Veterinary manure is an important pollution reservoir of antibiotics and antibiotic-resistant bacteria (ARB). However, little is known of the distribution of ARB in plant endophytic bacteria and the number/types of ARB in chicken manure. In this study, 454-pyrosequencing was used to investigate the distribution and composition of ARBs in chicken manure and fertilized vegetables. The prevalence of ARB in the samples of the chicken manure compost recovered from farms on which amoxicillin, kanamycin, gentamicin, and cephalexin were used was 20.91-65.9% for ARBs and 8.24-20.63% simultaneously resistant to two or more antibiotics (multiple antibiotic resistant bacteria (MARB)). Antibiotic-resistant endophytic bacteria were widely detected in celery, pakchoi, and cucumber with the highest rate of resistance to cephalexin. The pyrosequencing indicated that the chicken manure dominantly harbored Firmicutes, Bacteroidetes, Synergistetes, and Proteobacteria and that Bacteroidetes was significantly enhanced in farms utilizing antibiotics. In the total cultivable colonies, 62.58-89.43% ARBs and 95.29% MARB were clustered in Bacteroidetes with the dominant species (Myroides ordoratimimus and Spningobacterium spp., respectively) related to human clinical opportunistic pathogens.
This work describes
a high-yield extracellular biosynthesis of ZnS QDs via a unique molecular
mediation mechanism driven by the mixed sulfate reducing bacteria
(SRB). The mixed SRB have obtained the highest ever ZnS QD biosynthesis
rate of 35.0–45.0 g/(L·month). The biogenic ZnS QDs with
an average crystallite size (ACS) of 6.5 nm have greater PL activity
and better uniformity than that of a chemical route. Peculiar extracellular
proteins (EPs) with molecular weights of approximately 65 and 14 kDa
specially adhere to the ZnS QDs, which cover extraordinarily high
contents of acidic amino acids (14.0 mol % Glu and 13.0 mol % Asp)
and of nonpolar amino acids (12.0 mol % Ala, 11.0 mol % Gly, and 7.0
mol % Phe), for novel molecular mediation. The vast amount of negative
charges in Glu and Asp guides the strong absorption between the EPs
and Zn2+ via electrostatic attraction to reach a maximum
absorption capacity of 745.9 mg/g within 2.0 h, motivating large and
rapid nucleation as the first step of biosynthesis. Meanwhile, bridging
and interlinkage occur inside the EPs or between the EPs via hydrophobic
interactions dominated by the nonpolar amino acids, resulting in the
formation of massive microcavities to control and restrict the growth
of ZnS QDs as a template. The novel molecular mediation mechanism
triggered by the peculiar EPs with an extraordinary amino acid composition
and structure accounts for the high-yield biosynthesis of ZnS QDs.
The mixed SRB have also successfully fabricated other metal sulfide
QDs, including PbS, CuS, and CdS, through the novel molecular mediation.
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