Biodiversity of green algal biofilms on artificial hard substrates
by Opayi Dr. Mudimu
Date of Examination:2009-01-15
Date of issue:2025-06-27
Advisor:Prof. Dr. Thomas Friedl
Referee:Prof. Dr. Thomas Friedl
Referee:PD Dr. Michael Hoppert
Persistent Address:
http://dx.doi.org/10.53846/goediss-11277
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Abstract
English
Summary In this study, the diversity, phylogeny and taxonomy of algal communities in green biofilms on artificial hard substrates were investigated. A total of 86 samples were collected in different climatic regions, from which 52 were from Germany (Table 3.1a), 27 from other countries in Europe (10 from France, 6 from Poland, 4 from Ukraine, 4 from Spain, 2 from Belgium and 1 from Switzerland) and 7 samples from Africa (4 from South Africa, 2 from Morocco and 1 from Namibia) (Table 3.1b). Algal diversity of central Europe should be analyzed and compared with those of other European and African countries. Genomic DNA was isolated from all collected samples. The biodiversity of green algal biofilms was investigated by using culture dependent and independent approaches such as cloning, sequencing and DGGE methods. Clone libraries from 30 samples were established (Table 3.1). A total of 52 cultures from 15 samples were established (Table 3.1). Forty three samples were analysed using the DGGE approach (Table 3.1).The data obtained by sequencing the SSU rRNA gene were used to identify microalgae. For the investigation, a polymerase chain reaction (PCR) was performed on genomic DNA from environmental samples and from established pure cultures to amplify the 18S or 18S/ITS rRNA genes from all eukaryotic organisms. The results from the PCR of genomic DNA were perfect because the amplified genes consisted of optimal regions to assess the diversity at the genus and species levels (Helms et al. 2001; Buchheim and Chapman 1991). Sequencing of the small subunit rRNA genes is a well-established method for the investigation of algal diversity (Friedl 1998). Another reason for using the 18S rRNA gene was that most publicly accessible databases contain this region. Although the best option is to sequence the entire gene, most of our clones were only partially sequenced. The selected 600bp-long fragment, located between the 34th and 895th bp is the most variable fragment in the 18S rDNA (Neefs et al. 1993) and contains 40% of variable information. As the focus of this study was to analyze the diversity in the samples, this variable region was well suited for the purpose of the survey. The amount of information on 600bp-long sequences is enough for a BLAST search because this software creates, in pairwise fashion, local alignments that include only the most similar local region or regions, and does not force alignment of a partial sequence to a fulllength sequence. Furthermore the amount of information on the selected region is enough to obtain higher taxonomic resolution in ARB. Identified algal diversity by using molecular approaches This study described algal diversity in both the environmental samples and the cultures. The identified algal clones and cultures were mostly related to the green algal class Trebouxiophyceae. A total of 1388 positive clones and 52 cultures were partially sequenced. A total 801 clones and one culture were related to the clade Apatococcus (Table 4.3). Apatococcus was identified in 23 of 30 analyzed Clone libraries, making it the most frequent and dominant genus. Within the clade Apatococcus, the clones and culture were distributed into three subgroups, from which two subgroups need to be newly described. A total of 192 clones and 21 cultures were affiliated to the genera “Chlorella-like. The genus Chlorella-like (“C.” saccharophila SAG 211-9a X63505) was identified in 12 Clone libraries and isolated from seven samples, constituting the second most frequent and dominant genus. This genus included three species referred to as “C.” engadinensis, “C.” trebouxioides and “C.” saccharophila. The two latter species were identified in our study. Thrirty-six clones and six cultures were affiliated to the genus group reffered to as Chlorella-like (“C.” luteoviridis SAG 211-2a X73998). Chlorella-like (“C.” luteoviridis SAG 211-2a X73998) was identified in five Clone libraries and also isolated from five samples. This genus included three species referred to as “C.” luteoviridis, “C.” sp1 and “C.” sp2. The two latter species were identified in our study, are new species and need to be newly described (Table 5.1). Our investigation of SSU rDNA revealed that the two Chlorella-like genera were closely related. These genera, previously erroneously assigned to Chlorella, were clearly separated from Chlorella vulgaris, the type species of the genus (Fig. 5.1). The generic names Glaphyrella and Heterochlorella were suggested by Kalina (1996) and Neustupa (personal communication), respectively. Eighty clones were affiliated with the genus Trebouxia. Trebouxia was identified in nine Clone libraries. Within the genus Trebouxia, our clones were related to T. asymetrica, T. arboricola, T. impressa and T. sp. Most clones were only identified to genus level (Fig. 3.5). The clade Prasiola included the lineages Diplosphaera, Stichococcus2, Stichococcus/Desmococcus/Prasiola and Pseudostichococcus, all of which are related. Twenty clones and 1 culture were affiliated to the clade Prasiola. The algae from the clade Prasiola were identified in four Clone libraries (Table 3.1). Within the clade Prasiola, most clones formed new lineages or were affiliated to a polyphyletic lineage. They were also identified at the genus level. Five clones and three cultures were affiliated to the genus Pabia. The genus Pabia was identified in five Clone libraries and isolated from three samples. Within the genus Pabia, our cultures were similar to the strain P. signiensis SAG 7.90 AJ416108 and one clone was similar to the strain Chlorella saccharophila SAG 3.80, which needs to be renamed as Pabia. Three clones and one culture were related to the genus Radiococcaceae. This genus was identified in one Clone library and isolated from one sample. Our clones and culture formed a new lineage within the genus Radiococcaceae. Ten clones from the genus Coccomyxa were identified in four clone libraries. The genus Coccomyxa is polyphyletic. Following the suggestion of T. Friedl (Friedl et al 2007), the generic name Avernensia should be adopted for the lineages with the strains C. avernensis Jaag SAG 216-1 and C. sp. SAG 2040, which include our clones. One clone was related to the genus Elliptichloris and formed a new lineage (Fig. 3.5). Six clones were identified at the species level within the genus Dictyochloropsis. These clones were from two clone libraries. In a few cases, our clones and cultures were related to the classes Chlorophyceae, Ulvophyceae, the division Streptophyta as well as Fungi. From the above-mentioned description it can be concluded that the taxonomy and phylogeny of the green algal class Trebouxiophyceae is confusing and needs to be clarified. In this study, we contribute data for that purpose. Denaturing Gradient Gel Electrophoresis (DGGE) By comparing results from the sequencing of the clone libraries with results of the DGGE, we aimed to compare the number of species rather than bands per samples. The results revealed that the number of detected bands per samples in DGGE corresponded to the number of the identified lineages in our cloning analysis. However, not all species could be identified by DGGE. DGGE can be used for a general assessment of comparative biodiversity of a large number of samples. Rindi and Guiry (2004) identified different algal diversity in the north-west of Ireland as well as in southern France. Our analysis revealed that the variability of diversity was independent of geographic location of samples, as well as of the nature of the substrates.
Keywords: Biodiversity, green algal biofilms, artificial hard substrates
