Distribution survey of Cyanobacteria in three Greek caves of Peloponnese

Caves and hypogean environments host various phototrophic microorganisms, with Cyanobacteria constituting the major group. The spatial and temporal distribution of Cyanobacteria (156 taxa in total) from three Greek caves, located in the limestone arc of Peloponnese and differing in morphology, was studied. The community patterns in different ecological niches were analyzed in relation to environmental parameters (Photosynthetically Active Radiation, Temperature, and Relative Humidity). Cyanobacterial communities were found to thrive in patchy biofilms and showed known protective strategies against desiccation and irradiation. The nMDS analysis of the cumulative seasonal samples per sampling site showed no general pattern of distribution, with a clear differentiation of cyanobacterial communities among the three caves. Only in the typical cave ‘Kastria’, cyanobacterial taxa showed growth habits in accordance with the gradient of light from entrance inwards

Interplay between r- and K-strategists leads to phytoplankton underyielding under pulsed resource supply

Fluctuations in nutrient ratios over seasonal scales in aquatic ecosystems can result in overyielding, a condition arising when complementary life-history traits of coexisting phytoplankton species enables more complete use of resources. However, when nutrient concentrations fluctuate under short-period pulsed resource supply, the role of complementarity is less understood. We explore this using the framework of Resource Saturation Limitation Theory (r-strategists vs. K-strategists) to interpret findings from laboratory experiments. For these experiments, we isolated dominant species from a natural assemblage, stabilized to a state of coexistence in the laboratory and determined life-history traits for each species, important to categorize its competition strategy. Then, using monocultures we determined maximum biomass density under pulsed resource supply. These same conditions of resource supply were used with polycultures comprised of combinations of the isolated species. Our focal species were consistent of either r- or K-strategies and the biomass production achieved in monocultures depended on their efficiency to convert resources to biomass. For these species, the K-strategists were less efficient resource users. This affected biomass production in polycultures, which were characteristic of underyielding. In polycultures, K-strategists sequestered more resources than the r-strategists. This likely occurred because the intermittent periods of nutrient limitation that would have occurred just prior to the next nutrient supply pulse would have favored the K-strategists, leading to overall less efficient use of resources by the polyculture. This study provides evidence that fluctuation in resource concentrations resulting from pulsed resource supplies in aquatic ecosystems can result in phytoplankton assemblages' underyielding

Everything is not everywhere: can marine compartments shape phytoplankton assemblages?

The idea that ‘everything is everywhere, but the environment selects' has been seminal in microbial biogeography, and marine phytoplankton is one of the prototypical groups used to illustrate this. The typical argument has been that phytoplankton is ubiquitous, but that distinct assemblages form under environmental selection. It is well established that phytoplankton assemblages vary considerably between coastal ecosystems. However, the relative roles of compartmentalization of regional seas and site-specific environmental conditions in shaping assemblage structures have not been specifically examined. We collected data from coastal embayments that fall within two different water compartments within the same regional sea and are characterized by highly localized environmental pressures. We used principal coordinates of neighbour matrices (PCNM) and asymmetric eigenvector maps (AEM) models to partition the effects that spatial structures, environmental conditions and their overlap had on the variation in assemblage composition. Our models explained a high percentage of variation in assemblage composition (59–65%) and showed that spatial structure consistent with marine compartmentalization played a more important role than local environmental conditions. At least during the study period, surface currents connecting sites within the two compartments failed to generate sufficient dispersal to offset the impact of differences due to compartmentalization. In other words, our findings suggest that, even for a prototypical cosmopolitan group, everything is not everywhere

Nitrogen as the main driver of benthic diatom composition and diversity in oligotrophic coastal systems

Phytoplankton is the main indicator group for eutrophication in coastal ecosystems, however its high dispersal potential does not enable the assessment of localized effects of coastal nutrient enrichment. Benthic diatoms are sessile microalgae associated with sandy substrates and have the potential to reflect more localized pollution impacts. Although benthic diatoms are widely used bioindicators in freshwater systems, they have rarely been used for assessing the eutrophication status of oligotrophic environments such as the eastern Mediterranean Sea. In the present study, we assess the efficiency of benthic diatoms as bioindicators of nutrient enrichment in oligotrophic coastal systems, by investigating the effect of different physicochemical conditions and nutrient concentrations on the assemblage composition, diversity and individual species populations. To do this, we sampled along a eutrophication gradient formed by anthropogenic nutrient inputs from a metropolitan area. The main driver of assemblage composition, diversity and biomass of diatoms was nitrogen concentration and its temporal and spatial changes. Nitrogen loadings were positively correlated with increased biomass of Cocconeis spp. and negatively correlated with Mastogloia spp. Our findings suggest that in coastal ecosystems of oligotrophic marine ecoregions, benthic diatom assemblage structure and specific taxonomic groups can be reliable predictors of coastal eutrophication offering higher spatial resolution compared to phytoplankton

Resilience of coastal marine metacommunities to increasing hydraulic connectivity

Coastal ecosystems typically comprise water patches of different salinities that host distinct communities of species. This salinity-driven heterogeneity can be vulnerable to changes in between-patch connectivity due to altered water levels. Despite the potentially grave implications for higher trophic levels, the impact of increased connectivity on phytoplankton assemblages is largely unknown. Here, we investigate the effect of increasing connectivity on assemblage resistance and recovery along a strong salinity gradient of 40-61 psu. We deployed mesocosms within a saltwork system and hydraulically connected enclosures of 3 salinity levels at 3 connectivity levels. We hypothesized that assemblage composition of high salinity would be more resistant to press invasions during connectivity; however, high connectivity would decrease compositional resistance and recovery irrespective of salinity. We found that high salinity assemblages were indeed more resistant and recovered better at low connectivity. High connectivity also impacted the function of high salinity assemblages by replacing large diatoms with small flagellates, preventing assemblage recovery. Counterintuitively, low salinity assemblage composition recovered better at higher connectivity, and this was attributed to rescue effects of rarer and stenohaline species within a more variable nutrient environment. Here, we show that normal (i.e. marine) salinity assemblages are vulnerable to anticipated changes in coastal hydrological regimes whereas higher salinity assemblages are impacted above a certain connectivity threshold

Meloneis Gen. Nov., a New Epipsammic Genus of Rhaphoneidaceae (Bacillariophyceae)

The diatom family Rhaphoneidaceae is characterized by high generic diversity and low species diversity with most genera known to have long stratigraphic ranges. The genera within this family are neritic marine, and mostly epipsammic. A new modern and epipsammic genus, Meloneis gen. nov., is described herein and is compared to all genera within Rhaphoneidaceae and especially to Rhaphoneis Ehrenberg s.l. Within Meloneis three new species and one variety are distinguished and described herein: M. mimallis sp. nov., M. mimallis var. zephyria var. nov., M. akytos sp. nov., and M. gorgis sp. nov

Rare mutations predisposing to familial adenomatous polyposis in Greek FAP patients

BACKGROUND: Familial Adenomatous Polyposis (FAP) is caused by germline mutations in the APC (Adenomatous Polyposis Coli) gene. The vast majority of APC mutations are point mutations or small insertions / deletions which lead to truncated protein products. Splicing mutations or gross genomic rearrangements are less common inactivating events of the APC gene. METHODS: In the current study genomic DNA or RNA from ten unrelated FAP suspected patients was examined for germline mutations in the APC gene. Family history and phenotype were used in order to select the patients. Methods used for testing were dHPLC (denaturing High Performance Liquid Chromatography), sequencing, MLPA (Multiplex Ligation – dependent Probe Amplification), Karyotyping, FISH (Fluorescence In Situ Hybridization) and RT-PCR (Reverse Transcription – Polymerase Chain Reaction). RESULTS: A 250 Kbp deletion in the APC gene starting from intron 5 and extending beyond exon 15 was identified in one patient. A substitution of the +5 conserved nucleotide at the splice donor site of intron 9 in the APC gene was shown to produce frameshift and inefficient exon skipping in a second patient. Four frameshift mutations (1577insT, 1973delAG, 3180delAAAA, 3212delA) and a nonsense mutation (C1690T) were identified in the rest of the patients. CONCLUSION: Screening for APC mutations in FAP patients should include testing for splicing defects and gross genomic alterations

hMSH2 is the most commonly mutated MMR gene in a cohort of Greek HNPCC patients

Germline mutations in genes encoding proteins involved in DNA mismatch repair are responsible for the autosomal dominantly inherited cancer predisposition syndrome hereditary nonpolyposis colorectal cancer (HNPCC). We describe here analysis of hMLH1 and hMSH2 in nine Greek families referred to our centre for HNPCC. A unique disease-causing mutation has been identified in seven out of nine (78%) families. The types of mutations identified are nonsense (five out of seven) (hMLH1: E557X, R226X; hMSH2: Q158X, R359X and R711X), a 2 bp deletion (hMSH2 1704_1705delAG) and a 2.2 kb Alu-mediated deletion encompassing exon 3 of the hMSH2 gene. The majority of mutations identified in this cohort are found in hMSH2 (77.7%). Furthermore, four of the mutations identified are novel. Finally, a number of novel benign variations were observed in both genes. This is the first report of HNPCC analysis in the Greek population, further underscoring the differences observed in the various geographic populations