Microalgal flocculation and sedimentation: spatiotemporal evaluation of the effects of the pH and calcium concentration.

The high cost of harvesting microalgae is a major hurdle for the microalgae industry, and an efficient pre-concentration method is required. In this study, the effects of using different pH values (between pH 3 and 11) and calcium (Ca2+) concentrations (between 0 and 5 mM) on Chlorella vulgaris sedimentation were investigated by evaluating the spacio-temporal distributions of microalgae cells. Fast and efficient sedimentation occurred (within 10 min) at a high Ca2+ concentration (5 mM) at pH 9 and 11. However, the sediment volume was lower at a Ca2+ concentration of 3 mM than at a Ca2+ concentration of 5 mM. This indicated that the Ca2+ concentration strongly affected the sediment volume. Fast sedimentation and a low sediment volume were found at pH 7 and a Ca2+ concentration of 5 mM, probably because of the neutral charge in the system (adhesion to calcium precipitates would have occurred at a high pH). The highest Ca2+ recovery (82%) was achieved when sediment produced at pH 11 and a Ca2+ concentration of 5 mM was acidified to pH 3.

Draft genome sequences of three rhodopsin possessing Croceitalea sp. strains, isolated from the sea surface microlayer in Japan.

Here, we present the draft genome sequences of three Croceitalea sp. strains containing microbial rhodopsins, isolated from the Japanese coastal sea surface microlayer, which is exposed to intense sunlight. This study will contribute to the understanding of the genus Croceitalea and the diversity of microbial rhodopsins.

Ingestion rate estimated from food concentration and predatory role of copepod nauplii in the microbial food web of temperate embayment waters.

To quantitatively evaluate the role of copepod nauplii as predators in the microbial food web, the ingestion rate (IR) of copepod nauplii and the food requirement (FR) of microzooplankton were estimated monthly for 3 consecutive years in temperate embayment waters. The IR of dominant copepod nauplii (Acartia spp. nauplii) was estimated from water temperature, individual carbon weight and food concentration and peaked (>0.50 µgC ind-1 d-1) with relatively high food concentration (>57.5 µgC L-1). This result suggests that food concentration should be considered to estimate copepod naupliar IR in marine environments, especially where biological conditions fluctuate largely. The comparison of copepod naupliar and microprotozoan FR showed the dominance of naked ciliate FR (77.0-90.2%) during the study period except in spring when comparable values were observed between the FR of naked ciliates (41.6%) and copepod nauplii (33.6%). During spring, transfer efficiency (10.5%) from primary production (PP) to microzooplankton production was lower than in other seasons (16.2-17.1%). This study indicates that copepod nauplii are seasonally important micro-sized predators in the microbial food web of temperate embayment waters and that carbon flow through copepod nauplii is a pathway which inefficiently transfers PP to higher trophic levels.