Biodegradation of malathion by Acinetobacter johnsonii MA19 and optimization of cometabolism substrates

To enhance the removal efficiency of malathion in the wastewater from organophosphate pesticide mill, a bacterium, Acinetobacter johnsonii MA19, that could degrade malathion with cometabolisrn was isolated from malathion-polluted soil samples using enrichment culture techniques. Four kinds of additional compounds, sodium succinate, sodium acetate, glucose, and fructose were tested to choose a favorite carbon source for the cometabolism of strain MA19. The results showed that sodium succinate and sodium acetate could promote malathion biodegradation and cell growth. The investigation results of the effects of sodium succinate concentrations on the malathion biodegradation indicated that the more sodium succinate supplied resulted in quick degradation of malathion and fast ceils multiplied. Zero-order kinetic model was appropriate to describe the malathion biodegradation when the concentration of sodium succinate was more than 0.5144 g/L, The degradation rate constant （K） reached the maximum value of 3.5837 mg/（L·h） when the mass ratio of sodium succinate to malathion was 128.6 mg/mg. The aquatic toxicity of the malathion was evaluated using the test organism, Limnodrilus hoffmeisteri. The data obtained suggested that the toxicity of malathion could be ignored after 84 h biodegradation. Our result demonstrates the potential for using bacterium A. johnsonii MA19 for malathion biodegradation and environmental bioremediation when some suitable conventional carbon sources are supplied.

Cell-free supernatants of Bacillus inhibit the biofilms of Pseudomonas lundensis cultured with and without Acinetobacter johnsonii

[Objective] Pseudomonas as one of the dominant spoilage bacteria highly form biofilms in chilled meat products and processing environment when contaminating single or mixed with other species.This study aims to investigate the antibiofilm properties of the cell-free supernatants(CFSs) of three Bacillus species isolated from fermented food and rice seeds on Pseudomonas lundensis(PL) or and Acinetobacter johnsonii(AJ) as mono-or dual-species.[Methods] Biofilm biomass,extracellular polymeric substances(EPSs),and biofilm structure were measured by crystal violet staining,spectrophotometry,confocal laser scanning microscopy(CLSM),respectively,as well as transcription of biofilm-related genes determined by qPCR.[Results] The CFSs of Bacillus amyloliquefaciens ZG08,B.velezensis B5,and B.subtilis YB11 inhibited the biofilm formation of PL and AJ without affecting their growth.The treatment with 50% CFSs of ZG08 and B5 decreased the cell viability of two biofilms by 12.73%–21.04%,which was higher than that of YB11(0.15%–4.38%).The inhibition rates of 50% CFSs of the three strains were 59.75%–79.59% against the PL biofilm and 63.62%–78.57% against the biofilm of PL+AJ,in which the CFS of YB11 had weaker activity.The content of exopolysaccharides and exoprotein in the two biofilms treated with these CFSs were reduced by 53.77%–73.30% and 54.84%–62.38%,respectively.The treatment with the three CFSs also reduced the adhesive cells,loosened biofilm structures,and thinned their thickness by 57.63%–74.49% and 60.43%–64.64%,respectively.Moreover,the CFSs of ZG08 and B5 effectively eradicated by 41.77%–69.79% against the mature biofilms of PL and PL+AJ,compared to weak activity of YB11.In addition,the antibiofilm activities of the three CFSs were stable under four enzyme digestion and heating conditions.Compared with the control,the CFSs of ZG08 and B5 significantly down-regulated the expression of six biofilm-related genes,lapA,alg44,pelG,luxR,wspR,and rpoS.[Conclusion] The CFSs of ZG08 and B5 have strong antibiofilm activities against PL and AJ as mono-or dual-species.