Water quality assessment of the Sinchun stream based on epilithic diatom communities.

Water quality was assessed 11 sites on the Sinchun Stream, in the region of Daegu City (South Korea), from May 2007 to March 2008 using Diatom Assemblage Index to Organic Water Pollution (DAIpo) and Trophic Diatom Index (TDI). The reference sites were unaffected by effluent from a closed mine or treated sewage and had, epilithic diatom communities that were dominated by saproxenous taxa such as Achnanthes convergens and Cocconeisplacentula var. lineata. The water quality of these sites had DAIpo values ranging between 77.5-93.8 and TDI values between 51.3-67.6, indicating ß-oligosaprobic and mesotrophic environments, respectively. Study sites affected by effluent from the closed mine had epilithic diatom communities that were dominated by acidobiontic diatoms, such as Eunotia exigua and Achnanthidium minutissimum. The water quality of these sites had DAlpo values of 45.9-70.8, indicating ß-mesosaprobic to α-oligosaprobic environments, whereas TDI ranged between 1.7-66.9, indicating an oligotrophic to mesotrophic environment. Downstream sites affected by the influx of mine effluent and treated sewage had many species and a high percentage of saprophilous taxa, including Fragilaria construens var. venter and Nitzschia amphibia. The water quality of these regions had DAIpo values ranging between 21.8-33.1 and TDI values between 67.5-76.7, indicating α-mesosaprobic and eutrophic environments, respectively.

Phytoplankton functional groups as indicators of environmental changes in weir and non-weir sections of the lower Nakdong River, Republic of Korea.

The Nakdong River underwent water impoundment after eight weirs were constructed as part of South Korea's Four Major River Restoration Project from 2009 to 2012. In this study, we aimed to confirm whether the assemblage of phytoplankton based on phytoplankton functional groups (PFGs), could indicate environmental changes in the weir section (WS) and non-weir section (NWS) of the lower Nakdong River after the construction of the weir. Thus, we examined the relationships between PFGs and gradients in environmental drivers, such as physicochemical, meteorological, and hydrological variables. Environmental gradients were observed between the WS and NWS in dissolved oxygen (DO), electric conductivity (EC), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), dissolved total nitrogen (DTN), dissolved total phosphorus (DTP), ammonia nitrogen (NH3-N), nitrate nitrogen (NO3-N), and phosphorus (PO4-P), which were relatively higher in the WS. Seventeen PFGs were identified (A, B, C, D, E, F, G, H1, J, LM, LO, MP, P, T, W1, X1, and X2). Additionally, the LM and P groups, preferring an enriched lentic system more than other groups, were found to be the dominant PFGs that led the succession of assemblages. Traditional nutrients (N, P) and organic pollutants (BOD, COD) primarily affected the autochthonous growth of the most dominant PFGs in the WS as HRT (hydraulic retention time) increased. Furthermore, the hydrological variables associated with meteorological conditions have a synergistic effect on the composition of the major PFGs and chemical and physical variables in the WS. In other words, the WS may be a new source of inoculum that primarily determines the occurrence and maintenance of phytoplankton in the immediate downstream region (NWS). In particular, group LM (mainly potentially toxic Microcystis) developing in the upper weir impoundment is transported downstream, resulting in a high inoculation effect on further growth in the NWS during the summer monsoon season.

The Prokaryotic Microalga Limnothrix redekei KNUA012 to Improve Aldehyde Decarbonylase Expression for Use as a Biological Resource.

The prokaryotic microalga Limnothrix redekei KNUA012 isolated from a freshwater bloom sample from Lake Hapcheon, Hapcheon-gun, South Korea, was investigated for its potential as a biofuel feedstock. Microalgae produce straight-chain alkanes/alkenes from acyl carrier protein-linked fatty acyls via aldehyde decarbonylase (AD; EC 1.2.1.3), which can convert aldehyde intermediates into various biofuel precursors, such as alkanes and free fatty acids. In L. redekei KNUA012, long-chain ADs can convert fatty aldehyde intermediates into alkanes. After heterologous AD expression in Escherichia coli (pET28-AD), we identified an AD in L. redekei KNUA012 that can synthesize various alkanes, such as pentadecane (C15H32), 8-heptadecene (C17H34), and heptadecane (C17H36). These alkanes can be directly used as fuels without transesterification. Biodiesel constituents including dodecanoic acid (C13H26O2), tetradecanoic acid (C15H30O2), 9-hexa decenoic acid (C17H32O2), palmitoleic acid (C17H32O2), hexadecanoic acid (C17H34O2), 9-octadecenoic acid (C19H36O2), and octadecanoic acid (C19H38O2) are produced by L. redekei KNUA012 as the major fatty acids. Our findings suggest that Korean domestic L. redekei KNUA012 is a promising resource for microalgae-based biofuels and biofuel feedstock.

Environmental Factors Associated with the Eukaryotic Microbial Community and Microalgal Groups in the Mountain Marshes of South Korea.

The diversity indices of eukaryotic microalgal groups in the Jeonglyeongchi, Waegok, and Wangdeungjae marshes of Mount Jiri, Korea, were measured using Illumina MiSeq and culture-based analyses. Waegok marsh had the highest species richness, with a Chao1 value of 828.00, and the highest levels of species diversity, with Shannon and Simpson index values of 6.36 and 0.94, respectively, while Wangdeungjae marsh had the lowest values at 2.97 and 0.75, respectively. The predominant species in all communities were Phagocata sibirica (Jeonglyeongchi, 68.64%), Aedes albopictus (Waegok, 34.77%), Chaetonotus cf. (Waegok, 24.43%), Eimeria sp. (Wangdeungjae, 26.17%), and Eumonhystera cf. (Wangdeungjae, 22.27%). Relative abundances of the microalgal groups Bacillariophyta (diatoms) and Chlorophyta (green algae) in each marsh were respectively: Jeonglyeongchi 1.38% and 0.49%, Waegok 7.0% and 0.3%, and Wangdeungjae 10.41% and 4.72%. Illumina MiSeq analyses revealed 34 types of diatoms and 13 types of green algae. Only one diatom (Nitzschia dissipata) and five green algae (Neochloris sp., Chlamydomonas sp., Chlorococcum sp., Chlorella vulgaris, Scenedesmus sp.) were identified by a culture-based analysis. Thus, Illumina MiSeq analysis can be considered an efficient tool for analyzing microbial communities. Overall, our results described the environmental factors associated with geographically isolated mountain marshes and their respective microbial and microalgal communities.

Complex phylogeographic patterns in the freshwater alga Synura provide new insights into ubiquity vs. endemism in microbial eukaryotes.

The global distribution, abundance, and diversity of microscopic freshwater algae demonstrate an ability to overcome significant barriers such as dry land and oceans by exploiting a range of biotic and abiotic colonization vectors. If these vectors are considered unlimited and colonization occurs in proportion to population size, then globally ubiquitous distributions are predicted to arise. This model contrasts with observations that many freshwater microalgal taxa possess true biogeographies. Here, using a concatenated multigene data set, we study the phylogeography of the freshwater heterokont alga Synura petersenii sensu lato. Our results suggest that this Synura morphotaxon contains both cosmopolitan and regionally endemic cryptic species, co-occurring in some cases, and masked by a common ultrastructural morphology. Phylogenies based on both proteins (seven protein-coding plastid and mitochondrial genes) and DNA (nine genes including ITS and 18S rDNA) reveal pronounced biogeographic delineations within phylotypes of this cryptic species complex while retaining one clade that is globally distributed. Relaxed molecular clock calculations, constrained by fossil records, suggest that the genus Synura is considerably older than currently proposed. The availability of tectonically relevant geological time (107-108 years) has enabled the development of the observed, complex biogeographic patterns. Our comprehensive analysis of freshwater algal biogeography suggests that neither ubiquity nor endemism wholly explains global patterns of microbial eukaryote distribution and that processes of dispersal remain poorly understood.

STUDIES ON ULTRASTRUCTURE AND THREE-GENE PHYLOGENY OF THE GENUS MALLOMONAS (SYNUROPHYCEAE)(1).

The genus Mallomonas, a common and often abundant member of the planktic community in many freshwater habitats worldwide, consists of 180 species divided into 19 sections and 23 series. Classification of species is based largely on ultrastructural characteristics of the siliceous scales and bristles that collectively form a highly organized covering over the cell. However, the relative importance of the different siliceous features of the scales, such as the dome, V rib, and secondary structures, as well as the different types of scales, in understanding the evolution and phylogeny of the genus is little known. In this study, we investigated the scale and bristle ultrastructure, along with sequences of three genes, for 19 isolates (18 species) of Mallomonas (18 isolates were from Korean habitats). The isolates represented nine of the 19 sections. Sequences for both the nuclear SSU and LSU rDNA and plastid LSU of RUBISCO (rbcL) genes for each of the 19 Mallomonas isolates and four outgroups were determined. Bayesian and maximum-likelihood (ML) analyses of the data revealed that Mallomonas consists of two strongly supported clades. Mallomonas bangladeshica (E. Takah. et T. Hayak.) Siver et A. P. Wolfe was at the base of the first clade that included taxa from the sections Planae and Heterospinae, both of which lack a V rib on the shield of the scales. Our results indicated that the sections Planae and Heterospinae should be combined. The second clade, with Mallomonas insignis Penard and Mallomonas punctifera Korshikov at the base, contained taxa from the sections Mallomonas, Striatae, Akrokomae, Annulatae, Torquatae, Punctiferae, and Insignes, all of which have V ribs or well-developed marginal ribs on the scales. Sister relationships between Mallomonas and Striatae were strongly supported, but interrelations among the remaining sections were not resolved, probably due to inclusion of too few species. Our results suggest that the current classification of the genus Mallomonas at the section level will require some revision. Additional species will need to be added in future analyses.