Li Genbao

The correlation between the variation of microcystin content and environment factors in Dianchi Lake

This paper analyzed the distribution and variation of microeystin ( M C) and physicochemical factors in Macun and Haidong bay of Dianchi Lake from April to December in 2003. The correlation of some physiochemical factors, including the concentration of total nitrogen, total phosphorous, dissolve oxygen, chlorophyll-a and Seechi depth, light intensity, pH, water temperature and dominance of Microcystis population, with microcystin was evaluated. Correlation analysis showed that the distribution of MC was significantly positive correlated with TN and N: P (P < 0. 01); and affected by Seechi depth, light intensity, dominance of Microcystis ( P < 0. 05). Multiple continuously factors analysis indicated that the distribution of MC in water of the two bays was mainly affected by total nitrogen, Seechi depth, chlorophyll-a, dissolve oxygen and total phosphorous (R-2= 0. 560, P < 0. 017).

Historical changes of phytoplankton functional groups in Lake Fuxian,Lake Erhai and Lake Dianchi since 1960s

Phytoplankton is one of the major primary producers and plays important roles in the aquatic ecosystems. The temporal and spatial variations of the algae could reflect the environmental dynamics. In light of the morphological,physiological and ecological characteristics of algae,phytoplankton functional groups theory was applied first time for these lakes to describe the tolerance and preference of algae in detail. The phytoplankton assemblages were considered to be good indicators of environmental conditions. The data of phytoplankton composition dated from the 1960 s was collected and analyzed for Lake Fuxian,Lake Erhai and Lake Dianchi,respectively. Great changes have taken place in phytoplankton assemblages in the three lakes during the past 60 years. The historical change of dominant phytoplankton functional groups was demonstrated as C,X2,Lo,F,P( 1960s)-H1,C,P( 1980s)- P,C,T( 1990s)-T( after 2000) for Lake Fuxian; J,Lo,MP,C,H1( 1960s)-C,H1( 1980s)-C,H1( 1990s)-C,H1,M( after 2000) for Lake Erhai; J,N,P,MP,Lo( 1960s)-J,P,MP,M( 1980s)-J,M( 1990s)-M( after 2000) for Lake Dianchi. The reduction of low-temperature tolerance species and increase of high-nutrition preference species dated from the 1960 s might give some indication of the environmental changes of warmer temperature and nutrients increases in the three lakes.Phytoplankton is one of the major primary producers and plays important roles in the aquatic ecosystems. The temporal and spatial variations of the algae could reflect the environmental dynamics. In light of the morphological,physiological and ecological characteristics of algae,phytoplankton functional groups theory was applied first time for these lakes to describe the tolerance and preference of algae in detail. The phytoplankton assemblages were considered to be good indicators of environmental conditions. The data of phytoplankton composition dated from the 1960 s was collected and analyzed for Lake Fuxian,Lake Erhai and Lake Dianchi,respectively. Great changes have taken place in phytoplankton assemblages in the three lakes during the past 60 years. The historical change of dominant phytoplankton functional groups was demonstrated as C,X2,Lo,F,P( 1960s)-H1,C,P( 1980s)- P,C,T( 1990s)-T( after 2000) for Lake Fuxian; J,Lo,MP,C,H1( 1960s)-C,H1( 1980s)-C,H1( 1990s)-C,H1,M( after 2000) for Lake Erhai; J,N,P,MP,Lo( 1960s)-J,P,MP,M( 1980s)-J,M( 1990s)-M( after 2000) for Lake Dianchi. The reduction of low-temperature tolerance species and increase of high-nutrition preference species dated from the 1960 s might give some indication of the environmental changes of warmer temperature and nutrients increases in the three lakes.

Improving photosynthesis of microalgae by changing the ratio of light-harvesting pigments

Changing the ratio of light-harvesting pigments was regarded as an efficient way to improve the photosynthesis rate in microalgae, but the underlying mechanism is still unclear. In the present study, a mutant of Anabeana simensis (called SP) was selected from retrieved satellite cultures. Several parameters related with photosynthesis, such as the growth, photosynthesis rate, the content of photosynthetic pigment, low temperature fluorescence spectrum (77K) and electron transport rate, were compared with those of the wild type. It was found that the change in the ratio of light-harvesting pigments in the mutant led to more efficient light energy transfer and usage in mutant than in the wild type. This may be the reason why the mutant had higher photosynthesis and growth rates.

Comparison of the photosynthetic characteristics of two developmental stages in Nostoc sphaeroides kutzing (Cyanophyta)

The photosynthetic activities between two main developmental stages, colony and hormogonium, of the edible cyanobacteriumNostoc sphaeroides Kützing, were compared. Hormogonia have a higher content of chlorophyll than that of colonies. It showed that the ratios of phycocyain (PC), allophycocyain (APC) and phycoerythrocyanin (PEC) in hormogonia and colonies were different. The room temperature chlorophyll fluorescence, 77 K chlorophyll fluorescence, measurements of PS I and PS II activities all showed that colony has higher photosynthetic competence than hormogonia. Hormogonia had a higher respiration rate were very close. The responses of hormogonia and colonies to high light illuminations also were different. Both of their oxygen evolution rates decreased quickly with the prolonged high light illumination, but hormogonia can keep relatively higher PS II activity (Fv/Fm) than that of colonies. The results suggested that colony was photosynthetically more competent than hormogonia, while the ability of hormogonia to tolerate high light illumination was higher than that of colony.

ISOLATION, IDENTIFICATION AND CHARACTERIZATION OF A STRAIN OF BLUE-GREEN ALGAE-LYSING BACTERIUM FROM LAKE DIANCHI

In this study, one high-effect algae-lysing bacterium was isolated and purified from Lake Dianchi, which was tabled as the strain DC-L5. The effect, host range, biosafety, lysing mechanism and lysing phenomenon of the algae-lysing bacteria were analyzed. Results were as the followings: The strain was identified as Bacillus pumilus by means of morphological observation and 16S rDNA sequence analysis in the CCTCC (China Center for Type Culture Collection). Toxicity test with mouse primarily showed that the strain was non-toxic. 4 kinds of DC-L5 cultures of different growth phases were added to Microcystis aeruginosa, and the strongest algae-lytic ability was found in the log phase of DC-L5 cultures, Chlorophyll a contents in culture of Microcystis aeraginosa reduced by 83.33% in 5 days. For the host range experiment, 4 kinds of dominant cyanobacteria in Lake Dianchi was researched, and average reduction rates of Chlorophyll a of 62.25% in cultures of Microcystis viridis, Microcystis wesenbergii, Aphanizomenon flos-aquae and Anabaena flos-aquae was observed with the highest 67.6% and the lowest 58.5% in 4 days respectively. After centrifugation and sedimentation, both the cells of bacteria and the cell-free suspension had strong algae-lytic activity, but the bacteria culture had the strongest algae-lytic activity, so it maybe showed the strain DC-L5 could directly cause the cyanobacterial cells agglomerated, sinked down and further lysed while the strain could excrete extra-cellular substances able to lyse cyanobacterial cells. In order to improve the algae-lytic activity of the strain DC-L5 to nature bloom, the bacteria cultures were added to nature cyanobacterial bloom dominant with Microcystis aeruginosa, which were sampled from Lake Dianchi and cultured in the lab. The result of nature bloom experiment showed the strain DC-L5 firstly disaggregated the cyanobacterial colony, reduced the floatability, degraded the pigments and then released inclusions of algal cells.