Effect of hydrogen peroxide on a natural phytoplankton community focusing on cyanobacteria, evaluating its recovery and resistant

As cyanobacteria are established into the water, different strategies are used for mitigating that, such as oxidation processes mediated by H2O2. Several authors have described them as more sensitive than Green Algae (GA) to this treatment but few studies have assessed the recovery of planktonic communities and the potential mechanisms of resistance after H2O2 exposure. Here, we tested the effect of different concentrations of H2O2 (1, 10 and 100mg.L-1) on the survival of a phytoplankton community from a freshwater reservoir co-dominated by M. aeruginosa and R. raciborskii, as well as both in isolated cultures. Before H2O2, cyanobacteria chlorophyll(Chl) was 29μg.L-1 and it contributed to most of the Chl compared to GA (14μg.L-1). After 48h, total Chl decreased in all conditions, although cyanobacteria dominated the 10mg.L-1 treatment (59%). In the 100mg.L-1 treatment, Chl decreased to 1.9μg.L-1 with dominance of GA (86%). After 7 days, only GA were detected in the conditions, except 100mg.L-1. Evaluating the community recovery, after the 7th-day, ASM-1 was added and only GA were able to grow in all the conditions, except 100 mg.L-1. We are evaluating the expression of antioxidant enzymes as well as the influence of environmental contaminants on the efficiency of H2O2 for suppressing cyanobacteria. Acknowledgement: All the supporting funding for contribution and confidence to this study: CNPq and FAPERJ (Brazil) Key words: Cyanobacteria, Green algae, Oxidation, Mitigation, Environmental Contaminatio

Growth and Saxitoxin Production by Cylindrospermopsis raciborskii (Cyanobacteria) Correlate with Water Hardness

The cosmopolitan and increasing distribution of Cylindrospermopsis raciborskii can be attributed to its ecophysiological plasticity and tolerance to changing environmental factors in water bodies. In reservoirs in the semi-arid region of Brazil, the presence and common dominance of C. raciborskii have been described in waters that are considered hard. We investigated the response of a Brazilian C. raciborskii strain to water hardness by evaluating its growth and saxitoxin production. Based on environmental data, a concentration of 5 mM of different carbonate salts was tested. These conditions affected growth either positively (MgCO3) or negatively (CaCO3 and Na2CO3). As a control for the addition of cations, MgCl2, CaCl2 and NaCl were tested at 5 or 10 mM, and MgCl2 stimulated growth, NaCl slowed but sustained growth, and CaCl2 inhibited growth. Most of the tested treatments increased the saxitoxin (STX) cell quota after six days of exposure. After 12 days, STX production returned to concentrations similar to that of the control, indicating an adaptation to the altered water conditions. In the short term, cell exposure to most of the tested conditions favored STX production over neoSTX production. These results support the noted plasticity of C. raciborskii and highlight its potential to thrive in hard waters. Additionally, the observed relationship between saxitoxin production and water ion concentrations characteristic of the natural environments can be important for understanding toxin content variation in other harmful algae that produce STX

Complete genome sequence of the sugarcane nitrogen-fixing endophyte gluconacetobacter diazotrophicus PAL5

17 p. : il.Background: Gluconacetobacter diazotrophicus Pal5 is an endophytic diazotrophic bacterium that lives in association with sugarcane plants. It has important biotechnological features such as nitrogen fixation, plant growth promotion, sugar metabolism pathways, secretion of organic acids, synthesis of auxin and the occurrence of bacteriocins. Results: Gluconacetobacter diazotrophicus Pal5 is the third diazotrophic endophytic bacterium to be completely sequenced. Its genome is composed of a 3.9 Mb chromosome and 2 plasmids of 16.6 and 38.8 kb, respectively. We annotated 3,938 coding sequences which reveal several characteristics related to the endophytic lifestyle such as nitrogen fixation, plant growth promotion, sugar metabolism, transport systems, synthesis of auxin and the occurrence of bacteriocins. Genomic analysis identified a core component of 894 genes shared with phylogenetically related bacteria. Gene clusters for gum-like polysaccharide biosynthesis, tad pilus, quorum sensing, for modulation of plant growth by indole acetic acid and mechanisms involved in tolerance to acidic conditions were identified and may be related to the sugarcane endophytic and plant-growth promoting traits of G. diazotrophicus. An accessory component of at least 851 genes distributed in genome islands was identified, and was most likely acquired by horizontal gene transfer. This portion of the genome has likely contributed to adaptation to the plant habitat. Conclusion: The genome data offer an important resource of information that can be used to manipulate plant/bacterium interactions with the aim of improving sugarcane crop production and other biotechnological applications