Microbial Diversity and Community Structure on Corroding Concretes

The objective of this study was to analyze bacterial diversity in two different concrete samples to understand the dominant types of bacteria that may contribute to concrete corrosion. Two concrete samples, HN-1 from the sunny side and HN-2 from dark and damp side, were collected from Zijin Mountain in Nanjing and genomic DNA was extracted. The partial bacterial 16S rRNA gene fragment was PCR amplified and two clone libraries were constructed. Amplified ribosomal DNA restriction analysis (ARDRA) was performed by digestion of the 16S rRNA gene and each unique restriction fragment polymorphism pattern was designated as an operational taxonomic unit (OTU). Phylogenetic trees of bacterial 16S rDNA nucleotide sequences were constructed. Sample HN-1 and HN-2 contained 21 OTUs and 26 OTUs, respectively. Proteobacteria and Planctomycetes were the predominant bacteria in both samples, and they are distributed among Herbaspirillum, Archangium, Phyllobacteriaceae and Planctomycetaceae. Cyanobacteria and Rubrobacter sp. are dominant in HN-1; while Acidobacteriaceae, Adhaeribacter sp. and Nitrospira sp. are predominant in HN-2. This distribution pattern was consistent with local environmental conditions of these two samples. The inferred physiological characteristics of these bacteria, based on relatedness of the DNA clone sequences to cultivated species, revealed different mechanisms of concrete corrosion depending on the local environmental conditions.     

Competitive Formation of Hydroxycarbonate Green Rust 1 versus Hydroxysulphate Green Rust 2 in Shewanella putrefaciens Cultures

The formation of hydroxysulphate green rust 2, a Fe(II-III) compound commonly found during corrosion processes of iron-based materials in seawater, has not yet been reported in bacterial cultures. Here we used Shewanella putrefaciens, a dissimilatory iron-reducing bacterium to anaerobically catalyze the transformation of a ferric oxyhydroxide, lepidocrocite (γ-FeOOH), into Fe(II) in the presence of various sulphate concentrations. Biotransformation assays of γ-FeOOH were performed with formate as the electron donor under a variety of concentrations. The results showed that the competitive formation of hydroxycarbonate green rust 1 (GR1(CO₃ ^2?)) and hydroxysulphate green rust 2 (GR2(SO₄ ^{2 ?})) depended upon the relative ratio (R) of bicarbonate and sulphate concentrations. When R ≥ 0.17, GR1(CO₃ ^{2 ?}) only was formed whereas when R < 0.17, a mixture of GR2(SO₄ ^{2 ?}) and GR1(CO₃ ^{2 ?}) was obtained. These results demonstrated that the hydroxysulphate GR2 can originate from the microbial reduction of γ-FeOOH and confirmed the preference for carbonate over sulphate during green rust precipitation. The solid phases were characterized by X-ray diffraction, transmission Mössbauer spectroscopy and scanning electron microscopy. Diffuse reflectance infrared Fourier transform spectroscopy confirmed the presence of intercalated carbonate and sulphate in green rust's structure. This study sheds light on the influence of dissimilatory iron-reducing bacteria on microbiologically influenced corrosion.     

Seasonal Dynamics of Dimethylarsenic Acid Degrading Bacteria Dominated in Lake Kibagata

Degradation processes of organoarsenic compounds significantly influence arsenic cycles in aquatic environments and would depend on the bacterial activities. The bacterial population involving dimethylarsinic acid (DMAA) degradation was investigated in Lake Kibagata from April to December in 2003. During the experimental period, the methylated arsenic was not detected, although the inorganic arsenic concentration ranged from 3.4 nM to 9.2 nM. Moreover, in the sample water of Lake Kibagata to which DMAA added, DMAA decreased while inorganic arsenic increased for 25 days. These facts suggested that the bacteria remineralized methylate arsenic species to inorganic arsenic. In fact, monitoring the use of Most Probable Number (MPN) procedure demonstrated that the DMAA-degrading bacteria exist at cell densities ranged from 41 cells/ml to 510 cells/ml. To determine the composition of DMAA-degrading bacteria, the total 110 isolates obtained as dominated bacterial species were analyzed by the restriction-fragment-length polymorphism (RFLP) analysis of 16S rDNA. As a result, total 110 isolates were classified into 12 types, of which 4 types dominated during the spring and/or fall seasons, and the rest 8 types dominated during summer season. DMAA degrading activities of the 110 isolates ranged at various degrees. Especially, the some isolates of fall season tend to show high degradation activities. The phylogenetic analysis using 16S rDNA revealed that the representative isolates formed several clusters in the gram-positive bacterial group and the proteobacteria subdivision. The diverse compositions of DMAA-degrading bacteria would seasonally change to control the rates of organoarsenic degradation in Kibagata.     

The role of short-chain fatty acids in the interplay between diet,gut microbiota,and host energy metabolism

Short-chain fatty acids (SCFAs), the end products of fermentation of dietary fibers by the anaerobic intestinal microbiota, have been shown to exert multiple beneficial effects on mammalian energy metabolism. The mechanisms underlying these effects are the subject of intensive research and encompass the complex interplay between diet, gut microbiota, and host energy metabolism. This review summarizes the role of SCFAs in host energy metabolism, starting from the production by the gut microbiota to the uptake by the host and ending with the effects on host metabolism. There are interesting leads on the underlying molecular mechanisms, but there are also many apparently contradictory results. A coherent understanding of the multilevel network in which SCFAs exert their effects is hampered by the lack of quantitative data on actual fluxes of SCFAs and metabolic processes regulated by SCFAs. In this review we address questions that, when answered, will bring us a great step forward in elucidating the role of SCFAs in mammalian energy metabolism.     

Effect of Soybean Monoculture on the Bacterial Communities Associated with Cysts of Heterodera glycines

The soybean cyst nematode (SCN), Heterodera glycines, can cause significant reductions in soybean yield and quality in many parts of the world. Natural biological control may play an important role in regulating SCN population. In this study the bacterial communities associated with SCN cysts obtained from fields under different lengths of soybean monoculture were explored. Soil samples were collected in 2010 and 2011 from six fields that had been used for soybean monoculture for 2 to 41 yr. SCN population densities were determined and bacterial communities from SCN cysts were investigated by Biolog and PCR-DGGE methods. SCN population densities initially increased in the first 5 yr of soybean monoculture but then declined steeply as years of soybean monoculture increased. Catabolic diversity of bacterial communities associated with cysts tended to decline as number of years of monoculture increased. Some specific PCR-DGGE bands, mainly representing Streptomyces and Rhizobium, were obtained from the cysts collected from the long-term monoculture fields. Principal component analysis of Biolog and PCR-DGGE data revealed that bacterial communities associated with cysts could be divided into two groups: those from cysts obtained from shorter (< 8 yr) vs. longer (> 8 yr) monoculture. This research demonstrates that the composition of the bacterial communities obtained from SCN cysts changes with length of soybean monoculture; the suppressive impact of these bacterial communities to SCN is yet to be determined.     

Getting to the guts of the matter: The status and potential of ‘omics’ research of parasitic protists of the human gastrointestinal system

Parasitic protists are a major cause of diarrhoeal illnesses in humans globally. Collectively, enteric pathogens exceed all other forms of infectious disease, in terms of their estimated global prevalence and socioeconomic impact. They have a disproportionately high impact on children in impoverished communities, leading to acute (diarrhoea, vomiting, dehydration and death) and chronic disease (malabsorption, malnutrition, physical and cognitive stunting and predisposition to chronic, non-communicable disease) consequences. However, historically, investment in research and disease control measures has been disproportionately poor, leading to their current classification as neglected pathogens. A sound understanding of their biology is essential in underpinning detection, treatment and control efforts. One major tool in rapidly improving our knowledge of these parasites is the use of biological systems, including ‘omic’ technologies. In recent years, these tools have shown significant success when applied to enteric protists. This review summarises much of this knowledge and highlights the significant remaining knowledge gaps. A major focus of the present review was to provide a perspective on a way forward to address these gaps using advanced biotechnologies.     

Synthesis and antimicrobial activity of polyhalobenzonitrile quinazolin-4(3H)-one derivatives

A novel series of polyhalobenzonitrile quinazolin-4(3H)-one derivatives were synthesized and characterized by NMR, IR, MS, and HRMS spectra. All of the newly prepared compounds were screened for antimicrobial activities against four strains of bacteria (Gram-positive bacterial: Staphylococcus aureus and Bacillus cereus; Gram-negative bacterial: Escherichia coli and Pseudomonas aeruginosa) and one strain of fungi (Candida albicans). Among the synthesized compounds, 5-(dimethylamino)-8-(2,4,5-trichloro-isophthalonitrile) quinazolin-4(3H)-one (7k) exhibited significant activity towards Gram-positive bacterial, Gram-negative bacterial, and the fungi strains. The MIC (0.8–3.3 μg/mL) and MBC (2.6–7.8 μg/mL) for this compound were close to those of nofloxacin, chlorothalonil, and fluconazole, making it the most potent antimicrobial agents in the series.     

Nematicidal activity of Lysobacter capsici YS1215 and the role of gelatinolytic proteins against root-knot nematodes

Lysobacter capsici YS1215 is a soil-borne strain that could inhibit the growth of phytopathogenic fungi, including Phytophthora capsici, Rhizoctonia solani and Fusarium oxysporum, as well as root-knot nematodes. The effect of different concentrations of bacterial culture filtrate (BCF) of L. capsici YS1215 on the mortality of second-stage juveniles (J2) of Meloidogyne incognita was studied using 24-well plates. The J2 mortality increased with increasing concentrations of BCF. YS1215 also produces gelatinases in the culture filtrate. To study its role in nematicidal activities, the partial purification and the characterisation of gelatinolytic proteins were done from the culture medium of the YS1215. The partially purified proteins showed three clear bands with molecular weights estimated using zymography to be 255.7, 232.1 and 146.4 kDa. The optimal pH and temperature for the proteins were 8.0 and 40°C, respectively. The activity of the proteins was inhibited by ethylenediaminetetraacetic acid, FeCl₃ and 1,10-phenanthroline, whereas it was activated by MnCl₂. The proteins may belong to the group of metalloproteases. Moreover, the proteins could hydrolyse skimmed milk, collagen, gelatin and bovine serum albumin (BSA) as substrates, but not casein. The proteins could induce 75% J2 mortality in five days and degrade the J2 bodies. The present study demonstrates the role of the gelatinolytic proteins in the nematicidal potential of L. capsici YS1215.