Degradation of nitrocellulose-based paint by Desulfovibrio desulfuricans ATCC 13541.

Nitrocellulose is one of the most commonly used compounds in ammunition and paint industries and its recalcitrance to degradation has a negative impact on human health and the environment. In this study the capability of Desulfovibrio desulfuricans ATCC 13541 to degrade nitrocellulose as binder in paint was assayed for the first time. Nitrocellulose-based paint degradation was followed by monitoring the variation in nitrate, nitrite and ammonium content in the culture medium using Ultraviolet-Visible spectroscopy. At the same time cell counts and ATP assay were performed to estimate bacterial density and activity in all samples. Infrared spectroscopy and colorimetric measurements of paint samples were performed to assess chemical and colour changes due to the microbial action. Microscope observations of nitrocellulose-based paint samples demonstrated the capability of the bacterium to adhere to the paint surface and change the paint adhesive characteristics. Finally, preliminary studies of nitrocellulose degradation pathway were conducted by assaying nitrate- and nitrite reductases activity in D. desulfuricans grown in presence or in absence of paint. We found that D. desulfuricans ATCC 13541 is able to transform nitrocellulose as paint binder and we hypothesised ammonification as degradation pathway. The results suggest that D. desulfuricans ATCC 13541 is a good candidate as a nitrocellulose-degrading bacterium.

A new non-degenerate primer pair for the specific detection of the nitrite reductase gene nrfA in the genus Desulfovibrio.

Dissimilatory nitrate reduction to ammonia (DNRA) is the process in which nitrate is reduced, via nitrite, to ammonia. Bacteria known to carry out DNRA mainly originate from wastewater treatment plants, where DNRA is a relevant process. The ability to carry out DNRA is phylogenetically widespread, and the gene nrfA, encoding for the key enzyme of the second step of the pathway, could be used as a marker for this process. In this study we developed a new primer pair specific for nrfA in the genus Desulfovibrio. The specificity of the primer pair was tested on DNA from thirteen species of Desulfovibrio and DNA from two wastewater samples. PCR amplifications yielded products of the expected size (850 bp), and sequences obtained from Desulfovibrio strains and environmental sample clone libraries matched the Desulfovibrio nrfA gene. Nevertheless, we found nrfA gene sequences in the environmental samples that are not present in the databases. The new primer set can be used to obtain more sequences of the nrfA gene and improve our knowledge of the DNRA pathway in this genus, e.g. with the aim to improve the wastewater treatment process.

Feasibility of removing surface deposits on stone using biological and chemical remediation methods.

The study was conducted on alterations found on stone artwork and integrates microbial control and a biotechnological method for the removal of undesirable chemical substances. The Demetra and Cronos sculptures are two of 12 stone statues decorating the courtyard of the Buonconsiglio Castle in Trento (Italy). An initial inspection of the statues revealed putative black crusts and highlighted the microbial contamination causing discoloration. In 2006, the Cultural Heritage Superintendence of Trento commissioned us to study and remove these chemical and biological stains. Stereomicroscopy characterised the stone of the sculptures as oolitic limestone, and infrared analyses confirmed the presence of black crusts. To remove the black crusts, we applied a remediation treatment of sulphate-reducing bacteria, which removes the chemical alteration but preserves the original stone and the patina noble. Using traditional and biomolecular methods, we studied the putative microbial contamination and confirmed the presence of biodeteriogens and chose biocide Biotin N for the removal of the agents causing the discolouration. Denaturing gradient gel electrophoresis fluorescent in situ hybridisation established that Cyanobacteria and green algae genera were responsible for the green staining whereas the black microbial contamination was due to dematiaceous fungi. After the biocide Biotin N treatment, we applied molecular methods and demonstrated that the Cyanobacteria, and most of the green algae and dematiaceous fungi, had been efficiently removed. The reported case study reveals that conservators can benefit from an integrated biotechnological approach aimed at the biocleaning of chemical alterations and the abatement of biodeteriogens.