ABSTRACT The seasonal variation of bacterial production (BP) in a shallow, eutrophic Lake Kasumigaura was clarified from 2012 to 2016. During the studied period, BP fluctuated from 1.9 to 138 μ g C L −1 d −1 . There were no significant correlations between BP and bacterial abundance in any season, suggesting a strong top‐down regulation on BP throughout the year. On the other hand, BP was also related to bottom‐up regulation factors such as water temperature, phosphorus, and primary production (PP) annually. During winter, BP was positively correlated with chlorophyll a concentration, suggesting that autochthonous substrates were relatively important for BP. Moreover, BP was positively correlated with heterotrophic nanoflagellates, ciliates, and copepods, suggesting higher availability of substrates for BP. In summer, although there was no significant correlation between BP and PP, rainfall amount showed significant negative correlations with both BP and PP, suggesting depressed PP from relatively lower solar irradiance coupled with unfavorable weather conditions that decreased the substrate supply for bacteria. These results suggest that temporal variation of BP was regulated not by allochthonous, but by autochthonous substrates during both the highest (summer) and lowest (winter) productive seasons, even in a shallow, eutrophic lake. PP in autumn was approximately half that of spring due to lower solar irradiance, although water temperatures during both seasons were similar and nutrient concentrations during autumn were higher. On the other hand, BP in autumn was comparable with that in spring, and the bacterial carbon demand (= BP + bacterial respiration; 1.12 ± 0.79 g C m −2 d −1 ) was comparable to PP (1.16 ± 0.53 g C m −2 d −1 ), suggesting the relative importance of higher allochthonous substrates relative to other seasons.
We constructed a novel cell surface display system to control the ratio of target proteins on the Saccharomyces cerevisiae cell surface, using two pairs of protein-protein interactions. One protein pair is the Z domain of protein A derived from Staphylococcus aureus and the Fc domain of human immunoglobulin G. The other is the cohesin (Coh) and dockerin (Dock) from the cellulosome of Clostridium cellulovorans. In this proposed displaying system, the scaffolding proteins (fusion proteins of Z and Coh) were displayed on the cell surface by fusing with the 3' half of alpha-agglutinin, and the target proteins fused with Fc or Dock were secreted. As a target protein, a recombinant Trichoderma reesei endoglucanase II (EGII) was secreted into the medium and immediately displayed on the yeast cell surface via the Z and Fc domains. Display of EGII on the cell surface was confirmed by hydrolysis of beta-glucan as a substrate, and EGII activity was detected in the cell pellet fraction. Finally, two enzymes, EGII and Aspergillus aculeatus beta-glucosidase 1, were codisplayed on the cell surface via Z-Fc and Dock-Coh interactions, respectively. As a result, the yeast displaying two enzymes hydrolyzed beta-glucan to glucose very well. These results strongly indicated that the proposed strategy, the simultaneous display of two enzymes on the yeast cell surface, was accomplished by quantitatively controlling the display system using affinity binding.
Abstract Marine particle dynamics and carbon export, involving extracellular polymeric substances (EPS) like transparent exopolymer particles (TEP) and Coomassie Brilliant Blue‐stained particles (CSP), are poorly understood. Although TEP adhesive properties may enhance carbon export by facilitating aggregate formation, their low density can also enhance particle suspension. Factors influencing TEP regulation of particle dynamics remain unclear. To investigate EPS contributions to particle dynamics, we investigated ratios of TEP to particulate organic carbon (POC) and of CSP to POC in suspended and sinking particles collected with marine snow catchers. Samples were collected in a subarctic region near Hokkaido during a spring phytoplankton bloom and in the oligotrophic, subtropical Kuroshio region. At Hokkaido, the mean TEP : POC ratio of sinking particles (0.075 μ g Xeq. : μ g C) was > 30× lower than in suspended particles (2.3), consistent with a model prediction of selective retention of buoyant TEP‐rich particles in the upper water column. In the Kuroshio region, sinking particles also contained fewer TEP than suspended particles; however, the TEP : POC ratio of sinking particles (1.0) was > 10× higher than at Hokkaido, suggesting that TEP constitute a significant carbon component of sinking particles. These findings indicate that TEP facilitate aggregation of high‐density particles and particle sinking in the Kuroshio region. Distributions of CSP : POC ratios between suspended and sinking particles resembled TEP : POC ratios in both regions, implying a significant contribution of CSP to particle dynamics. We propose that EPS have divergent effects on suspension and sinking of marine particles, which vary with particle composition and biogeochemical conditions.
Phospholipase D (PLD), secreted into the culture medium of an actinomycete, Streptoverticillium cinnamoneum, has been purified to homogeneity and characterized. The Stv. cinnamoneum PLD efficiently catalyzes both the hydrolysis and transphosphatidylation of various phospholipids, including phosphatidylethanolamine (PE), phosphatidylcholine (PC), and phosphatidylserine (PS). However, the substrate specificity differs between the two reactions; PE serves as the most preferred substrate for the hydrolysis, but PC and PS are better substrates than PE for the transphosphatidylation. In addition, the transphosphatidylation but not the hydrolysis of PE and PC is markedly activated on the addition of metal ions, especially Al3+. Nucleotide and amino acid sequence determination of the Stv. cinnamoneum PLD revealed the presence of common structural motifs identified in all PLD sequences from various species.
