BIOAUGMENTATION FOR AEROBIC DEGRADATION OF CIS-1,2-DICHLOROETHENE - Bioaugmentation for Groundwater Remediation - page 198

6 0.10

Growth (OD 600 )

cis -DCE

5

0.08

cis -DCE consumed

4

Chloride

0.06

3

0.04

2

0.02

1

0

0.00

0 100 200 300 400

Time (hours)

Figure 7.2. Mineralization of cis-DCE by JS666 showing amount of cis-DCE (triangles) and optical
density (OD 600 , circles) (adapted from Coleman et al., 2002a ).

JS666 can tolerate and transform cis -DCE at aqueous concentrations of 0.5-0.9 millimolar
(mM), but concentrations above 1 mM are inhibitory (Jennings, 2009 ). The optimum growth
temperature is 22 C, with no growth at 30 C, suggesting no potential for human pathogenicity -
always a concern with cultures proposed for bioaugmentation. Degradation is inhibited at pH
below 6.5 with an optimum around 7.2. The sensitivity of JS666 to low pH may require the
addition of buffer for in situ bioaugmentation. Phosphate buffer (20-40 mM) is currently being
using in laboratory studies to maintain neutral pH. JS666 tolerates higher equivalents/liter (eq/L)
of orthophosphates than carbonates. JS666 cultures challenged with high oxygen levels (partial
pressure of oxygen 0.34 and 0.77 atmospheres [atm]) degrade less cis -DCE than cultures with

levels below 0.21 atm (Jennings, 2009 ). JS666 is capable of using oxygen to levels below
analytical detection (ca. 0.01 milligrams per liter [mg/L]). The results indicate that oxygen levels
at 0.21 atm or lower are optimum for cis -DCE degradation by JS666; addition of excess oxygen
to stimulate degradation is not necessary and may even hinder degradation in the field.
JS666 was observed to prefer low-ionic-strength environments (conductivity < 15 millisie-
mens per centimeter [mS/cm]), and high chlorides accumulated through dechlorination of
repeated additions of cis -DCE can be problematic (S. Nishino and J.C. Spain, Georgia Institute
of Technology, unpublished). For culture maintenance, a strategy of periodic transfer of
inocula to fresh media has normally been employed. Alternatively, growth to high densities
involved biomass separation and exchange of medium.

¼

7.2.3 Insight About Metabolic Pathways from Genomics
and Proteomics

cis -DCE degradation pathways in JS666 have not been determined. The genome of JS666
has been completely sequenced, but genomic analysis did not reveal any obvious cis -DCE
degradation operon (Mattes et al., 2008 ). Genes potentially involved in cis -DCE degradation
(e.g., flavin-containing monooxygenase, cytochrome P450, glutathione S-transferase, and
haloacid dehalogenase) are scattered among the chromosome and two large plasmids.
It seems likely that the cis -DCE degradation pathway in JS666 was assembled recently by