Characterization of Microbial Mats from a Desert Wadi Ecosystem in the Sultanate of Oman

Desert wadis are widespread in the Arabian Peninsula and play a vital role in the ecology of the region; nevertheless, these ecosystems are among the least studied. Various types of microbial mats are predominant in wadis, but information on their bacterial diversity and spatial distribution is very scarce. We investigated bacterial diversity, pigments and lipid composition of ten mats located at the down-, mid- and upstream of a desert wadi in Oman. Direct microscopy revealed the existence of different unicellular and filamentous cyanobacteria, with the dominance of the heterocystous genera Calothrix and Scytonema. The majority of MiSeq 16S rRNA sequences (44-76%) were affiliated to Cyanobacteria and Proteobacteria. While Alphaproteobacteria was the most dominant proteobacterial class (10 to 48% of total sequences), Gamma- and Deltaproteobacteria were subdominant. Cluster analysis showed that the mats’ bacterial communities at the different locations along the wadi were different and shared less than 60% of their operational taxonomic units (OTUs). Chlorophyll a and scytonemin were the most predominant pigments in all mats. Different saturated, branched and mono- and poly-unsaturated fatty acids were detected in all mats, with C₁₆ and C₁₈ compounds as most dominant. The detected pigments and fatty acids indicate a major role of cyanobacteria in the wadi mats and the adaptation of microorganisms therein to the harsh wadi environment. Detection of diadinoxanthin and fucoxanthin confirmed the presence of diatoms. We conclude that microbial mats are important elements in wadi ecosystems and exist in a great variety of structure and community composition.     

Stable assembly of PsaE into cyanobacterial photosynthetic membranes is dependent on the presence of other accessory subunits of photosystem I

We studied assembly of the PsaE subunit of photosystem I into photosynthetic membranes of cyanobacterial mutant strains that lack specific photosystem I subunits. Radiolabeled PsaE was incubated with photosynthetic membranes, and their binding and assembly were assayed by resistance to removal by chaotropic agents and proteolytic digestion. PsaE incorporated into the wild-type membranes was resistant to these treatments. In the absence of PsaD, it was resistant to proteolytic digestion, but was removed by NaBr. When the membranes were isolated from a mutant strain in which the psaF and psaJ genes have been inactivated, PsaE assembled in vitro could not be removed. PsaE could associate with the membranes of the strain DF in which the psaD, psaJ and psaF genes have been mutated. However, the radiolabeled PsaE associated with these membranes was removed both by the proteolytic as well as by the chaotropic agents. Characterization of PsaE present in vivo revealed similar results. These observations suggest that PsaD and PsaF/J may interact with PsaE and stabilize it in the photosystem I complex.     

Growth characteristics of the diatoms Pseudonitzschia pungens and P. fraudulenta exposed to ultraviolet radiation

Interest in the biology of planktonic, chain-forming Pseudonitzschia species has grown recently after the discovery of toxin production in Pseudonitzschia pungens and related taxa, following the outbreak of shellfish toxicity in Canada in 1987. As part of a broader study on the effects of enhanced ultraviolet light on the growth of bloom-forming phytoplankton, we have examined the growth rates and production of the toxin domoic acid and two additional chemicals [bacillariolides I and II] by Pseudonitzschia pungens varieties and Pseudonitzschia fraudulenta from Narragansett Bay, Rhode Island. Growth of P. fraudulenta is significantly inhibited by enhanced UV, P. pungens var. pungens shows slight inhibition, and P. pungens var. multiseries is unaffected. Production of bacillariolides I and II by P. pungens var. multiseries is similar in enhanced and deleted UV light. Tolerance of UV light by P. pungens var. multiseries appears to be acquired, and persistent. If ambient UV light continues to increase as a result of global ozone depletion, one may expect UV-resistant taxa such as P. pungens var. multiseries to become more prominent in coastal phytoplankton communities.     

Can ants equal honeybees as effective pollinators of the energy crop Jatropha curcas L. under Mediterranean conditions?

Jatropha curcas L. is the subject of many research and breeding programs concerned with its potential as an oil crop for biodiesel production. Despite an increasing amount of information regarding this relatively new crop, pollination requirements of this plant are largely neglected. The aim of the study was to evaluate the relative significance of ants and honeybees as potential pollinators of J. curcas grown under Mediterranean conditions. Jatropha curcas plants bloomed throughout the summer and fall, peaking twice, in early summer and late fall. During this period, the plants were visited by 70 species of insects representing 45 families from seven orders, with most species rarely being observed. Ants and Honeybees were the most common species, accounting for >95% of all flower visits. The foraging behavior of the honeybees followed the pattern of bloom phenology, especially during the summer, and mostly promoted cross‐pollination. Ants on the other hand, mostly promoted self pollination showing no such correlative behavior, reacting often too late to nectar availability, and were highly susceptible to climatic changes. Pollinator exclusion treatments revealed that during summer, fruit and seed sets, as well as seed size and oil and protein contents, were relatively similar for ant and bee‐pollinated flowers. During fall, however, reproductive success of bee‐pollinated flowers was relatively high (66%), while fruit set of ant‐pollinated flowers was significantly reduced from 71 to 11%. In conclusion, while both groups are equal in their pollination effectiveness in the summer, during the fall the honeybees are almost the sole pollinators of the plant. Based on bloom phenology and pollination activity data, the honeybees are responsible for the pollination of more than 80% of the annual reproductive potential of J. curcas, under Mediterranean conditions.     

Effects of the novel allelochemical ethyl 2-methylacetoacetate from the reed (<Emphasis Type="Italic">Phragmitis australis</Emphasis> Trin) on the growth of several common species of green algae

Bioassays were performed to investigate the effects of the novel allelochemical, ethyl 2-methylacetoacetate (EMA), isolated from the reed (Phragmitis australis) on the growth of three common species of algae; Scenedesmus obliquus, Selenastrum capricornutum and Chlamydomonas reinhardtii. The results demonstrated that EMA has three quite different types of effect on these three species of algae. The growth of S. capricornutum was significantly inhibited by EMA during the whole cultivation period. The EC₅₀ values of EMA on S. capricornutum was 0.6 mg L⁻¹(7 days). However, the inhibitory effect of EMA on S. obliquus was apparent during the first 4 days of batch cultivation and then the inhibitory effect disappeared, and a stimulating effect was observed instead. The EC₅₀ value of EMA on S. obliquus was 0.43 mg L⁻¹(4 days). In addition, following the addition of EMA, the cells of S. obliquus and S. capricornutum became significantly larger than the normal untreated one and the algal cells changed morphologically. The microstructure of the algal cells was disrupted by the addition of EMA. There was no significant inhibition of the growth of C. reinhardtii by EMA, but cell motility was affected.     

Winter blooms of centric diatoms in the River Danube and in its side-arms near Budapest (Hungary)

Although the phytoplankton in large eutrophic rivers is often abundant, data on winter populations are scarce. Phytoplankton has been sampled since 1979 in the main arm of the River Danube at Göd (20 km north from Budapest), and also from two side-arms, upstream and downstream of Budapest. Analysis of winter samples has shown high population densities of phytoplankton blooms on several occasions. In general centric diatoms (20 taxa determined) were abundant and dominant during the blooms. The most abundant taxon in November was Stephanodiscus hantzschii f. tenuis, and in February S. minutulus. The most important factors in forming winter blooms of Centrales are rich nutrient supply, slow current speed and high transparency.Massive phytoplankton blooms occurred several times between November and March in the small side-arm at Göd. In the large side-arm downstream of Budapest (Soroksári-Dung) large blooms of centric diatoms were found in winter (often under ice, which was covered by snow in many cases). Here S. hantzschii f. tenuis and S. minutulus were the most abundant species.     

The effects of temperature and nutrients on the growth and dynamics of toxic and non-toxic strains of Microcystis during cyanobacteria blooms

In temperate latitudes, toxic cyanobacteria blooms often occur in eutrophied ecosystems during warm months. Many common bloom-forming cyanobacteria have toxic and non-toxic strains which co-occur and are visually indistinguishable but can be quantified molecularly. Toxic Microcystis cells possess a suite of microcystin synthesis genes (mcyA–mcyJ), while non-toxic strains do not. For this study, we assessed the temporal dynamics of toxic and non-toxic strains of Microcystis by quantifying the microcystin synthetase gene (mcyD) and the small subunit ribosomal RNA gene, 16S (an indicator of total Microcystis), from samples collected from four lakes across the Northeast US over a two-year period. Nutrient concentrations and water quality were measured and experiments were conducted which examined the effects of elevated levels of temperatures (+4 °C), nitrogen, and phosphorus on the growth rates of toxic and non-toxic strains of Microcystis. During the study, toxic Microcystis cells comprised between 12% and 100% of the total Microcystis population in Lake Ronkonkoma, NY, and between 0.01% and 6% in three other systems. In all lakes, molecular quantification of toxic (mcyD-possessing) Microcystis was a better predictor of in situ microcystin levels than total cyanobacteria, total Microcystis, chlorophyll a, or other factors, being significantly correlated with the toxin in every lake studied. Experimentally enhanced temperatures yielded significantly increased growth rates of toxic Microcystis in 83% of experiments conducted, but did so for non-toxic Microcystis in only 33% of experiments, suggesting that elevated temperatures yield more toxic Microcystis cells and/or cells with more mcyD copies per cell, with either scenario potentially yielding more toxic blooms. Furthermore, concurrent increases in temperature and P concentrations yielded the highest growth rates of toxic Microcystis cells in most experiments suggesting that future eutrophication and climatic warming may additively promote the growth of toxic, rather than non-toxic, populations of Microcystis, leading to blooms with higher microcystin content.     

Solution structure of a cyanobacterial phytochrome GAF domain in the red-light-absorbing ground state

The unique photochromic absorption behavior of phytochromes (Phys) depends on numerous reversible interactions between the bilin chromophore and the associated polypeptide. To help define these dynamic interactions, we determined by NMR spectroscopy the first solution structure of the chromophore-binding cGMP phosphodiesterase/adenylcyclase/FhlA (GAF) domain from a cyanobacterial Phy assembled with phycocyanobilin (PCB). The three-dimensional NMR structure of Synechococcus OS-B′ cyanobacterial Phy 1 in the red-light-absorbing state of Phy (Pr) revealed that PCB is bound to Cys138 of the GAF domain via the A-ring ethylidene side chain and is buried within the GAF domain in a ZZZsyn,syn,anti configuration. The D ring of the chromophore sits within a hydrophobic pocket and is tilted by approximately 80° relative to the B/C rings by contacts with Lys52 and His169. The solution structure revealed remarkable flexibility for PCB and several adjacent amino acids, indicating that the Pr chromophore has more freedom in the binding pocket than anticipated. The propionic acid side chains of rings B and C and Arg101 and Arg133 nearby are especially mobile and can assume several distinct and energetically favorable conformations. Mutagenic studies on these arginines, which are conserved within the Phy superfamily, revealed that they have opposing roles, with Arg101 and Arg133 helping stabilize and destabilize the far-red-light-absorbing state of Phy (Pfr), respectively. Given the fact that the Synechococcus OS-B′ GAF domain can, by itself, complete the Pr → Pfr photocycle, it should now be possible to determine the solution structure of the Pfr chromophore and surrounding pocket using this Pr structure as a framework.     

Genome sequence of the moderately thermophilic sulfur-reducing bacterium Thermanaerovibrio velox type strain (Z-9701T) and emended description of the genus Thermanaerovibrio

Thermanaerovibrio velox Zavarzina et al. 2000 is a member of the Synergistaceae, a family in the phylum Synergistetes that is already well-characterized at the genome level. Members of this phylum were described as Gram-negative staining anaerobic bacteria with a rod/vibrioid cell shape and possessing an atypical outer cell envelope. They inhabit a large variety of anaerobic environments including soil, oil wells, wastewater treatment plants and animal gastrointestinal tracts. They are also found to be linked to sites of human diseases such as cysts, abscesses, and areas of periodontal disease. The moderately thermophilic and organotrophic T. velox shares most of its morphologic and physiologic features with the closely related species, T. acidaminovorans. In addition to Su883^T, the type strain of T. acidaminovorans, stain Z-9701^T is the second type strain in the genus Thermanaerovibrio to have its genome sequence published. Here we describe the features of this organism, together with the non-contiguous genome sequence and annotation. The 1,880,838 bp long chromosome (non-contiguous finished sequence) with its 1,751 protein-coding and 59 RNA genes is a part of the Genomic Encyclopedia of Bacteria and Archaea project.     

甲藻的异养营养型

综述了甲藻的异养类型。目前已知异养营养型在甲藻中广泛存在,只有很少几种甲藻营严格自养营养方式。有近一半的甲藻物种是没有色素体的,还有很多甲藻即使具有色素体也会有异养营养需求,称为兼养营养类型。这些兼养类群不一定主要以有机物作为其获取碳的来源,而仅仅是补充一些生长必需的有机物如维生素、生物素等。兼养类群以渗透营养和腐食营养方式进行,同时也可以寄生方式和共生方式进行兼养生活。无色素体的甲藻以有机物作为碳的唯一来源,仅仅依靠异养方式生存,属于严格异养营养方式,又称有机营养型。它们是甲藻异养营养型的主体,其主要类型有寄生、渗透营养和吞噬营养。由于吞噬营养是甲藻异养的主要类型,因此论述了3种吞噬营养型:吞噬营养方式、捕食茎营养方式和捕食笼营养方式。吞噬营养方式在无甲类和具甲类甲藻中都有存在,主要通过甲藻细胞的纵沟或底部对猎物进行吞噬,也有研究发现吞噬部位为顶孔或片间带。捕食茎营养方式是通过捕食茎刺穿猎物细胞膜并吸食其细胞质来获取营养,在异养甲藻中也较常见。捕食笼营养方式只在原多甲藻属(Protoperidinium)和翼藻属(Diplopsalis)里发现,是甲藻通过鞭毛孔分泌细胞质到胞外形成捕食笼将猎物包裹并进行消化来摄食的。甲藻摄食对象尺寸范围变化较大,小至几微米,大至几百微米。有些甲藻具有摄食选择性,通过感应猎物释放的化学物质来判断猎物的位置并进行摄食,摄食完成后由于体积的增加经常会发生细胞分裂和蜕鞘。对于甲藻异养的其他形式如拦截摄食营养方式、伪足摄食营养方式、口足摄食营养方式、触手摄食营养方式等只作简单介绍。还就甲藻异养的研究方法、其生态学意义和进化学意义进行简要论述,并对相关研究进行展望。