2. INTRODUCTION
Diatom is a unicellular eukaryotic alga that has a siliceous covering and a
symmetrical body. Diatoms are a plethora of unicellular organisms that range in
number from 20,000 to 2 million species.
● Diatoms comprise the taxonomic phylum Bacillariophyta.
● Diatoms are usually aquatic creatures found in fresh, and saltwater.
● Some diatoms are also found in moist places, such as soil.
● Diatoms might be found alone or in colonies.
● When they are in colonies, they form shapes such as zigzags, stars, or fans.
Diatoms are encased in a frustule, which is a silica shell made up of two separate
valves that enclose the plasma membrane. Frustules are incredibly detailed, with
microscopic pores arranged in a pattern designed specifically for catching the
sunlight.
3. INTRODUCTION
Diatoms are members of the taxonomic phylum Bacillariophyte. Diatoms are
members of the Kingdom Protista.
● Diatoms are among the most important microscopic aquatic organisms.
● They are directly or indirectly useful as food for many animals.
● Diatomaceous earth, a substance made up of fossil diatoms, is used in filters,
insulation, abrasives, paints, and varnishes.
● Diatoms may be unicellular or found in colonies.
● Diatoms can be broadly divided into two orders on the basis of symmetry and
shape.
● Round Non-motile Centrales have radial markings and Elongated Pennales that
have pinnate markings
6. INTRODUCTION
Characteristics of Diatoms
The various characteristics of diatoms are as follows:
● Habitat: Diatoms may be found in both freshwater and saltwater.
● Diatom Shell: The shell wall of diatoms contains silica. Their cell wall is referred to as a shell or frustule.
○ Diatoms have shell walls that overlap.
○ The shells of diatoms are often translucent in color.
○ These creatures' cell walls are often made of cellulose.
○ The silica particles are inserted in several locations throughout this cellulose cell wall.
○ As a result, the cell wall looks to be comprised of silica.
7. INTRODUCTION
● Diatom Nucleus: The diatom contains a diploid nucleus.
● Diatoms Have Pigments: Diatoms have chloroplasts in their cell walls.
○ Pigments are found in the chloroplasts of diatoms.
○ Chlorophyll a, chlorophyll c, and xanthophyll are the pigments involved.
○ Fucoxanthin is another name for this xanthophyll.
○ Diatoms seem golden in hue as a result of their pigments.
● Diatom Movement: Diatoms are immotile due to the lack of flagella in them.
○ They float on the surface of the water because of the low molecular weight of stored lipids.
○ Some diatoms move with the assistance of a slimy fluid.
○ The slimy excretion is composed of an oily substance secreted by diatoms.
○ This offers lubrication for the diatoms' movement.
8. INTRODUCTION
Examples of Diatoms
Some examples of diatoms are:
● Pinnularia is a mucilaginous diatom that has an elongated, elliptical shape.
● Navicula is a genus of the Naviculaceae family, order Naviculales, and class Bacillariophyceae. It is the genus that
creates around one-quarter of the oxygen on the planet. Members of this genus are considered keystone species
since they provide food for numerous aquatic animals.
● Chaetoceros is one of the most numerous planktonic diatom genera in marine seas.
● Bacillaria is a genus of the Bacillariaceae family, Bacillariales order, and Bacillariophyceae class that has elongated
cells.
9. INTRODUCTION
Classification of Diatoms
There are two kinds of diatoms found in nature. One is circular, whereas the other one is elongated. Diatoms are
categorized into two categories based on their form. These categories are described more below:
● Pennate Diatoms: These diatoms have an extended form. These diatoms can be split in two. As a result, they exhibit
bilateral symmetry. Pennate diatoms are naturally mobile. They move in a gliding motion.
● Centric Diatoms: These diatoms have a round-circular form. They have radial symmetry. These diatoms are not
mobile in nature.
12. DNA SEQUENCING
DNA sequencing can also be used in testing diatoms. DNA sequencing analyzes the base sequence of a
DNA fragment from the diatom and can identify species by DNA markers. PCR technique can be used to
amplify the gene which is to be analyzed.
In addition to diatoms, other algae in the water can be detected in tissue samples by analyzing the DNA,
which is unfamiliar with the human genome. In distinction to chemical digestion ways, sequence-based alga
testing has higher sensitivity and is simpler to implement.
13. FORENSIC SIGNIFICANCE
Diatoms are unicellular, photosynthetic, eukaryotic organisms, but many more are yet to be discovered.
Diatoms are diverse microscopic organisms with silica cell walls. They are photosynthesizing algae. They
vary in different characteristics such as colour, shape, and size. There are 15,000 known species of
diatoms.
These microscopic organisms mainly inhabit freshwater, marine water and soil as well. They can’t survive in
domestic pools due to cleaning agents such as chlorine. They may be simple or branched, filamentous, and
have a gelatinous envelope. All diatoms are enclosed by a frustule formed from two valves together by a
connective at the girdle. They are mainly non-motile.
14. FORENSIC SIGNIFICANCE
Forensic Limnology focuses on the study of diatoms in crime scene samples and
bodies. In forensic science, diatom testing is a technique used for the
determination of death due to drowning. A body recovered from the water does not
always infer that death was due to drowning. When an individual drowns, as the
diatoms are microscopic contents of the water, they will pass into the bloodstream
through ruptures in the alveoli of lungs before being carried to the other organs
such as the brain, liver, heart, kidney and bone marrow.
When a body is recovered from the water, and if suspicion arises if the case is of antemortem (before death) or
postmortem (after death) drowning, a diatom test can be done. Diatom in organs can be diagnosed as death by
drowning by conducting a ‘diatom test‘.
