Pseudomonas Mendocina Case Study

Pseudomonas mendocina EGD AQ5 degraded benzoate as a sole carbon source unto 40mM as revealed by spectrophotometry and HPLC analysis (Figure 2). Under static mode of incubation, Pseudomonas mendocina showed pellicle growth under high concentration (40mM) of benzoate after 3 days of incubation, while the release of planktonic cells started after 3rd day and highest at 12thday (Figure 2II) indicating adaptation of biofilm bacteria with benzoate (40mM) stress through pellicle formation and metabolite accumulation. HPLC analysis showed catechol accumulation in the culture supernatant. It was observed that untill 72hrs catechol accumulation has been insignificant. After 72hrs, catechol intermediate has been detected. Catechol metabolite accumulated

The results indicated the adaptation of Pseudomonas mendocina (biofilm forming bacteria) to high concentrations of benzoate (40mM) stress. It has been reported that several Pseudomonas species forms matrix associated sessile microbial structures called biofilms which allowed its existence in a variety of environmental stresses (Friedman and Kolter.2004; Singh et al.2006; Mc Dougald et al.2011). Biofilms protects its underlying cells from environmental cues, but mediates efficient biodegradation of toxic substances with less accumulation of metabolic intermediates (Vernhagen et al.2011). It has been observed that high concentration of organic compounds like benzoate in environment or in reactors at times create shock load and stressful situation to bacterial physiology (Ampe and Lindley.1996). To overcome such situations, bacterial cells enter biofilm mode and sustain (Bazire et al.2007). It has been observed that under biofilm mode of growth Pseudomonas mendocina EGD AQ5 could effectively overcome the stress and degrade 40 mM benzoate which has been regarded as highest concentration (Ampe and

In accordance with the maximum biofilm formation and benzoate degradation at 3rd day (Figure 2II), transcription of pelA and benA in presence of 40mM benzoate has been upregulated by 5.6 and 3.7 folds respectively as compared to 0th day (considered benzoate untreated). After 3rd day, transcription of pelA was deregulated by -1.165 folds, but benA continued to get expressed, but less than 3rd day by 1.21 folds (Figure 2III and 2IV). As after 3rd day, benzoate utilization continued without accumulation of intermediates such as catechol and cells dispersed from the biofilm state to continue their surface associated planktonic phases of their life cycle. Biofilm formation was also found to be decreased after 3rd day indicating cell dispersing for planktonic growth (Figure2). Results clearly supported that pel genes have been involved in benzoate degradation. At 6th day when benzoate was degraded to maximally and catechol was also used up, at that time pelA expression has been downregulated (cells in planktonic growth phase), which prompted efficient degradation of benzoate under biofilm conditions. Similar results were obtained in the biodegradation of chloropropham where accumulation of its metabolic intermediate 3-chloroaniline was minimum in biofilm mode of growth (Verhagen et al.