Sporulated bacteria: Introduction, Mechanism of spore formation

Sporulated Bacteria: Introduction, Mechanism of Spore Formation

Sporulated bacteria in Gram stain

Sporulated bacteria, Clostridium species is in Gram stain as shown above picture and most common spore-forming bacteria are genera Bacillus and Clostridium.

Introduction of Sporulated Bacteria

When conditions for vegetative growth are not favorable, especially when carbon and nitrogen become unavailable spore formation occurs Spore-forming species are represented in most classes, including the Bacilli, the Clostridia, the Erysipelotrichi are able to survive by forming resistant endospores. Spore formation involves a change in enzyme activity and morphology. The spore may be positioned at the end (terminal) of the bacterium or centrally (median). It may be round, oval, or elongate. Endospores being dense and thick-walled, are able to withstand dehydration, heat, cold, and the action of disinfectants. A spore is unable to multiply but when conditions for vegetative growth return, it is able to produce a bacterial cell that is capable of reproducing. Spores of Bacillus species are dormant and extremely resistant to many environmental stresses including, heat, desiccation, radiation, and a variety of toxic chemicals. As a consequence, spores can survive for extremely long periods, certainly hundreds of years and perhaps much longer. Spore resistance is due to a variety of factors, including the outer spore coats and the relative impermeability of the spore’s inner membrane. There are also novel features of the spore’s central region or core, the site of spore DNA, which plays a major role in spore resistance.

Mechanism of Endospore Formation in Bacillus subtilis

Bacteria thrive in amazingly diverse ecosystems and often tolerate large fluctuations within a particular environment. One highly successful strategy that allows a cell or population to escape life-threatening conditions is the production of spores. Bacterial endospores have been described as the most durable cells structures. These bacteria have been found in the gut of batrachian tadpoles, although their affiliation within the phylum, Firmicutes has not been established. The diversity of endospore-producing bacteria and their varied lifestyles suggest that the sporulation pathway is finely tuned to life in a particular environment, and is an advantageous means of cellular survival, dispersal, and, in some cases, reproduction. The basic and most familiar mode of sporulation involves an asymmetrical cell division that leads to the formation of a mother cell and a smaller forespore. Unique transcriptional programs within these cells result in distinct fates for the forespore and the mother cell. The initiation of sporulation in Bacillus subtilis is triggered by a lack of nutrients and by high cell density. The decision to sporulate is tightly regulated because this energy-intensive process serves as a last resort for these starving cells. In the early stages of sporulation, gene regulation mainly depends on the stationary-phase sigma factor σH and the master transcriptional regulator Spo0A . Activation ofSpo0A in B. subtilis is governed by a phosphorelay system involving several kinases, each of which transmits information about cell condition and environmental stimuli to determine the phosphorylation state of the intracellular pool of Spo0A . Prior to asymmetric cell division, the chromosome replicates, and each replication origin rapidly migrates to a different pole of the cell. Subsequently, the origin-proximal regions become tethered to opposite poles and the chromosomal DNA stretches from one pole to the other to form an axial filament. During division, only∼30%of the origin-proximal portion of one chromosome is trapped within the forespore, and the rest is translocated into the forespore by SpoIIIE, a DNA transporter protein. The other chromosome copy remains in the mother cell. Differential activation of sporulation-specific sigma factors in the mother cell and forespore manages the fate of each cell. First,σF is activated exclusively in the forespore. Shortly thereafter, a signal is sent to the mother cell to process and hence activate σE. Both early sigma factors promote the expression of genes necessary for forespore engulfment, as well as genes needed for the production and activation of the late sporulation sigma factors. Remodeling of septal peptidoglycan allows migration of the mother-cell membrane around the forespore. Eventually, the leading edge of the migrating mother-cell membrane meets, and fission establishes the double-membrane-bound fore-spore within the mother cell. Completion of forespore engulfment, combined with further intercellular signaling, allows activation ofσGin the forespore and the subsequent activation of σ Kin the mother cell. These sigma factors regulate the genes necessary for spore maturation and germination. Ultimately, the mother cell undergoes programmed cell death and lysis, which releases the mature endospore.

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