Molecular profiling of 18S rRNA reveals seasonal variation and diversity of diatoms community in the Han River, South Korea

Abstract

Diatoms are groups of eukaryotic unicellular micro­ algae and are some of the most common organic matter in an aquatic ecosystem. They play an important role as the primary producers in freshwater and marine environ­ ments, and they contribute significantly to the photosyn­ thesis activity on Earth (Lee et al., 2019). In addition, dia­ toms are used widely across the world for environmental monitoring because different species of diatom typically have specific habitat preferences, and they react quickly to environmental changes (Dixit et al., 1992; Round et al., 2007). For example, species like Cyclotella meneghiniana and Thalassiosira pseudonana (Baek et al., 2011; Adenan et al., 2013) have distinct ranges of pH and salinity where they will grow (Spaulding et al., 2019). In addition, they have ranges and tolerance for other environmental factors, such as nutrient concentration, suspended sediment, flow regime, elevation, and for different types of human distur­ bances (Spaulding et al., 2019). Hence, they are consid­ ered susceptible indicators of water quality and environ­ mental change. For these reasons, diatoms have received considerable attention from past and ongoing research (Dixit et al., 1992; Adenan et al., 2013; Hilaluddin et al., 2020). In general, diatoms have been discriminated morphologi­ cally by using a light microscope (LM) and scanning elec­ tron microscope (SEM). However, some diatoms may have few discernible structural differences when viewed with a microscope. In addition, different lineages have often adapted in similar ways to analogous habitats. As a result, there are many examples of diatoms species that look very similar at the microscopic level, but are not closely related (Graham et al., 2009). Since the early 1980s, molecular techniques by using carbohydrates, toxins, proteins, and nucleic acids as markers have been developed to detect and discriminate phytoplankton (Ebenezer et al., 2012; Sun et al., 2012). Among DNA based methods such as terminal restriction fragment length polymorphism, micro­ array, real­time PCR, the high­throughput sequencing (HTS) of small­subunit rRNA genes from environmental DNA techniques has already been widely applied for the assessment of microbial diversity and micro­planktonic community structure (Eiler et al., 2012; Ghiglione and Murray, 2012). These methods allowed high resolution and rapid analysis of microbial and phytoplankton com­ Journal of Species Research 10(1):46­56, 2021