New Mechanism of Extractive Electrospray Ionization Mass Spectrometry for Heterogeneous Solid Particles.

Real-time in situ mass spectrometry analysis of airborne particles is important in several applications, including exposure studies in ambient air, industrial settings, and assessing impacts on visibility and climate. However, obtaining molecular and 3D structural information is more challenging, especially for heterogeneous solid or semisolid particles. We report a study of extractive electrospray ionization mass spectrometry (EESI-MS) for the analysis of solid particles with an organic coating. The goal is to elucidate how much of the overall particle content is sampled, and determine the sensitivity of this technique to the surface layers. It is shown that, for NaNO3 particles coated with glutaric acid (GA), very little of the solid NaNO3 core is sampled compared to the GA coating, whereas for GA particles coated with malonic acid (MA), significant signals from both the MA coating and the GA core are observed. However, conventional ESI-MS of the same samples collected on a Teflon filter (and then extracted) detects much more core material compared to EESI-MS in both cases. These results show that, for the experimental conditions used here, EESI-MS does not sample the entire particle but, instead, is more sensitive to surface layers. Separate experiments on single-component particles of NaNO3, GA, or citric acid show that there must be a kinetics limitation to dissolution that is important in determining EESI-MS sensitivity. We propose a new mechanism of EESI solvent droplet interaction with solid particles that is consistent with the experimental observations. In conjunction with previous EESI-MS studies of organic particles, these results suggest that EESI does not necessarily sample the entire particle when solid, and that not only solubility but also surface energies and the kinetics of dissolution play an important role.

Antibacterial activity of marine and black band disease cyanobacteria against coral-associated bacteria.

Black band disease (BBD) of corals is a cyanobacteria-dominated polymicrobial disease that contains diverse populations of heterotrophic bacteria. It is one of the most destructive of coral diseases and is found globally on tropical and sub-tropical reefs. We assessed ten strains of BBD cyanobacteria, and ten strains of cyanobacteria isolated from other marine sources, for their antibacterial effect on growth of heterotrophic bacteria isolated from BBD, from the surface mucopolysaccharide layer (SML) of healthy corals, and three known bacterial coral pathogens. Assays were conducted using two methods: co-cultivation of cyanobacterial and bacterial isolates, and exposure of test bacteria to (hydrophilic and lipophilic) cyanobacterial cell extracts. During co-cultivation, 15 of the 20 cyanobacterial strains tested had antibacterial activity against at least one of the test bacterial strains. Inhibition was significantly higher for BBD cyanobacteria when compared to other marine cyanobacteria. Lipophilic extracts were more active than co-cultivation (extracts of 18 of the 20 strains were active) while hydrophilic extracts had very limited activity. In some cases co-cultivation resulted in stimulation of BBD and SML bacterial growth. Our results suggest that BBD cyanobacteria are involved in structuring the complex polymicrobial BBD microbial community by production of antimicrobial compounds.

Effect of freezing on PCR amplification of 16S rRNA genes from microbes associated with black band disease of corals.

Molecular analysis of black band disease of corals revealed that samples frozen immediately after collection yielded more proteobacterial 16S rRNA sequences, while unfrozen samples produced more cyanobacterial and sulfur-oxidizing bacterial sequences. These results suggest the need to use multiple approaches for preparation of samples to characterize this complex polymicrobial disease.

Coral disease dynamics in the central Philippines.

Limited quantitative research has been conducted on coral disease in the Philippines and baseline data are much needed. Field surveys for prevalence and distribution patterns were conducted from November 2002 to August 2003. Sites included the islands of Negros, Cebu, Siquijor, Panglao, Olango, Sumilon, Bantayan, Pescador, Balicassag and Palawan. In 154 belt transects, 10 026 Porites colonies were examined at 28 sites covering 3080 m2. Two syndromes, Porites ulcerative white spot (PUWS) and coral tumors, occurred at high prevalence. Tumors as high as 39.1% occurred among massive Porites, and PUWS was as high as 53.7% among massive and branching Porites. In 8 mo, 116 tagged colonies showed slow progression and low mortality. Along a 41 km human impact gradient centered on Dumaguete City (Negros), 15 sites were examined. Correlation analyses linked higher disease prevalence to anthropogenic influence (Spearman's rank correlation coefficient [r(s)] = -0.54, p = 0.04 for tumors and r(s) = -0.69, p = 0.005 for PUWS). In most sites disease prevalence was lower than in the sites near Dumaguete. High PUWS prevalence near uninhabited Sumilon Island appeared to be linked to the highly diseased reefs near Dumaguete City due to transmission of disease along a cross-shelf front formed between the Tañon Strait and Bohol Sea. Other observations included 12 potential new host species for PUWS (4 new genera and 1 octocorallia) and 5 likely new hosts for black band disease (BBD) in the Philippines, and a relatively high prevalence (7.8%) of BBD in 1 site in western Palawan.

Fabrication and use of nanometer-sized electrodes in electrochemistry.

Electrodes with electrochemical dimensions as small as 10 angstroms have been fabricated and used for electrochemical studies. These nanometer-scale electrodes have enabled the measurement of electron-transfer rate constants, k(het), that are two orders of magnitude faster than k(het) values accessible with any other electrochemical method.