Performance of a Combined Bacteria/Zeolite Permeable Barrier on the Rehabilitation of Wastewater Containing Atrazine and Heavy Metals

Several chemicals, such as pesticides and heavy metals, are frequently encountered together in environment matrices, becoming a priority concerning the prevention of their emissions, as well as their removal from the environment. In this sense, this work aimed to evaluate the effectiveness of a permeable biosorbent bio-barrier reactor (PBR) on the removal of atrazine and heavy metals (copper and zinc) from aqueous solutions. The permeable bio-barrier was built with a bacterial biofilm of R. viscosum supported on 13X zeolite. One of the aims of this work is the investigation of the toxic effects of atrazine, copper and zinc on the bacterial growth, as well as the assessment of their ability to adapt to repeated exposure to contaminants and to degrade atrazine. The growth of R. viscosum was not affected by concentrations of atrazine bellow 7 mg/L. However, copper and zinc in binary solutions were able to inhibit the growth of bacteria for all the concentrations tested (5 to 40 mg/L). The pre-acclimation of the bacteria to the contaminants allowed for an increase of 50% of the bacterial growth. Biodegradation tests showed that 35% of atrazine was removed/degraded, revealing that this herbicide is a recalcitrant compound that is hard to degrade by pure cultures. The development of a PBR with R. viscosum supported on zeolite was successfully performed and the removal rates were 85% for copper, 95% for zinc and 25% for atrazine, showing the potential of the sustainable and low-cost technology herein proposed.

Arthrobacter wenxiniae sp. nov., a novel plant growth-promoting rhizobacteria species harbouring a carotenoids biosynthetic gene cluster

A bacterial strain, designated AETb3-4^T was isolated from the rhizosphere of lily. Comparison of 16S rRNA gene sequences showed that the sequence from strain AETb3-4^T exhibits high sequence similarity with those of Arthrobacter silviterrae KIS14-16^T (97.9%), Arthrobacter livingstonensis LI2^T (97.2%) and Arthrobacter stackebrandtii CCM 2783^T (97.0%). Whole genome average nucleotide identity (ANI) and the digital DNA-DNA hybridization (dDDH) values between strain AETb3-4T and the reference strains A. silviterrae DSM 27180^T, A. livingstonensis L12^T and A. stackebrandtii DSM 16005^T were below 83.6% and 27.7%, respectively, values which are considerably below the proposed thresholds for the species delineation, consistent with the proposal that strain AETb3-4^T represents a novel species. The genome size of strain AETb3-4^T is 4.33 Mb and the genomic DNA G + C content is 67.3%. The main polar lipids were identified as phosphatidylglycerol, diphosphatidylglycero, phosphatidylinositol and an unidentified glycolipid. The major fatty acids (> 10%) were identified as anteiso-C_{15: 0} and anteiso-C_{17: 0}. The predominant menaquinone was found to be menaquinone 9 (MK-9) (H₂) (82.2%). Phenotypic tests allowed the strain to be differentiated from its close phylogenetic neighbors. Based on the results obtained, it is proposed that the strain AETb3-4^T (= CFCC 16390^T = LMG 31708^T) represents a novel species in the genus Arthrobacter, for which the names Arthrobacter wenxiniae sp. nov. is proposed. In addition, the novel strain AETb3-4^T has multiple plant growth-promoting characters including ACC-deaminase activity and production of IAA. Furthermore, the genome contains secondary metabolite biosynthesis gene clusters, including a carotenoid biosynthetic gene cluster, suggesting potential capacities for secondary metabolite synthesis. These data suggest that strain AETb3-4^T may have potential applications both in medicine and sustainable agriculture.

The biopolymer produced by Rhizobium viscosum CECT 908 is a promising agent for application in microbial enhanced oil recovery

Polymer flooding is one of the most promising techniques used to increase the productivity of mature oil reservoirs. Polymers reduce the mobility ratio of the injected water relative to the crude oil, improving the displacement of the entrapped oil and consequently, increasing oil recovery. Biopolymers such as xanthan gum have emerged as environmentally friendly alternatives to the chemical polymers commonly employed by the oil industry. However, in order to seek more efficient biomolecules, alternative biopolymers must be studied. Here, the applicability of a biopolymer produced by Rhizobium viscosum CECT 908 in Microbial Enhanced Oil Recovery (MEOR) was evaluated. This biopolymer exhibited better rheological properties (including higher viscosity) when compared with xanthan gum. Its stability at high shear rates (up to 300 s^-1), temperatures (up to 80 °C) and salinities (up to 200 g/L of NaCl) was also demonstrated. The biopolymer exhibited better performance than xanthan gum in oil recovery assays performed with a heavy crude oil, achieving 25.7 ± 0.5% of additional recovery. Thus the R. viscosum CECT 908 biopolymer is a promising candidate for application in MEOR.

Arthrobacter silvisoli sp. nov., isolated from forest soil

A novel Gram-stain-positive, strictly aerobic strain, NEAU-SA1^T, which showed a rod-coccus growth life cycle, was isolated from forest soil from Zhangjiajie, Hunan Province, China. The isolate grew at 10-40 °C (optimum 28 °C), at pH 5.0-10.0 (optimum pH 7.0) and in the presence of up to 5 % (w/v) NaCl, although NaCl was not required for growth. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain NEAU-SA1^T belonged to the genus Arthrobacter and was closely related to Arthrobacter cupressi DSM 24664^T (98.1 % similarity). Average nucleotide identity values between NEAU-SA1^T and A. cupressi DSM 24664^T were 88.91 and 87.41 % by ANIm and ANIb analysis, respectively. The in silico DNA-DNA hybridization value between strain NEAU-SA1^T and A. cupressi DSM 24664^T was 34.20 %, again indicating they belong to different taxa. The genomic DNA G+C content was 66.74 mol%. The major cellular fatty acids (>10 %) were anteiso-C15 : 0, anteiso-C17 : 0 and iso-C16 : 0. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and two unidentified glycolipids. The predominant menaquinone was MK-9(H2). The peptidoglycan type was A3α with an interpeptide bridge comprising l-Lys and l-Ala. Glucose, ribose and galactose were the whole-cell sugars. On the basis of morphological, physiological, biochemical and chemotaxonomic analysis, strain NEAU-SA1^T was classified as representing a novel species in the genus Arthrobacter, for which the name Arthrobacter silvisoli sp. nov. is proposed. The type strain is NEAU-SA1^T (=DSM 106716^T=CCTCC AB 2017271^T).