One of the most important factors in the development of a bacterial community is whether the bacteria are able to grow in that habitat. The regulation of bacterial growth is generally studied in relation to physicochemical conditions, however, how bacterial communities regulate themselves remains unclear. In our previous study, it was demonstrated that a cell-to-cell communication molecule, 2-heptyl-3-hydroxy-4-quinolone, referred to as the Pseudomonas quinolone signal (PQS), affects respiring-activity in Pseudomonas aeruginosa without requiring its cognate receptor PqsR. The results suggested that PQS may affect other bacterial species, which was further examined in this study. PQS repressed the growth of several species including both Gram-negative and Gram-positive bacteria. In most cases, this effect differed from the bacteriostatic or bacteriolytic actions of antibiotics. The growth repression by PQS was inhibited when iron was added to the medium, indicating iron-chelating activity to be involved. In addition, PQS affected oxygen consumption in some species tested, and may have other underlying effects. Thus, this cell-to-cell communication molecule may influence the development of bacterial communities by regulating bacterial growth, and physicochemical factors such as iron would be important in determining its effect.
While Escherichia coli is widely used as an indicator of fecal contamination of waterways, recent studies suggest that this bacterium may become "naturalized" to soils. In this study, we investigated the survival and growth of naturalized E. coli in temperate soil in northern Minnesota. A spontaneously-occurring, antibiotic resistant E. coli strain, KS7-NR, was added to a field site at 103 cells (g soil)-1. The survival and growth of E. coli KS7-NR were followed from June to October, by using colony counts on agar plates supplemented with antibiotics, and by using quantitative PCR (qPCR) with strain-specific primers developed based on suppressive subtractive hybridization. Both plate count and qPCR analyses indicated that E. coli KS7-NR survived for more than 2 months in the field soil. Laboratory experiments showed that soil temperature, moisture, nutrients, and the presence of other soil organisms influenced growth and survival of E. coli KS7-NR in soil. Moreover, our results indicated that summer drought conditions that occurred during the field study likely limited in situ growth of E. coli at the field site. Taken together, these results suggest that E. coli strains can survive long-term and grow in soils, provided that abiotic factors are within their tolerance limits.
In situ detection of functional genes is informative for understanding microbial physiology. Most methods of detecting functional genes employ multiple oligonucleotides or polynucleotide probes. However, single oligonucleotide probes are superior in terms of specificity and flexibility in probe design. Here we describe the detection of a single copy functional gene, the methyl coenzyme M reductase gene, in a methanogen by two-pass tyramide signal amplification-fluorescence in situ hybridization (two-pass TSA-FISH) with a single oligonucleotide probe without pre-amplification of target nucleic acids. Locked-nucleic-acid-incorporated DNA probes were employed to achieve high specificity and affinity. Although problems associated with non-removable nonspecific binding of the antibody could not be overcome completely, single copy gene detection was carried out with single mismatch descriminatable specificity; however, only around 15% of cells were detected. The detection rate increased when a multiple copy gene like rrn in Escherichia coli was targeted, indicating that a certain number of target molecules are necessary to achieve a high detection rate. Although possible applications of this technique to environmental samples remain restricted, the results presented the potential of gene detection by FISH with single oligonucleotide probes.
The atmospheric movement of arid soil can play an important role in the movement of microorganisms attached to soil microparticles. Bacterial community structures in Asian dust collected at Beijing were investigated using the 16S rRNA gene sequence and compared to those in arid soil, a possible source of the dust. Asian dust samples contained 2.5×107 to 3.5×109 copies of the 16S rRNA gene gram-1. Therefore, more than 1013 bacterial cells (km)-2 per month were estimated to arrive in Beijing via Asian dust. Terminal restriction fragment length polymorphism analysis revealed that the bacterial community structures in Asian dust samples differed greatly according to the scale of the dust event. The bacterial communities from major dust events were similar to those from an arid region of China.
Seasonal change in the vertical distribution of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in temperate forest soil was examined from March 2008 to January 2009 by quantitative PCR of the amoA genes. Abundances of AOA amoA genes (ranging from 2.0×108 to 1.2×109 copies per gram dry soil) were significantly higher than those of AOB amoA genes (1.9×105 to 1.7×107 copies). A significant increase in AOB was observed at a depth of 0-5 cm in July when net nitrification was also high in the top soil, while AOA increased significantly at depths of 5-10 cm, 10-15 cm, and over 15 cm in July. Sequencing of the crenarchaeotal amoA gene revealed shifts in major AOA components along the soil depth profile and among sampling dates. Betaproteobacterial amoA clone libraries at 0-5 cm in March, May, and July were dominated by Nitrosospira clusters 1 and 4. A microcosm experiment at 0-5 cm in July revealed a decrease in the ratio of AOA/AOB amoA genes in microcosms. These results suggest that AOB play an important role in net nitrification in the top layer in temperate forest soil.
We established artificial consortia of bacteria inoculated from soil and a green alga, Chlorella vulgaris NIES-227. The bacteria and the alga were mixed in a tube or partitioned in a dialysing culture vessel, and the bacterial composition was examined after cultivation. The community of bacteria formed in the consortia included those phylogenetically closely related to the genera Phenylobacterium, Brevundimonas, Phyllobacterium, Afipia, Sphingomonas, Sandaracinobacter, Ramlibacter, Ralstonia, Cellvibrio, and so on. The community also included bacteria belonging to unknown genera within the phyla Bacteroidetes, Verrucomicrobia, and Acidobacteria. It was indicated that Ralstonia sp. and Cellvibrio sp. were attached to the algal cells and Phenylobacterium sp. Ramlibacter sp., Methylophilus sp., and Rhizobiaceae bacterium were not. It was suggested that bacteria belonging to the phylum Bacteroidetes and the class Alphaproteobacteria could be hemi-selectively enriched by the alga.
Surface waters along the Kalamazoo River, USA, were examined for occurrence and population trends of fecal indicator bacteria (FIB) with culture-based and culture-independent methods. The two methods recorded discrepancies in FIB counts, with the culture-independent method revealing more consistent numbers between the river sites. FIB cells that hybridized with the ECO1482 probe were highest in the downstream site, while the upstream site recorded higher ENF343 hybridized cells. Spatial and temporal differences in FIB populations were probably attributable to contrasting fecal pollution influences, vegetation type, varying environmental conditions as well as several in-stream factors between the two river sites.
We analyzed the quantity and diversity of nitrite reductase genes (nirS and nirK) in rice paddy soil before and after inducing denitrification. A quantitative PCR analysis showed that the copy number of nirK, but not nirS, increased significantly in response to the denitrification-inducing conditions. Diverse nirS and nirK clones were identified by clone library analyses. Clones related to the NirS of Burkholderiales and Rhodocyclales, and NirK distantly related to known denitrifiers increased their proportion in response to the denitrification-inducing conditions, and therefore, might be involved in denitrification in rice paddy soil.
Mass transport into the interior of biofilms and biological aggregates is a critical factor that affects their metabolic activity. In this study, we demonstrated the utility of a simple procedure that combines confocal reflection microscopy and fluorescent confocal laser scanning microscopy to visually explain the effects of biofilm structure on mass transport.
The bacterial community structure in four geographically isolated arid regions on the Loess plateau, China, a source of Asian dust, was investigated using a 16S rRNA gene. Denaturing gradient gel electrophoresis and sequencing demonstrated that community diversity in the Loess plateau was low, and a common Alphaproteobacteria phylotype was identified. Phylogenetic analyses of arid soils revealed that most phylotypes had low similarity with known strains in various phyla, suggesting that these regions contain phylogenetically divergent and unknown bacteria.
Inoculation experiments with the endophytic bacterium Azospirillum sp. strain B510, an isolate from surface-sterilized stems of field-grown rice, were conducted in pots in a greenhouse, and in paddy fields in Hokkaido, Japan. B510 significantly enhanced the growth of newly generated leaves and shoot biomass under greenhouse conditions. When rice seedlings were treated with 1×108 CFU ml-1, then transplanted to paddy fields, tiller numbers and seed yield significantly increased. Azospirillum sp. strain B510 is a promising bacterial inoculant for plant growth promotion and agricultural practices.