Interactions Between Light and Production of Microcystins in the Toxic Cyanobacterium Microcystis

Cyanobacterial harmful algal blooms (cHABs) are characterized by the formation of toxins that can impact animal health, cause water quality issues, and recreational hazards. Microcystis, a common genus of cyanobacteria, produces the potent protein phosphatase inhibitor microcystins. Microcystins are nitrogen-rich and have an associated metabolic cost for production. Some outstanding questions in the study of cHABs is why are microcystins produced, what are the benefits of toxin formation, and why only some Microcystis strains produce microcystins? We examined a potential biochemical role for microcystins in the cyanobacterial photosystem regulation in response to various light conditions. Single-celled culture strains of toxic and non- toxic Microcystis aeruginosa were grown under different light irradiances. High-light conditions caused light stress based on decreased photosynthetic efficiency. Cells responded over 2-3 days by decreasing their chlorophyll and phycobilisome content per cell in unison. Looking at a natural system over a diurnal cycle of changing light intensities, Microcystis responded to high-light environments via vertical migration deeper in the water column to avoid light stress. In one culture and in situ, there were no changes in microcystins concentration per cell, but one strain showed decreased microcystins under low-light. Therefore, microcystins protein phosphatase activity may not be involved with phosphorylation/dephosphorylation under high-light. High-light environments are also associated reactive oxygen species (ROS) production. We investigated if microcystins were linked to ROS sensitivity by examining how three chlorophytes and seven cyanobacteria responded to the ROS compound hydrogen peroxide (H2O2). There was no evidence that toxic cyanobacteria were more sensitive to ROS than non-toxic cyanobacteria or chlorophytes. Addition of H2O2 did not change the microcystins concentration per cell. While these experiments did not elucidate the biochemical function of microcystins in Microcystis, they provided valuable information for water quality managers. cHAB monitoring programs must carefully consider vertical migration away from the surface during high-light conditions. The use of H2O2 as a control mechanism may not selectively remove toxic cyanobacteria. Despite visual similarities, Microcystis is composed of diverse species with a wide-range of responses to light and ROS. Care must be taken when applying conclusions using a limited number of strains to broader populations

Increased autoantibodies against brain tissue in schizophrenia

The present study investigates the short- and long-term outcomes of a computer-assisted cognitive remediation (CACR) program in adolescents with psychosis or at high risk. 32 adolescents participated in a blinded 8-week randomized controlled trial of CACR treatment compared to computer games (CG). Clinical and neuropsychological evaluations were undertaken at baseline, at the end of the program and at 6-month. At the end of the program (n = 28), results indicated that visuospatial abilities (Repeatable Battery for the Assessment of Neuropsychological Status, RBANS; P = .005) improved signifi cantly more in the CACR group compared to the CG group. Furthermore, other cognitive functions (RBANS), psychotic symptoms (Positive and Negative Symptom Scale) and psychosocial functioning (Social and Occupational Functioning Assessment Scale) improved signifi cantly, but at similar rates, in the two groups. At long term (n = 22), cognitive abilities did not demonstrated any amelioration in the control group while, in the CACR group, signifi cant long-term improvements in inhibition (Stroop; P = .040) and reasoning (Block Design Test; P = .005) were observed. In addition, symptom severity (Clinical Global Improvement) decreased signifi cantly in the control group (P = .046) and marginally in the CACR group (P = .088). To sum up, CACR can be successfully administered in this population. CACR proved to be effective over and above CG for the most intensively trained cognitive ability. Finally, on the long-term, enhanced reasoning and inhibition abilities, which are necessary to execute higher-order goals or to adapt behavior to the ever-changing environment, were observed in adolescents benefi ting from a CACR