Abundance and distribution of toxic Alexandrium tamarense resting cysts in the sediments of the Chukchi Sea and the eastern Bering Sea

Abundance and distribution of the toxic dinoflagellate Alexandrium tamarense species complex resting cyst were investigated in the eastern Bering Sea and the Chukchi Sea for the first time. Sediment samples (top 0–3 cm depth) were collected from the continental shelf of the eastern Bering Sea (17 stations) and the Chukchi Sea (13 stations) together with a long core sample (top 0–21 cm depth) from one station in the Chukchi Sea during 2009–2012. The cysts were enumerated using the primuline staining method. Species identification of the cysts was carried out with multiplex PCR assay and the plate morphology of vegetative cells germinated from cysts in the both areas. Alexandrium cysts were widely detected in the both areas, ranging from not detected (<1 cysts cm⁻³) to 835 cysts cm⁻³ wet sediment in the eastern Bering Sea and from not detected (<1 cysts cm⁻³) to 10,600 cysts cm⁻³ in the Chukchi Sea, and all isolated cysts were genetically and morphologically identified as the North American clade A. tamarense. Their cysts were mainly distributed in the shallow continental shelf where the water depth was less than 100 m in both areas. The cysts were detected from the deep layer (18–21 cm depth of sediment core) of the long core sample. The present study confirmed the abundant existence of A. tamarense with wide range of distribution in these areas. This fact suggests that A. tamarense vegetative cells have appeared in the water column in the both areas. Furthermore, these abundant cyst depositions indicate that this species originally distributed in the Arctic and subarctic regions and well adapted to the environments in the marginal ice zone.     

Abundance and distribution of Ulva microscopic propagules associated with a green tide in the southern coast of the Yellow Sea

The presence of Ulva microscopic propagules may play an important role in the rapid development of high-biomass blooms of green algae in the Yellow Sea. Six cruises were conducted, to determine the abundance and distribution of Ulva microscopic propagules associated with a green tide that developed in the southern coastal waters of the Yellow Sea from April to August, 2012. Results indicated that Ulva microscopic propagules were widespread in these waters, with the highest density being up to 4800 ind. L⁻¹, prior to the appearance of the green tide in April. High densities were also widely distributed along the coast during May and June, after the appearance of the floating green tide. The quantity of Ulva microscopic propagules significantly decreased when the floating green tide declined in July, reaching densities of up to 162 ind. L⁻¹, following the disappearance of the floating green tide in August. Quantitative studies on the distribution patterns of Ulva microscopic propagules along the southern coast of the Yellow Sea indicated a significant correlation between density and salinity, turbidity and nutrient concentrations. Temporal and geographical distribution patterns of Ulva microscopic propagules were also significantly affected by the presence of a large biomass of attached, or floating, Ulva species algae.     

Pulleniatina Minimum Events in the Andaman Sea (NE Indian Ocean): Implications for winter monsoon and thermocline changes

The late Quaternary record of Pulleniatina obliquiloculata was investigated from two well dated sediment cores from the Andaman Sea (NE Indian Ocean) to examine its paleoceanographic significance and the presence of the Pulleniatina Minimum Events (PME) in the western North Pacific. As in the Pacific, our study shows that PMEs exist in the Indian Ocean albeit with a lower intensity. The Holocene PME occurs between 4.5 and 3.0 cal ka BP with a considerable reduction in P. obliquiloculata abundance, and which matches well with the Pacific records influenced by the Kuroshio Current. Additionally, two significant minimum events of P. obliquiloculata are also seen during the Younger Dryas (YD) and late Last Glacial Maximum (LGM, 20–18 cal ka BP). Overall, the PMEs of the Andaman Sea are not current driven events like in the western Pacific margin either by the weakening of the Kuroshio Current or reduced winter SSTs. The PMEs of the Andaman Sea are characterised by lower abundances of thermocline species indicating the increased depth of the thermocline (DOT) and reduced winter SSTs mainly during the minimum events of the YD and late LGM. The high SSTs during the Holocene PME make this event a mystery. However, the presence of PMEs in the Andaman Sea suggests that these events are not confined to areas influenced by the Kuroshio Current but may be responding to a broad scale oceanographic–climatic process or mechanism which needs to be explored with a detailed study.     

Isolation,improvement and characterization of an ammonium excreting mutant strain of the heterocytous cyanobacterium,Anabaena variabilis PCC 7937

Besides potential applications in the agriculture field as natural nitrogen fertilizer, N₂-fixing cyanobacteria have recently gained some attentions for new applications linked to the potential production of biologically active molecules or biohydrogen. Ammonium bioproduction is also gaining attention with the potential use of microalgae in biofuels production and the concerns about the increasing needs for nitrogen substrates. This study has investigated some phenotypic traits linked to biomass production and ammonium release in multicellular cyanobacteria, Anabaena variabilis PCC 7937. It confirms that this wild-type strain has no natural ability for ammonium excretion under diazotrophic conditions. A mutant strain, A. variabilis PCC 7937-C9, was obtained after double random mutagenesis treatments with ethyl methane–sulfonate and screening in batch cultures for resistance to the effect of a glutamine synthetase inhibitor, l-methionine-d,l-sulfoximine (MSX). Although significantly characterized by shorter cell filaments, the growth parameters in photobioreactors of the mutant strain cultures were in the same range of values than those of the wild type. In the presence of MSX this strain was shown to produce extracellular ammonium, with specific rates up to 4.9 μmol NH₄⁺ mg Chl a⁻¹ h⁻¹. The efficiency of this strain, estimated by its specific rate of ammonium excretion, was shown to be improved after consecutive batch cultures with increasing concentrations of MSX. Such mutant strains are of potential use for investigating ways to improve extracellular ammonium bioproduction.     

The rise of toxic benthic Phormidium proliferations: A review of their taxonomy,distribution, toxin content and factors regulating prevalence and increased severity

There has been a marked increase in the distribution, intensity and frequency of proliferations of some species of the benthic mat-forming, toxin-producing genus Phormidium in rivers globally over the last decade. This review summarises current knowledge on their taxonomy, distribution, toxin content, environmental drivers of proliferations, and monitoring and management strategies in New Zealand. Although toxic Phormidium proliferation occurs in rivers worldwide little is known about these factors in most countries. Proliferations, defined as >20% cover of a riverbed, have been identified in 103 rivers across New Zealand. Morphological and molecular data indicate the main species responsible is Phormidium autumnale. In New Zealand Phormidium produces anatoxins (anatoxin-a, homoanatoxin-a, dihydroanatoxin-a, and dihydrohomoanatoxin-a) and these were detected in 67% of 771 samples from 40 rivers. The highest concentration measured was 712 mg kg⁻¹ dried weight (Oreti River, Southland), with considerable spatial and temporal variability in anatoxin concentrations between and within rivers. A synthesis of field based studies suggests that Phormidium proliferations are most likely when there is some enrichment of dissolved inorganic nitrogen but when water-column dissolved reactive phosphorus is less than 0.01 mg L⁻¹. Once established Phormidium-dominated mats trap sediment and internal mat biogeochemistry can mobilise sediment-bound phosphorus, which is then available for growth. Removal of Phormidium-dominated mats is primarily due to shear stress and substrate disturbance, although there is also evidence for autogenic detachment. A combination of factors including; changes to riparian margins, increased nitrate and fine sediment loads, and alterations in flow regimes are likely to have contributed to the rise in Phormidium proliferations.     

The prevalence of benthic dinoflagellates associated with ciguatera fish poisoning in the central Red Sea

This study confirms the presence of the toxigenic benthic dinoflagellates Gambierdiscus belizeanus and Ostreopsis spp. in the central Red Sea. To our knowledge, this is also the first report of these taxa in coastal waters of Saudi Arabia, indicating the potential occurrence of ciguatera fish poisoning (CFP) in that region. During field investigations carried out in 2012 and 2013, a total of 100 Turbinaria and Halimeda macroalgae samples were collected from coral reefs off the Saudi Arabian coast and examined for the presence of Gambierdiscus and Ostreopsis, two toxigenic dinoflagellate genera commonly observed in coral reef communities around the world. Both Gambierdiscus and Ostreopsis spp. were observed at low densities (<200 cells g⁻¹ wet weight algae). Cell densities of Ostreopsis spp. were significantly higher than Gambierdiscus spp. at most of the sampling sites, and abundances of both genera were negatively correlated with seawater salinity. To assess the potential for ciguatoxicity in this region, several Gambierdiscus isolates were established in culture and examined for species identity and toxicity. All isolates were morphologically and molecularly identified as Gambierdiscus belizeanus. Toxicity analysis of two isolates using the mouse neuroblastoma cell-based assay for ciguatoxins (CTX) confirmed G. belizeanus as a CTX producer, with a maximum toxin content of 6.50 ± 1.14 × 10⁻⁵ pg P-CTX-1 eq. cell⁻¹. Compared to Gambierdiscus isolates from other locations, these were low toxicity strains. The low Gambierdiscus densities observed along with their comparatively low toxin contents may explain why CFP is unidentified and unreported in this region. Nevertheless, the presence of these potentially toxigenic dinoflagellate species at multiple sites in the central Red Sea warrants future study on their possible effects on marine food webs and human health in this region.     

Stratigraphic distribution of the radiolarian Spongodiscus biconcavus Haeckel at IODP Site U1340 in the Bering Sea and its paleoceanographic significance

The temporal and spatial distributions of the radiolarian species Spongodiscus biconcavus Haeckel are investigated to understand the paleoceanographic evolution of the Bering Sea region during the last 4.3 Myr based on extensive study of samples collected at Site U1340 during the IODP Expedition 323. The biostratigraphic resolution for the region is also improved by multidisciplinary studies of radiolarians, diatoms, dinoflagellates, ebridians, and silicoflagellates. The results demonstrate that the abundance variation of S. biconcavus during the last 4.3 Myr is closely related to global climate changes, and the species can be used as a warm water and climate proxy in the Bering Sea. Based on the downhole profiles of S. biconcavus and other parameters, we conclude that the southern Bering Sea was associated with a warm water mass prior to 3.147 Ma but it gradually cooled thereafter. From 2.793 Ma to 0.889 Ma, a cold water mass and sea-ice predominated in the Bering Sea, in response to the early Northern Hemisphere glaciation (NHG). Furthermore, the climate suddenly became much cooler post 0.889 Ma. Nevertheless, a reversal of this cooling trend occurred after the Mid-Pleistocene Climatic Transition (∼1.2 Ma), marked by reoccurrence of warm water and reduced sea-ice in the Bering Sea until the final retreat of warm water mass from the Bering Sea after 0.239 Ma. These processes are correlated with biogeographic expansion and retreat of warm water planktonic species.     

Genetic structure of Octopus vulgaris (Cephalopoda,Octopodidae) in the central Mediterranean Sea inferred from the mitochondrial COIII gene

The polymorphism of the mitochondrial gene cytochrome oxidase III was studied in the Mediterranean octopus, Octopus vulgaris Cuvier, 1797. A total of 202 specimens from seven sampling sites were analysed with the aim of elucidating patterns of genetic structure in the central Mediterranean Sea and to give an insight into the phylogeny of the Octopus genus. Phylogenetic analyses showed that individuals from the central Mediterranean belong to the O. vulgaris species whose limits should nevertheless be clarified. Concerning genetic structure, two high-frequency haplotypes were present in all locations. The overall genetic divergence (Φ_ST = 0.05, P < 0.05) indicated a significant genetic structuring in the study area and an AMOVA highlighted a significant break between western and eastern Mediterranean basins (Φ_CT = 0.094, P < 0.05). Possible explanations for the observed patterns of genetic structuring are discussed with reference to their relevance for fisheries management.     

Populations of the red tide forming dinoflagellate Noctiluca scintillans (Macartney): A comparison between the Black Sea and the northern Adriatic Sea

Populations of Noctiluca scintillans (hereafter Noctiluca) were compared from two regions: the northeastern-central Black Sea and the northern Adriatic Sea. In both seas samples were collected in near-shore waters 2–3 times per month during 2004–2012. For analysis of feeding activities and seasonal dynamics additional cruise data on the open waters of the Black Sea were used. Comparison between the two populations shows similarity in size structure with two classes 401–500 μm and 501–600 μm being the most numerous. Seasonal changes in cell abundance in both seas demonstrated a regular annual maximum with the peak period of high abundances in May–June with additional sporadic peaks in other seasons. In spring the average number of food vacuoles in the cell (1.78) and the proportion of feeding cells in populations (79%) in the Adriatic Sea were similar to those in the Black Sea (1.58 and 76%). In September–October, these parameters were lower both in the Adriatic Sea (0.69 and 49%) and in the Black Sea (1.46 and 65%) demonstrating that Noctiluca was better provided with food in spring. Among biotic parameters (wet phytoplankton biomass, chlorophyll biomass and zooplankton species) only the concentration of the eggs of Calanus euxinus was significantly positively correlated with abundance of Noctiluca. The possible effect of a high concentration of copepod eggs on the growth of Noctiluca in the peak period is discussed. An obvious negative relationship was observed between Noctiluca cell numbers in the peak period and wind velocity in both seas. The most significant negative correlation was observed between the number of windy hours per month (velocity more than 5–6 m s⁻¹) and cell concentrations in the Black Sea (r = −0.92) and in the northern Adriatic Sea (r = −0.67). On this basis, a new hypothesis has been proposed and discussed: in connection with features of the food behavior of Noctiluca, its outbursts during the peak period are controlled by the wind. An evident positive relationship was observed between the number of Noctiluca in the peak period and its quantity in the preceding months in both seas. Thus, we suggest that abundance data during early spring and weather forecasts (winds) may be used for medium-term prediction of Noctiluca outbursts and red tides.     

Deposit-feeders accumulate the cyanobacterial toxin nodularin

Blooms of toxic cyanobacteria may potentially affect food web productivity and even be a human health hazard. In the Baltic Sea, regularly occurring summer blooms of nitrogen-fixing cyanobacteria are often dominated by Nodularia spumigena, which produces the potent hepatotoxin nodularin. Evidence of sedimentation of these blooms indicates that benthic fauna can be exposed to nodularin. In a one month experiment, we simulated the settling of a summer bloom dominated by N. spumigena in sediment microcosms with three species of sediment-dwelling, deposit-feeding macrofauna, the amphipods Monoporeia affinis and Pontoporeia femorata and the bivalve Macoma balthica, and analyzed nodularin in the animals by HPLC–ESI–MS (high-performance liquid chromatography–electrospray ionization–mass spectrometry). We found nodularin in quantities of 50–120 ng g⁻¹ DW. The results show that deposit-feeding macrofauna in the Baltic Sea may contribute to trophic transfer of nodularin.     

Identification and expression analysis of the gene associated with geosmin production in Lyngbya kuetzingii UTEX 1547 (cyanobacteria)

Cyanobacteria are the major producers of geosmin in natural waters. To identify a gene involved in geosmin biosynthesis in cyanobacteria, the polymerase chain reaction (PCR) was used to amplify a 2298-bp open reading frame (ORF) from the geosmin-producing cyanobacterium Lyngbya kuetzingii UTEX 1547. This ORF encoded a protein of 765 amino acids. Alignment of the deduced amino acid sequence demonstrated that geoL had high similarity to the corresponding genes of Oscillatoria sp. PCC 6506 (100% identity), Calothrix sp. PCC 7507 (89%), Anabaena ucrainica CHAB 1432 (88%), A. ucrainica CHAB 2155 (87%), Nostoc punctiforme PCC 73102 (87%), Phormidium sp. P2r (84%) and Cylindrospermum stagnale PCC 7417 (83%), and modest similarity to myxobacteria (61–73%). It also indicated geoL with low similarity to the corresponding genes of actinomycetes (<60%). The encoded protein GEOL was estimated to have two geosmin synthase domains, and each contained two strictly conserved Mg²⁺-binding motifs (aspartate-rich motif and NSE triad). The geoL gene was shown to be responsible for geosmin biosynthesis in L. kuetzingii UTEX 1547. Then, geoL had been cloned into pET21a(+) vector and expressed in Escherichia coli BL21(DE3) with the isopropyl-β-d-thiogalactoside (IPTG) induction. The recombinant GEOL protein was purified and exhibited a single band (M_W ∼ 90 kDa) on the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), which was consistent with the predicted molecular weight (M_W) of 87,046 Da. In conclusion, this study has confirmed that geosmin synthase gene and its expression product can be identified and characterized from cyanobacteria, which will help understand the fundamental biological mechanism of geosmin biosynthesis in cyanobacteria.     

Bioactive pigment production by Pseudomonas spp. MCC 3145: Statistical media optimization,biochemical characterization,fungicidal and DNA intercalation-based cytostatic activity

Multifunctional redox-active pyocyanin (PYC) produced by Pseudomonas aeruginosa has diverse biotechnological applications, but no efforts have been made to improve its yield. The yield obtained in initial study using Pseudomonas spp. MCC 3145 was 24.21 mg L⁻¹ PYC in pigment production medium D; hence, optimization of the media components using statistical tools for more production of PYC was undertaken. Of the 11 medium constituents screened for PYC production using Plackett–Burman design (PBD), glycerol, peptone, and CuSO₄ were recognized as the most significant variables. The optimal concentration of the variables for maximum PYC production was evaluated using a five-level three-factor central composite design (CCD). Optimal concentration of the three variables, glycerol, peptone and CuSO₄ showed 313.94 ± 10.09 mg L⁻¹ the PYC production, with an 18-fold increase. Fine structural details of PYC were verified by chromatographic and various spectroscopic analyses. In vitro bioactivity studies demonstrated significant antifungal activity of PYC against fungal phytopathogens and substantial cytostatic activity against four major cancer cell lines. Furthermore, PYC displayed nonspecific DNA intercalation, which may be the reason for proliferation arrest in cancer cells. Thus, the study rigorously improved PYC production through medium optimization and further demonstrated its agricultural and therapeutic applications.     

A mutualistic interaction between the bacterium Pseudomonas asplenii and the harmful algal species Chattonella marina (Raphidophyceae)

Several studies on various Chattonella species have reported that bacteria may play an important role in Chattonella bloom initiation, however, no studies have described how these bacteria promote the growth of C. marina. The interaction between C. marina and bacteria was investigated for identification and characterization of potential growth-promoting bacteria. In preliminary tests, the growth promoting effect of Pseudomonas species (25 strains) was investigated and P. asplenii (≥2.27) was determined as a growth-promoting bacteria for both C. marina strains (CCMP 2049 and 2050). This bacterium exerted optimal growth-promoting effects on C. marina, causing an increase in the initial density of P. asplenii to approximately 1 × 10⁷ cells mL⁻¹, which was used as the initial density in this study. To determine whether the growth-promoting activity was direct or indirect, P. asplenii was incubated in the algal media and then a filtrate of this culture was added to both C. marina strains. The P. asplenii filtrate stimulated the growth of C. marina and maintained the growth-promoting effects after high temperature (121 °C for 20 min) and pressure (15 psi) treatment. Thus, P. asplenii is able to promote C. marina growth through the release of a heat-resistant substance, such as inorganic nutrients. A nutrient analysis indicated that this bacterium elevated the phosphate concentration. Interestingly, P. asplenii was unable to survive in phosphate-limited media but could grow in phosphate-limited media incubating C. marina. Moreover, this bacterium could secrete significantly more phosphate in the presence of C. marina (p < 0.0001). These results suggested that P. asplenii and C. marina may have a mutualistic interaction.     

Applicability of massively parallel sequencing on monitoring harmful algae at Varna Bay in the Black Sea

In this study the plankton diversity in 13 environmental samples from Varna Bay (in the western Black Sea) was analyzed using massively parallel sequencing (MPS). This preliminary study was undertaken to assess the potential of this technology for future implementation in monitoring programs in the Black Sea. Amplicon sequences of the 18S rRNA gene (V4-5 regions) were obtained using the Illumina MiSeq 250PE platform. A total of 1137 operational taxonomic units (OTUs) were obtained among which 242 OTUs with >0.990 BLAST top hit similarity (21.3% of all detected OTUs) closely related to sequences belonging to −protists. A large portion (175 OTUs = 72.3%) was identified at the species levels, including species typical for the Bulgarian Black Sea plankton community, as well as many that haven’t been reported earlier in the Bulgarian Black Sea coast (124 OTUs = 51.2%). Dinoflagellates were represented by the highest species number (77 OTUs comprising 31.8% of protist species), with dominant genera Gyrodinium and Heterocapsa. The present survey revealed the presence of 12 species listed as harmful, some of which have been previously overlooked, such as Cochlodinium polykrikoides, Karenia bicuneiformis, and Karlodinium veneficum. Species identification was possible for 10.3–36.0% of the detected OTUs in the six major supergroups. The frequency in Rhizaria was significantly lower than that in other major groups (p < 0.05–0.01), implying difficulties in the classification from morphology-based observations. The metagenetic data had an insufficient resolution of the 18S rRNA gene for species identification in many genera. These issues may hamper the implementation of MPS-based surveys for plankton monitoring, especially for detecting harmful algal blooms (HAB). The sequencing technology is steadily improving and it is expected that sequence length and quality issues will be resolved in the near future. The ongoing efforts to register taxonomic information and quality controls in the international nucleotide sequence databases (INSDs) will be essential for improving taxonomic identification power.     

Sea surface environment inferred from planktonic foraminifera in the southern South China Sea since the last glacial period

Detailed analyses of planktonic foraminifera at Site 17964 from the southern South China Sea (SCS) disclose that warm-water species have a higher percentage during the Holocene, while temperate-water species have a higher content for the last glacial period. Therefore, the sea surface temperature (SST) is a main factor that affects the foraminiferal assemblage at this site. A remarkable faunal variation at Site 17964 is recognized for Pulleniatina obliquiloculata over the last glacial–interglacial periods: higher P. obliquiloculata content during the glacial period and abrupt drop at the beginning of Termination I (16.5–15 kyr B.P.). The characteristic P. obliquiloculata variation can be correlated with other sites in the southern SCS and thus can be adopted as a stratigraphic tool in the region. A detailed analysis of Orbulina universa shell morphometrics at Site 17964 shows the test size from 0.83 to 1.45 mm and the shell porosity up to 36.7%, much larger than those in the Indian and Atlantic Oceans, which indicates a warmer and less saline surface water in the equatorial–tropical western Pacific. The diameter and shell porosity of O. universa increased from the last glacial to the Holocene, corresponding to the increase of SST recorded by the U^k₃₇ alkenone index. A higher correlation coefficient (89%) between the O. universa test size and SST implies that intraspecific O. universa test size be used as an index of the sea surface temperature in the South China Sea.     

Temporal and spatial variability in nitrogen uptake kinetics during harmful dinoflagellate blooms in the East China Sea

Temporal and spatial variability in the kinetic parameters of uptake of nitrate (NO₃⁻), ammonium (NH₄⁺), urea, and glycine was measured during dinoflagellate blooms in Changjiang River estuary and East China Sea coast, 2005. Karenia mikimotoi was the dominant species in the early stage of the blooms and was succeeded by Prorocentrum donghaiense. The uptake of nitrogen (N) was determined using ¹⁵N tracer techniques. The results of comparison kinetic parameters with ambient nutrients confirmed that different N forms were preferentially taken up during different stages of the bloom. NO₃⁻ (V_max 0.044 h⁻¹; K_s 60.8 μM-N) was an important N source before it was depleted. NH₄⁺ (V_max 0.049 h⁻¹; K_s 2.15 μM-N) was generally the preferred N. Between the 2 organic N sources, urea was more preferred when K. mikimotoi dominated the bloom (V_max 0.020 h⁻¹; K_s 1.35 μM-N) and glycine, considered as a dominant amino acid, was more preferred when P. donghaiense dominated the bloom (V_max 0.025 h⁻¹; K_s 1.76 μM-N). The change of N uptake preference by the bloom-forming algae was also related to the variation in ambient N concentrations.     

Isolation of novel chitinolytic bacteria and production optimization of extracellular chitinase

Chitin is one of the most abundant biopolymers widely distributed in the marine and terrestrial environments. Chitinase enzyme has received increased attention due to its wide range of biotechnological applications, especially in agriculture for biocontrol of phytopathogenic fungi and harmful insects. In the present study, 58 bacterial isolates were screened for chitinolytic activity and on the basis of chitin hydrolysis zone 6 isolates were selected for chitinase production in broth media. Based on enzyme production, two most potent isolates identified as Aeromonas hydrophila HS4 and Aeromonas punctata HS6 were selected for further study. The effects of media composition and various fermentation conditions for optimization of chitinase production were studied. The maximum chitinase production was obtained at 37 °C and pH 8.0 after 24–48 h of incubation by HS4; and at 37 °C and pH 7 after 48 h incubation by HS6. Among the substrates colloidal chitin was the best for both the strains. Regarding carbon sources, starch (1%) was the best for both strains; while malt and yeast extract (1%) was found as the best nitrogen source for HS4 and HS6, respectively. Out of metal ions Mn²⁺ and Cu²⁺ enhanced enzyme production in the case of HS6. However, Co²⁺ was the most appropriate for HS4.     

Biochemical characterization of an endoxylanase from Pseudozyma brasiliensis sp. nov. strain GHG001 isolated from the intestinal tract of Chrysomelidae larvae associated to sugarcane roots

Endo-xylanases play a key role in the hydrolysis of xylan and recently they have attracted much attention due to their potential applications on the biofuel and paper industries. We isolated a Pseudozyma brasiliensis sp. nov. strain from the intestinal tract of Chrysomelidae larvae that parasitize sugarcane roots. This basidiomycetous yeast produces a xylanase designated PbXynA which was purified and characterized. The molecular weight of PbXynA is 24 kDa, it belongs to the GH11 family and its optimum pH and optimum temperature are 4.0 and 55 °C, respectively. PbXynA has as secondary structure predominantly β-sheets and sigmoidal kinetic behavior with elevated speed conversion from substrate-to-products (V_max = 2792.0 μmol product/min/mg protein). It is highly activated by bivalent cations such as Ca²⁺, however in the presence of Cu²⁺ xylanase activity was inhibited. It has a high specific activity and produces xylooligosaccharides that have a variety of industrial applications, indicating PbXynA has a great biotechnological potential.     

Bioconversion of spent coffee grounds into carotenoids and other valuable metabolites by selected red yeast strains

Spent coffee grounds (SCG) represent the main coffee industry residues with a great potential to be reutilized in various biotechnological processes. In this study, several carotenogenic yeasts strains were exploited for the production of vitamin-enriched biomass, cultivating in SCG-based media. The fermentation was firstly carried out in Erlenmeyer flasks in order to select the best biomass and pigment producer. Among four tested strains, Sporobolomyces roseus showed the highest potential for the accumulation of carotenoids. Maximum pigment concentration and yield was obtained when cultivating in SCG-based media, 12.59 mg l⁻¹ and 1.26 mg g⁻¹, respectively. Comparing both, the batch and the fed-batch cultivation modes, the strategy of sequential addition of pre-concentrated SCG media in the bioreactor gave higher biomass yield (maximum 41 g l⁻¹ during 41–48 h after the beginning of fermentation). Thus, SCG can be considered as potentially promising industrial waste stream for economically feasible production of enriched yeasts biomass.     

Ostreopsis cf. ovata in the Gulf of Gabès (south-eastern Mediterranean Sea): morphological,molecular and ecological characterization

In the last few decades, the frequency of the toxic benthic dinoflagellate Ostreopsis cf. ovata proliferation has increased in the Mediterranean Sea. These blooms are associated with harmful effects on human health and the environment. The present work provides the first long term study on the spatio-temporal distribution of O. cf. ovata in relation to physical parameters in the Gulf of Gabès coastal waters (south-eastern Mediterranean Sea), as well as its morphological, molecular and physiological features. The strains of O. cf. ovata were identified morphologically by light and epifluorescence microscopy. The morphology and the size range of cultured strains were similar to those described regarding O. cf. ovata isolated from the Mediterranean Sea. The ultrastructural analysis of O. cf. ovata cells using the transmission electron microscopy showed the presence of numerous vesicles (VE) containing spirally coiled fibers (SCFs) connected to the mucus canal (CH). The phylogenetic tree based on the internal transcribed spacer region containing the 5.8S rDNA (ITS-5.8S rDNA) revealed that O. cf. ovata strains were placed into the Mediterranean/Atlantic clade. In addition, O. cf. ovata toxicity was evaluated by the mouse bioassay and a dose level ≥ 4 × 10⁴ cells was found to be lethal to mice. The examination of the O. cf. ovata occurrence in the Gulf of Gabès at a large temporal scale (1997–2012) revealed a clear seasonal pattern with dominance from midsummer (July) to late autumn (November). Furthermore, a positive correlation was found between the abundance of O. cf. ovata and salinity, whereas no correlation was found as regards temperature. The occurrence of O. cf. ovata was only detected at salinity above 35 and the highest concentrations were observed at 45. Laboratory experiments confirmed such a result and showed that isolated O. cf. ovata strains had optimal growth at salinity ranging between 35 and 45, with its peak at 40.