Cyanolichens can have both cyanobacteria and green algae in a common layer as major contributors to photosynthesis

Background and Aims

Cyanolichens are usually stated to be bipartite (mycobiont plus cyanobacterial photobiont). Analyses revealed green algal carbohydrates in supposedly cyanobacterial lichens (in the genera Pseudocyphellaria, Sticta and Peltigera). Investigations were carried out to determine if both cyanobacteria and green algae were present in these lichens and, if so, what were their roles.

Methods

The types of photobiont present were determined by light and fluorescence microscopy. Small carbohydrates were analysed to detect the presence of green algal metabolites. Thalli were treated with selected strengths of Zn²⁺ solutions that stop cyanobacterial but not green algal photosynthesis. CO₂ exchange was measured before and after treatment to determine the contribution of each photobiont to total thallus photosynthesis. Heterocyst frequencies were determined to clarify whether the cyanobacteria were modified for increased nitrogen fixation (high heterocyst frequencies) or were normal, vegetative cells.

Key Results

Several cyanobacterial lichens had green algae present in the photosynthetic layer of the thallus. The presence of the green algal transfer carbohydrate (ribitol) and the incomplete inhibition of thallus photosynthesis upon treatment with Zn²⁺ solutions showed that both photobionts contributed to the photosynthesis of the lichen thallus. Low heterocyst frequencies showed that, despite the presence of adjacent green algae, the cyanobacteria were not altered to increase nitrogen fixation.

Conclusions

These cyanobacterial lichens are a tripartite lichen symbiont combination in which the mycobiont has two primarily photosynthetic photobionts, ‘co-primary photobionts’, a cyanobacterium (dominant) and a green alga. This demonstrates high flexibility in photobiont choice by the mycobiont in the Peltigerales. Overall thallus appearance does not change whether one or two photobionts are present in the cyanobacterial thallus. This suggests that, if there is a photobiont effect on thallus structure, it is not specific to one or the other photobiont.     

ECOTYPIC VARIATION IN CYSTOCLONIUM PURPUREUM (RHODOPHYTA) SYNCHRONIZES LIFE HISTORY EVENTS IN DIFFERENT REGIONS1

Temperature and daylength responses were determined in culture for isolates of the red alga Cystoclonium purpureum (Hudson) Batters from Nova Scotia (NS, Canada), Helgoland (HE, Germany), and Roscoff (RO, France). Most isolates survived temperatures of –1.5°/–2° to 23°C, whereas 25°C was lethal. Only the RO-gametophytes died at 23°C. Optimal growth conditions were 10°–20°C in both long and short days for the NS isolates and 8°–15°C and 8°–18°C at daylengths of >12 h for the RO and HE isolates, respectively. Tetrasporophytes and gametophytes of the NS isolate reproduced at 10°–20°C in long and short days within 5 months. At lower temperatures reproduction was limited or slow. The European isolates formed tetrasporangia at 10°–20°C (HE) or 5°–l8°C(RO), spermatangia at 5°–15°C (HE) or 5°–20°C (RO), and carpospores at 5°–15°C(HE) or 10°–15°C (RO). Short days either blocked or delayed reproduction of the European isolates. The phenology of C. purpureum was studied at Helgoland and Roscoff, where similar seasonal patterns were observed. In early spring, growth was rapid and plants started to form reproductive structures. In summer, tetra-and carpospores were shed followed by degeneration of the upright axes while branched holdfasts persisted. New upright axes and juvenile plants were formed in autumn, but these remained small during the winter months. Published data indicate that the seasonal pattern at Nova Scotia is similar, although the onset of growth and reproduction is delayed until the end of spring. These observations correspond well with the results of the experiments. The life history of C. purpureum is regulated by temperature and daylength. In the eastern Atlantic, the limiting effect of short days confines growth and reproduction to spring and summer. In the western Atlantic, low winter temperatures alone bring about the same seasonal pattern. After plants have reproduced, uprights degenerate in spite of continuing favorable conditions.     

Evaluation and Reliability of a Simplified Method for Identification of Food-Borne Yeasts

A simplified identification key described by Deak and Beuchat (T. Deak and L. R. Beuchat, J. Food Prot. 50:243-264, 1987) and the computer method of Barnett et al. (J. A. Barnett, R. W. Payne, and D. Yarrow, Yeast Identification Program, 1985) were used to identify 12 reference strains and 382 yeasts isolated from cultured milk products. Because the simplified key failed to account for species variability with regard to physiological, morphological, and sexual reproduction characteristics, poor agreement of the identification results was obtained. A reevaluation of the basic theoretical assumptions of the simplified key only confirmed the practical results and indicates that this identification method is unsatisfactory     

ECOTYPIC VARIATION IN PHYLLOPHORA PSEUDOCERANOIDES (RHODOPHYTA) ENSURES WINTER REPRODUCTION THROUGHOUT ITS GEOGRAPHIC RANGE1

Responses to temperature and daylength were determined in laboratory culture for isolates of the red alga Phyllophora pseudoceranoides (Gmelin) Newroth et A.R.A. Taylor from Nova Scotia, Iceland, Roscoff (France), and Helgoland (Germany). All isolates grew from 3° to 25° C and survived from -2° or 0° C to 27° C but not 30° C. Reproductive requirements differed between life history phases and isolates. Isolates from Helgoland and Roscoff formed sporangial sori at 3°-20° C, tetraspores at 3°-12° C, and procarps at 10°-20° C, irrespective of daylength. Spermatangia developed at 10°-23° C but only in long days. As the other European isolates, the isolate from Iceland formed tetrasporangia at 3°-12° C, but it had an additional requirement for short days. The Nova Scotian isolate formed sori at 10°-20° C and sporulated at 10°-18° C. When grown plants were transferred from noninductive to inductive conditions, sori were formed after 4 months and tetraspores developed and were shed (1-)3 months later. Procarps formed 1(-3) months after transfer. The phenology of P. pseudoceranoides was studied at Helgoland and Roscoff, where similar seasonal patterns were observed. Plants were perennial, forming new blades from October to June, which degenerated between August and February. In June, reproductive structures (sori, spermatangia, and procarps) started to appear on the new blades. From October to April, mature cystocarps were found. Mature tetrasporangia were observed only in February. The life history of P. pseudoceranoides is regulated by temperature and daylength. Differential effects on the different life history phases all serve to confine the production of spores (both carpospores and tetraspores) to the winter season. Differences in response between isolates from different geographic regions bring about the same effect: spores are shed only in winter. The nature of the geographic boundaries of P. pseudoceranoides is discussed.     

Mapping the transition state for a binding reaction between ancient intrinsically disordered proteins

Intrinsically disordered protein domains often have multiple binding partners. It is plausible that the strength of pairing with specific partners evolves from an initial low affinity to a higher affinity. However, little is known about the molecular changes in the binding mechanism that would facilitate such a transition. We previously showed that the interaction between two intrinsically disordered domains, NCBD and CID, likely emerged in an ancestral deuterostome organism as a low-affinity interaction that subsequently evolved into a higher-affinity interaction before the radiation of modern vertebrate groups. Here we map native contacts in the transition states of the low-affinity ancestral and high-affinity human NCBD/CID interactions. We show that the coupled binding and folding mechanism is overall similar but with a higher degree of native hydrophobic contact formation in the transition state of the ancestral complex and more heterogeneous transient interactions, including electrostatic pairings, and an increased disorder for the human complex. Adaptation to new binding partners may be facilitated by this ability to exploit multiple alternative transient interactions while retaining the overall binding and folding pathway.     

HIV Prevention in Care and Treatment Settings: Baseline Risk Behaviors among HIV Patients in Kenya,Namibia, and Tanzania

HIV care and treatment settings provide an opportunity to reach people living with HIV/AIDS (PLHIV) with prevention messages and services. Population-based surveys in sub-Saharan Africa have identified HIV risk behaviors among PLHIV, yet data are limited regarding HIV risk behaviors of PLHIV in clinical care. This paper describes the baseline sociodemographic, HIV transmission risk behaviors, and clinical data of a study evaluating an HIV prevention intervention package for HIV care and treatment clinics in Africa. The study was a longitudinal group-randomized trial in 9 intervention clinics and 9 comparison clinics in Kenya, Namibia, and Tanzania (N = 3538). Baseline participants were mostly female, married, had less than a primary education, and were relatively recently diagnosed with HIV. Fifty-two percent of participants had a partner of negative or unknown status, 24% were not using condoms consistently, and 11% reported STI symptoms in the last 6 months. There were differences in demographic and HIV transmission risk variables by country, indicating the need to consider local context in designing studies and using caution when generalizing findings across African countries. Baseline data from this study indicate that participants were often engaging in HIV transmission risk behaviors, which supports the need for prevention with PLHIV (PwP).

Trial Registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT01256463","term_id":"NCT01256463"}}NCT01256463     

FMNL2 drives actin-based protrusion and migration downstream of Cdc42

Cell migration entails protrusion of lamellipodia, densely packed networks of actin filaments at the cell front. Filaments are generated by nucleation, likely mediated by Arp2/3 complex and its activator Scar/WAVE. It is unclear whether formins contribute to lamellipodial actin filament nucleation or serve as elongators of filaments nucleated by Arp2/3 complex. Here we show that the Diaphanous-related formin FMNL2, also known as FRL3 or FHOD2, accumulates at lamellipodia and filopodia tips. FMNL2 is cotranslationally modified by myristoylation and regulated by interaction with the Rho-guanosine triphosphatase Cdc42. Abolition of myristoylation or Cdc42 binding interferes with proper FMNL2 activation, constituting an essential prerequisite for subcellular targeting. In vitro, C-terminal FMNL2 drives elongation rather than nucleation of actin filaments in the presence of profilin. In addition, filament ends generated by Arp2/3-mediated branching are captured and efficiently elongated by the formin. Consistent with these biochemical properties, RNAi-mediated silencing of FMNL2 expression decreases the rate of lamellipodia protrusion and, accordingly, the efficiency of cell migration. Our data establish that the FMNL subfamily member FMNL2 is a novel elongation factor of actin filaments that constitutes the first Cdc42 effector promoting cell migration and actin polymerization at the tips of lamellipodia.