Effect of nutrient conditions on the toxicity of naphthalene to Chlorella pyrenoidosa

The toxicity of naphthalene to a freshwater microalga, Chlorella pyrenoidosa, and the subsequent recovery of algae from the damage were investigated under two nutrient conditions, either enriched with nitrogen （N） and phosphorus （P）, or starved of N and E Results showed that C. pyrenoidosa was more sensitive to naphthalene under N,P-enriched condition, and the inhibitory rate generally increased at first and then decreased gradually with the evaporation of naphthalene under both nutrient conditions. Enriched N, P reduced the inhibitory rate at initial naphthalene concentration of 5 and 10 mg/L, but enhanced it at 100 mg/L, at which more severe ultrastructure damages were found than those under N,P-starved condition. Observed damages included partly or totally disappearance of nucleolus, nuclear, and plasma membranes. According to the chlorophyll content and cell density measurements, C. pyrenoidosa could recover from naphthalene damage with initial concentrations ≤ 50 mg/L in 7 days under both nutrient conditions, while they could not recover if the initial concentration of naphthalene was at 100 mg/L. Under the N,P-starved condition, the inability of C. pyrenoidosa to recover from the naphthalene damage was consistent with the results of high inhibitory rate, low value of specific growth rate （SGR, 0.05 day-l）, and the severe destruction of cell structure. However, under the N,P-enriched conditions, the observed lower inhibitory rate, higher value of SGR （0.55 day^-1）, and the intact cell structure of most cells suggested that algae could potentially recover from the naphthalene damage.

Biomass,nutrient uptake and fatty acid composition of Chlamydomonas sp.ICE-L in response to different nitrogen sources

Nitrogen removal from media by microalgae provides the potential benefit of producing lipids for biodiesel and biomass. However, research is limited on algal growth and biomass under different nitrogen sources and provides little insight in terms of biofuel production. We studied the influences of nitrogen sources on cell growth and lipid accumulation of Chlamydomonas sp. ICE-L, one of a promising oil rich micro algal species. Chlamydomonas sp.ICE-L grown in NH_4 Cl medium had maximum growth rate. While the highest dry biomass of 0.28 g/L was obtained in media containing NH_4NO_3, the highest lipid content of 0.21 g/g was achieved under nitrogendeficiency condition with a dry biomass of 0.24 g/L. In terms of total polyunsaturated fatty acids（PUFAs）production, NH_4NO_3 and NH_4 Cl media performed better than nitrogen-deficiency and KNO_3 media.Furthermore, NH_4NO_3 and NH_4 Cl media elucidated better results on C18：3 and C20：5 productions while KNO_3and-N conditions were better in C16：0, C18：1 and C18：2, comparatively.

Effects of growth and starvation conditions on bacterial adhesion to plastic surfaces

The effects of nutrient conditions on the formation of plastisphere were unclear.This study investigated the impacts of growth and starvation conditions on the adhesion of both Gram-negative and Gram-positive bacteria to six plastics in both salt solution and river water.We found that bacteria grown in nutrient-rich condition(LB)contained higher adhesion capability to all six plastics than those grown in nutrient-restricted condition(M9).Starvation process yet decreased bacterial adhesion to plastics under all examined solution conditions.Via deep investigation of the respective contribution of bacterial shape,motility,flagella,and extracellular polymeric substances(EPS)particularly its overall amount,functional groups,major components together with their corresponding secondary structure,as well as its hydrophobicity,the mechanisms driving to the different adhesion capability of bacteria onto plastics subjected to varied nutrient conditions were systemically determined.We found that the enhanced hydrophobicity of bacteria grown in LB contributed to the greater bacterial adhesion to six plastics than those grown in M9.While the changed bacterial shape,the reduced bacteria motility,loss of flagella,and the reduced hydrophobicity of EPS resulted from the change of the composition of proteins and monosaccharides all contributed to the reduced bacteria adhesion to plastics after starvation process.This study indicated that the formation of plastisphere in environment could be greatly influenced by the nutrient condition for bacterial survival,which would affect the environmental risks of plastics.