The effects of predation by planktivorous juvenile fish on the microbial food web

The feeding impact of planktivorous fish on microbial organisms is still poorly understood. We followed the seasonal dynamics of the food web in two natural fishponds for two years: one was stocked with planktivorous whitefish while the other had no planktivorous fish. The aim of the study was the simultaneous assessment of the feeding behaviours of planktivorous fish and of bacterivorous meta-/protozooplankters. We hypothesized that in the presence of planktivorous fish there would be fewer metazooplankton, more protozoans and decreased numbers of bacteria. Our results showed that the amount of metazooplankton eaten by the fish was indeed negatively correlated with metazooplankton biomass. The feeding impact of planktivorous fish in shaping the microbial loop was remarkable. The main grazers of bacteria in the fishpond were ciliates, whereas in the pond without fish these were heterotrophic nanoflagellates. In the fishless pond the role of the top predator shifted to the predaceous metazooplankter Leptodora kindtii which controlled the abundance of herbivorous metazooplankters. We found a negative relationship between the number of bacteria and flagellates in the fishless pond, while the number of bacterivorous ciliates was suppressed by predaceous ciliates. Therefore the bacteria-grazing activity was higher in the absence of planktivorous fish.     

Two-stage heterotrophic and phototrophic culture strategy for algal biomass and lipid production

A two-stage heterotrophic and phototrophic culture strategy for algal biomass and lipid production was studied, wherein high density heterotrophic cultures of Chlorellasorokiniana serve as seed for subsequent phototrophic growth. The data showed growth rate, cell density and productivity of heterotrophic C.sorokiniana were 3.0, 3.3 and 7.4 times higher than phototrophic counterpart, respectively. Hetero- and phototrophic algal seeds had similar biomass/lipid production and fatty acid profile when inoculated into phototrophic culture system. To expand the application, food waste and wastewater were tested as feedstock for heterotrophic growth, and supported cell growth successfully. These results demonstrated the advantages of using heterotrophic algae cells as seeds for open algae culture system. Additionally, high inoculation rate of heterotrophic algal seed can be utilized as an effective method for contamination control. This two-stage heterotrophic phototrophic process is promising to provide a more efficient way for large scale production of algal biomass and biofuels.     

Quantification of individual flagellate - bacteria interactions within semi-natural biofilms

Here we present a new approach to quantify food-web interactions within semi-natural biofilms by combining the establishment of biofilms from natural rivers in flow cells with video microscopy. In a first application of this approach, we focused on the surface-gliding heterotrophic flagellates (HF) Neobodo designis, Rhynchomonas nasuta and Planomonas sp. It was shown that the three HF generally ingested single biofilm-associated bacteria whereas bacteria within microcolonies were attacked but not ingested. However, grazing strategies differed considerably. While the kinetoplastids N. designis and R. nasuta displayed long search and short handling times, Planomonas sp. showed the opposite grazing characteristics. The latter behaviour resulted in a high relative predation success of 80% (precent of attacked prey ingested), whereas the relative predation success of the two kinetoplastids was only 20%. However, the two contrasting strategies resulted in similar ingestion rates for Planomonas sp. and N. designis of 0.5 to 0.6 ingestions flagellates(-1) minute(-1), respectively. Our results showed distinct differences in the feeding behaviour of three flagellates having similar life forms and provide direct evidence that microcolony formation in biofilms protects bacteria from grazing by HF in situ. The new approach provides individual-based insights into the complex food web interactions within biofilms.     

Culturable bacterial diversity at the Princess Elisabeth Station (Utsteinen, Sør Rondane Mountains, East Antarctica) harbours many new taxa

We studied the culturable heterotrophic bacterial diversity present at the site of the new Princess Elisabeth Station at Utsteinen (Dronning Maud Land, East Antarctica) before construction. About 800 isolates were picked from two terrestrial microbial mat samples after incubation on several growth media at different temperatures. They were grouped using rep-PCR fingerprinting and partial 16S rRNA gene sequencing. Phylogenetic analysis of the complete 16S rRNA gene sequences of 93 representatives showed that the isolates belonged to five major phyla: Actinobacteria, Bacteroidetes, Proteobacteria, Firmicutes and Deinococcus-Thermus. Isolates related to the genus Arthrobacter were the most prevalent whereas the genera Hymenobacter, Deinococcus, Cryobacterium and Sphingomonas were also recovered in high numbers in both samples. A total of 35 different genera were found, the majority of which has previously been reported from Antarctica. For the genera Aeromicrobium, Aurantimonas, Rothia, Subtercola, Tessaracoccus and Xylophilus, this is the first report in Antarctica. In addition, numerous potential new species and new genera were recovered; many of them currently restricted to Antarctica, particularly in the phyla Bacteroidetes and Deinococcus-Thermus.     

Local bioprospecting for high-lipid producing microalgal strains to be grown on concentrated municipal wastewater for biofuel production

Mass cultivation of microalgae for biofuel production depends heavily on the performance of the microalgae strains used. In this study, 60 algae-like microorganisms collected from different sampling sites in Minnesota were examined using multi-step screening and acclimation procedures to select high-lipid producing facultative heterotrophic microalgae strains capable of growing on concentrated municipal wastewater (CMW) for simultaneous energy crop production and wastewater treatment. Twenty-seven facultative heterotrophic microalgae strains were found, among which 17 strains were proved to be tolerant to CMW. These 17 top-performing strains were identified through morphological observation and DNA sequencing as Chlorella sp., Heynigia sp., Hindakia sp., Micractinium sp., and Scenedesmus sp. Five strains were chosen for other studies because of their ability to adapt to CMW, high growth rates (0.455-0.498 d⁻¹) and higher lipid productivities (74.5-77.8 mg L⁻¹ d⁻¹). These strains are considered highly promising compared with other strains reported in the literature.     

Effect of membrane bioreactor configurations on sludge structure and microbial activity

The aim of this paper was to determine the effect of two different membrane bioreactor (MBR) configurations (external/immersed) on sludge structure and microbial activity. Sludge structure was deduced from rheological measurements. The high shear stress induced by the recirculation pump in the external MBR was shown to result in decreasing viscosity due to activated sludge (AS) deflocculation. Besides, soluble microbial products (SMP) release was higher in the external MBR (5 mg_COD g_MLVSS⁻¹) than in the immersed configuration (2 mg_COD g_MLVSS⁻¹). Microbial activity was followed from respirometry tests by focusing on the distinction between heterotrophs and autotrophs. An easier autotrophic microbe development was then observed in the immersed MBR compared to the external one. However, the external MBR was shown to allow better heterotrophic microbe development.     

Winter phytoplankton communities of Utah Lake,Utah, USA

Phytoplankton samples were collected from ice-covered Utah Lake during February and March, 1979 in order to characterize the winter algal flora. These samples were analyzed for presence and abundance of diatoms and non-diatom algae as well as selected water chemical parameters. A total of 159 diatom taxa and 20 non-diatoms was found in the water column under the ice. The flagellates Carteria stellifera, Euglena gracilis and Chlamydomonas globosa dominated the winter non-diatom flora while Stephanodiscus cf. dubius, Cyclotella meneghiniana, Navicula minima, Fragilaria construens var. venter, and Melosira granulata var. angustissima dominated the winter diatom flora. Species richness and abundance were elevated in the major bays of the lake.     

Effects of short-term nutrient addition on microfauna density in a Mediterranean stream

We performed a stream fertilisation experiment in an oligotrophic, forested, undisturbed stream by increasing nitrogen and phosphorus concentrations. The effect of nutrient loading on microfauna was studied over 6 months. A before after control impact (BACI) design was used to determine the outcome of the addition by comparing three upstream non-enriched reaches with an enriched one downstream. Ciliates such as Hymenostomata (Frontonia, Lembadion, Paramecium, Cyclidium) and Pleurostomatida (Litonotus) showed a positive response to fertilisation. No significant changes were detected for flagellates and testate amoebae. Mean density values observed (0.2–3×10³ ind cm⁻²) were compared with those found in literature.