Browsing by Author "Techkarnjanaruk, Somkiet"

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Characterization of extracellular chitinolytic activity in biofilms
(2001) Baty, Ace M.; Diwu, Zhenjun; Dunham, G.; Eastburn, Callie C.; Geesey, Gill G.; Goodman, Amanda E.; Suci, Peter A.; Techkarnjanaruk, Somkiet
Differentiation of chitinase-active and non-chitinase-active subpopulations of a marine bacterium during chitin degradation
(2000-08) Baty, Ace M.; Eastburn, Callie C.; Diwu, Zhenjun; Techkarnjanaruk, Somkiet; Goodman, Amanda E.; Geesey, Gill G.
The ability of marine bacteria to adhere to detrital particulate organic matter and rapidly switch on metabolic genes in an effort to reproduce is an important response for bacterial survival in the pelagic marine environment. The goal of this investigation was to evaluate the relationship between chitinolytic gene expression and extracellular chitinase activity in individual cells of the marine bacterium Pseudoalteromonas sp. strain S91 attached to solid chitin. A green fluorescent protein reporter gene under the control of the chiA promoter was used to evaluate chiA gene expression, and a precipitating enzyme-linked fluorescent probe, ELF-97-N-acetyl-b-D-glucosaminide, was used to evaluate extracellular chitinase activity among cells in the bacterial population. Evaluation of chiA expression and ELF-97 crystal location at the single-cell level revealed two physiologically distinct subpopulations of S91 on the chitin surface: one that was chitinase active and remained associated with the surface and another that was non-chitinase active and released daughter cells into the bulk aqueous phase. It is hypothesized that the surface-associated, non-chitinase-active population is utilizing chitin degradation products that were released by the adjacent chitinase-active populations for cell replication and dissemination into the bulk aqueous phase.
Iron sulfides and sulfur species produced at hematite surfaces in the presence of sulfate-reducing bacteria
(2001-01) Neal, Andrew L.; Techkarnjanaruk, Somkiet; Dohnalkova, Alice; McMready, D.; Peyton, Brent M.; Geesey, Gill G.
In the presence of sulfate-reducing bacteria (desulfovibrio desulfuricans) hematite (a-Fe2O3) dissolution is affected potentially by a combination of enzymatic (hydrogenase) reduction and hydrogen sulfide oxidation. As a consequence, ferrous ions are free to react with excess H2S to form insoluble ferrous sulfides. X-ray photoelectron spectra indicate binding energies similar to ferrous sulfides having pyrrhotite-like structures (Fe2p3/2 708.4 eV; S2p3/2 161.5 eV). Other sulfur species identified at the surface include sulfate, sulfite and polysulfides. Thin film X-ray diffraction identifies a limited number of peaks, the principal one of which may be assigned to the hexagonal pyrrhotite (102) peak (d = 2.09 Å; 22 = 43.22°), at the hematite surface within 3 months exposure to sulfate-reducing bacteria (SRB). High-resolution transmission electron microscopy identifies the presence of a hexagonal structure associated with observed crystallites. Although none of the analytical techniques employed provide unequivocal evidence as to the nature of the ferrous sulfide formed in the presence of SRB at hematite surfaces, we conclude from the available evidence that a pyrrhotite stoichiometry and structure is the best description of the sulfides we observe. Such ferrous sulfide production is inconsistent with previous reports in which mackinawite and greigite were products of biological sulfate reduction (Rickard 1969a; Herbert et al., 1998: Benning et al., 1999). The apparent differences in stoichiometry may be related to sulfide activity as the mineral surface, controlled in part by H2S autooxidation in the presence of iron oxides. Due to the relative stability of pyrrhotite at low temperatures, ferrous sulfide dissolution is likely to be reduced compared to the more commonly observed products of SRB activity. Additionally, biogenic pyrrhotite formation will also have implications for geomagnetic field behavior of sediments.
Spatial and temporal variations in chitinolytic gene expression and bacterial biomass production during chitin degradation
(2000-08) Baty, Ace M.; Eastburn, Callie C.; Techkarnjanaruk, Somkiet; Goodman, Amanda E.; Geesey, Gill G.
Growth of the chitin-degrading marine bacterium S91 on solid surfaces under oligotrophic conditions was accompanied by the displacement of a large fraction of the surface-derived bacterial production into the flowing bulk aqueous phase, irrespective of the value of the surface as a nutrient source. Over a 200-h period of surface colonization, 97 and 75% of the bacterial biomass generated on biodegradable chitin and a nonnutritional silicon surface, respectively, detached to become part of the free-living population in the bulk aqueous phase. Specific surface-associated growth rates that included the cells that subsequently detached from the substrata varied depending on the nutritional value of the substratum and during the period of surface colonization. Specific growth rates of 3.79 and 2.83 day-1 were obtained when cells first began to proliferate on a pure chitin film and a silicon surface, respectively. Later, when cell densities on the surface and detached cells as CFU in the bulk aqueous phase achieved a quasi-steady state, specific growth rates decreased to 1.08 and 0.79 day-1 on the chitin and silicon surfaces, respectively. Virtually all of the cells that detached from either the chitin or the cilicon surfaces and the majority of cells associated with the chitin surface over the 200-h period of surface colonization displayed no detectable expression of the chitin-degrading genes chiA and chiB. Cells displaying high levels of chiA-chiB expression were detected only on the chitin surface and then only clustered in discrete areas of the surface. Surface-associated, differential gene expression and displacement of bacterial production from surfaces represent adaptations at the population level that promote efficient utilization of the limited resources and dispersal of progeny to maximize access to new sources of energy and maintenance of the population.