CHARACTERIZATION OF PSYCHROPHILIC OSCILLATORIANS (CYANOBACTERIA) FROM ANTARCTIC MELTWATER PONDS

Oscillatorian cyanobacteria dominate benthic microbial mat communities in many polar freshwater ecosystems. Capable of growth at low temperatures, all benthic polar oscillatorians characterized to date are psychrotolerant (growth optima > 15° C) as opposed to psychrophilic (growth optima ≤ 15° C). Here, psychrophilic oscillatorians isolated from meltwater ponds on Antarctica's McMurdo Ice Shelf are described. Growth and photosynthetic rates were investigated at multiple temperatures, and compared with those of a psychrotolerant isolate from the same region. Two isolates showed a growth maximum at 8° C, with rates of 0.12 and 0.08 doublings·d ^{? 1}, respectively. Neither displayed detectable growth at 24° C. The psychrotolerant isolate showed almost imperceptible growth at 4° C and a rate of 0.9 doublings·d ^{? 1} at its optimal temperature of ～23° C. In both photosynthesis versus irradiance and photosynthesis versus temperature experiments, exponentially growing cultures were acclimated for 14 days at 3, 8, 12, 20, and 24° C under saturating light intensity, and [¹⁴C] photoincorporation rates were measured. Psychrophilic isolates acclimated at 8° C showed greatest photosynthetic rates; those acclimated at 3° C were capable of active photosynthesis, but photoincorporation was not detected in cells acclimated at 20 and 24° C, because these isolates were not viable after 14 days at those temperatures. The psychrotolerant isolate, conversely, displayed maximum photosynthetic rates at 24° C, though photoincorporation was actively occurring at 3° C. Within acclimation temperature treatments, short‐term photosynthetic rates increased with increasing incubation temperature for both psychrophilic and psychrotolerant isolates. These results indicate the importance of temperature acclimation before assays when determining optimal physiological temperatures. All isolates displayed photosynthetic saturation at low light levels (<128 μmol·m ^{? 2}·s ^{? 1}) but were not photoinhibited at the highest light treatment (233 μmol·m ^{? 2}·s ^{? 1}). Field studies examining the impact of temperature on photosynthetic responses of intact benthic mats, under natural solar irradiance, showed the mat communities to be actively photosynthesizing from 2 to 20° C, with maximum photoincorporation at 20° C, as well as capable of a rapid response to an increase in temperature. The rarity of psychrophilic cyanobacteria, relative to psychrotolerant strains, may be due to their extremely slow growth rates and inability to take advantage of occasional excursions to higher temperatures. We suggest an evolutionary scenario in which psychrophilic strains, or their most recent common ancestor, lost the ability to grow at higher temperatures while maintaining a broad tolerance for fluctuations in other physical and chemical parameters that define shallow meltwater Antarctic ecosystems.     

GROWTH OF ANTARCTIC CYANOBACTERIA UNDER ULTRAVIOLET RADIATION: UVA COUNTERACTS UVB INHIBITION1

A mat-forming cyanobacterium (Phormidium mur-rayi West and West) isolated from an ice-shelf pond in Antarctica was grown under white light combined with a range of UVA and UVB irradiances. The 4-day growth rate decreased under increasing ultraviolet (UV) radiation, with a ninefold greater response to UVB relative to UVA. In vivo absorbance spectra showed that UVA and to a greater extent UVB caused a decrease in phycocyanin/ chlorophyll a and an increase in carotenoids/chlorophyll a. The phycocyanin/chlorophyll a ratio was closely and positively correlated to the UVB-inhibited growth rate. Under fixed spectral gradients of UV radiation, the growth inhibition effect was dominated by UVB. However, at specific UVB irradiances the inhibition of growth depended on the ratio of UVB to UVA, and growth rates increased linearly with increasing UVA. These results are consistent with the view that UVB inhibition represents the balance between damage and repair processes that are each controlled by separate wavebands. They also underscore the need to consider UV spectral balance in laboratory and field assays of UVB toxicity.     

ANTARCTIC CYANOBACTERIA: LIGHT,NUTRIENTS, AND PHOTOSYNTHESIS IN THE MICROBIAL MAT ENVIRONMENT1

The microenvironmental and photosynthetic characteristics of Antarctic microbial mats were measured in a series of ponds near McMurdo Sound. As elsewhere in Antarctica, these cold-water benthic communities were dominated by oscillatoriacean cyanobacteria. Despite large variations in mat thickness, surface morphology, and color, all of the communities had a similar pigment organization, with a surface carotenoid-rich layer that overlaid a deep chlorophyll maximum (DCM) enriched in phycocyanin as well as chlorophyll a. Spectroradiometric analyses showed that the DCM population inhabited an orange-red shade environment. In several of the mats, the deep-living trichomes migrated up to the surface of the mat within 2 h in response to a 10-fold decrease in surface irradiance. The euphotic layer of the mats was supersaturated in oxygen and contained ammonium and dissolved reactive phosphorus concentrations in excess of 100 mg N·m^?3 or P·m^?3. Integral photosynthesis by core samples was saturated at low irradiances and varied two- to threefold throughout the continuous 24-h radiation cycle. Oxygen microelectrode analyses showed that the photosynthetic rates were slow to negligible near the surface and maximal in the DCM. These compressed, nutrient-rich euphotic zones have some properties analogous to planktonic systems, but the integrated photosynthetic responses of the community reflect the strong self-shading within the mat and physiological dominance by the motile, DCM populations.     

Reptodigitus Chapmanii (Nostocales,Hapalosiphonaceae) Gen. Nov.: A Unique Nostocalean (Cyanobacteria) Genus Based on a Polyphasic Approach1

The Nostocales is a monophyletic, heterocytous lineage of cyanobacteria capable of akinete production and division in multiple planes, depending upon family-level clade. While present in a variety of ecosystems, the diversity of the Nostocales has been poorly elucidated. Due to environmentally -induced phenotypic plasticity, morphology alone is often insufficient to determine the true phylogenetic placement of these taxa. In order to bridge this gap, taxonomists now employ the polyphasic approach, combining methods such as morphological analysis, phylogenetic analysis based on DNA sequence and genetic identity based on ribosomal genes, and secondary structure of the 16S-23S ITS and 16S rRNA gene sequences, as well as ecological characterization. Using this combined approach, a new genus and species (Reptodigitus chapmanii gen. et sp. nov.) isolated from the St. Johns River (Jacksonville, Florida, USA) within the Nostocales is herein described. Phylogenetic analyses place this taxon within the Hapalosiphonaceae, sister to the clade containing Fischerella, Hapalosiphon, and Westiellopsis. The 16S-23S ITS secondary folding structure analysis also supports the erection of this new genus.     

THE CONTRIBUTION OF SUB‐SAHARAN AFRICAN STRAINS TO THE PHYLOGENY OF CYANOBACTERIA: FOCUSING ON THE NOSTOCACEAE (NOSTOCALES,CYANOBACTERIA)1

To date, phylogenies have been based on known gene sequences accessible at GenBank, and the absence of many cyanobacterial lineages from collections and sequence databases has hampered their classification. Investigating new biotopes to isolate more genera and species is one way to enrich strain collections and subsequently enhance gene sequence databases. A polyphasic approach is another way of improving our understanding of the details of cyanobacterial classification. In this work, we have studied phylogenetic relationships in strains isolated from freshwater bodies in Senegal and Burkina Faso to complement existing morphological and genetic databases. By comparing 16S rDNA sequences of African strains to those of other cyanobacteria lineages, we placed them in the cyanobacterial phylogeny and confirmed their genus membership. We then focused on the Nostocaceae family by concatenated analysis of four genes (16S rDNA, hetR, nifH, and rpoC1 genes) to characterize relationships among Anabaena morphospecies, in particular, Anabaena sphaerica var. tenuis G. S. West. Using a polyphasic approach to the Nostocaceae family, we demonstrate that A. sphaerica var. tenuis is more closely related to Cylindrospermospsis/Raphidiopsis than to other planktonic Anabaena/Aphanizomenon. On the basis of phylogeny and morphological data, we propose that these three significantly different clusters should be assigned to three genera.     

MOLECULAR AND MORPHOLOGICAL CHARACTERIZATION OF TEN POLAR AND NEAR‐POLAR STRAINS WITHIN THE OSCILLATORIALES (CYANOBACTERIA)1

An approximately 1400‐bp region of the 16S rRNA gene was sequenced for 10 polar or near‐polar strains putatively placed in the Oscillatorialean genera Oscillatoria, Phormidium, and Lyngbya obtained from the University of Toronto Culture Collection to assess phylogenetic relationships. The strains were also examined for thylakoid structure and cell division type with TEM as well as traditional morphology with LM. Phylogenetic trees constructed using parsimony, distance, and maximum likelihood methods were similar in topology. If the original epithets applied to the sequenced strains (both polar and those from GenBank) were used, it was clear that taxa were not monophyletic. However, using the revised taxonomic system of Anagnostidis and Komárek, we were able to reassign these strains to their current correct taxa (species, genus, and family). When these assignments were made, it was determined that the molecular sequence data analyses were congruent with morphology and ultrastructure. Nine of the polar strains were found to be new species, and eight were described as such: Arthronema gygaxiana Casamatta et Johansen sp. nov., Pseudanabaena tremula Johansen et Casamatta sp. nov., Leptolyngbya angustata Casamatta et Johansen sp. nov., Phormidium lumbricale Johansen et Casamatta sp. nov., Microcoleus glaciei Johansen et Casamatta sp. nov., Microcoleus rushforthii Johansen et Casamatta sp. nov., Microcoleus antarcticus Casamatta et Johansen sp. nov., Microcoleus acremannii Casamatta et Johansen sp. nov. Some genera (Leptolyngbya and Microcoleus) were clearly not monophyletic and require future revision.     

中国狼蛛科娲蛛属(娲蛛亚科)分类地位的探讨

采用DNA测序方法,获得了中国狼蛛科Lycosidae4亚科6属26种mtDNA-16S rRNA基因的部分序列,比较来自北美狼蛛科豹蛛属2种豹蛛的同一基因序列,并选取漏斗蛛科1种蜘蛛作为外群,采用Bayesian方法和最大简约法(MP)构建分子系统树.两种建树方法均支持娲蛛属和豹蛛属形成一大的单系;这一结果与现行狼蛛科传统分类体系中娲蛛属的分类地位有差别.据此,作者认为:娲蛛属和豹蛛属可以归为同一个分类亚单位.狼蛛科6属间的分子系统关系为(Rirata(Hippasa(Trochsa Arctosa(Pardosa Wadicosa)))).     

水稻褐飞虱内生共生细菌Arsenophonus的鉴定和系统分析

利用16S rDNA通用引物扩增了水稻褐飞虱Nilaparvata lugens（Stål）体内共生细菌的序列,经克隆、测序和NCBI数据库比对,发现褐飞虱体内存在杀雄菌属Arsenophonus类共生细菌,系统发育上与粉虱科和木虱科体内的Arsenophonus属亲源关系较近。在褐飞虱体内该共生细菌具有两种长度不同的16S rDNA序列,分别为1 504 bp和547 bp,其中后者为前者中间缺失了957 bp,其余序列相同。通过重新设计两对引物进行扩增,进一步确认不同褐飞虱地理种群及寄主种群均存在两种片段。Arsenophonus特异的 23S rDNA引物的扩增结果表明,Arsenophonus存在于所有检测的褐飞虱种群中,但不存在于水稻寄主中。荧光定量PCR检测发现3个褐飞虱室内寄主种群Arsenophonus属共生细菌含量不同,其中TN1种群明显高于Mudgo种群和ASD7种群。此为水稻褐飞虱体内存在Arsenophonus属共生细菌的首次报道。     

A molecular phylogenetic survey of sea-ice microbial communities (SIMCO)

16S rDNA clone library analysis was used to identify bacterial biodiversity in a variety of sea-ice microbial communities (SIMCO). DNA was extracted from seven Antarctic sea-ice samples and one Arctic sea-ice sample and 16S rDNA PCR-amplified using universal and Archaea-specific primers. Recombinant 16S rDNA clones were obtained and dereplicated using restriction fragment length polymorphism analysis (RFLP). After RFLP analysis, 100 distinct phylotypes (a unique clone or group of clones with sequence similarity of >0.98) were defined. From the clone libraries 16S rDNA sequences of bacterial and eukaryotic origin were detected, however Archaea were not detected either with universal or Archaea-specific 16S rDNA primer sets. Bacterial phylotypes grouped within the alpha and gamma proteobacteria, the Cytophaga-Flavobacterium-Bacteroides division, the Gram-Positive bacteria and the orders Chlamydiales and Verrucomicrobiales. The majority of bacterial phylotypes were affiliated with heterotrophic taxa and many grouped closely with cultivated genera and species. Eukaryotic clones were affiliated with a variety of autotrophic and heterotrophic nanoplankton and included a large number of chloroplast 16S rDNA genes. The findings of this investigation corroborated culture data indicating bacterial biodiversity increased in SIMCO displaying high levels of primary production, however the bacterial communities within SIMCO were highly heterogeneous at the genus/species-level between different samples. A comparison of Antarctic and Arctic SIMCO revealed certain sea-ice dwelling bacterial genera are common at both poles.     

POLYPHASIC CHARACTERIZATION OF THREE STRAINS OF ANABAENA RENIFORMIS AND APHANIZOMENON APHANIZOMENOIDES (CYANOBACTERIA) AND THEIR RECLASSIFICATION TO SPHAEROSPERMUM GEN. NOV. (INCL. ANABAENA KISSELEVIANA)1

Occurrences of rare cyanobacteria Anabaena reniformis Lemmerm. and Aphanizomenon aphanizomenoides (Forti) Horecká et Komárek were recently detected at several localities in the Czech Republic. Two monoclonal strains of An. reniformis and one strain of Aph. aphanizomenoides were isolated from distant localities and different sampling years. They were characterized by a combination of morphological, genetic, and biochemical approaches. For the first time, partial 16S rRNA gene sequences were obtained for these morphospecies. Based on this gene, all of these strains clustered separately from other planktonic Anabaena and Aphanizomenon strains. They appeared in a cluster with Cylindrospermopsis Seenaya et Subba Raju and Raphidiopsis F. E. Fritsch et M. F. Rich, clustered closely together with two An. kisseleviana Elenkin strains available from GenBank. A new generic entity was defined (Sphaerospermum gen. nov., with the type species S. reniforme, based on the traditional species An. reniformis). These results contribute significantly to the knowledge base about genetic heterogeneity among planktonic Anabaena–like and Aphanizomenon–like morphospecies. Accordingly, the subgenus Dolichospermum, previously proposed for the group of planktonic Anabaena, should be revaluated. Secondary metabolite profiles of the An. reniformis and Aph. aphanizomenoides strains differed considerably from 17 other planktonic Anabaena strains of eight morphospecies isolated from Czech water bodies. Production of puwainaphycin A was found in both of the An. reniformis strains. Despite the relatively short phylogenetic distance from Cylidrospermopsis, the production of cylindrospermopsin was not detected in any of our strains.     

用DGGE技术分析污水人工快速渗滤系统中微生物种群分布

从深圳运行中的人工快速渗滤系统(CRI)的砂层填料中以5cm~10cm间隔垂直取10个样品,进行16S rDNAV3区的DGGE分析,结果表明,CRI系统中微生物种群随着深度的增加逐渐减少,在快渗池砂层填料的30cm深度范围内,微生物群落组成至少有18种,主要是Firmicutes、alpha proteobacterium中的异养菌,它们是COD降解的主要参与者;而在40cm及更深范围,菌群减少为12种甚至更少,优势菌是Acidovorax sp.、Nitrospira sp.、Clostridium sp.等,表明快渗池下部存在较强的硝化作用和厌氧的微环境,快渗池上、下层之间呈现出不同的多样性。结果揭示出CRI系统中的微生物种群空间分布状况,为其处理效果的稳定和提高提供了理论基础。     

滑桃树不同器官伴生细菌多样性的分子特征

应用不依赖于培养的16S rRNA基因技术,揭示滑桃树根皮、茎皮以及种子伴生细菌的种类多样性,为建立伴生细菌的宏基因组文库奠定基础。基于我们新近发表的植物伴生菌富集方法,建立富集和未富集样品的全长16S rRNA基因文库,随机挑取至少100个克隆进行酶切分型并测序,根据16S rDNA的部分序列推测其所属伴生菌的种类。结果表明,所检测的细菌克隆大部分属于γ-Proteobacteria,有少量来源于α-Proteobacteria或放线菌（Actinobacteria）,也包括不可培养或分类地位不明确的细菌。经过富集,16S rRNA基因文库中细菌克隆的比例和序列多样性显著增加,根皮的伴生细菌种类最为丰富,其次是成熟种子和茎皮;幼嫩种子16S rDNA文库的细菌克隆比例较小（1．18％）,说明幼嫩种子的伴生菌最少。     

RESOLVING EVOLUTIONARY RELATIONSHIPS AMONG THE BROWN ALGAE USING CHLOROPLAST AND NUCLEAR GENES1

The brown algae are one of the largest and most important groups of primary producers in benthic coastal marine environments. Despite their biological importance, consensus regarding their taxonomic or evolutionary relationships remains elusive. Our goal was to produce a taxon‐rich two‐gene (rbcL and LSU rDNA) phylogeny. Key species were sequenced to represent each order and family in the analyses across all 19 orders and ～40 families, including selected outgroups Schizocladiophyceae and Xanthophyceae. Our results are in sharp contrast to traditional phylogenetic concepts; the Ectocarpales are not an early diverging clade, nor do the Fucales diverge early from other brown algae. Rather, Choristocarpus is sister to the remaining brown algae. Other groups traditionally considered to have primitive features are actually recently diverged lineages, turning traditional phylogenetic concepts upside down. Additionally, our results allow for the assessment, in the broadest context, of many of the historical and more recent taxonomic changes, resulting in several emended groups along with proposals for two new orders (Onslowiales, Nemodermatales) and one new family (Phaeosiphoniellaceae).     

MORPHOLOGICAL AND MOLECULAR CHARACTERIZATION OF PLANKTONIC CYANOBACTERIA FROM BELGIUM AND LUXEMBOURG1

For the first time in Belgium and Luxembourg, the diversity and taxonomy of 95 cyanobacterial strains isolated from freshwater blooms were assessed by the comparison of phenotypes and partial 16S rRNA gene sequences. The results showed the high diversity of nanoplanktonic, picoplanktonic, and benthic–periphytic cyanobacteria accompanying the main bloom‐forming taxa. Indeed, besides 15 morphotypes of bloom‐forming taxa, seven non‐bloom‐forming planktonic morphotypes and 11 morphotypes from benthic–periphytic taxa were isolated in culture from the plankton samples of 35 water bodies. The bloom‐forming strains belonged to the genera Microcystis, Woronichinia, Planktothrix, Anabaena, and Aphanizomenon, whereas the other strains isolated from the same samples were assigned to the nanoplanktonic Aphanocapsa, Aphanothece, Snowella, and Pseudanabaena; to the picoplanktonic Cyanobium; and to the benthic–periphytic Geitlerinema, Komvophoron, Leptolyngbya, Lyngbya, Phormidium, Calothrix, Nostoc, and Trichormus. The results supported both the polyphyletism of genera such as Aphanocapsa, Aphanothece, Leptolyngbya, Geitlerinema, Anabaena, and Aphanizomenon as well as the validity of genera such as Microcystis, Planktothrix, and Pseudanabaena with gas vesicles and cells constricted at the cross wall. The results obtained showed the close relationship between Snowella and Woronichinia for which very few sequences exist. The first sequence of Komvophoron appeared poorly related to other available cyanobacterial sequences. Although in a few cases a good agreement existed between phenotypic and genotypic features, there was generally a discrepancy. Strains with identical morphotypes show small differences in the 16S rRNA sequences, which might be related to the different chemical properties of their habitats. The results showed the importance of the polyphasic approach in order to improve the taxonomy of cyanobacteria.     

GROWTH REGULATION OF rRNA CONTENT IN PROCHLOROCOCCUS AND SYNECHOCOCCUS (MARINE CYANOBACTERIA) MEASURED BY WHOLE‐CELL HYBRIDIZATION OF rRNA‐TARGETED PEPTIDE NUCLEIC ACIDS1

The cyanobacteria Synechococcus and Prochlorococcus are important primary producers in marine ecosystems. Because currently available approaches for estimating microbial growth rates can be difficult to apply in the field, we have been exploring the feasibility of using quantitative rRNA measurements as the basis for making such estimates. In this study we examined the relationship between rRNA and growth rate in several Synechococcus and Prochlorococcus strains over a range of light‐regulated growth rates. Whole‐cell hybridization with fluorescently labeled peptide nucleic acid (PNA) probes was used in conjunction with flow cytometry to quantify rRNA on a per cell basis. This PNA probing technique allowed rRNA analysis in a phycoerythrin‐containing Synechococcus strain (WH7803) and in a non–phycoerythrin‐containing strain and in Prochlorococcus. All the strains showed a qualitatively similar tri‐phasic relationship between rRNA·cell^?1 and growth rate, involving relatively little change in rRNA·cell^?1 at low growth rates, linear increase at intermediate growth rates, and a plateau and/or decrease at the highest growth rates. The onset of each phase was associated with the relative, rather than absolute, growth rate of each strain. In the Synechococcus strains, rRNA normalized to flow cytometrically measured forward angle light scatter (an indicator of size) was well‐correlated with growth rate across strains. These findings support the idea that cellular rRNA may be useful as an indicator of in situ growth rate in natural Synechococcus and Prochlorococcus populations.     

IDENTIFICATION OF THE CYTOKININ ISOPENTENYLADENINE IN A STRAIN OF ARTHRONEMA AFRICANUM (CYANOBACTERIA)

Isopentenyladenine was isolated from a strain of the cyanobacterium Arthronema africanum (Schwabe et Simons) Komárek et Lukavský using a combination of biological and chemophysical techniques, including the soybean callus bioassay, cation exchange resin chromatography, paper chromatography, HPLC, and GC-MS. Positive identification of the major biologically active compound was achieved.     

Wolbachia在熊蜂中的双重感染

Wolbachia是一类广泛存在于节肢动物体内细胞质遗传的细菌,它可以通过诱导产雌孤雌生殖、引起细胞质不亲和、遗传雄性的雌性化、雄性致死和增强生殖力等作用方式引起其寄主生殖行为的改变.本文以16S rDNA为标记检测了3种熊蜂不同组织(头,胸,足,卵巢或雄外生殖器)的Wolbachia感染.其中明亮熊蜂Bombus l...     

COLEOFASCICULUS GEN. NOV. (CYANOBACTERIA): MORPHOLOGICAL AND MOLECULAR CRITERIA FOR REVISION OF THE GENUS MICROCOLEUS GOMONT1

Species currently classified within the cyanobacterial genus Microcoleus were determined to fall into two distinct clades in a 16S rDNA phylogeny, one containing taxa within the Oscillatoriaceae, the other containing taxa within the Phormidiaceae. The two lineages were confirmed in an analysis of the 16S–23S internal transcribed spacer (ITS) region sequences and secondary structures. The type species for Microcoleus is M. vaginatus Gomont, and this taxon belongs in the Oscillatoriaceae. Consequently, Microcoleus taxa in the Phormidiaceae must be placed in separate genera, and we propose the new genus Coleofasciculus to contain marine taxa currently placed in Microcoleus. The type species for Coleofasciculus is the well‐studied and widespread marine mat‐forming species Microcoleus chthonoplastes (Mert.) Zanardini ex Gomont. Other characters separating the two families include type of cell division and thylakoid structure.     

A RIBOSOMAL DNA PHYLOGENY SUPPORTS THE CLOSE EVOLUTIONARY RELATIONSHIPS AMONG THE SPOROCHNALES,DESMARESTIALES, AND LAMINARIALES (PHAEOPHYCEAE)1

We report six complete 18S ribosomal DNA (rDNA) sequences representing five brown algal orders: Sporochnus comosus C. A. Agardh (Sporochnales), Chorda tomentosa Lyngbye (Chordaceae, Laminariales), Saccorhiza polyschides (Lightfoot) Batters (Phyllariaceae, Laminariales), Desmarestia ligulata (Lightfoot) Lamouroux (Desmarestiales), Ectocarpus siliculosus (Dillwyn) Lyngbye (Ectocarpales), and Scytosiphon lomentaria (Lyngbye) J. G. Agardh (Scytosiphonales). These sequences were compared with published laminarialean (Alaria marginata Postel et Ruprecht [Alariaceae] and Macrocystis integrifolia Bory [Lessoniaceae]) and fucalean (Fucus gardneri Silva) rDNA sequences for phylogeny inference using both the distance-matrix and parsimony methods. The inferred 18S phylogenies clustered Sporochnus, Desmarestia, Chorda, Saccorhiza, Alaria, and Macrocystis in an assemblage. This Sporochnales–Desmarestiales–Laminariales (S-D-L) complex was consistently separated from the Ectocarpales, Scytosiphonales, and Fucales by bootstrap analyses. The inferred phylogenies are consistent with several possible evolutionary processes leading to this S-D-L complex. Members in this assemblage lack eyespots in their sperm, and their sperm have the atypical brown algal flagellation: shorter anterior and longer posterior flagella. In addition, they are oogamous with a heteromorphic alternation of generations between a microscopic gametophyte and a macroscopic sporophyte. Members of the S-D-L complex can be separated into different phylogenetic lines based on the presence/absence of eyespots in their meiospores. Our findings support the contention that the Sporochnales, Desmarestiales, and Laminariales are closely related. In addition, our rDNA tree suggests that the Laminariales is paraphyletic.