aeruginosa FACHB 469, and the green microalga Chlamydomonas microsphaera FACHB 52. In monocultures, the growth of all three strains was inhibited by UVB. In mixed cultures, enhanced UVB radiation resulted in decreased percentages of the two M. aeruginosa strains (19%–22% decrease on d 12 of the competition experiment). UVB radiation resulted in increased contents of chlorophyll a, b, and carotenoids (CAR) in C. microsphaera, and decreased contents of allophycocyanin (APC) or phycocyanin in the two Microcystis strains. All Wnt inhibitor three strains showed increased levels of UVabsorbing compounds and intracellular reactive oxygen species

under 0.372 W · m−2 UVB radiation, and decreased light compensation points, dark respiratory rates, and maximal quantum efficiency of PSII. After a 20 h recovery, the photosynthetic oxygen evolution of C. microsphaera was restored to its maximum value, but that of Microcystis strains continued to decrease. Nonphotochemical quenching was increased by UVB radiation in C. microsphaera, but was unaffected in the two M. aeruginosa strains. Our results indicated that C. microsphaera has a competitive advantage relative to Microcystis during exposure to UVB irradiation. “
“The mechanisms of microalgal senescence may play an important role in nutrient recycling and enhanced survival. However, the aging physiology of microalgae is an understudied phenomenon. To investigate

the patterns of conditional senescence in Chlamydomonas reinhardtii P. A. Dangeard, we used MCE a cell wall-less strain, transformed PXD101 with a reporter gene to infer changes in photosynthetic gene expression. We examined plastid ultrastructure, photosynthetic function, and photoprotective mechanisms during aging in batch cultures. LHCII transcription levels decreased before the population entered stationary phase, and the characteristic transcriptional light-shift response was lost. A decline in

photosynthetic proteins with a concomitant increase in the photoprotective protein, LHCSR, was observed over time. However, nonphotochemical quenching remained stable during growth and stationary phase, and then declined as alternative quenching mechanisms were up-regulated. Photosynthetic efficiency declined, while Fv/Fm remained stable until the death phases. As the culture progressed through stationary phase, disorganization of the chloroplast was observed along with an increase in cytoplasmic oil bodies. We also observed a partial recovery of function and proteins during the final death phase, and attribute this to the release of nutrients into the medium from cell lysis and/or active secretion while cells were senescing. Allowing open gas exchange resulted in high levels of sustained starch production and maintained maximum cell density, prolonging the stationary phase. “
“Dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP) are sulfur compounds that may function as antioxidants in algae.