Bacterial diversity and bioaugmentation in floodwater of a paddy field in the presence of the herbicide molinate

Abstract

This work aimed at studying variations on the diversity and composition of the bacterial community of a rice paddy field floodwater, subjected to conventional management, namely by using the herbicide molinate. The promotion of the herbicide biodegradation either by the autochthonous microbiota or by a bioaugmentation process was also assessed. This study comprehended four sampling campaigns at key dates of the farming procedures (seeding, immediately and 6 days after application of the herbicide molinate, and after synthetic fertilization) and the subsequent physic-chemical and microbiological characterization (pH, DOC and molinate contents, total cells, cultivable bacteria and DGGE profiling) of the samples. Multivariate analysis of the DGGE profiles showed temporal variations in the bacterial community structure and the Shannon's index values indicated that the bacterial diversity reached its minimum at the molinate application day. The highest bacterial diversity coincided with the periods with undetectable concentrations of the herbicide, although microcosm assays suggested that other factors than molinate may have been responsible for the decrease of the bacterial diversity. The ability of autochthonous microorganisms to degrade molinate and the influence of the herbicide on the bacterial community composition were assessed in microcosm assays using floodwater collected at the same dates. Given molinate was not degraded by autochthonous microorganisms, and considering it represents an environmental contaminant, bioaugmentation microcosms were assayed aiming the assessment of the feasibility of a bioremediation process to clean contaminated floodwater. A molinate-mineralizing culture, previously isolated, promoted molinate removal, induced alterations in the autochthonous bacterial community structure and diversity, and was undetected after 7 days of incubation, suggesting the feasibility of the process.

Culture-dependent and culture-independent diversity surveys target different bacteria: a case study in a freshwater sample

“…Cell enumerations were made in triplicate as described previously (Manuel et al 2007;Barreiros et al 2011).…”

“…Four fractions of 0.5 l of water sample were filtered through polycarbonate membranes (0.2 lm porosity, Whatman). DNA extraction was made as described by Barreiros et al (2011), with an additional period of 30 min of incubation at 65°C. Four DNA extracts were obtained for further analysis.…”

“…The DGGE profiles of the four DNA extracts were 100% concordant. Thus, one lane was selected for further analysis, with the excision and analysis of all bands as described before by Barreiros et al (2011). For bands, sequencing analysis was used the InsTAclone TM PCR cloning kit (MBI Fermentas, Heidelberg, Germany), according to the manufacturer's instructions.…”

Functional Genes of Microorganisms, Comprehending the Dynamics of Agricultural Ecosystems

“…Through this, is possible identified all species present in agroecosystems and verified the influence in crop management above which species and the utilization of pesticides 9 , fertilizers 127 , and root exudates 35 . For the16SrRNA gene, Sánchez 93 compared 6 sets of primers regarding their efficiency in obtaining profiles of bacterioplankton communities (63f and 518r; 357f and 907rM; 357f and 907r; 357f and 518r; 968f and 1401r; 1055f and 1392r) and the best result came from the 357f-GC and 907rM set.…”

“…Agroecosystems provide different environments with a wide variety of microhabitats. Rice fields, for instance, remain irrigated during most of the culture cycle 9 , and may have a quite complex bacterial community 10 . Culture management and farming systems also interfere with microorganisms composition.…”