Taizo Sakata

Use of live and dead probiotic cells in tilapia Oreochromis niloticus

To investigate the effect of live and dead probiotic cells on the non-specific immune system of tilapia Oreochromis niloticus, probiotics were introduced by feeding either in the form of live or dead cells, or supplying live cells to the rearing water in a closed recirculating system. The probiotics treatment enhanced non-specific immune parameters such as lysozyme activity, migration of neutrophils and plasma bactericidal activity, resulting in improvement of resistance to Edwardsiella tarda infection. Especially, oral administration of live cells seemed to be more effective compared with other probiotic treatments such as oral administration of dead probiotic cells and supply of live probiotic cells to the rearing water. These results indicate that probiotics treatment is promising as an alternative method to antibiotics for disease prevention in aquaculture, and the viability of probiotic bacteria is a key factor to induce more potential effect of probiotics used for fish production.

Novel ecological niche of Cetobacterium somerae, an anaerobic bacterium in the intestinal tracts of freshwater fish

Aims:  This study was conducted to clarify the taxonomic status of Bacteroides type A strains with high vitamin B12‐producing ability that is widely distributed in the intestinal tracts of freshwater fish.

Algicidal activity and identification of an algicidal substance produced by marine Pseudomonas sp. C55a-2

A substance produced extracellularly by a marine bacterium, Pseudomonas C55a-2 strain, and possessing algal-killing activity against a diatom, Chaetocerosceratosporum, was isolated from the culture supernatant of the bacterium in order to identify its chemical structure. The algicidal substance extracted with ethyl acetate from the culture supernatant was purified by using Sep-Pak treatment, reverse phase column chromatography with Sephadex LH-20, and high performance liquid chromatography (HPLC) with Mightysil RP-18 GP. The purified substance was identified as 2,3-indolinedione (isatin) (molecular weight 147) based on hydrogen-nuclear magnetic resonance (H-NMR) and gas chromatograph-mass spectrometry (GC-MS) analysis. Among artificial synthetic compounds examined for algicidal activity against Chaetoceros cells on the double-layer plates, 2,3-indolinedione (isatin) appeared the most effective and indoline showed relatively less activity than isatin.

Volatilization of mercury compounds by methylmercury-volatilizing bacteria in Minamata Bay sediment.

Minamata Bay has been heavily polluted by high mercury concentrations which gave rise for a long time to methylmercury poisoning, Minamata disease (Kutsuna 1968; Irukayama 1977). The mercury still exists in the sediments of the Bay. The population of mercury-resistant bacteria in the sediments of Minamata Bay is larger than that in the sediments of other marine environments. The mercury-resistant bacteria isolated from a marine environment have been found to transform organic and inorganic mercury compounds into mercury vapor. The mercury-resistance confirmed in various bacterial genera has been shown to be plasmid-mediated volatilization. However, there has been little definitive information on the volatilization of organic mercury by the bacteria living in the mercury-polluted environment. It is important to know what bacterial transformations of mercury have been taking place and how the mercury-resistant bacteria may be playing a role in the mercury cycle in the marine environment of Minamata Bay. The object of the present study is to clarify the characteristics of the methylmercury-volatilizing bacteria in the sediments of Minamata Bay and of the volatilization of various mercury compounds by these bacteria.

Bacteriolytic activity and growth of marine isolates of labyrinthulids on dead bacterial cells

Thirteen strains of labyrinthulids were isolated from the coastal area of Kagoshima Bay, Kagoshima Prefecture, Japan and from Batan Bay, Panay Island, the Phillippines by using diatom double-layer agar plates. The cells of labyrinthulid isolates grew axenically on the dead bacterial cells and extract plus egg yolk agar medium (NSBEY agar). Three representative isolates were demonstrated to belong to the labyrinthulid phylogenetic group (LPG) based on 18S rDNA sequence analysis. As bacteriolytic activity of labyrinthulid isolates was examined, it was found that they could lyze only the dead cells of gram-negative bacteria and not those of gram-positive bacteria during incubation in both agar and liquid media. The optimum temperature range for bacteriolysis was 25–31°C. Orange carotenoid pigment was accumulated during the stationary growth phase of strain 00-Bat-05, Philippine isolate, cultured in an L-shaped tube containing a bacterial dead cell suspension. Concomitant rapid cell movement of developing zoospores was observed.

Characterization and expression of Saprospira cytoplasmic fibril protein (SCFP) gene from algicidal Saprospira spp. strains

The Saprospira sp. strain SS98-5 cells form colonies on a nutrient-rich agar medium, but are motile by gliding under low-nutrient condition and then numerous microtubule-like fibril structures are found intracellularly. The fibril structures are composed of a proteinous subunit SCFP; this gene was cloned previously. Here, the organization of ORFs adjacent to the SS98-5 SCFP gene and its transcription were investigated, and a SCFP gene homolog was cloned from Saprospira sp. SS03-4, a relative strain of SS98-5. The SCFP gene was also encoded within the SS03-4 chromosome, and grouped into a phage tail sheath protein family, suggesting its bacteriophage genome origin. Four ORFs adjacent to the SCFP gene were identified and their organization was in common with several prokaryotes. The SCFP mRNA was detected by reverse transcriptase polymerase chain reaction from gliding and non-gliding cells, implying that the SCFP gene was transcribed independent of existence or absence of the fibril structures.

Potentiality of Artificial Sea Water Salts for the Production of Carrageenase by a Marine Cytophaga sp.

Production of an extracellular enzyme complex (carrageenase) was studied by examining cell‐free fluids from cultures of a marine Cytophaga, 1k‐C783, growing on different media.

Studies on malate dehydrogenases of marine bacteria. I. Comparison between marine and terrestrial species.

The activities of various malate dehydrogenases (MDH and malic enzymes) were studied by comparing marine Pseudomonads and Vibrios with their terrestrial counterparts and with fish intestinal isolates. In addition, the relationship between the enzyme activity produced under cultivation and the NaCl concentration in the culture medium was studied. The medium used was ZoBell 2216E, the NaCl varying in concentration from 0.5 to 7%. The results showed that the activities of both MDH and malic enzymes varied in accordance with genera and with habitat, while NaCl exerted little effect in any of the strains.

Studies on the electrophorsis of marine bacterial enzymes - II esterase, malate dehydrogenase, and Lactate dehydrogenase.

Electrophoretic zymograms of the three enzymes, esterase, malate dehydrogenase (MDH), and lactate dehydrogenase (LDH) were determined for 11 strains of marine isolates. For comparison, some terrestrial bacteria of the same or similar genera were also analyzed. The results obtained indicated that there were zymographic differences between the various genera, irrespective of the enzymes concerned. Clear differences in both esterase and MDH isozyme-zymograms were noticed between the marine and terrestrial specimens of Pseudomonas.