Biofilm formation on agricultural waste pretreated with cold low-pressure nitrogen plasma and corona plasma discharges

Abstract

35Agricultural waste (AW) was pretreated with cold low-pressure nitrogen plasma 36 (LPD) and corona atmospheric plasma discharges (CAPD), in an attempt to increase the 37 bacterial attachment and biofilm formation. Biofilm formation was examined in the 38 presence of exogenously added P. putida and B. cereus as well as in a sterile medium 39 where only the indigenous bacteria which grow naturally on the wood surface could 40 form biofilm. The exposure of AW to (LPD) led to a 3.5-fold increase in biofilm 41 formation of the exogenously add P. putida F1 in MMT (minimal medium supplied with 42 toluene) and a 1.6-fold increase in MMG (minimal medium supplied with glucose) 43 compared to the untreated AW. The increase in biofilm formation was also observed 44 with the exogenously added B. cereus or with indigenous bacteria that grow naturally 45 on the AW. The effect of the CAPD on biofilm formation was weak. SEM analysis of 46 the LPD-treated AW showed an increase in surface roughness, which we assume is one 47 of the reasons for the enhancement of the biofilm formation. The apparent contact angle 48 of a sessile drop on the surface of LPD-treated AW as well as on the bacterial layer 49 showed their hydrophilic nature. In conclusion, the increase in biofilm formation of the 50 exogenously added P. putida or B. cereus was due to the LPD treatment. 51 Importance. To the best of our knowledge, this is the first study to describe the 52 effect of wood plasma treatment on biofilm formation. This technology can be further 53 implemented for bioremediation of contaminated soils.54 55 Introduction 56Plasma is one of the four forms of the naturally occurring matter states, and is 57 mostly comprised of ions and electrons (1). Plasmas are considered as an ionized gas 58 which can be divided into two types according to their gas temperature, "Hot" plasmas 59 (near-equilibrium plasmas) and "Cold" plasmas (non-equilibrium plasmas). Hot 60 plasmas are characterized by very high temperatures of electrons and heavy particles, 61 whereas cold plasmas are composed of low temperature particles and relatively high 62 temperature electrons. Hot plasmas include electrical arcs, plasma jets of rocket 63 engines, thermonuclear reaction generated plasmas, etc. Cold plasmas include low-64 pressure direct current (DC), radio frequency (RF) discharges (silent discharges), and 65 discharges appearing in fluorescent (neon) illuminating tubes. Corona plasma 66 discharges are also identified as cold (however, atmospheric pressure) plasmas (2).67 3 Cold plasma discharges are effectively used for a plethora of technological 68 processes, including modification of chemical and physical properties of organic 69 (synthetic and natural) surfaces (3), polymerization (4), antibacterial treatment of non-70 woven fabrics (5) and advanced agriculture technologies (6), etc. 71Due to the relatively small energy of particles, inherent to the cold plasma 72 discharges, the depth of influence (penetration) of these discharges into organic 73 substrates is na...