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This article will primarily discuss the morphology of bacteria. It will include an in-depth discussion of the various shapes and sizes of certain bacteria and how it exists in various environments. It will also discuss the efficiency due to the morphology of bacteria and furthermore discuss the advantages and disadvantages in their environment activated by their morphology. This article is meant to provide a general understanding of the morphology of bacteria and not for any specific research use, for further in depth information please refer to the references cited.

To understand the general concept behind the varying sizes of bacteria, we must understand basic biology. Bacteria are prokaryotic, single-celled microscopic organisms, are generally much smaller than eukaryotic cells, and are very complex despite their tiny size. Bacteria come in a wide variety of shapes and sizes, in which we call the morphology of an organism. Another criterion in which is used to distinguish bacteria is based on the cell wall structure. There are multiple types of cells wall that give different staining characteristics with a series of stains and reagents known as the Gram stain. Essentially, the gram negative will stain red, and gram positive will be stained violet. The difference is that the negative usually has a thin wall and the positive has a thick wall.

Morphology is defined as the existence of the shape and size of something. In this article, bacteria exhibits many different shapes and sizes such as spiral, spherical, or rod shaped. The Morphology also refers to the size as well which will be discussed in another section. Studying the morphology of bacteria will allow us to understand how and why they are shaped the way they are and how size makes a big difference in their life cycles. The efficiency and adaptation to an ecosystem will be observed to explain the morphology of certain bacteria. What should be understood is that every bacteria's morphology has its reason in being shaped or sized a certain way, furthermore, the actively changing morphology of certain bacteria (ability to adapt) shows significance in possible evolution in the future. The ability to adapt to an environment by altering their morphology is certainly an important biological function. This may also include multiple shapes in a single bacteria, for example, say if a certain bacteria had a flagella attached to the body, the purpose of having this flagella is to aid their ability to move swifter in water. The adaptation of bacteria by altering their morphology will also be discussed more in detail in another section.

There are three common physical appearances of bacteria which can be seen in table 1.0, shape-wise they are spherical, rod-like, and spiral-like. Four specific bacteria chosen will attempt to represent generally the three shape categories. This includes the halococcus, bacillus subtillis, vibrio, and spirillum. Another physical aspect that is of importance to consider is each bacteria cell's cell wall. In certain situations, distinguishing the bacteria type may require information about the cell's cell wall. The process commonly used is the gram-stain technique to determine the positively or negatively stain.

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Coccus bacteria are general spherical or close to being spherical, and are called coccus to distinguish them from being bacillus and the other kinds of bacteria. The occurence of coccus comes in many different arrangedments which is dependent on their planes of division. The planes of division will group cocus into different arrangements starting with pairs as diplococci, groups of 4 or 8 known as tetrads/sarcina, chains of cocci known as streptococci, and clusters known as staphylococci. The average size of a cocci is approximately 0.5 to 1 micrometer. The representative cocci chosen is the Halococcus. A common bacteria found in water, especially in areas of high salinity because Halococcus is of the genus halophilic archaea meaning it is necessary for them have high salt levels for growth.

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Bacillus are bacteria that look rod shaped which is easily distinguishable compared to coccus and others. This type of bacteria is ubiquitous in nature and has both free-living and pathogenic species. In stressful environmental conditions, bacillus can produce oval-shaped endospores that can stay hibernated for extended periods of time. The cell wall of bacillus is what makes it outstanding. The cell wall exists outside of the cell which forms a second barrier between the bacterium and the environment, this cell wall is composed of various salts and acids which takes the role of a cytoskeleton to maintain its shape and maintain the cells structure. Representing Bacillus, is Bacillus subtillis, a very commonly studied bacteria which is also known as grass bacillus. It is a gram-positive bacteria that is commonly found in soil. It has the ability to form the protective endospore which allows this bacteria to be very durable and can tolerate extreme environmental conditions. The cell wall for this bacteria is a rigid structure outside the cell which is composed of peptidoglycan (polymer of sugars and amino acids). This bacteria is commonly used for studying endospore formation.

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Other bacteria other than cocci and bacilli include common bacteria such as vibrio and spirillum which are not classified as either cocci or bacilli. Two examples will be used in an attempt to demonstrate any other bacteria morphology in this category. Vibrio and spirillum are two of the most common non-cocci and non-bacilli bacteria.

Vibrio bacteria are gram-negative and are primarily halophilic. Few of these species are nonhalophilic though, which is dependent on the NaCl requirement. Generally all Vibrio are also oxidase-positive, most of these bacteria are sensitive to acidic pH and are tolerant to alkaline pH. The morphology of Vibrio are generally rod-like and curvey (note: the difference between vibrio and halococcus). Vibrio also have single polar flagellum which enables travelling for them much easier. Specific species such as Vibrio fischeri have the characteristic of being bioluminescent. They are heterotrophic organisms that can obtaint their nutrients from their mutualistic/parasitic/pathogenic relationships based on other organisms presence. Vibrio's method of reproduction is through asexual division. Please refer to Table 1.0 for sample image

Spirillum bacteria are large chemotrophic spirilla that have spiral-like physical appearance of up to 5 helical turns. Unlike other flexible spiral-like bacteria, spirillum are rigid. Spirillum also possoess bipolar tufts of flagella, at first was confused that it was a single flagella, which was later on discovered that there were fascicles of multiple flagella. Please refer to Table 1.0 for sample image

Bacteria size plays a large role in terms of efficiency of travel for bacteria. Larger bacteria will have more storage for energy and smaller bacteria will obviously have less. Bacteria are known to be smaller than most cells in comparison, but are significantly larger than those classified as viruses. Measured by micrometers, the typical size of a bacteria is 0.5 to 5.0 micrometers. Halococcus in particular is ranged from 0.6 to 1.5 microns in length. Bacillus are up to 5.0 microns in length. Vibrio are 0.5 to 1.5 microns and Spirillum are 1.4 to 1.7 microns in length.

Even though all these bacteria vary so greatly in morphology, there is one attribute that is similar among all of them, they all divide by binary fission. This process allows one bacteria cell to double into its original size and then splits into two genetically identical cells. This also known as cloning. The exception here is that say the original form of the bacteria was not a single cell, assume a chain of cocci, the entire chain of cocci and all of its progeny will form a single colony. Therefore, a colony forming unit may include the progeny of a single cell or may include several cells that were originally attached to each other. The outcome will change the morphology and depending on its environment, often colonies will either disperse and separate into single cells, or cluster up into colonies. This leads to certain advantages and disadvantages based on the evolving morphology.

Some advantages that morphology incurs for certain bacteria are its efficiency in travel based on size and shape. Single celled bacteria that are small and versatile will be much more efficient than a single celled bacteria that is large and poorly shaped (flat surfaced cells will make it difficult to travel quickly). For example, most coccus bacteria are spherical which makes their efficiency to travel rather difficult because if their symmetry. Whereas, Bacillus being more dimensional, allow them swim quicker. Above all, however, are small bacteria with flagella such as spirochete. Relatively smaller bacteria say less than 1 micron in length with a flagella will naturally maximize its efficiency to travel and will save a lot of energy travelling allowing more time for grazing.

Motility and Morphology are closely tied due to the physical correlation of the two. One thing that should be made clear is that any sort of changes to their size or shape will greatly affect the motility of any bacteria. All forms of motility generally place a very strong physical and energetic demand on the cell's general shape. Therefore, the optimal morphology for a bacteria in a given environment would be key to their advantage in surviving. Exceptional cases for all bacteria would be the occurence of clustering, when more than one of the same bacteria are joined together causing greater strain in motility.

There are also other effects that motility has on bacteria, this includes special types of movements when near crowded areas or solid surfaces such as rocks. Vibrio alginolyticus is a good example of reaction motility, where this type of bacteria will naturally swim forward in a straight line, but when near a flat surface while swimming backwards, it will naturally swim in circles. The explanation for this particular behaviour is so that it maximizes its efficiency to either travel, feed, or reproduce. To summarize motility of bacteria, fast moving bacteria are better to be rod-like with the right length to width proportion to maximize speed. Then for slower moving cells, it must have the ability to adopt to certain shapes to maximize efficiency in minimizing the energy required to perform the movement, this would mean the bacteria would need to have certain curves, flagella, and other characteristics that allow them to move less but travel further.

The past, the present, and the future of bacteria evolution. Bacteria are constantly evolving whether they are merging with each other, separating back to single cells, mutating, reproducing and more. Essentially, the only causes for evolution would be changes to their environment, such as, temperature (of water), which leads to salinity and pH levels. Density and texture would also affect the outcome of certain bacteria.

To conclude, this article's aim is to provide a clear understanding of bacteria morphology and its related effects it has. Beginning with the common cocci and bacilli bacteria, the shape and size differences are made clear to distinguish the reason of why they are shaped and sized the way they are. Furthermore, discussing the effects of morphology and how it influences the efficiency of bacteria is crucial in understanding ecosystem balance. As more studies are done, a more thorough understanding of the mechanisms that regulate the morphology would help us understand how these morphological changes affect the survival patterns for different environmental conditions. Ideally, the outcome of such studies should help clearing many of the current existing morphological theories for bacteria. Some other studies that may be of interest include, crystallization and morphology of bacterial thermoplastic: poly-3-hydroxybutyrate (PHB), which is a study done to show a number of interesting results on the physical properties of PHB. Another study done is on comparative morphology and biology of the Fungi, Mycetozoa, and Bacteria. Also effects of hydrostatic pressure on the multiplication and morphology of marine bacteria.

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