Identification of opsA , a Gene Involved in Solute Stress Mitigation and Survival in Soil, in the Polycyclic Aromatic Hydrocarbon-Degrading Bacterium Novosphingobium sp. Strain LH128

Abstract

The aim of this study was to identify genes involved in solute and matric stress mitigation in the polycyclic aromatic hydrocarbon (PAH)-degrading Novosphingobium sp. strain LH128. The genes were identified using plasposon mutagenesis and by selection of mutants that showed impaired growth in a medium containing 450 mM NaCl as a solute stress or 10% (wt/vol) polyethylene glycol (PEG) 6000 as a matric stress. Eleven and 14 mutants showed growth impairment when exposed to solute and matric stresses, respectively. The disrupted sequences were mapped on a draft genome sequence of strain LH128, and the corresponding gene functions were predicted. None of them were shared between solute and matric stress-impacted mutants. One NaCl-affected mutant (i.e., NA7E1) with a disruption in a gene encoding a putative outer membrane protein (OpsA) was susceptible to lower NaCl concentrations than the other mutants. The growth of NA7E1 was impacted by other ions and nonionic solutes and by sodium dodecyl sulfate (SDS), suggesting that opsA is involved in osmotic stress mitigation and/or outer membrane stability in strain LH128. NA7E1 was also the only mutant that showed reduced growth and less-efficient phenanthrene degradation in soil compared to the wild type. Moreover, the survival of NA7E1 in soil decreased significantly when the moisture content was decreased but was unaffected when soluble solutes from sandy soil were removed by washing. opsA appears to be important for the survival of strain LH128 in soil, especially in the case of reduced moisture content, probably by mitigating the effects of solute stress and retaining membrane stability.

Sphingomonas wittichii RW1 gene reporters interrogating the dibenzofuran metabolic network highlight conditions for early successful development in contaminated microcosms

“…In order to improve our general understanding of the process, recent studies have attempted to more systematically measure and interpret global reactions of introduced bacteria for bioremediation into complex systems (Fida et al ., 2012; 2013; Iino et al ., ; Maphosa et al ., ; Gunasekera et al ., ; Moreno‐Forero and van der Meer, ; Scheublin et al ., ). This has been complemented with global transposon mutagenesis approaches in order to identify gene functions with fitness benefit for growth and survival in soil (Roggo et al ., ; Fida et al ., ).…”

Physiological and Transcriptome Response of the Polycyclic Aromatic Hydrocarbon Degrading Novosphingobium sp. LH128 after Inoculation in Soil

“…20−26 Studies showed that inoculation of soils with pollutant-degrading Sphingomonads was followed by a rapid decrease of number of CFU in the soil, directly after inoculation. 2,27 As for other organic pollutant degrading strains that show immediate decrease in CFU after soil inoculation, this decrease in CFU number is not wellunderstood.…”

“…Upon inoculation, strain LH128 shows a rapid decline in CFU numbers which increased afterward with concomitant removal of phenanthrene. 27 As a common practice in bioaugmentation procedures, the strain was cultured on a carbon source, i.e., glucose, that allows reaching relatively rapid high cell densities, and hence inoculation at high cell densities. The reason behind this decline in CFU numbers was explored by using a GFPexpressing variant of strain LH128 (LH128-GFP) enabling cultivation-independent counting of LH128 in aqueous soil extracts.…”

Clover Root Exudates Favor Novosphingobium sp. HR1a Establishment in the Rhizosphere and Promote Phenanthrene Rhizoremediation

“…In bioaugmentation strategies for contaminant bioremediation, the selected introduced bacteria have to establish interactions with a dynamic environment, and the balance between the cooperative and antagonistic forces will determine the outcome of this strategy ( 46 ). When bioaugmentation is required in rhizoremediation strategies, the biodegrading bacteria have to be metabolically active and have to be able to mineralize the contaminant.…”