Key physiological traits and chemical properties of extracellular polymeric substances determining colony formation in a cyanobacterium

Colony formation of cyanobacteria is crucial for the formation of surface blooms in lakes.However,the underlying mechanisms of colony formation involving in physiological and cell surface characteristics remain to not well be established.Six cyanobacterial Microcystis strains(including both unicellular and colonial ones)were employed to estimate the influences of their physiological traits and the composition of extracellular polymeric substances(EPS)on colony or aggregate formation.Results show that raising the number of the photosynthetic reaction center and light-harvesting antenna in the PSII and reducing the growth rate were the major physiological strategies of Microcystis to produce excess EPS enhancing colony formation.Tightly bound EPS(T-EPS)was responsible for colony formation,which approximately accounted for 50%of the total amount of EPS.Five fluorescent components(protein-,tryptophan-,and tyrosine-like components and two humic-like components)were found in the T-EPS,although the amounts of these components varied with strains.Importantly,colonial strains contained much higher tyrosine-like substances than unicellular ones.We suggest that tyrosine-like substances might serve as a crosslinking agent to connect other polymers in EPS(e.g.,proteins or polysaccharides)for colony formation.Our findings identified key physiological traits and chemical components of EPS for colony formation in Microcystis,which can contribute to a better understanding on the formation of Microcystis blooms.

Arbuscular Mycorrhizal Fungi Alleviates Salt-Alkali Stress Demage on Syneilesis aconitifolia

Syneilesis aconitifolia is a potential ground cover and decorative material in gardens,which exhibits a strong salt-alkali tolerance,and also has medicinal value.In this study,the arbuscular mycorrhizal(AM)fungi community in the soil surrounding S.aconitifolia roots in the Songnen saline-alkali grassland was used as the inoculation medium for a pot cultivation experiment.After normal culture for 90 days,NaCl and NaHCO_(3) solutions were applied to subject plants to salt or alkali stress.Solution concentrations of 50,100,and 200 mmol/L were applied for 10 days,and mycorrhizal colonization,biomass,relative water content(RWC),chlorophyll concentration,malondialdehyde(MDA)concentration,antioxidant system activity,and osmomodulator concentration were determined to identify the effects of AM fungi on root colonization status and salinity tolerance in S.aconitifolia.There were three key results.(1)Compared to the controls,the intensity and rate of colonization decreased under saline-alkali stress,and the adaptability of AM fungi under low concentration alkali stress was higher than that under salt stress.(2)The AM fungi could increase the biomass,RWC,and chlorophyll concentration,and decrease the MDA concentration of S.aconitifolia to some extent.With an increase in the salt or alkali solution concentration,AM fungi not only upregulated the activity of the antioxidant system,but also increased the concentration of osmotic regulatory substances.(3)A multivariate analysis of variance(ANOVA)and radar map analysis showed that the mechanisms of resistance to salt and alkali stress were not the same in S.aconitifolia.In the salt treatment,AM fungi mainly regulated salt stress through osmotic regulatory substances such as soluble sugars,soluble proteins,and proline.In the alkali treatment,AM fungi mainly regulated alkali stress through glutathione(GSH),soluble sugars,and MDA.The results showed that the colonization rate of S.aconitifolia under low concentration alkali stress was higher than that under salt stress,and the inoculation of AM fungi could significantly reduce the MDA concentration of S.aconitifolia plants under salinity and alkali stress,and improve the antioxidant enzyme activity and osmoregulatory substance accumulation,thereby improving the salinity tolerance of S.aconitifolia.