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Cadmium recovery by a sulfate-reducing magnetotactic bacterium, Desulfovibrio magneticusstrain RS-1, was investigated. D. magneticusprecipitated >95% of cadmium at an initial concentration of 1.3 ppm in the growth medium. Electron microscopic analysis revealed that D. magneticusformed electron-dense particles on its surface when cultivated in the presence of cadmium ions (Cd2+). Sulfide was also found in the precipitate, and the composition ratio of sulfide/cadmium was 0.7. Sixty percent of viable RS-1 cells was recovered by a simple magnetic separation revealing the removal of 58% cadmium from the culture medium.

Among forty strains of marine cyanobacteria isolated in our laboratory, five strains had 1–3 different plasmids. The unicellular marine cyanobacterium,Synechococcussp. NKBG 042902, contains at least three plasmids (pSY09, pSY10, and pSY11). However, these plasmids are cryptic. Therefore, a hybrid plasmid pUSY02 containing the 1.4kb HindIII fragment of pSY11 andEscherichia coliplasmid pUC18 was constructed. The plasmid pUSY02 transformed both marineSynechococcussp. NKBG042902-YG1116, which is a cured strain, and fresh waterAnacystis nidulansR2 by dark incubation or Ca2+treatment. However, the plasmid pSG111 constructed from the plasmid DNA ofA. nidulansR2 failed to transform marineSynechococcussp. Electroporation was also applicable to transformation of marineSynechococcussp. and fresh waterA. nidulansR2. The plasmid pUSY02 was rapidly introduced into marineSynechococcussp.

A photobioreactor was constructed in the form of a Perspex column 900 mm tall with an internal diameter of 70 mm. The reactor volume was 1.8 L and the light source consisted of a metal-halide lamp to reproduce sunlight. Light was distributed through the culture using a new type of optical fiber that diffuses light out through its surface, perpendicular to the fiber axis. A cluster of 661 light-diffusing optical fibers (LDOFs) pass from the light source through the reactor column (60-cm culture depth) and are connected to a mirror at the top of the reactor. This biosolar reactor has been used for the production of glutamate from CO2by the marine cyanobacterium Synechococcus sp. NKBG040607. We present here details of the construction of the biosolar reactor and characterization of its properties. The effect of light intensity on glutamate production was measured. Carbon dioxide-to-glutamate conversion ratios were determined at different cell densities: the maximum conversion ratio (28%) was achieved at a cell density of 3x108cells/mL. A comparison of glutamate production using the LDOF biosolar reactor described here with production by batch culture using free or immobilized cells showed that use of an optical-fiber biosolar reactor increased glutamate-production efficiency 6.75-fold. We conclude that as a result of its high surface-to-volume ratio (692/m) increased photoproduction of useful compounds may be achieved. Such a system is generally applicable to all aspects of photobiotechnology.

The aim of this work is to elucidate the iron uptake mechanism in the magnetic bacteriumAquaspirillumsp. AMB-1, which can utilize a wide variety of iron chelates. However, no siderophore could be detected in spent culture. A 400-bp DNA fragment was amplified by polymerase chain reaction (PCR) from the genomic DNA of AMB-1, using primers designed from thesfuCgene ofSerratia marcescens. This gene encodes a nucleotide binding protein in the periplasmic binding protein (PBP) dependent iron transport system. The amplified fragment was homologous with the conserved sequence ofsfuC. Our results suggest that a nucleotide binding protein mediated iron transport system similar to that observed inSerratia marcescensis present inAquaspirillumsp. AMB-1.

A light diffusing optical fiber (LDOF) photobioreactor with an improved gas input system has been used for the high-density culture of a marine cyanobacterium Synechococcus sp. Optimum conditions for CO2 removal and biomass production were investigated. Maximum CO2 removal of 4.44 g/L/d was achieved using an initial cell concentration of 6.8 g/L. The biomass yield was 0.97 g/L for a 12-culture time. Continuous cultures, in which medium was filtered using a ceramic membrane module, showed enhanced growth, with a final cell concentration of 11.2 g/L. These results demonstrate the potential of LDOF photobioreactor units for CO2 removal and biomass production using marine cyanobacteria.