Studies On Chemical Compositions Of Natural Colloids And Their Biological Effects

Colloids generally refer to microparticles, macromolecule or macromoleculepolymers, of which molecular weights range from 1 k Dalton to 100 k Dalton, orparticle size between 1 nm to 1μm. They widely exist in natural fresh water orseawater environment and origin mainly from terrigenous river input, resuspendedseawater sediment and biological metabolism process in water column. Besides,colloidal organic substance can also be produced by the transformation of particleorganic substance during biological or non-biological processes. Therefore naturalcolloid mainly contains organic polymer(such as polyoses, protein, polypeptide, fulvicacid and cell chippings) and inorganic particle(such as iron oxides, manganese oxides,silicon dioxide and clay minerals), as well as living body(bacteria and virus). Becauseof the small size, huge specific area and abundance of organic functional group, theybecome important vector of nutritive organic carbon, nutrients, trace metal, traceorganic matter and pigment. Researches showed that growth and metabolism rate ofbacteria in the existence of high molecular weight colloids were three to six timeshigher than those of lower molecular weight colloids. Colloidal organic mattersexposed to sunshine can release bio-available nitrogen-rich components and promotebiological degradation. Dissolved organic matter is an important source ofbio-available nitrogen for coastal bacteria and phytoplankton. Increase of their contentswill promote the propagation and growth of sea algae, and lead to red tide at certainconditions. As the result, studies on chemical compositions of natural colloids and their biological effects will make significant sense for discovering the mechanism of globalclimate change and marine red-tide as well as further understanding the bioavailabilityof biogenic element and their biological effects.In our previous work, biogeochemical behavior and chemical compositions, ofmarine colloid had been studied, however, the description of chemical composition, aswell as bioavailability need to be farther proved. In this work, photosynthetic bacteria,natural bacterial community; marine algae were the targets for study of influence ofcolloids collected from different sources and with different particle size and organiccarbon content, on the growth of organism. Nitrogen, phosphorus, iron, amino acid andcarbohydrate contents in their truly dissolved phase and colloidal phase fromJiulongjiang river, Jiulongjiang estuary and seawater of Fujian, as well as theirdistribution pattern were also investigated to reveal the relationship between thechemical compositions and the bioavailability of natural colloids, and explore themechanism that how natural colloids effect the organism growth. The results are asfollows:1. In the water samples of Jiulongjiang river, Jiulongjiang estuary and XiamenBay, inorganic nitrogen, all species of phosphorus and ferric ion mainly distributed intheir truly dissolved phase(＜10 kDa), and organic nitrogen and ferrous iron mainly incolloidal phase(10 kDa～0.22μm), during the study period. In both truly dissolvedand colloidal phase, all species of nitrogen and total iron contents decreased fromriver-end to sea-end. Content of truly dissolved Fe²⁺ was the lowest in estuary sampleswhile contents of "dissolved" and colloidal Fe²⁺ was the highest in estuary samples.2. In the Jiulongjiang river estuary, amino acids and carbohydrate from seawatersample mainly distributed in truly dissolved phase, and amino acid from both river andestuarine water samples mainly in colloidal phase. while their carbohydrate mainly intruly dissolved phase. Colloids had 16 kinds of amino acid components from threesources. The dominance components were glycine+ threonine, aspartate, glutamic acidand alanine+tyrosine. The compositions of neutral aldose from three sources were similar with each other. Glucose and galactose were dominant components in colloidalphase.3. Marine colloids had significant enhancement effect on the growth of PSB. Withthe condition suitable for PSB, marine colloids with particle size of 10 kDa～0.22μmcan increase the relative growth rate by 11.3%～22.6%, which were higher than that ofmarine colloids with particle size of 1 kDa～10 kDa. Relative growth rates of PSB ofsamples from three sources with different organic carbon concentrations were 3.6%～196.2% on average, and 48.4%～133.9% for natural bacterial community on average,both of which had non-correlation with organic carbon concentration. Enhancementeffect for PSB of colloids of river water was much higher than that of seawater, both ofwhich were higher than that of estuarine water. Marine colloids of high molecularweigh could increase contents of monounsaturated fatty acid C_16:1 and C_18:1 andcontent of high unsaturated fatty acid C_20:4 in PSB.4. Marine colloids also had significant enhancement effect on the growth ofmarine Chlorella, Platymonas subcordiformis and Isochrysis galbana. Their averagegrowth rates were 2.9%～28.9% in marine colloids with particle size of 10 kDa～0.22μm and organic carbon concentrations of 4.8μmol/L～238.4μmol/L, havingrelationship with organic carbon concentrations. Enhancement effect of colloids withparticle size of 10 kDa～0.22μm was 1.2～1.9 times higher than that of colloids withparticle size of 1 kDa～10 kDa for these three algae, indicating that the bioactivity ofhigh molecule weights colloids was higher than low molecule weights colloids. Whatwas more, enhancement effect of river colloids on marine Chlorella was larger thanestuarine colloid.5. The influences of colloid to fatty acid components of marine algae differedfrom each alga. Fatty acid contents in Marine Chlorella and P. subcordiformis werehighest when they were cultured in truly dissolved phase while fatty acid contents in I.galbana were highest when C_COC=119.2μmol/L in kinds of culture mediums withdifferent organic carbon concentrations(C_COC) and particle size of 10 kDa～0.22μm. Fatty acid contents in marine Chlorella and I. galbana cultured in colloidal mediaswith particle size of 10 kDa～0.22μm were higher than those cultured in colloidalmedias with particle size of 1 kDa～10 kDa, but it was inversed for P. subcordiformis.Saturated fatty acid contents in marine Chlorella cultured in colloids from river waterwere higher than those cultured in colloids from estuarine water; however, theunsaturated fatty acid contents were lower. Contents of total unsaturated fatty acid inthese three kinds of algae were highest in the algae cultured with colloid as solenitrogen source and followed by the algae cultured with colloid as sole phosphorussource, while lowest in the algae cultured with colloid as sole iron source.