Microbial mats often seen in neutral and alkaline hot springs are generally formed by phototrophic bacteria. These mat-forming thermophiles comprise oxygenic phototrophs, namely cyanobacteria, and the other group of phototrophic bacteria, so-called filamentous anoxygenic phototrophs (FAPs). FAPs contain bacteriochlorophyll(s) as photosynthetic pigments and conduct photosynthesis without producing oxygen. They are all affiliated to the order Chloroflexales in the phylum Chloroflexi, and are classified into three genera, Chloroflexus, Heliothrix and Roseiflexus. Chloroflexus species have greenish brown to brown filaments and a typical light-harvesting apparatus called the chlorosome, while the others are red to reddish orange and completely lack chlorosomes. FAPs form colorful and variously shaped microbial mats with cyanobacteria. Distinctive microbial mats composed of these bacteria, e.g. complexly layered or ruffled fur-like mats, can be seen in some Japanese hot springs. While FAPs phylogenetically differ from all other phototrophs, the group is known to have a "chimeric" photosynthetic system: The photochemical core complex in the FAPs, essential to photosynthesis, resembles that in the purple bacteria; their light-harvesting apparatus is similar to that in green sulfur bacteria. The photosynthetic peculiarity found in the FAPs is important to solving the evolution of photosynthesis.

View full abstract

Microorganisms associated with the foam and their status before and after foaming in a submerged membrane bioreactor situated in Japan, are described. The microorganisms associated with membrane bioreactors have not yet been fully explored, as this is a relatively recent technology. An important finding was that one of the most discussed filaments Microthrix parvicella, the occurrence of which has rarely been reported in Japan, dominated in the foam of this bioreactor. Various types of filaments were identified in the foam based on morphology and available specifies-specific oligonucleotide probes but they were mainly Nocardia spp., Microthrix parvicella, Nostocoida limicola, type 1851, type 0041, type 1701, type 0675, type 021n, type 0914 etc. Also Microthrix pervicella, species from Mycolata groups and total eubacteria in the before and after foaming-samples were quantified using the oligonucleotide probes MPA 223, MYB and EUB, respectively. The ratio of MPA to EUB (approx. 22%) in the foam was found to be much higher than the ratio of MYB to EUB (approx. 6%). The investigation suggested that Microthrix parvicella was mainly responsible for the onset of foaming in this plant. This study provides information about the occurrence, composition and ratio of foaming filaments that might occur in a membrane bioreactor (MBR) along with the most important and discussed filament Microthrix parvicella.

View full abstract

Selective enrichment of phosphate-accumulating organisms (PAOs) and denitrifying phosphate-accumulating organisms (DNPAOs) was conducted using a sequencing batch reactor (SBR). To elucidate biomarkers for DNPAOs, quinone profiles were monitored during selective enrichment. As a result, a high correlation between the mole fraction of ubiquinone with eight isoprene units (Q-8) and anoxic phosphate uptake ability was observed, indicating that Q-8 was one of the biomarkers for DNPAOs. In addition, the mole ratio of ubiquinones to menaquinones (Q/MK) increased throughout this selective enrichment.

View full abstract

The distribution of tet(34) was examined among oxytetracycline (OTC) resistant Vibrio strains isolated from Japan, Korea and the Philippines. tet(34) was detected in 10 isolates (6 in fish, 4 in seawater) from Japan and Korea, suggesting that it is widely distributed among fish and seawater bacteria in these countries. Ninety-eight percent of the Vibrio strains in the Philippines were sensitive to OTC, but none of the 60 isolates from the Philippines. The minimum inhibitory concentration (MIC) of OTC-resistant isolates increased 2 to 8 fold in the presence of Mg²⁺, and MICs were higher in the Japanese and Korean isolates than the Philippine isolates. The MIC for furaltadone (FD) was low in Japanese (23.9%) isolates at over 3.1 μg/ml and high in Korean (50%) and Philippine (56.7%) isolates. This was probably due to the different frequency of use of FD in these countries. Sequences of 16S rDNA of tet(34)-positive isolates were 100% identical, suggesting that tet(34) is conveyed in a particular Vibrio species.

View full abstract

A cyanobacterial strain was isolated from cyanobacterial crusts taken from soil in Hyogo Prefecture, Japan and identified as a Nostoc species. This Nostoc strain is drought-tolerant, and its cells differentiated into a particular type, hormogonia, under dark and nutrient-poor conditions. The strain grows well in a liquid medium with a simple nutrient composition that was originally developed for the cultivation of symbiotic Nostoc. The maximum growth rate was attained at pH 8. The DNA sequences of the 16S rRNA region and trnL(UAA)-intron region were determined to classify this Nostoc species. The trnL(UAA)-intron sequence was homologous to a symbiotic Nostoc, and also to some extent to Anabaena sp. PCC 7120. This cyanobacterium, named Nostoc sp. HK-01, is promising as an improver of arid and nutrient-poor soils.

View full abstract

The direct total count of bacteria and the concentration of isoprenoid quinones were measured in 82 samples from different aquatic and soil environments. The geometric mean of the total count (TC)/total quinine (TQ) ratios obtained with different environments ranged from 1.1 to 2.2×10³ cells fmol^-1. When the concentration of the total respiratory quinone (TRQ), i.e., ubiquinones and menaquinones, were taken into account, the geometric mean of the TC/TRQ ratios fell into a range of 2.2 to 4.1×10³ cells fmol^-1. A high positive correlation was noted between TC and TQ (r²=0.9864) or TRQ (r²=0.9990). Based on the relationship between TC and TRQ, 1 nmol of the total quinone was estimated to be equivalent to 2.5×10⁹ cells of bacteria on average. These results indicate that the concentration of the respiratory quinones can be used as a good measure of bacterial counts and biomass in the environment.

View full abstract

Different types of commercially available personal composters which were designed for repeated fed-batch treatment of garbage were operated for more than one month in order to study microbial populations at the steady state of this process. Both microscopic direct counts and viable plate counts of bacteria recorded had an order of magnitude of 10¹¹ per g dry weight of solid waste-compost mixture (SCM), and the culturability of the resident bacteria was estimated to be 54% on average. High culturability was also demonstrated by comparative quinone profiling of the SCM itself and bacterial colonies recovered on the plates therefrom. These results suggest that conventional cultivation methods work much better for studying microbial community structure in the fed-batch composting process than in natural environments. The colony quinone profiling method may have great promise for the evaluation of culture bias and culturability of in situ microbial populations.

View full abstract

We report here that certain kinds of foods can act as media that induce genetic competency of Escherichia coli. Of 42 food samples tested, more than 10 showed an ability to induce competency. Among them, tofu supernatant showed the highest activity, corresponding to about one half of the activity obtained with 100 mM CaCl₂. These results suggest that some populations of E. coli in food environments exist as "competent cells". There were no clear correlations between transformation frequencies and the chemical indices of foods (Ca²⁺ or Mg²⁺ concentrations and pH), suggesting that complex factors in foods affect competency development.

View full abstract