Fig. 1. Neighbor joining tree based on partial 16S rRNA gene sequences showing the diversity of bacteria capable of utilizing methyl halide as a growth substrate. Methyl halide-degrading bacteria are shown in bold type, the scale bar corresponds to 10% sequence divergence.

Fig. 2. The MeCl utilization pathway of Methylobacterium chloromethanicum CM4 as proposed by Vannelli and coworkers (modified from Vannelli et al., 1999). Names of enzymes catalyzing steps in the degradation pathway are shown on the left of the diagram.

Fig. 3. Gene clusters of methyl halide-utilizing strains containing genes with proven and putative function in the CmuA methyl halide utilization pathway. Homologous genes have identical shading.

Fig. 4. Phylogenetic tree based on neighbor joining analysis of amino acid sequence alignment of CmuA sequences (methyltransferase I/corrinoid-binding protein) from methyl halide-degrading bacteria and environmental samples. Closely related sequences have been grouped, whereby those groups without cultivated representatives have been shaded grey. Numbers in parentheses indicate the number of sequences of each group. Labels left of groups indicate representative sequences, including cultivated members. The scale bar represents 10% sequence divergence.

Fig. 5. MeBr concentrations in soil gas during the first 4 days of field fumigation with MeBr (67%) and chloropicrin (33%). MeBr was added around 20 cm depth on day 0 at a rate of 160 kg/acre.

Fig. 6. Bromide ion (Br⁻) extracted from soil fumigated with MeBr and chloropicrin (6 days) collected under various soil surface treatments.

Properties of Methyl Halides and Their Effect on Atmospheric Chemistry

N.A., not applicable.

Anthropogenic Sources of Atmospheric Methyl Halides in Gg year⁻¹ (Best Estimates)

N.A., not applicable.

Properties of Bacterial Isolates Capable of Growth on Methyl Halides

n.a., data not available.

Summary of Observations Suggesting Different Pathways of Methyl Halide Degradation