| Achnanthidium catenatum belongs to Achnanthes,which is a special algae in Achnanthes diatoms.Species from Achnanthes mostly are periphytic except A.catenatum,which is the only diatom that can grow both in plankton and fixedly,exist in monomer and survive in the form of chain colony.At present,the A.catenatum is the only fresh water bloom-forming species in Achnanthes because of its planktonic characteristics.The A.catenatum blooms have been found in freshwater lakes and reservoirs around the world.Therefore,in this experiment,we explored the A.catenatum strain which were collected from Dongqian Lake,in Ningbo,Zhejiang province.It can provide scientific basis for the prevention and control of A.catenatum blooms.Nutrient salts(nitrogen(N),phosphorus(P),silicon(Si))and bacteria were two main factors affecting the growth of A.catenatum,the environmental factors such as N,P,Si nutrients at different concentrations and biological factors such as Escherichia coli(DH-5α),Pseudomonas spp(BNCC223900),mixture of E.coli and P.spp were designed under laboratory conditions.By measuring monomer and colony-forming cell density,extracellular polysaccharide content,malondialdehyde content,photosynthetic activity of A.catenatum,and the effects of these environmental and biological factors on the growth of A.catenatum were analyzed.The experimental results showed that:1.N,P and Si nutrients all had significant effects on cell density of A.catenatum(P < 0.05).The monomer and colony-forming cell density of A.catenatum increased with the increase of P(0-3.5 mg/L)and Si(0-10 mg/L)nutrients concentration in each experimental group under the different concentration of P and Si;compared with high concentration of N(0-5 mg/L)nutrients,the growth of A.catenatum in low N nutrient concentration was better than that in high N concentration,the growth of monomers and colony-forming cells of A.catenatum was inhibited when the concentration of N increased to 80 mg/L,and the concentration of malondialdehyde reached the highest at the same time.These results showed that,A.catenatum was more suitable for growth under low N concentration,but it could adapt to a wide range of P and Si nutrient concentration.The results of physiological indexes during the experiment showed that,the content of colloidal and attached exopolysaccharides increased with the increase of N and Si nutrient concentration;however,under high P concentration(3.5 mg/L),the content of colloidal and attached exopolysaccharides of A.catenatum was lower than that in the middle phosphorus(0.5 mg/L).The results showed that the high concentration of N and Si promoted the exopolysaccharide secretion of A.catenatum,while the high concentration of P inhibited the exopolysaccharide secretion of A.catenatum.2.The results of co-culture experiments of different concentrations of E.coli,P.spp and mixed E.coli and P.spp with A.catenatum showed that: the total cell density decreased with the increase of E.coli concentration,but the content of exopolysaccharide continued to increase;the change of total cell density of A.catenatum showed that low concentration of P.spp(< 0.6%)promoted the growth of A.catenatum,but high concentration(1%)inhibited the growth of A.catenatum significantly.The results showed that different bacteria had different effects on the growth of A.catenatum,and there were significant differences in cell density between different bacterial concentrations(P < 0.05).E.coli and P.spp inhibited the growth of monomer cells in A.catenatum,while the growth of chain colony-forming cells was obviously promoted.Under mixed bacteria conditions,the effects of different concentration of bacteria on the growth of A.catenatum were different,but there was no significant effect on malondialdehyde content and photosynthetic activity(Fv: Fm value)of A.catenatum(P > 0.05). |
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