Upright Filaments Research Articles

Mesoproterozoic siliciclastic stromatolites of Chapada Diamantina (Brazil): Morphological types, genesis and environmental context

Laminations of organosedimentary structures can be formed by three distinct processes: (i) bio-induced mineral precipitation, (ii) trapping and binding, and (iii) abiotic mineral precipitation and each of these processes predominates in a certain geological time interval. Agglutinated stromatolites are rare and seem to form in specific environmental conditions. Siliciclastic stromatolites are an even rarer class of agglutinated stromatolites, which are formed in response to the process of trapping and binding of siliciclastic grains by upright filaments or by extracellular polymeric substances (EPS). This study describes and interprets one of the oldest siliciclastic stromatolites of the geological record and discusses the microbial evidence and mechanisms that controlled their accumulation and preservation. Two compound sections were analyzed and ten thin sections were prepared to characterize the siliciclastic stromatolites from the Mesoproterozoic Caboclo Formation (Brazil). Stromatolites are present in two different lithofacies associations: (i) shoreface and (ii) offshore transition. The shoreface stromatolites are characterized by silty to sandy texture and poor lamination, and the distal ones by clay, silt grains, less sand, and distinct lamination. The volume of siliciclastic grains composing the stromatolite fabric is >85% in the shoreface and >30% in offshore transition. These stromatolites were deposited in a favorable environment for trapping and binding of siliciclastic sediments: a wave-dominated siliciclastic ramp with the availability of siliciclastic grains and frequent water column agitation. The marine environment is favorable for forming EPS with good adhesive properties. Besides, the Caboclo Formation age (1.3–1.0 Ga) coincides with an abrupt fall in the amount of atmospheric CO2 reflected in CaCO3 saturation in the oceans. This change in ocean chemistry may have led to a change in stromatolite fabric, from the sparry crust and fine-grained precipitated to agglutinated.

Molecular phylogeny of Zeacarpa (Ralfsiales, Phaeophyceae) proposing a new family Zeacarpaceae and its transfer to Nemodermatales.

Zeacarpa leiomorpha is a crustose brown alga endemic to South Africa. The species has been tentatively placed in Ralfsiaceae, but its ordinal assignment has been uncertain. The molecular phylogeny of brown algae based on concatenated DNA sequences of seven chloroplast and mitochondrial gene sequences (atpB, psaA, psaB, psbA, psbC, rbcL, and cox1) of taxa covering most of the orders revealed the most related phylogenetic relationship of Z.leiomorpha to Nemoderma tingitanum (Nemodermatales) rather than Ralfsiaceae (Ralfsiales). Morphologically, Zeacarpa and Nemoderma share crustose thallus structure and multiple discoidal chloroplasts without pyrenoids in each cell, however, the formation of lateral unilocular zoidangia in tufts in loose upright filaments in Zeacarpa is distinctive in brown algae. Considering the relatively distant genetic divergence between the two taxa, comparable to that among families or orders in representative brown algae, in addition to the above-mentioned unique morphological features, we propose the classification of Zeacarpa in a new family Zeacarpaceae in the order Nemodermatales.

Quantitative Analysis of Filament Branch Orientation in Listeria Actin Comet Tails

Several bacterial and viral pathogens hijack the host actin cytoskeleton machinery to facilitate spread and infection. In particular, Listeria uses Arp2/3-mediated actin filament nucleation at the bacterial surface to generate a branched network that will help propel the bacteria. However, the mechanism of force generation remains elusive due to the lack of high-resolution three-dimensional structural data on the spatial organization of the actin mother and daughter (i.e., branch) filaments within this network. Here, we have explored the three-dimensional structure of Listeria actin tails in Xenopus laevis egg extracts using cryo-electron tomography. We found that the architecture of Listeria actin tails is shared between those formed in cells and in cell extracts. Both contained nanoscopic bundles along the plane of the substrate, where the bacterium lies, and upright filaments (also called Z filaments), both oriented tangentially to the bacterial cell wall. Here, we were able to identify actin filament intersections, which likely correspond to branches, within the tails. A quantitative analysis of putative Arp2/3-mediated branches in the actin network showed that mother filaments lie on the plane of the substrate, whereas daughter filaments have random deviations out of this plane. Moreover, the analysis revealed that branches are randomly oriented with respect to the bacterial surface. Therefore, the actin filament network does not push directly toward the surface but rather accumulates, building up stress around the Listeria surface. Our results favor a mechanism of force generation for Listeria movement where the stress is released into propulsive motion.

Studies of the green algaPercursaria dawsonii(=Blidingia dawsoniicomb. nov., Kornmanniaceae, Ulvales) in British Columbia

SUMMARYWe cultured and sequenced newly collected material ofPercursaria dawsoniiHollenberg et I. A. Abbott, a poorly known epibiont of limpets found along the west coast of North America. Zoospores, parthenogametes, and zygotes exhibited empty‐spore germination, which produced a prostrate system that expanded by stolon‐like development. A dense carpet of initially uniseriate filaments arose from the prostrate system. These upright filaments soon became biseriate proximally and pluriseriate distally, where they were flat, twisted and distromatic for approximately four‐fifths of their length and rarely became hollow in larger individuals. These fronds became fertile distally and released quadriflagellate zoospores and/or biflagellate isogametes. Individual gametophytic fronds were dioecious, and alternated with isomorphic sporophytic fronds. The gametes moved rapidly and often exhibited an unusual side‐to‐side vibration that made them appear like winged insects. Comparisons of 18S rRNA gene and ITS sequences indicated thatP. dawsoniishould be included in the genusBlidingia, family Kornmanniaceae.

Genesis of large siliceous stromatolites at Frying Pan Lake, Waimangu geothermal field, North Island, New Zealand

AbstractLilypad stromatolites, up to 3 m long and 1·5 m wide, were found to be actively growing in the shallow marginal waters of Frying Pan Lake and its outflow channel. These stromatolites, composed of Phormidium (> 90%), Fischerella, and a variety of other microbes, develop through a series of distinct growth stages. Dark green microbial mats cover the floor of the outflow channel and give rise to columns of various sizes and shapes in the shallower marginal waters. Once the columns reach the water level, the mats spread laterally to form a lilypad stromatolite. The lilypads are characterized by a raised, dark green rim, 4–5 mm high, that encircles a flat interior covered with a distinctive orange‐red mat. The microbes forming the columns and lilypad plate are being actively silicified. The stromatolites are formed of: (i) flat‐lying Phormidium filaments (P‐laminae), (ii) upright filaments of Phormidium that are commonly associated with Fischerella (U‐laminae), and (iii) mucus, diatoms and pyrite framboids (M‐laminae). P‐laminae dominate most of the columns, with tripartite cycles of P‐, U‐, to M‐laminae being found mostly in the upper parts of the stromatolites. The transition from the P‐ to U‐laminae is marked by a change in the growth pattern of the Phormidium and branching of Fischerella, which was probably triggered by a change in environmental conditions. In the Frying Pan Lake outflow channel, this change may be related to fluctuations in water level and flow rates that are caused by periods of heavy rain, seasonal changes, long‐term variations in rainfall, and/or the unique 40‐day hydrological cycle that exists between Frying Pan Lake and Inferno Crater, which is a nearby hydrothermal crater lake.

First record of Asteronema rhodochortonoides (Phaeophyceae) for the Pacific Ocean

SUMMARY Morphological observations of a minute, filamentous, branched brown alga epiphytic on Sargassum thun-bergii (Mertens ex Roth) Kuntze were made on material collected at Tsuyazaki (33°48′N, 130°27′E), Fukuoka Prefecture, southern Japan. This alga was assignable to Asteronema rhodochortonoides (Borgesen) Moller et Parodi in having stellately arranged chloroplasts with several pyrenoids grouped in the center, predominantly apical growth, narrow filaments, and elliptical or broadly elliptical plurilocular zoidangia that are apically or laterally formed on upright filaments. A comparison of partial nuclear small subunit rDNA sequences between the Japanese material and A. rhodochortonoides from the Canary Islands showed only two or three nucleotide differences. This supports our assignment of the Japanese material to this species as a first report for the Pacific Ocean. In laboratory cultures, zoids released from plurilocular zoidangia developed into plants with morphology similar to the field-collected plants. This cycle repeated without production of unilocular zoidangia in our cultures.

Seasonal dynamics and recruitment strategies of the invasive seaweed Grateloupia doryphora (Halymeniaceae, Rhodophyta) in Narragansett Bay and Rhode Island Sound, Rhode Island, USA

Although there is considerable interest in the introduction and spread of invasive species, there has been little research documenting growth patterns of a specific organism from the time of its first arrival. This paper addresses the seasonality and recruitment of Grateloupia doryphora, a large red algal species that arrived in Narragansett Bay, Rhode Island, USA, in 1994. From 1997 to 1999 inclusive, this species exhibited a distinct seasonal pattern, with the lowest percent cover occurring in May–June and the highest percent cover in October. This timing of low and high percent cover was observed concurrently at three stations over a two-year period. Percent cover was a function of blade size and numbers. New blades appeared year-round. In addition to percent cover, blade colour changed seasonally from light red (June–August) to dark burgundy (August–January) to yellow red (February–May). Strategies for recruitment of G. doryphora were observed in the field, on both natural and artificial substrata (fixed plastic plates coated with sand), and in culture. Recruitment on sand-coated plates in Narragansett Bay and Rhode Island Sound resulted from spore settlement and subsequent crust and blade development. On a single plate, hundreds of juvenile upright blades appeared in May–June 1999, and the largest blades grew to 25 cm long by August. In addition to recruitment on plates, crusts appeared on bare rock, and new blades arose from crusts and from proliferations of older blades. Laboratory cultures clarified the developmental sequence from spore to crust to blade and/or upright filaments to new crusts and new blades. The crustose form may provide a strategy for survival during unfavourable environmental conditions, enabling G. doryphora to establish residency in Rhode Island waters. The effect of this invasive species on other organisms has yet to be determined.

Microfossil populations in the context of synsedimentary micrite deposition and acicular carbonate precipitation: Mesoproterozoic Gaoyuzhuang Formation, China

Silicified stratiform stromatolites of the Mesoproterozoic Gaoyuzhuang Formation (1.4–1.5 Ga), China, contain well-preserved microfossils. The cherts also harbor varied synsedimentary precipitates and void-filling cements, replaced by early diagenetic silica minerals. These precipitates disclose microenvironments characterized by supersaturated solutions in protected, shallow depressions within an intertidal setting. The precipitates provided surfaces for selective microbial settlement, and rigid sediment matrix for microbial growth. Together with early silicification, the frequent precipitation events contributed to preservation of microfossils by reducing sediment compaction and shearing. Fossiliferous cherts display fine, flat and wavy lamination, characterized by an alternation of highly silicified, thin organic-rich layers with thick sediment-rich layers. Organic-rich layers are dominated either by coccoid or by filamentous microfossils, whereas sediment-rich layers contain abundant synsedimentary precipitates, within which the microfossils are preserved in their growth position. Four dominant microfossils Coccostratus dispergens n. gen. et sp., Eoentophysalis belcherensis, Eoschizothrix composita and Siphonophycus inornatum occur contiguously through several tens of laminae, and are identified as main frame-building biological components of Gaoyuzhuang stromatolites. Community composition, microbial density, distribution, orientation and developmental patterns of the frame-building microfossils are closely correlated with the changing depositional events of Gaoyuzhuang cherts, contrasting conditions of sedimentary kinetics with those of sedimentary stasis. Each assemblage of frame-building microfossils responded to sedimentation with different mechanisms to escape burial. High sedimentation rates correlate with scattered colonies of coccoids and with loose webs of predominantly upright filaments. Low sedimentation rates correlate with dense, laterally connected colonies of coccoids and with a change in filament orientation from vertical to horizontal. In multi-trichomous microfossil Eoschizothrix composita, low sedimentation rates are also accompanied with an increase in number of trichomes per filament. The observed morphological variability of the frame-building microfossils is explained by microbial development, reproduction and behavior by interactions between sedimentological and biological controls.

New observations on the Tilopteridaceae (Phaeophyceae). II. Culture studies determine Phaeosiphoniella as an arctic species and crusts as systems for perennation and propagation

Abstract Previous field studies on the seasonality of the Tilopteridales have been complemented by culture studies. Special reference was made to prostrate systems and upright filaments of Haplospora and Phaeosiphoniella and their light and temperature requirements. Apical cells of rhizoids produced disc-shaped crusts upon contact with the substratum, especially under adverse culture conditions. Prostrate discs withstood 20°C and 15 μmol m−2s−1, indicating their suitability for perennation of both species during summer. Phaeosiphoniella uprights appeared at less than 8 μmol m−2s−1 and below 10°C, but showed early senescence at 5°C, whereas antheridia and oogonia appeared occasionally above 5°C and 6.5°C, respectively. Propagation was facilitated by immediate development of rhizoids from each abscised fragment of disintegrated plants and subsequent renewal of whole upright systems. The discrepancy between the temperature limitations for vegetative growth and reproduction might indicate that Phaeosiphoniell...

Studies of protonemal morphogenesis in mossesII Orthotrichum obtusifoliumBrid.

Abstract The protonema of Orthotrichum obtusifolium, regenerated from leafy shoots, comprises a dense mass of largely unbranched exclusively upright filaments. All the cells have transverse cross-walls and contain numerous chloroplasts which become larger and discoidal in older filaments. Differentiation into chloro- and caulonema is absent. When upright filaments are transplanted onto an agar surface, they act as the main axes for a further set of upright branches. Buds and side branches are produced symmetrically at right angles to the mother cells. Protonemal morphogenesis hardly changes on nutrientfree medium and spherical brood cells are not produced after prolonged culture or in the presence of abscisic acid. Rhizoids with oblique septa and pigmented walls arise from the base of gametophores. These revert to protonemata when in contact with nutrient agar.The upright filaments produce terminal and intercalary filamentous gemmae with well defined abscission cells. The latter swell and lose their conte...

Reproductive ecology of the freshwater red alga Batrachospermum boryanum Sirodot in a temperature headwater stream

Spatial distribution and abundance of Batrachospermum boryanum gametophytes within a headwater stream in Rhode Island, USA varied considerably over a period of two yeas due to significant changes in dominant substrata. However, periodicity of these plants was similar each year. Juvenile gametophytes were produced by the aseasonal annual ‘chantransia’ stage most abundantly in September and October. Macroscopic gametophytes appeared in Novemberand attained a peak in development during late winter and spring, correlating with relative light penetration through the surrounding tree canopy. The ratio of female to male plants increased from 1:1 in January 4:1 at the end of the growing season in June during both years. Spermatangia production was continuous throughout the growth period, averaging 26000 mm−2; mean carpogonial density was 60 mm−2. Approximately 500 spermatia were released for each carpogonium present and the mean proportion of fertilized carpogonia was 22%. Carposporophyutes typically became detached and acted as dispersal agents, settling at 0.075cm s−1. Current velocities in the stream varied from 10 to 50 cm s−1 and were calculated to carry the carposporophytes 5–35 m downstream. Monospores released by ‘chantransia’ upright filaments also added to population spread.

Algal Colonization under Four Experimentally-Controlled Current Regimes in High Mountain Stream

Algal colonization and assemblage development were examined on unglazed ceramic tiles in flow-through troughs over a 42-d period (summer 1987) in the regulated upper Colorado River (∼2400 m a.s.l.). The unusually constant discharge of the stream, coupled with the trough design, allowed the establishment and maintenance of four controlled current regimes that differed with respect to range of free-stream velocity and associated near-substratum hydraulic conditions: 1) depositional (free-stream current velocity <1 cm/s); 2) slow and hydraulically-smooth (range 14-20 cm/s); 3) fast and hydraulically-smooth (range 36-47 cm/s); and, 4) fast and hydraulically-rough or turbulently mixed (range 15-46 cm/s). Biomass was on average 30-40× higher in the two slow velocity treatments than in the two fast velocity treatments. Chlorophytes, bacillariophytes, and cyanophytes exhibited distinctly different successional trajectories and end-points in all treatments. Ulothrix zonata, established by day 4, was the dominant alga at all velocities for the first two weeks, after which it was replaced by a more diverse assemblage of chlorophytes, except in the Fast-rough regime. Diatoms were common in all treatments, but were only numerically dominant during the latter part of the study. Cyanophytes dominated only in the two lowest current regimes and only at the end of the study. Scanning electron microscopy revealed that physiognomy of algal assemblages also varied across current regimes. The two low velocity treatments were characterized by dense, upright filaments within one week, while three-dimensional assemblage structure in the two high velocity treatments did not develop over the 42-d period. Differences in species composition, successional trajectories and physiognomy across treatments demonstrated that current regime (free-stream velocity and pattern of flow) was an important determinant of algal assemblage structure in the absence of hydrologic and grazing disturbances.

A crustose tetrasporophyte in the life history of Nothogenia erinacea (Turner) Parkinson (Galaxauraceae, Rhodophyta)

A Cruoriopsis-like tetrasporophytic phase in the life history of the southern African species Nothogenia erinacea (formerly Chaetangium erinaceum) is described. Carpospores from the foliose female gametophytes give rise to crusts in culture which consist of centrifugally radiating basal filaments supporting tightly cohesive upright filaments. Subsequently the upright filaments grow further, but nolonger adhere tightly to one another. Scattered tetrasporangia develop, immersed among the loose filaments. Division of tetraspores is cruciate or cruciate/decussate. In culture tetraspores give rise to further crusts, which are morphologically identical to those from carpospores. The probable mode of development of gametophytes from these crusts is described. Evidence is provided of a similar crustose tetrasporophyte in the life history of Nothogenia ovalis (formerly Chaetangium ovale).

OBSERVATIONS ON THE LIFE HISTORY OF PAPENFUSSIELLA CALLITRICHA (PHAEOPHYCEAE, CHORDARIALES) IN CULTURE1

ABSTRACTPapenfussiella callitricha (Rosenv.) Kylin from eastern Canada was studied in culture. Zoids from unilocular sporangia develop into microscopic, filamentous, dioecious gametophytes which produce isogametes in filament cells and few‐chambered plurilocular gametangia. Unfused gametes germinate to reproduce the gametophytes. Fusion takes place between a settled (“female”) and a motile (“male”) gamete. The zygote gives rise to a filamentous plethysmothallus that reproduces asexually by zoids formed in thallus cells and in few‐chambered plurilocular zoidangia. Erect macrothalli are produced on the plethysmothallus, beginning with the formation of upright filaments. Later on, these filaments become the terminal assimilators of the macrothalli. Further assimilatory filaments, rhizoids, and unilocular sporangia are produced in a branching region at the base of the terminal assimilator. Zoids from unilocular sporangia formed in culture germinate to reestablish the gametophyte phase. Chromosome counts yielded n = 19 ± 3 for the gametophytes, and 32 ± 6 for the sporophyte, both plethysmothallus and macrothallus.

A new species of Basicladia on Australian freshwater turtles

1. A new species of the genus Basicladia is described. It occurs on the Australian freshwater turtle, Chelodina longicollis (Shaw). 2. This species differs from those hitherto described, because it has profusely branched upright filaments, hence the choice of the name Basicladia ramulosa. 3. The classification and affinities of the genera Basicladia and Dermatophyton are discussed. Both genera are placed in the family Arnoldiellaceae, order Cladophorales.