Chemotaxis Increases the Retention of Bacteria in Porous Media with Residual NAPL Entrapment

Abstract

Chemotaxis has the potential to decrease the persistence of nonaqueous phase liquid (NAPL) contaminants in aquifers by allowing pollutant-degrading bacteria to move toward sources of contamination and thus influence dissolution. This experimental study investigated the migratory response of chemotactic bacteria to a distribution of residual NAPL ganglia entrapped within a laboratory-scale sand column under continuous-flow at a superficial velocity of 0.05 cm/min. Naphthalene dissolved in a model NAPL 2,2,4,4,6,8,8-heptamethylnonane partitioned into the aqueous phase to create localized chemoattractant gradients throughout the column. A pulse mixture of equal concentrations of Pseudomonas putida G7, a strain chemotactic to naphthalene, and Pseudomonas putida G7 Y1, a nonchemotactic mutant, was introduced to the column and effluent bacterial concentrations were measured with time. Breakthrough curves (BTCs) for the two strains were noticeably different upon visual inspection. Differences in BTCs (compared to nonchemotactic controls) were quantified in terms of percent recovery and were statistically significant ( p < 0.01). Chemotaxis reduced percent recovery in the effluent by 45% thereby increasing the population of bacteria that were retained within the column in the vicinity of residual NAPL contaminants. An increase in flow rate to a superficial velocity of 0.25 cm/min did not diminish cell retention associated with the chemotactic effect.

Bacterial hopping and trapping in porous media

“…7,8 In agriculture, the migration of rhizosphere bacteria through soil impacts crop growth and productivity, [9][10][11][12] while in environmental settings, the process of bioremediation relies on motile bacteria migrating towards and degrading contaminants trapped in soils, sediments, and subsurface formations. [13][14][15] However, despite their potentially harmful or beneficial consequences, how motile bacteria move through 3D porous media remains completely unknown. As a result, our ability to accurately model migration in porous media is limited.…”

Migration of Active Rings in Porous Media

“…The effective migration of neutrophils or other leukocytes through mucus is related to their ability to function in the human mucosal immune system or to serve as vectors for the translocation of infectious pathogens like HIV [45]. In bio-remediation, microscopic organisms migrate through the soil and sediments to remove or neutralize the environmental pollutants by metabolic processes [46][47][48]. To migrate through crowded environments, cells consume energy from ATP hydrolysis in two ways; by the action of myosin molecular motors on actin filaments [49][50][51] or by a propulsive mechanism using the plasma membrane blebs [52].…”

Microfluidic hotspots in bacteria research: A review of soil and related advances

“…Spatial heterogeneity in the distribution of soil moisture, nutrients, and pollutants has led to the evolution of complex chemotaxis mechanisms, affecting colony spatiotemporal distribution and compositional diversity, which thereafter alters soil physicochemical properties. Bacterial chemotaxis promotes nutrient cycling (Pedler et al, 2014) and the degradation of soil organic pollutants (Krell et al, 2013;Gupta et al, 2015;Adadevoh et al, 2016Adadevoh et al, , 2018; however, the mechanisms involved are still a mystery. To simulate the physical structures of soil and soil pores, microfluidic platforms have moved from linear concentration gradients to multidimensional systems with fluid variables such as concentration, velocity and temperature, and scaffolding variables such as surface roughness, hardness and wettability (Cruz et al, 2017).…”