

•Stag IV موادي يك بوسيله اسپور پيش دوغشاءپروتوپالست بين ناحيهبنام سلولي ديواره كورتكسيك Cortexشبيه شود مي پر

peptidoglycan با تركيبات لحاظ از اما باشد peptidoglycanمي. باشد مي متفاوت فعال باكتريهاي سلولي مرحله ديواره اين درطيو ازمحيط شده گرفته اسپور پيش بوسيله كه dipicolinic acidكلسيم

. رابطه گردند مي سنتز اسپور درپيش ندارند وجود فعال درباكتريهايو كلسيم . dipicolinic acidبين به كلسيم باشد مي يك به يك نسبت

dipicolinic acid وتشكيل شده مي Caleium dipicolinateateباندتا آن مقدار . 15دهدكه يك% گيرد مي رادربر بالغ اسپور خشك وزن

از مجزا ديواره peptidoglycanاليه اين شود مي تشكيل كورتكس زيرشود دامي رويان اسپور سلولي ديواره كه باشد مي اوليه سلوليمادر باسلول آيد مي بوجود كورتكس تشكيل براي كه هايي آنزيم

ابتدايي سلولي ديواره براي آنزيم كه حالي در كند مي همكاري . حضور بوسيله مرحله اين كند مي باپروتوپالست glucoseهمكاري

dehydrogenase نامشخصمي آنزيم اين عمل ولي شود مي كنترلباشد.

•Stage V زيادي مقدار داراي كه پروتئيني پوششاز غشاءاطراف Cysteneبااليي در باشد مي

. كند مي پيدا تجمع كورتكس•Stag VI افتد مي اتفاق مرحله دراين شدن بالغ

است قادر اندرسپور مرحله اين ودرانتهايو آلي،اشعه حرارت،حاللهاي lysozymeدرمقابل

. كند مقاومت•Stag VII sporangium گردد تخريب است ممكن

. شود رها محيط به بالغ واندرسپور

Mechanism of Spore resistance and its implecations.

مواد • زيرا باشند مي شيميايي مواد به حساس ها ارگانيسم ( ) ويا ها آنزيم شود مي مهم هاي پروتئين هيدرليز باعث شيميايي

اسيد شيميايي نوكلئيك مواد به مقاوم بسيار بنابراين اسپورنياز مورد هيدروليز جهت آب كه ندارد وجود آزاد آب زيرا هستند

. سه بدليل + ظاهرا اسپور توسط گرما به مقاومت باشد مي. باشد مي آنها -inherent moleculor Component 2-1تركيب

dehydration 3- mineralization. حرارتي • درجه به وابسته ذاتي ويا اصلي مولكولهاي تركيب

ديگر عبارت به دهد مي اسپور تشكيل ارگانيسم كه استthermophils ) حرارت به ومقاوم زياد بادرجه اسپورهايي توليد

( توليد دارند حرارت به بيشتري مقاومت كه اسپورهايي كند مي . ماكرومولكولهايي وجود بخاطر + احتماال گرما به تطابق كنند مي

. است رسيده ارث اسپوربه به است

Mechanism of Spore resistance and its implecations

مختلف .• درنقاط دراسپور آب توزيع كه دارد وجود مداركي. باشد مي + coreمتفاوت نسبتا كه dehydrateاسپور درحالي بوده

cortex . مقدار باشد مي آب بيشتري مقدار دارايdehydration ،core. كند مي راتعيين حرارت به مقاومت درجه

•Mineralization روي كه باشد مي خارجي عامل مهمترينdehydration : مانند عنصر يك غلظت مثال براي گذارد مي اثردرجه اسپوررا dehydrationكلسيم معدني مواد كند مي كنترل را

. مثال براي درپليمر مواد بااين آب جابجايي بوسيله كند مي ثابتCalcium dipicolinate درمولكولDNA ولذا گرفته قرار

. آورد مي بعمل جلوگيري آن به ازهيدروليز مقاومت مكانيسمنوع) U.Vاشعه( يك شودكه مي زده حدس است نشده معين هنوز

مي آيدسنتز بوجودمي اسپور كه درزماني مخصوص پروتئينهاي ازاسيدنوكلوئيك با پروتئين واين واكنش interactشود و اند تداخل

اشعه به مقاومت وباعث داده انجام آن وتغييردرشكل داده انجامو رفته بين از پروتئين رويش،اين روند طي در شود DNAمي

به .V.Vحساس شود مي

Mechanism of Spore resistance and its implecations.

شرايط • در ها ارگانيسم اين ماندن زنده بر عالوهمي. پزشكي درجوامع اي عمده مشكل اسپورها سخت

جنس اسپور + مخصوصا . Bacillus باشند براي وكلسترديومشاربن، Bacillus anthracisمثال عامل Clobotulinuعامل

و غذايي مسموميت مي clotetaniبوتوليسم كزاز عاملوبسياري. بيوتيك جوش،آنتي به باكتريها اين اسپورها باشند

. وقارچها باكتريها فعال فرم باشند مي مقاوم سپيتيك ازآنتيحرارتuْْ 5-10درعرض در ولي 80دقيقه روند مي ازبين

330. اسيدبوتدنيوم براي اسپور 90دقيقه دقيقهاسپور 30كزاز، الزم gas gangremدقيقه جوش حرارت

آنها همه كه حالي در بروند ازبين اسپورها اين تا استحرارت بمدت 15فشار cu121دردرجه بين 15پوند از دقيقه

. روند مي

• Some bacteria produce spore-like structures distinct from endospores. Exospores are heat resistant spores produced by a budding process in members of the genus Metylosinus and Rhodomicrobium. Cysts are resistant to drying and are formed singly within vegetative cells by Azotobacter, Myxococcus, and Sporocytophaga. Conidia are heat-susceptible asexual reproductive spores produced by various genera of branching bacteria belonging to the group Actinomycetes

nuclear fusion

After nuclear fusion, the club-shaped structure (now 2n) will produce and bear haploid spores at the four tips of the cell.

meiosis

cytoplasmic fusion

Diploid Stage

Haploid Stage

Club-shaped structures having two nuclei (n + n) form at the margin of each gill.

gills

After cytoplasmic fusion, a “dikaryotic” (n + n) mycelium gives rise to spore-bearing bodies (e.g., mushrooms).

cap

stalk

spore (n)

Spores are released.

Each germinating spore gives rise to a hypha that grows and becomes a branching mycelium.

Conidiospres and sporangiospores

• Actinomycetes form branching hyphae; spore developing, singly or in chains, from the tips of these hyphae by crosswall formation (septation).

• If the spores are contained in an enclosing sac (sporangium), they are termed sporangiospores

• If the spores are not contained in an enclosing sac, they are called conidiospores or conidia

• The spore do not have the high heat resistance but can survive long periods of drying

• Generation of active vegetative cell:– Activation

• Prepares for germination• Often heat-induced process

– Germination• Breaks out of spore coat

– Outgrowth• Active growth – vegetative state

• Dormancy for thousands of years is possible

Properties of endospores

• Heat resistant– some species can survive boiling water for

several hours

• Resistant to drying– spores can survive in dry dust for many years

(possibly centuries)

• Resistant to chemical and physical agents– eg ultra-violet light and chemical disinfectants

Relationship between structure and properties

Calcium dipicolonate– makes up about 10% of the dry weight of the spore– possibly stabilises proteins in the spore

Low water content– increases heat and chemical resistance– stops enzyme activity

Small acid-soluble spore proteins– bind tightly to DNA and protect it– serve as a carbon and energy source during

germination

Spore structure

– The spore can be differentiated into 4 distinct parts:

• Core: Nucleic acids, ribosome, low levels of enzyme activity, Calcium dipicolonic acid (CDPA) & low water content. Low level of metabolic activity

– Two wall like layers: » Cortex: Surrounds the core, mainly electron light

peptidoglycan » Coat: Surrounds the cortex, mainly protein

• Exosporium: The outer most thin layer

Electron Micrograph of Clostridium botulinum

Caption:-- Clostridium botulinum - Gram-positive, endospore-forming, rod prokaryote. Vegetative and spore stages: note the flagella. Causes food poisoning (botulism), wound infections and infant botulism.

Infections transmitted to humans by endospores include

• anthrax, caused by Bacillus anthracis;

• tetanus, caused by Clostridium tetani;

• botulism, caused by Clostridium botulinum; and

• gas gangrene, caused by Clostridium perfringens

Endospore stain of Bacillus megaterium

Note green endospores within pink bacilli. Many spores have already been released from the vegetative cells

Endospores

• Resistant to heat, drying, etc.

• Survival, not procreation-

• Spores in amber (25-40 My)

• Bacillus and Clostridium

cysts

• Ressistant to dehydration but not to heat and hence unlike spores

• Deposition of layers & layers of cell wall around the cell rather than within the cell as in case of spores

• Azotobacter (free living nitrogen fixing bacterium found in soil) and Myxbacteria

• Involved in nitrogen fixation and protection

ENDOSPORES - UNIQUE CELL TYPE FORMED WHEN CELLS FACE STARVATION

1. GRAM POSITIVE - ONLY SOME SPECIES

2. NOT GRAM NEGATIVE CELLS

3. ENDOSPORES HAVE UNUSUAL STAINING & RESISTANCE PROPERTIES.

4. MANY ENDOSPORE - PRODUCING BACTERIA CAUSE DISEASE

The cycle of spore formation and germination

 

• Distribution •   • Bacteria• Fungi•  Present in some genera Present Protective & dispersal function Reproductive

function Endospores Endo- or Exo- spores One per cell but C. disporicum=2; C. polypendens=5Numerous

•   • Size

– Larger (distends the cell) or smaller than the cell • Shape

– Cylindrical – Ellipsoidal – Spherical

• Location – Central – Terminal – Sub-terminal

• Cells with endospores can be identified by spore-staining – B. megaterium,an aerobe: Small cylindrical sub-terminal spores – C. tetani, an anaerobe: Large (distend) spherical terminal spores

•  

•A dormant structure which enables bacteria to resist harsh environmental conditions•Formed by Gram-positive bacteria – (e.g. Bacillus, Clostridium, Sporosarcina, Sporolactobacillus, Desulfotomaculum)–Medically significant: anthrax, botulism, gas gangrene, tetanus

Structure of spore

Spore structure

– Spores are formed during unfavourable growth conditions & germinate under favourable conditions

– The spore can be differentiated into 4 distinct parts:

•  Core: Nucleic acids, ribosome, low levels of enzyme activity, Calcium dipicolonic acid (CDPA) & low water content. Low level of metabolic activity

– Two wall like layers: » Cortex: Surrounds the core, mainly electron light

peptidoglycan » Coat: Surrounds the cortex, mainly protein

• Exosporium: The outer most thin layer

• Sporogenesis (sporulation) induced when nutrient concentration is low– A septum separates the DNA to be

encapsulated– The sporangium = the mother cell housing the

spore– Location and size of endospore varies

(Genus-specific)– DNA stabilized by calcium dipicolinate

structure

• The completed endospore consists of multiple layers of resistant coats (including a cortex, a spore coat, and sometimes an exosporium) surrounding a nucleoid, some ribosomes, RNA molecules, and enzymes.

Endospore Cycle, Step 1

A vegetative bacterium about to enter the endospore cycle

Endospore Cycle, Step 2

The nucleoid replicates

Endospore Cycle, Step 3

A spore septum forms

Spore resistance

• Resistance to radiation, drying, and toxic chemical– After cell become refractile– Cysteine rich– Keratin-like spore coat protein

Thermal resistancevery low water of protoplast

at the time of cortex formationat the time of spore appear as a refractile object

concentration of calciumdepicolonic acid

is a chelating agentas a calcium salt in the protoplast10 % of the dry weight of the mature sporeintercalates within the helical structure of DNAdisplacing intramolecular water