High-throughput cultivation of heterotrophic bacteria during a spring phytoplankton bloom in the North Sea

On-going studies of phytoplankton-bacterioplankton interactions at the long-term ecological research site Helgoland Roads have indicated that many of the heterotrophic bacterial taxa have not yet been cultivated. A high-throughput approach combining whole cell matrix-assisted laser desorption ionization – time of flight mass spectroscopy with 16S rRNA gene sequencing was applied to the spring bloom of 2016. Aiming at an assessment of cultivability during a spring bloom, cultivation on solid marine media had to be used since dilution to extinction would not have been feasible for a high-throughput approach, as performed in this study. A total of 5023 isolates were obtained from nine weekly samples on eight different solid media between the early-bloom and post-bloom periods. Most of the 4136 strains identified affiliated with Bacteroidetes (13.3%), Gammaproteobacteria (26.9%), Alphaproteobacteria (40.6%) and Actinobacteria (6.7%). Of the 271 operational phylogenetic units (OPUs) identified, 13 are likely to represent novel genera and 143 novel species. A comparison with 16S rRNA gene tag data indicated that most of the isolates were rather rare in surface waters, with the exception of five OPUs affiliating with Rhodobacteraceae, Polaribacter, Psychromonas and Pseudoalteromonas. The effort yielded many novel isolates, yet most of the abundant heterotrophic bacteria still remained elusive. The large strain collection obtained will not only provide insights into the succession of the cultivable fraction of the bacterioplankton, but also enable fine-tuned taxonomic and physiological follow-up studies for improving our knowledge on heterotrophic bacteria in North Sea waters.     

Excess sludge reduction by biological way: from experimental experience to a real full scale application

The aim of this study was to investigate the ability of a biological process applied in the sludge line and based on the alternation of oxic and anoxic phases, to minimize the waste sludge production. After some tests in pilot scale, the process was applied in a real municipal wastewater treatment plant of 35,000 PE trying out one setting of working experimental conditions. A rate of the recycle flow was conditioned in a treatment basin, maintaining an HRT of 10 days. The control device operated for the 50% of time in the ORP range between -400 and -200 mV, and for the 50% in the ORP range between -200 and +50 mV. The mass balance defined an actual observed growth yield equal to 0.09 kgTVSkgCODr(-1), and the heterotrophic yield values, assessed by batch tests, seemed to be a suitable marker for the sludge reduction and for the energy uncoupling.     

Heterotrophic nitrification and aerobic denitrification by the bacterium Pseudomonas stutzeri YZN-001

A strain YZN-001 was isolated from swine manure effluent and was identified as Pseudomonas stutzeri. It can utilise not only nitrate and nitrite, but also ammonium. The strain had the capability to fully remove as much as 275.08 mg L⁻¹ NO₃⁻–N and 171.40 mg L⁻¹ NO₂⁻–N under aerobic conditions. Furthermore, At 30 °C, the utilization of ammonium is approximately 95% by 18 h with a similar level removed by 72 h and 2 weeks at 10 and 4 °C, respectively. Triplicate sets of tightly sealed serum bottles were used to test the heterotrophic nitrifying ability of P. stutzeri YZN-001. The results showing that 39% of removed NH₄⁺–N was completely oxidised to nitrogen gas by 18 h. Indicating that the strain has heterotrophic nitrification and aerobic denitrification abilities, with the notable ability to remove ammonium at low temperatures, demonstrating a potential using the strain for future application in waste water treatment.     

Control of microbial communities by the macrofauna: a sensitive interaction in the context of extreme summer temperatures?

Climate models predict an increasing frequency of extremely hot summer events in the northern hemisphere for the near future. We hypothesised that microbial grazing by the metazoan macrofauna is an interaction that becomes unbalanced at high temperatures due to the different development of the grazing rates of the metazoans and the growth rates of the microbial community with increasing temperature. In order to test this hypothesis, we performed grazing experiments in which we measured the impact of increasing temperatures on the development of the grazing rates of riverine mussels in relation to the growth rates of a unicellular prey community (a natural heterotrophic flagellate community from a large river). In a first experimental series using Corbicula fluminea as a grazer and under the addition of a carbon source (yeast extract), the increase of the prey’s growth rates was considerably stronger than that of the predator’s grazing rates when temperatures were increased from 19 to over 25°C. This was also the outcome when the mussels had been acclimatized to warm temperatures. Hereafter, specific experiments with natural river water at temperatures of 25 and 30°C were performed. Again, a strong decrease of the mussels’ grazing rates in relation to the flagellate growth rates with increasing temperature occurred for two mussel species (C. fluminea and Dreissena polymorpha). When performing the same experiment using a benthic microbial predator community (biofilms dominated by ciliates) instead of the benthic mussels, an increase of the grazing rates relative to the growth rates with temperature could be observed. Our data suggest that predator–prey interactions (between metazoans and microbes) that are balanced at moderate temperatures could become unbalanced at high temperatures. This could have significant effects on the structure and function of microbial communities in light of the predicted increasing frequency of summer heat waves. Priority programme of the German Research Foundation—contribution 7.     

Estimation of autotrophic and heterotrophic components of soil respiration by trenching is sensitive to corrections for root decomposition and changes in soil water content

This study aims to assess the effects of corrections for disturbances such as an increased amount of dead roots and an increase in volumetric soil water content on the calculation of soil CO₂ efflux partitioning. Soil CO₂ efflux, soil temperature and superficial soil water content were monitored in two young beech sites (H1 and H2) during a trenching experiment. Trenching induced a significant input of dead root mass that participated in soil CO₂ efflux and reduced the soil dissolved organic carbon content, while it increased superficial soil water content within the trenched plot. Annual soil CO₂ efflux in control plots was 528 g C m⁻² year⁻¹ at H1 and 527 g C m⁻² year⁻¹ at H2. The annual soil CO₂ efflux in trenched plots was 353 g C m⁻² year⁻¹ at H1 and 425 g C m⁻² year⁻¹ at H2. By taking into account annual CO₂ efflux from decaying trenched roots, the autotrophic contribution to total soil CO₂ efflux reached 69% at H1 and 54% at H2. The partitioning calculation was highly sensitive to the initial root mass estimated within the trenched plots. Uncertainties in the remaining root mass, the fraction of root C that is incorporated into soil organic matter during root decomposition, and the root decomposition rate constant had a limited impact on the partitioning calculation. Corrections for differences in superficial soil water content had a significant impact on annual respired CO₂ despite a limited effect on partitioning.     

Production of paramylon,a β‐1,3‐glucan,by heterotrophic growth of Euglena gracilis on potato liquor in fed‐batch and repeated‐batch mode of cultivation

Recently, it had been shown that Euglena gracilis was able to grow heterotrophically not only on synthetic media, but also on media based on potato liquor. Supplementation with glucose in both cases led to the accumulation of paramylon, a β‐1,3‐glucan. Thus, such a process may yield a valuable product accompanied by the revaluation of an otherwise annoying waste stream of the potato‐starch industry. Actually, process strategies have been evaluated in order to optimise the concentration of paramylon obtained at the end of the cultivation process. Therefore, cultivation processes based on fed‐batch and in particular repeated‐batch strategies have been studied. It is shown that repeated‐batch operation maybe particularly suited for such a process since E. gracilis seems to adapt gradually to the cultivation medium so that the concentration of media components may be increased step by step. Repeated‐batch cultivation of E. gracilis leads to biomass concentrations in access of 20 g/L with a consistent paramylon mass fraction of about 75%. Cultivations have been carried out at an operating temperature of 27.5°C. As had been found earlier already, pH control is not required during cultivation. On the basis of these results it is clear that repeated‐batch cultivation represent a simple and economic way for the production of paramylon by heterotrophic cultivation of E. gracilis.     

Impact of suspended mussels (Mytilus edulis L.) on plankton communities in a Magdalen Islands lagoon (Québec, Canada): A mesocosm approach

The Grande-Entrée Lagoon (Magdalen Islands, Canada) has supported mussel (Mytilus edulis) cultivation for the last 25 years. Algal biomass in this lagoon is relatively low while heterotrophic plankton biomass is high. Although often considered herbivorous, it is known that filter-feeding bivalves can consume various types of food, from bacteria to zooplankton. We hypothesize that along with phytoplankton, heterotrophs constitute an important food resource for the Grande-Entrée mussels. In situ mesocosm experiments were undertaken at different seasons using short socks filled with mussels from the same cohort taken from an aquaculture farm, in order to determine the impact of cultured mussels on local plankton communities and assess the role of heterotrophs. Filtration activity by the mussels and associated epibionts present in the socks was expressed as clearance rates (CR). The average CR over all taxa was lowest in June and highest in October. Diatoms, dinoflagellates and heterotrophic protists constituted the bulk of planktonic carbon removed by mussels. While smaller-sized taxa contributed little (< 5%) to mussel carbon intake, large-sized heterotrophs (namely ciliates) contributed 69 to 88%. Taxon-marker pigment analyses generally confirmed these observations for groups containing phototrophic pigments. The high heterotrophic biomass retained by mussels indicates they are a major food source for mussels in this environment and should be considered both in the evaluation of mussel feeding and in assessing the influence of cultured mussels on local plankton ecosystems.     

Bacterial and phytoplankton dynamics in a sub-tropical estuary

Heterotrophic bacterial and phytoplankton biomass, production, specific growth rates and growth efficiencies were studied in July 2001 and January 2002 during both spring and neap tides, along a tidal cycle, at three sites in a subtropical estuary. Major freshwater inputs located in the Northern region led to differences in both phytoplankton and bacterioplankton biomass and activity along the estuary. While in the Northern region phytoplankton is light-limited, with mean phytoplankton production (PP) between 1.1 and 1.9 μg C l⁻¹ h⁻¹ and mean specific growth rates (PSG) between 0.14 and 0.16 d⁻¹, the Southern region registered values as high as 24.7 μg C l⁻¹ h⁻¹ for PP and 2.45 d⁻¹ (mean PP between 3.4 and 7.3 μg C l⁻¹ h⁻¹; mean PSG between 0.28 and 0.57 d⁻¹). On the other hand, maximum bacterial production (BP: 63.8 μg C l⁻¹ h⁻¹) and specific growth rate (BSG: 32.26 d⁻¹) were observed in the Northern region (mean BP between 3.4 and 12.8 μg C l⁻¹ h⁻¹; mean BSG between 1.98 and 6.67 day⁻¹). These bacterial activity rates are among the highest recorded rates in estuarine and coastal waters, indicating that this system can be highly heterotrophic, due to high loads of allochthonous carbon (mainly derived from mangrove forest). Our results also showed that, despite that BP rates usually exceeded PP, in the Southern region BP may be partially supported (∼45%) by PP, since a significant regression was observed between BP and PP (r = 0.455, P < 0.001). Handling editor: P. Viaroli