Enhanced Exopolymer Production and Chromium Stabilization inPseudomonas putidaUnsaturated Biofilms

Abstract

Chromium-contaminated soils threaten surface and groundwater quality at many industrial sites. In vadose zones, indigenous bacteria can reduce Cr(VI) to Cr(III), but the subsequent fate of Cr(III) and the roles of bacterial biofilms are relatively unknown. To investigate, we cultured Pseudomonas putida, a model organism for vadose zone bioremediation, as unsaturated biofilms on membranes overlaying iron-deficient solid media either containing molecular dichromate from potassium dichromate (Cr-only treatment) or with deposits of solid, dichromate-coated hematite (Fe؉Cr treatment) to simulate vadose zone conditions. Controls included iron-deficient solid medium and an Fe-only treatment using solid hematite deposits. Under iron-deficient conditions, chromium exposure resulted in lower cell yield and lower amounts of cellular protein and carbohydrate, but providing iron in the form of hematite overcame these toxic effects of Cr. For the Cr and Fe؉Cr treatments, Cr(VI) was completely reduced to Cr(III) that accumulated on biofilm cells and extracellular polymeric substances (EPSs). Chromium exposure resulted in elevated extracellular carbohydrates, protein, DNA, and EPS sugars that were relatively enriched in N-acetyl-glucosamine, rhamnose, glucose, and mannose. The proportions of EPS protein and carbohydrate relative to intracellular pools suggested Cr toxicity-mediated cell lysis as the origin. However, DNA accumulated extracellularly in amounts far greater than expected from cell lysis, and Cr was liberated when extracted EPS was treated with DNase. These results demonstrate that Cr accumulation in unsaturated biofilms occurs with enzymatic reduction of Cr(VI), cellular lysis, cellular association, and extracellular DNA binding of Cr(III), which altogether can facilitate localized biotic stabilization of Cr in contaminated vadose zones.

The RNA Processing Enzyme Polynucleotide Phosphorylase Negatively Controls Biofi lm Formation by Repressing Poly-N-Acetylglucosamine (PNAG) Production in Escherichia coli C

“…The overall correlations between EPS concentration and substratum stability were highly significant (stability -carbohydrates r = 0.728, n = 29, p,0.001; stability -proteins r = 0.414, n = 29, p,0.05); giving evidence of the important role of EPS for both, developing and reversing substratum stability. The bacterial biofilm under TCS exposure did not show elevated EPS levels as might have been expected, especially at the beginning on the incubation, as a possible defense strategy of the microbes to create a barrier between cell and toxicant [35]. On the contrary, the EPS carbohydrate concentrations were significantly highest in the positive control, followed by the biofilm exposed to low and medium (,20 mg L -1 ) TCS levels and significantly lowest in the treatments with high TCS exposure (50 -100 mg L -1 ).…”

Analysis of engineered nanomaterials in complex matrices (environment and biota): General considerations and conceptual case studies

“…In most cases, microscope images are amenable to quantitative analysis, for example, by some analysis of feature frequency [37] or perhaps by quantitative image analysis using GIS software tools [47,48]. To enable quantitation including statistical analysis, a significant number of images acquired at random locations within a specimen are needed, as well as image acquisition from many independent replicates.…”

“…1, pp. [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49]2012 # 2011 SETAC Printed in the USA DOI: 10.1002/etc.723 This paper evolved from discussions held at a SETAC-endorsed Technical Workshop held at Clemson University in August, 2010. The workshop was sponsored by the United States Environmental Protection Agency (U.S. EPA), Arcadis-US, and the Clemson University Institute of Environmental Toxicology.…”

Microorganisms as potential corrosion inhibitors of metallic materials

“…U zavisnosti od bakterijske vrste koje sintetišu EPS i uslova rasta, zavisi i udeo navedenih organskih jedinjenja koja ulaze u sastav EPS [18]. Zbog prisustva različitih funkcionalnih grupa u EPS poput karboksilnih, sulfhidrilnih, fenolnih, hidroksilnih grupa, EPS mogu formirati kompleks sa jonima metala [19][20][21] Neki autori su zabeležili da dolazi do ubrzane korozije metala u prisustvu mikroorganizama odnosno bakterija koje formiraju biofilm [22,23]. Do intenzivnijeg procesa korozije dolazi u prisustvu biofilma koji je sintetisan u prisustvu različitih bakterija.…”