A simple and specific strategy based on the bioconjugation
of a
photosensitizer protophophyrin IX (PpIX) with a lipopolysaccharide
(LPS) binding antimicrobial peptide YI13WF (YVLWKRKRKFCFI-Amide) has
been developed for the effective fluorescent imaging and photodynamic
inactivation of Gram-negative bacterial strains. The intracellular
fluorescent imaging and photodynamic antimicrobial chemotherapy (PACT)
studies supported our hypothesis that the PpIX-YI13WF conjugates could
serve as efficient probes to image the bacterial strains and meanwhile
indicated the potent activities against Gram-negative bacterial pathogens
especially for those with antibiotics resistance when exposed to the
white light irradiation. Compared to the monomeric PpIX-YI13WF conjugate,
the dimeric conjugate indicated the stronger fluorescent imaging signals
and higher photoinactivation toward the Gram-negative bacterial pathogens
throughout the whole concentration range. In addition, the photodynamic
bacterial inactivation also demonstrated more potent activity than
the minimum inhibitory concentration (MIC) values of dimeric PpIX-YI13WF
conjugate itself observed for E. coli DH5a (∼4 times), S. enterica (∼8 times), and other Gram-negative strains including antibiotic-resistant E. coli BL21 (∼8 times) and K. pneumoniae (∼16 times). Moreover, both
fluorescent imaging and photoinactivation measurements also demonstrated
that the dimeric PpIX-YI13WF conjugate could selectively recognize
bacterial strains over mammalian cells and generate less photo damage
to mammalian cells. We believed that the enhanced fluorescence and
bacterial inactivation were probably attributed to the higher binding
affinity between dimeric photosensitizer peptide conjugate and LPS
components on the surface of bacterial strains, which were the results
of efficient multivalent interactions.
This manuscript presents a comparison of the A-stage and B-stage sludges in terms of anaerobic biodegradability and low molecular weight compounds present in the supernatant using Gas Chromatography-Mass Spectrometry (GC-MS). The GC-MS analysis of A-stage and B-stage supernatants identified respectively 43 and 19 organic compounds consisting mainly of aromatics (27.9% and 21%), alcohols (25.6% and 15%) and acids (30.2% and 15%). The methane potential was found to be 349±1 mL CH4/g VS and 238±12 mL CH4/g VS, respectively. After anaerobic digestion of these sludges, a greater proportion of aromatics (42% and 58%) and a lower proportion of acids (10% and 10%) and alcohols (16% and 10%) was observed.
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