Table 1. Phylogenetic composition of the 2226 microarray probe set.

Phylum	All probes	Expressed probes	% of expressed	April	June	August	November
Euryarchaeota	356	296	83.1	0.99	0.97	0.97	0.99
Crenarchaeota	113	100	88.5	1.09	1.15	1.15	1.08
Gammaproteobacteria	595	564	94.8	1.65	1.68	1.68	1.67
Alphaproteobacteria	426	418	98.1	2.13	2.11	2.12	2.09
Betaproteobacteria	187	184	98.4	1.6	1.59	1.62	1.61
Deltaproteobacteria	147	145	98.6	2.44	2.45	2.29	2.32
Chlorobi	81	81	100.0	1.99	2.05	2.11	1.94
Firmicutes	76	72	94.7	1.59	1.8	1.67	1.75
Actinobacteria	51	47	92.2	2.41	1.95	2.09	2.12
Bacteroidetes	47	39	83.0	1.27	1.2	1.14	1.29
Planctomycetes	37	36	97.3	1.73	1.93	1.67	1.67
Chloroflexi	28	27	96.4	2.11	2.57	2.5	2.57
Epsilonproteobacteria	27	24	88.9	1.42	1.33	1.31	1.47
Magnetococci	13	13	100.0	2.9	3.91	3.01	3.52
Thermotogae	12	12	100.0	1.44	1.86	1.87	1.57
Verrucomicrobia	10	10	100.0	2.92	2.97	4.64	2.68
Zetaproteobacteria	7	7	100.0	1.95	2.19	1.81	2.09
Aquificae	7	7	100.0	2.15	1.84	1.58	2.17
Acidobacteria	6	6	100.0	2.32	3.07	2.62	2.67

The probes were selected as expressed if corresponding signal intensities exceeded the baseline value (background plus 3X standard deviations) in at least 2 samples. The median expression levels were calculated for probes corresponding to expressed genes for each phylogenetic group, and then represented as fold changes over the median signal intensity of the whole microarray data set. Median expression levels for archaeal divisions are shown in bold.