Starvation Improves Survival of Bacteria Introduced into Activated Sludge

Abstract

A phenol-degrading bacterium, Ralstonia eutropha E2, was grown in Luria-Bertani (LB) medium or in an inorganic medium (called MP) supplemented with phenol and harvested at the late-exponential-growth phase. Phenol-acclimated activated sludge was inoculated with the E2 cells immediately after harvest or after starvation in MP for 2 or 7 days. The densities of the E2 populations in the activated sludge were then monitored by quantitative PCR. The E2 cells grown on phenol and starved for 2 days (P-2 cells) survived in the activated sludge better than those treated differently: the population density of the P-2 cells 7 days after their inoculation was 50 to 100 times higher than the population density of E2 cells without starvation or that with 7-day starvation. LB medium-grown cells either starved or nonstarved were rapidly eliminated from the sludge. The P-2 cells showed a high cell surface hydrophobicity and retained metabolic activities. Cells otherwise prepared did not have one of these two features. From these observations, it is assumed that hydrophobic cell surface and metabolic activities higher than certain levels were required for the inoculated bacteria to survive in the activated sludge. Reverse transcriptase PCR analyses showed that the P-2 cells initiated the expression of phenol hydroxylase within 1 day of their inoculation into the sludge. These results suggest the utility of a short starvation treatment for improving the efficacy of bioaugumentation.

Survival Trend of Lead Solubilizing Strains of Pseudomonas Species in Lead Polluted Soil Samples

“…Furthermore, reduction growths of 55.4%, 65% and 30.5% was also observed in the loamy soil sample. This observation which is similar to the reports of previous studies [3,7,14] may be due to the toxic effect of the Lead metal on the strains and/or that the substrate in the soil is not bio-available to the organisms.…”

“…However, many factors including predation, competition with indigenous microorganisms, nutrient availability, physicochemical parameters and other environmental factors necessary for growth has been found to influence the survival of bioaugmented microbes as well as their bioremediation efficiencies [1,2,3].…”

“…Many of the previous studies reported the use of activated contaminated soils or sludge as inoculants for bioaugmentation [3,4,5] but the fair of transferring more hazardous contaminants through the activated soil or sludge is also seen as a concern hence, the report of possible usage of uncontaminated soil with potential contaminant degrader as inoculants [6]. Although this technique has been seen as a potential alternative to address the use of activated sludge, but the direct use of harvested microbial cells could be a better option in that one is sure of the organism being introduced into the environment.…”

Development and Evaluation of an Online CO 2 Evolution Test and a Multicomponent Biodegradation Test System

“…The drawback of this method is the possible reduction in the number of viable bacterial cells and subsequently the loss of biodegradation potential. The influence of a starvation process on the viability of degrading bacteria has been discussed controversially (50). Improved survivability has been reported (48), while another study found no significant effects on survivability (49).…”

“…In our study, a short starvation period of about 18 to 24 h was sufficient to reduce endogenous CO 2 production effectively. Extended starvation periods up to 10 days cause a significant decrease in respiration and dehydrogenase activity (50) and may also result in a decrease in biodegradation potential.…”