The breadth of the humoral immune response following SARS-CoV-2 infection was indicated to be important for recovery from COVID-19. Recent studies have provided valuable insights regarding the dynamics of the antibody response in symptomatic COVID-19 patients. However, the information regarding the dynamics of the serological and cellular memory in COVID-19 recovered patients in scarce. It is imperative to determine the persistence of humoral memory in COVID-19 recovered patients as it will help to evaluate the susceptibility of recovered patients to re-infection. Here, we describe the dynamics of both the SARS-CoV-2 specific serological and B cell response in COVID-19 recovered patients. We found that symptomatic SARS-CoV-2 patients mount a robust antibody response following infection however, the serological memory decays in recovered patients over the period of 6 months. On the other hand, the B cell response as observed in the SARS-CoV-2 specific memory B cell compartment, was found to be stable over time. Moreover, the frequency of SARS-CoV-2 specific B cell plasmablasts was found to be associated with the SARS-CoV-2 specific antibody levels. These data, suggests that the differentiation of short-lived plasmablasts to become long-lived plasma cells is impaired and the main contributor of antibody production are the short-lived plasmablasts. Overall, our data provides insights regarding the humoral memory persistence in recovered COVID-19 patients. Notwithstanding the insights from this study, it is still to be determined if the persistence of SARS-CoV-2 memory B cells can be considered as a correlate of protection in the absence of serological memory.

The D5 desaturase mutant (P127) of the microalga Lobosphaera incisa is a promising organism for large-scale production of the valuable LC-PUFA dihomo-g-linolenic acid (DGLA, 20:3 n-6). We examined the potential of P127 for DGLA production under nitrogen (N) starvation conditions, triggering the deposition of DGLA in triacylglycerols, and developed a strategy for optimization of the DGLA productivity in highdensity cultures. Towards this end, the effects of initial biomass concentration (1, 2, and 4 g L À1 ) and PAR irradiance (170 and 400 mmol m À2 s À1 ) on DGLA and total fatty acid (TFA) production were studied. The highest DGLA and TFA percentages (10 and 38% of dry weight, respectively) were displayed by the cultures initiated at 1 g L À1 and grown under a moderate irradiance. Higher irradiances and lower starting biomass content facilitated oleic acid accumulation at the expense of DGLA. Maximum volumetric productivities of TFA and DGLA were recorded in the cultures started at 2 g L À1 biomass and grown under 400 mmol PAR m À2 s À1 . We show that a sufficiently high starting culture density should be combined with a mild light stress to facilitate the production of biomass enriched in DGLA-containing triacylglycerols.Practical applications: The D5 desaturase mutant of L. incisa, P127, is a rare green source of DGLA, a LC-PUFA with valuable pharmaceutical and neutraceutical properties. We report on the optimization of DGLA production by the nitrogen-starving indoor cultures of P127. Stresses, such as N starvation and/or high irradiances, promote accumulation of lipids by microalgal cells. On the other hand, excessively severe stress is deteriorative for the target LC-PUFA accumulation. An important outcome of the present work is establishing physiological constrains of DGLA productivity and finding an approach to balance starting cell density vs. irradiance in order to maximize DGLA yields. Findings of the present work lay a foundation of the efficient production of DGLA using upscaled cultures of P127.

Here, we describe the longitudinal kinetics of the serological response in COVID-19 recovered patients over the period of 14 months. The antibody kinetics in a cohort of 200 recovered patients with 89 follow up samples at 2-4 visits reveal that RBD-specific antibodies decay over the period of 14 month following the onset of symptoms. The decay rate is associated with the robustness of the response thus, recovered patients that exhibit elevated antibody levels at the first visit, experience faster decay. We further explored the longitudinal kinetics differences between recovered patients and naive BNT162b2 vaccinees. We found a significantly faster decay in naive vaccinees compared to recovered patients suggesting that the serological memory following natural infection is more robust compared to vaccination. Our data highlights the differences between serological memory induced by natural infection vs. vaccination, facilitating the decision making in Israel regarding the 3rd dose vaccination.