To understand the functional roles of microorganisms in aquaculture, the interaction between the microalga Nannochloropsis oculata and the ciliate Euplotes sp., which occurs in mass culturing of the rotifer Brachionus plicatilis, was examined. We carried out culture experiments of Euplotes sp. initially inoculated at densities of 1 cell/drop 0.15ml, 30 cells ml-1, and 400 cells ml-1. Euplotes sp. were fed dietary bacteria together with N. oculata (initial density; 1×107 cells ml-1), the algal culture filtrate, or no algae (control experiment). N. oculata at a density of 1×107 cells ml-1 or more clearly suppressed the growth of Euplotes sp. in all experiments. The final yields were 20∼49% of the controls. However, the culture filtrate of N. oculata did not suppress the growth of Euplotes sp. On the contrary, the co-existence of increased Euplotes sp. of ca. 1000 cells ml-1 or more distinctly caused the algae to aggregate, and inhibited the algal growth by 80% of the final densities. Consequently, antagonistic interactions, appearing to be density-dependent, were found to occur between these microbes. To our knowledge, this is the first report on the anti-ciliate activity of the algae.
A mutant (RCD1) defective in rhizosphere competence of Burkholderia cepacia MRT11, an effective root colonizer of radish, was isolated by successive single colony transfers. The ability of RCD1 to colonize radish root was reduced to about one % of that of the wild type strain MRT11. The properties considered to be involved in the colonization of the roots were compared between the two strains. There were no significant differences between the two strains in motility, chemotactic response to root exudates, cell surface hydrophobicity, adherence to roots, and in vitro antibiosis to fungal pathogens. There were also not significant differences in the growth of most media used in this study, such as nutrient broth, minimum medium with glucose, galactose, or casamino acids as the sole carbon source. However, the growth of MRT11 in radish root exudate was greater than that of RCD1, suggesting that the ability to utilize root exudates might be responsible for part of the rhizosphere competence of B. cepacia MRT11. The properties that were impaired in RCD1 are further discussed in relation to the utilization of root exudate.
Growth of the marine bacterial strain KE10, Vibrio harveyi, Cytophaga latercula, and Escherichia coli was examined in two different concentrations of organic nutrients; 0.2 and 200mg carbon per liter (C/1). All bacteria grew at these two concentrations with a relatively lower growth rate at 0.2mg C/1. The ratio of the growth rate at 0.2mg C/1 to 200mg C/1 ranged from 0.70 to 0.44 for KE10 and 0.34 to 0.16 for the other bacterial strains tested. At the lower concentration, 0.2mg C/1, KE10 showed the highest growth rate among the strains examined. At the stationary growth phase, KE10 reached 2.8×106cells/ml, which was ten times higher than the maximum cell densities of other bacterial species. KE10 was a gram-negative, aerobic, rod-shaped bacterium and was motile by flagella. A phylogenetic analysis based on 16S rRNA gene and phenotypic characteristics showed that KE10 belonged to the genus Alteromonas and was closely related to Alteromonas infernus.
The present study revealed that although very low concentrations (≤5μg/ml) of 2, 4-Dichlorophenoxyacetic acid (2, 4-D), a common herbicide, stimulated nitrate reductase (NR), nitrite reductase (NiR) and leghaemoglobin, in root nodules of Glycine max, higher cocentrations (>5μg/ml) were inhibitory. The results have also shown that treatment of rhizobia with different concentrations of 2, 4-D also affected NR and NiR of cytosol fraction of root nodules. This shows that there is a relationship between plant NR, NiR and the bacteroids in the root nodules.
The abundance of culturable aerobic heterotrophic bacteria and fungi, as well as some physicochemical parameters of the topsoils of vegetation systems, were assessed during the dry and wet seasons of 1996. The physicochemical parameters did not vary significantly among the plots. Bacterial populations ranged from 104 to 107cfu/g, while fungal counts were in the order of 104cfu/g. Bacteria densities and the bacteria/fungi ratio were higher during the wet season, while the fungal counts were consistently lower than bacterial counts in all cases. The bacterial and fungal species isolated did not follow any defined distribution pattern.
The occurrence and distribution of Dictyostelid Cellular Slime Molds (CSMs) in the forest soils of Izu Peninsula, Shizuoka were examined. Dictyostelium mucoroides complex, D. purpureum, Polysphondylium violaceum and P. pallidum were isolated. The total number of clones isolated was 2, 837 and the total sample frequency was 98%. Reference was made to the correlation between environmental conditions and occurrence of CSMs.
To examine diversity of endophytic microbes in plants, we have devised a method for isolation. We could isolate at least one kind of microbes from all the plants examined. One hundred sixty two fungi and 166 bacteria were obtained from 57 plants in Hokkaido Japan and 86 fungi and 56 bacteria were obtained from 20 plants in Java Indonesia. Among those isolates shown to have interesting bioactivities, 9 filamentous fungi were selected and taxonomic study was carried out on the basis of 18S rDNA base sequence analyses. These experiments suggest that endophytes from various plants have great diversity and useful characteristics for biotechnological applications.
The world population is estimated to reach 9.8 billion in 2050. To secure food resources, methods of protecting agricultural products from harmful insects, microorganisms and other organisms have been examined using various synthetic chemical pesticides. However, many pesticides act as endocrine disrupters in humans and other organisms. To prevent these effects, biological controls of biological hazards are useful and effective to safely produce food resources such as fishery and agricultural products. The following mini-reviews present clues to solve the latest problems. 1) Improvement and mechanism of action of microbial pesticides (Bt) (Michio Himeno) 2) Possibility for bio-control of harmful diatom blooms in Coscinodiscus wailesii by marine bacteria (Satoshi Nagai and Ichiro Imai) 3) Virus adaptation to plants (Iwao Furusawa) 4) Biological control of fish viral diseases by Anti-Viral Substance Producing Bacteria (Mamoru Yoshimizu and Yoshio Ezura)
The spore-forming, gram-positive bacterium, Bacillus thuringiensis (Bt), is a ubiquitous soil micro-organism. Since the first Bt was isolated as a pathogen of silkworm in 1901, it has become possible to group these isolates into 50 serovars. At present it has been estimated that over 60, 000 isolates are being maintained in culture collections worldwide. The delta-endotoxin products in Bt during spore-forming stage are most widely used as biological control agents and pesticides that do not pollute the enviroment. The delta-endotoxin is an insecticidal protein that be coded by cry gene to constructs a crystalline protein bodies. After a susceptible insect ingested these crystalline bodies, the proteins are dissolved in midgut by the digestive juice and changed to an active toxin protein. In this review, the mode of action of the delta-endotoxin, improvement of Bt products by gene manipulation for the development of biopesticides (recombinant microbes) against Bt-resistance pests and also transgenic plants incorporating the cry genes were introduced.
In recent years, increasing interest has focused on bacteria that affect the physiology and ecology of microalgae such as survival and sexual reproduction. In the Japanese coastal sea areas such as Harima-Nada, the giant diatom Coscinodiscus wailesii can cause serious damage to Nori (Porphyra) culture during the autumn and following spring. A marine bacterium Alteromonas sp., lethal to C. wailesii, was isolated from eastern Seto Inland Sea, Japan. The existence of bacteria that induce sperm formation in this diatom was also confirmed in the coastal area. To try to regulate those harmful algal blooms by microorganisms, the interactions between these bacteria and microalgae have been investigated. Namely, the lethal processes, the algicidal ranges, the effects of incubation conditions such as temperature, irradiance, cell densities of bacteria on these bacterial activities, and the chemicals produced by bacteria were studied. These studies strongly suggest that these bacteria play an important role in the development and decomposition of algal blooms, and in the usual succession of microalgal community structures. Since, there is a possibility of controlling the occurrence and extermination of these harmful algal blooms such as C. wailesii, the efforts should be offered to investigate these microorganisms.
Bromoviruses are a group of spherical plant RNA viruses. Their genome consists of approximately 8, 000 nucleotides in total and contains only four genes: 1a and 2a genes necessary for viral RNA replication, 3a gene required for viral cell-to-cell movement and the coat protein gene. Bromoviruses produce a large number of progeny virus particles in host plants, but never induce death. Therefore, we suppose that these viruses are adapted to host plant cells in various ways. Here, I describe molecular mechanisms of bromovirus adaptation to host plant cells and non-host plants.
Many bacteria producing anti-viral substances were isolated from the aquatic environment. Fish intestinal bacteria such as Aeromonas spp. and Vibrio spp. producing anti-viral substances were isolated from intestinal contents of masu salmon (Oncorhynchus masou), Japanese flounder (Paralichthys olivaceus) and barfin flounder (Verasper moseri). These Aeromonas strains produced anti-infectious hematopoietic necrosis virus (IHNV) substances and Vibrio strains showed anti-IHNV, Oncorhynchus masou virus (OMV) and barfin flounder nervous necrosis virus (BF-NNV) activities. When Aeromonas spp. strains M-26 and M-38 were mixed with food pellets and fed to rainbow trout (O. mykiss) and masu salmon, both bacteria became dominant in the intestinal microflora and anti-IHNV activity was observed in homogenates of intestinal contents. These rainbow trout and masu salmon fed the Aeromonas spp. showed more resistance to the artificial IHNV challenge test. Barfin flounder fed Vibrio sp. strain 2IF6a with Altemia salina showed the anti-OMV and BF-NNV activities in the intestinal contents. Larvae fed the Vibrio sp. showed a higher survival rate than the fish cultured using the virus free sea water.