What is Bacterial Morphology? 

The bacteria are prokaryotic organisms that are single-celled, and are found to exist as free-living and possess a microscopic size. The morphology is found to vary in the bacteria, where some of them are identified as individual organisms and the others are detected as colonies. The size and shape of the bacterial cell also represent its morphology. 

Bacterial Cell Size

These single-cell microbes have the capacity to perform the functions to sustain life. The genetic materials including ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) reside in the bacteria. They are detected in a wide variety of regions including the food, air, soil, and water due to their adaptive features. Some of the bacterial species have the capacity to thrive in higher levels of pressure, pH, and temperature. 

The size of the bacteria cell is found to vary drastically and the cell size ranges between 0.5 micrometers to 5.0 micrometers in the length. They are only detected by the microscopes. The structure of the bacterial cell becomes only visible after the application of the complementary stains and they are observed in a magnification of 1000x using a compound microscope. The internal structure of the bacteria is studied employing an electron microscope. The members of mycoplasma have a cell size ranging up to 0.3 micrometers.  

Bacterial Cell Shapes    

There are diverse shapes in bacteria and they are classified in morphology according to their cell shapes that are observed under the microscope. The important shapes of the bacterial cell encompass cocci, vibrio, spirilla, and bacilli. 

• The cocci are detected to be very small in nature and they have a spherical shape. The arrangements of the cocci are found to vary with diverse organisms. The ones existing as an individual organism are called the coccus. Two individual cocci form a structure called diplococci. Some of the bacterial organisms existing in the diplococci stage form an encapsulation around them and are called the encapsulated diplococci. The staphylococci are found to be in the form of the colony and the streptococci exist as a chain of individual organisms. Cocci are also found in the shape of the tetrad. 
• The rod-shaped bacterial organisms are called the bacilli. In these cells that are rod-shaped, some of them possess the same width and length and they are called the coccobacilli. Multiple individuals are organized in the form of a chain in a structure called streptobacilli. Some of them exist in the shape of palisades. Two individuals of a bacilli, form structure called diplobacilli and the individual bacterium with the rod-like shape are called bacillus. In this way, particular rod-shaped cell exhibits different morphological changes.    
• The vibrio has a comma-shaped bacterial cellular morphology and the spirillum has a spiral structure of the bacterial organism. 

• The spirillum is a gram-negative organism and they are characterized by the presence of lophotrichous or amphitrichous flagella. They possess a rigid body and have a helical shape. There are other samples of bacteria organisms called the spirochetes and they possess a flexuous spiral-shaped structure.  
• The actinomycetes are considered filamentous bacterial species and they possess a rigid cell wall in their body. They give rise to the formation of different branches in their body. The bacterial species lacking a proper cell wall is called mycoplasma and they lack a proper morphology and are detected as oval bodies connected with interlacing filaments.    

The actinobacteria are found to form elongated filament-like structures and the myxobacteria are detected to be in the form of aggregates. These structures are observed in particular conditions. Some of the bacteria have the capacity to form structures called biofilms, where the species adjoin with the surfaces for the generation of aggregations. The huge aggregation of the bacteria and the surface results in the formation of microbial mats. These mats possess different species of bacteria. 

Extracellular Structures in Bacteria    

The extracellular structures identified in the bacterial organism encompass the flagella, capsule, pili, plasma membrane, and cell wall. The flagella are the cytoplasmic appendages with a hair-like appearance. They possess a thin, long, and slender shape and are the reason for the locomotion exhibited by the bacterial species. The flagellar size differs between 0.01 to 0.02 micrometer in diameter. The length of the flagella varies between 3 to 20 micrometers in length. The region of the flagellum includes the basal body, hook, and filament. The diameter is maintained constant throughout the structure of the flagellum, the structure is connected to a wider hook-like structure. The basal body is formed from a set of rings connected to the central rod. 

The bacteria possessing an individual flagellum are called monotrichous and the individual with two flagella are called lophotrichous. The bacteria with flagellum on distinct poles are said to be amphitrichous. The peritrichous body possesses numerous flagella enclosing their body.     

An organic amorphous polymeric structure is concerned with the generation of the capsule in the bacteria, and it is composed of numerous complex polypeptides. The water molecules are the most important substance of the bacterial capsule, the capsular structure is sometimes loosely connected to the bacterium and can be easily removed and this loose layer is known as the slime layer. These bacteria are concerned with the formation of smooth colonies and the rough colonies are formed by the encapsulated bacteria. 

The cell wall is concerned with the protection of the cell. It resists cell drying and also guards the bacteria body against phages and anti-bacterial substances. The phospholipids form 30 percent of the bacterial plasma membrane and the rest is formed by the proteins. The prokaryotes lack sterols and are less rigid than the eukaryotes.     

Intracellular Structures in Bacteria

The intracellular structures encompass the cytoplasm, mesosome spores, and ribosomes. The cytoplasm consists of a viscous water solution with various inorganic solutes. They do not possess complex cellular organelles. They possess proteins, ribosomes, and water-soluble substances as the saved substrates. The extrachromosomal DNA called the plasmid is detected in the bacteria. The respiratory regions detected in the bacteria are called mesosomes and they are connected to the bacterial chromosome. They are associated with the generation of the DNA during the process of cell division and are mostly detected in gram-positive organisms.     

Context and Applications  

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for     

• B.Sc. Microbiology 
• B.Sc. Biotechnology 
• B.Sc. Biochemistry    

This course plays a significant role in the field of microbiology by serving various studies on medical conditions. These studies involve the examination of various microbes which has to be understood carefully with the help of the microbiology department. 

Related Concepts

Genetically modified bacteria, Bacterial orders, and psychotropic bacteria.