Longevity of bacteria: Considerations in environmental release

Changes in root bacterial communities associated to two different development stages of canola (Brassica napus L. var oleifera) evaluated through next-generation sequencing technology

Crop production may benefit from plant growth-promoting bacteria. The knowledge on bacterial communities is indispensable in agricultural systems that intend to apply beneficial bacteria to improve plant health and production of crops such as canola. In this work, the diversity of root bacterial communities associated to two different developmental phases of canola (Brassica napus L.) plants was assessed through the application of new generation sequencing technology. Total bacterial DNA was extracted from root samples from two different growth states of canola (rosette and flowering). It could be shown how bacterial communities inside the roots changed with the growing stage of the canola plants. There were differences in the abundance of the genera, family, and even the phyla identified for each sample. While in both root samples Proteobacteria was the most common phylum, at the rosette stage, the most common bacteria belonged to the family Pseudomonadaceae and the genus Pseudomonas, and in the flowering stage, the Xanthomonadaceae family and the genus Xanthomonas dominated the community. This implies in a switch in the predominant bacteria in the different developmental stages of the plant, suggesting that the plant itself interferes with the associated microbial community.

Taxonomic analysis of extremely halophilic archaea isolated from 56-years-old dead sea brine samples

A taxonomic study comprising both phenotypic and genotypic characterization, has been carried out on a total of 158 extremely halophilic aerobic archaeal strains. These strains were isolated from enrichments prepared from Dead Sea water samples dating from 1936 that were collected by B. E. Volcani for the demonstration of microbial life in the Dead Sea. The isolates were examined for 126 morphological, physiological, biochemical and nutritional tests. Numerical analysis of the data, by using the S(J) coefficient and UPGMA clustering method, showed that the isolates clustered into six phenons. Twenty-two out of the 158 strains used in this study were characterized previously (ARAHAL et al., 1996) and were placed into five phenotypic groups. The genotypic study included both the determination of the guanineplus-cytosine content of the DNA and DNA-DNA hybridization studies. For this purpose, representative strains from the six phenons were chosen. These groups were found to represent some members of three different genera - Haloarcula (phenons A, B, and C), Haloferax (phenons D and E) and Halobacterium (phenon F) - of the family Halobacteriaceae, some of them never reported to occur in the Dead Sea, such as Haloarcula hispanica, while Haloferax volcanii (phenons D and E) was described in the Dead Sea by studies carried out several decades later than Volcani's work.

In vitro colonization and increase in nitrogen fixation of seedling roots of black mangrove inoculated by a filamentous cyanobacteria

An isolate of the filamentous cyanobacterium Microcoleus sp. was obtained from black mangrove aerial root (pneumatophore) and inoculated onto young mangrove seedlings to evaluate N2-fixation and root-colonization capacities of the bacterium under in vitro conditions in closed-system experiments. N2 fixation (acetylene reduction) gradually increased with time and reached its peak 5 days after inoculation. Later, it decreased sharply. The level of N2 fixation in the presence of the plant was significantly higher than the amount of nitrogen fixed by a similar quantity of cyanobacteria on a N-free growth medium. The main feature of this root colonization was the gradual production of a biofilm in which the cyanobacterial filaments were embedded. Visible biofilm production increased with time until it completely covered the entire root system of the plant. The in-and-out movement of cyanobacterial filaments from the biofilm probably allows colonization of uncolonized portions of the root several days after the initial inoculation. This is, to the best of our knowledge, the first report of the artificial inoculation of cyanobacteria on marine mangroves.Key words: Avicennia germinans, beneficial bacteria, biofilm, black mangrove, diazotrophic cyanobacteria, Microcoleus sp., nitrogen fixation, plant growth-promoting bacteria, root colonization.

Enhanced biodegradation of a hard bis-quaternary ammonium salt

Bacterial strains with a high biodegradation potential were isolated from activated sludge. Their ability to decompose the hard bis-quaternary ammonium salt FB was determined by the method of chemical oxygen demand (COD) in a mineral medium, where the compound FB was the only source of carbon. The COD values were very low after 21 d and in the course of this period they reached zero level twice. The contribution of adsorption to decrease the COD value was small. The maximum COD decrease was accompanied by an increase of cell respiration. It is suggested that FB is effectively decomposed in spite of the fact that according to its structure it is a typical hard detergent.