Suitability of pre-digested dairy effluent for mixotrophic cultivation of the hydrogen-producing microalgae Tetraselmis subcordiformis.

The costs associated with microalgal biomass production can be reduced by leveraging alternative and cheap growth media. Digestate from fermentation reactors is a particularly interesting candidate for use in cultivating mixotrophic species. The aim of the present study was to assess whether pre-digested milk-industry effluent can be harnessed to grow Tetraselmis subcordiformis and produce hydrogen. The experimental series with 25% and 50% effluent in the growth medium performed the best, producing more than 2000 mgVS biomass/dm3. The biogas produced in these variants contained over 60% hydrogen. Increasing the effluent in the medium to 75% led to significant deterioration of performance, both in terms of T. subcordiformis biomass growth and biohydrogen production. The highest efficiency of nitrogen and phosphorus removal, respectively 98.1 ± 1.9% and 97.1 ± 1.4%, was observed in the system to which 25% of sewage was introduced. Increasing the share of fermented wastewater directly reduced the efficiency of removing biogenic compounds. A very strong negative correlation was found between initial N-NH4 in the growth medium and T. subcordiformis biomass production rates (R2 = 0.9177).

Liquid fraction of digestate pretreated with membrane filtration for cultivation of Chlorella vulgaris.

To make microalgae cultivation economically feasible, different waste streams that may serve as cultivation media are being searched for. The aim of this study was membrane filtration of the liquid fraction of digestate (LFD) to produce permeate that will be an effective medium for the cultivation of Chlorella vulgaris. Microfiltration (MF) and ultrafiltration (UF) with ceramic membranes were used in one- and two-stage systems at transmembrane pressures (TMP) of 0.2, 0.3, and 0.4 MPa. The hydraulic capacities of the membrane modules allowed MF at 0.2 MPa to be selected as the most feasible variant of the one-stage variants. The use of MF permeates for microalgae cultivation resulted in the highest biomass yield, due to optimum pH (about 8.8), low color, and high nutrient concentration (about 290 mg/dm3 of ammonium and about 22 mg/dm3 of orthophosphates). The high pH (about 9.7) of the UF permeates, which increased the concentration of free ammonia, reduced microalgae growth by 50% compared to the growth noted with the MF permeates. Due to the low nutrient concentration, the use of permeates from the two-stage systems resulted in microalgae growth more than two times lower than the use of MF permeates. Mathematical modeling indicated that the component of the cultivation medium that most significantly affected microalgae growth was the initial ammonium concentration.

Applicability of water from the Bay of Gdansk as a growth medium for mixotrophic culture of Platymonas subcordiformis.

P. subcordiformis is a potentially promising species with commercial, environmental and technological viability for industrial applications. The great potential of these microalgae lies in their fast biomass growth, pollution resistance, and compatibility with different culture media. This study aimed to determine the efficiency of P. subcordiformis biomass production in a medium prepared with water from the Bay of Gdansk. The tested medium supported high biomass growth rates which reached 317.58 ± 42.31 mgV⁢S/dm3⋅d in the best-performing variant, with a final concentration of 3493.3 ± 465.4 mgV⁢S/dm3⋅d. In the autotrophic culture, nitrogen and phosphorus removal exceeded 98%. Amending the mixotrophic culture with glucose did not affect P. subcordiformis concentrations. However, it did significantly limit the demand for nutrients in the biomass and reduced chlorophyll a production in the cells.

Regulation of alginate catabolism involves a GntR family repressor in the marine flavobacterium Zobellia galactanivorans DsijT.

Marine flavobacteria possess dedicated Polysaccharide Utilization Loci (PULs) enabling efficient degradation of a variety of algal polysaccharides. The expression of these PULs is tightly controlled by the presence of the substrate, yet details on the regulatory mechanisms are still lacking. The marine flavobacterium Zobellia galactanivorans DsijT digests many algal polysaccharides, including alginate from brown algae. Its complex Alginate Utilization System (AUS) comprises a PUL and several other loci. Here, we showed that the expression of the AUS is strongly and rapidly (<30 min) induced upon addition of alginate, leading to biphasic substrate utilization. Polymeric alginate is first degraded into smaller oligosaccharides that accumulate in the extracellular medium before being assimilated. We found that AusR, a GntR family protein encoded within the PUL, regulates alginate catabolism by repressing the transcription of most AUS genes. Based on our genetic, genomic, transcriptomic and biochemical results, we propose the first model of regulation for a PUL in marine bacteria. AusR binds to promoters of AUS genes via single, double or triple copies of operator. Upon addition of alginate, secreted enzymes expressed at a basal level catalyze the initial breakdown of the polymer. Metabolic intermediates produced during degradation act as effectors of AusR and inhibit the formation of AusR/DNA complexes, thus lifting transcriptional repression.

The effect of pressure and temperature pretreatment on the biogas output from algal biomass.

This paper presents data on methane fermentation of algal biomass containing Chlorella sp. and Scenedesmus sp. The biomass was obtained from closed-culture photobioreactors. Before the process, the algae were subjected to low temperature and pressure pretreatment for 0.0, 0.5, 1.0 and 2.0 h. The prepared biomass was subjected to mesophilic methane fermentation. The amount and composition of the biogas formed in the process were determined. The amount of biogas produced was larger when the biomass was subjected to thermal preprocessing. The proportion of methane in the gas also increased. Extending the heating time beyond 1.0 h did not significantly improve the biogassing effects.

Metaphylogenomic and potential functionality of the limpet Patella pellucida's gastrointestinal tract microbiome.

This study investigated the microbial diversity associated with the digestive tract of the seaweed grazing marine limpet Patella pellucida. Using a modified indirect DNA extraction protocol and performing metagenomic profiling based on specific prokaryotic marker genes, the abundance of bacterial groups was identified from the analyzed metagenome. The members of three significantly abundant phyla of Proteobacteria, Firmicutes and Bacteroidetes were characterized through the literature and their predicted functions towards the host, as well as potential applications in the industrial environment assessed.