Effect of electrical charges and fields on injury and viability of airborne bacteria

In this study, the effects of the electric charges and fields on the viability of airborne microorganisms were investigated. The electric charges of different magnitude and polarity were imparted on airborne microbial cells by a means of induction charging. The airborne microorganisms carrying different electric charge levels were then extracted by an electric mobility analyzer and collected using a microbial sampler. It was found that the viability of Pseudomonas fluorescens bacteria, used as a model for sensitive bacteria, carrying a net charge from 4100 negative to 30 positive elementary charges ranged between 40% and 60%; the viability of the cells carrying >2700 positive charges was below 1.5%. In contrast, the viability of the stress-resistant spores of Bacillus subtilis var. niger (used as simulant of anthrax-causing Bacillus anthracis spores when testing bioaerosol sensors in various studies), was not affected by the amount of electric charges on the spores. Because bacterial cells depend on their membrane potential for basic metabolic activities, drastic changes occurring in the membrane potential during aerosolization and the local electric fields induced by the imposed charges appeared to affect the sensitive cells' viability. These findings facilitate applications of electric charging for environmental control purposes involving sterilization of bacterial cells by imposing high electric charges on them. The findings from this study can also be used in the development of new bioaerosol sampling methods based on electrostatic principles.     

The role of microbial reductive dechlorination of TCE at a phytoremediation site

In April 1996, a phytoremediation field demonstration site at the Naval Air Station, Fort Worth, Texas, was developed to remediate shallow oxic ground water (< 3.7 m deep) contaminated with chlorinated ethenes. Microbial populations were sampled in February and June 1998. The populations under the newly planted cottonwood trees had not yet matured to an anaerobic community that could dechlorinate trichloroethene (TCE) to cis-1,2-dichloroethene (DCE); however, the microbial population under a mature (approximately 22-year-old) cottonwood tree about 30 m southwest of the plantings had a mature anaerobic population capable of dechlorinating TCE to DCE, and DCE to vinyl chloride (VC). Oxygen-free sediment incubations with contaminated groundwater also demonstrated that resident microorganisms were capable of the dechlorination of TCE to DCE. This suggests that a sufficient amount of organic material is present for microbial dechlorination in aquifer microniches where dissolved O2 concentrations are low. Phenol, benzoic acid, acetic acid, and a cyclic hydrocarbon, compounds consistent with the degradation of root exudates and complex aromatic compounds, were identified by gas chromatography/mass spectrometry (GC/MS) in sediment samples under the mature cottonwood tree. Elsewhere at the site, transpiration and degradation by the cottonwood trees appears to be responsible for loss of chlorinated ethenes.     

Studies on the utilization of methionine sulfoxide and methionine sulfone by rumen microorganisms in vitro

Summary.  An in vitro experiment was conducted to test the ability of mixed rumen bacteria (B), protozoa (P), and their mixture (BP) to utilize the oxidized forms of methionine (Met) e.g., methionine sulfoxide (MSO), methionine sulfone (MSO₂). Rumen contents were collected from fistulated goats to prepare the microbial suspensions and were anaerobically incubated at 39°C for 12 h with or without MSO (1 mM) or MSO₂ (1 mM) as a substrate. Met and other related compounds produced in both the supernatants and hydrolyzates of the incubation were analyzed by HPLC. During 6- and 12-h incubation periods, MSO disappeared by 28.3 and 42.0%, 0.0 and 0.0%, and 40.6 and 62.4% in B, P, and BP suspensions, respectively. Rumen bacteria and the mixture of rumen bacteria and protozoa were capable to reduce MSO to Met, and the production of Met from MSO in BP (156.6 and 196.1 μmol/g MN) was about 17.3 and 14.1% higher than that in B alone (133.5 and 171.9 μmol/g MN) during 6- and 12-h incubations, respectively. On the other hand, mixed rumen protozoa were unable to utilize MSO. Other metabolites produced from MSO were found to be MSO₂ and 2-aminobutyric acid (2AB) in B and BP. MSO₂ as a substrate remained without diminution in all-microbial suspensions. It was concluded that B, P, and BP cannot utilize MSO₂; but MSO can be utilized by B and BP for producing Met. Received December 28, 2001 Accepted May 21, 2002 Published online October 14, 2002 Acknowledgements The authors are extremely grateful to Professor H. Ogawa, the University of Tokyo, Japan and Dr. Takashi Hasegawa, Miyazaki University, Japan for inserting permanent rumen fistulae in goats. We would like to thank MONBUSHO for the award of a research scholarship to Mamun M. Or-Rashid since 1996–2001. Authors' address: Shaila Wadud, Laboratory of Animal Nutrition and Biochemistry, Division of Animal Science, Miyazaki University, Miyazaki 889-2192, Japan, Fax. +81-985-58-7201, E-mail: rafatkun@hotmail.com     

Microstructural characteristics of thin biofilms through optical and scanning electron microscopy

The combination of a conventional optical microscope with a specially designed glass flow cell was used to visualize in situ biofilms formed on opaque thin biomaterials through a simple non-invasive way (optical microscopy of thin biofilms, OMTB). Comparisons of OMTB with scanning electron microscopy (SEM) images were made. Thin metallic dental biomaterials were used as substrata. They were immersed in a synthetic saliva and in a modified Mitis–Salivarius medium inoculated with a consortium of oral microorganisms. To study the effect of bacterial motility, Pseudomonas fluorescens cultures were also used. The processes which give rise to the formation of the biofilm were monitored through OMTB. Biofilm microstructures like pores, water channels, streamers and chains of Streptococci, attached to the surface or floating in the viscous interfacial environment, could be distinguished. Thickness and roughness of the biofilms formed on thin substrata could also be evaluated. Distortions introduced by pretreatments carried out to prepare biological materials for SEM observations could be detected by comparing OMTB and SEM images. SEM images (obtained at high magnification but ex situ, not in real time and with pretreatment of the samples) and OMTB images (obtained in situ, without pretreatments, in real time but at low magnification) in combination provided complementary information to study biofilm processes on thin substrata.     

遗传工程微生物细胞间发生的自然遗传转化

将两株具有不同遗传标记的枯草芽孢杆菌在基本培养基中分别培养至对数生长后期后进行短时间混合静置培养 ,经选择平板筛选、DNaseI敏感性试验、质粒检测和产蛋白酶活性检测 ,发现两菌株之间可通过自然遗传转化进行染色体DNA和质粒DNA的交换。研究结果表明 ,自然遗传转化可在细胞间进行 ,这对揭示微生物群居的自然环境中可能存在的细胞间的DNA转移 ,以及正确评估遗传工程微生物(GEMs)的安全使用具有重要意义。     

Phylogeny of sulfate-reducing bacteria(1)

Three starvation regimes (a deficient culture medium, a saline buffer solution and distilled water) were evaluated for their possible effect on cell surface characteristics of Azospirillum lipoferum 1842 related to the initial adsorption of the bacterium to surfaces. The bacteria survived for 7 days in all media although they did not multiply. Upon transfer from a rich growth medium (nutrient agar) to starvation conditions, cell surface hydrophobicity dropped sharply but recovered its initial value within 24 to 48 h, except in phosphate-buffered saline, the length of the recovery period depending on the starvation medium. Starvation affected the sugar affinity of the A. lipoferum cell surface mainly towards p-aminophenyl-alpha-D-mannopyranoside, to a lesser extent to glucose, but not to other monosaccharides tested. Starvation changed the concentration of several cell surface proteins but did not induce the synthesis of new ones. The cell surface hydrophobic protein (43 kDa) of A. lipoferum 1842 was unaffected by any starvation treatment for a period of up to 48 h, but later disappeared. These data showed that starvation is not a major factor in inducing changes in the cell surface which lead to the primary phase of attachment of Azospirillum to surfaces.     

Application of 13C NMR to investigate the transformations and biodegradation of organic materials by wood- and soil-feeding termites, and a coprophagous litter-dwelling dipteran larva

Solid-state 13C nuclear magnetic resonance spectroscopy has been used to characterize the C in samples of the food (wood), gut contents and faeces from the wood-feeding termite, Microcerotermes parvus; soil in the guts and mound material from the soil-feeding termite, Thoracotermes macrothorax; and the food and faeces from the litter-feeding, coprophagous larvae of the dipteran fly, Bibio marci. Spectra from the wood-feeding termite indicated preferential loss of polysaccharide and accumulation of lignin with some modification to the O-aromatic-C and methoxyl-C (O-methyl-C) components during passage through the gut. Spectra for the soil-feeding termite indicated little change in the distribution of 13C between resonances following passage through the gut, except for some evidence of preferential polysaccharide loss. Interpretation of the spectra from these organisms was restricted by the relatively low C content of the soils and mound material, and by the large contribution to the NMR spectra from the gut tissue rather than the gut contents. Spectra for the litter-feeding dipteran larvae indicated preferential feeding on the polysaccharide-rich component of the litter and then overall loss of polysaccharide-C and accumulation of both aromatic-C and methoxyl-C in the gut. These changes were greater for the second passage than for the first passage through the gut, suggesting that principally mechanical and physical changes occurred initially and that chemical digestion was prevalent during the second passage.     

Effect of buffering on the phosphate-solubilizing ability of microorganisms

Native microflora present in the alkaline vertisols and two phosphate-solubilizing bacteria (PSB) isolated from soil using conventional screening media could not release phosphorus from alkaline Indian vertisol soils supplemented with carbon and nitrogen sources. The two PSBs could solubilize both rock phosphate and di-calcium phosphate in unbuffered media but failed to solubilize rock phosphate in buffered media. The organic acids secreted by these PSBs were 20–50 times less than that required to solubilize phosphorus from alkaline soil.     

The origin of prokaryotic life and molecular evolution

The origin of prokaryotic life is discussed with an emphasis on the self-assembly of early life in a microscale environment where ordered cellular structures and integrated functions evolved from disorder. Early molecular evolution may have been due to both molecular chaos and evolving molecular order.