for examining and monitoring microbial communities and is even being used for metatranscriptome analysis (van Vliet, 2010) . However, while many of the technical challenges of microarrays and high-throughput sequencing have been overcome, each still has some distinct advantages and disadvantages, which make them ideal as complementary approaches: (i) Random sampling errors. In most sequencing studies, only a small proportion of the microbial community is actually sampled (McKenna et al., 2008) and while theoretically with true random sampling the probability of sampling the same fraction of the community multiple times is low , one would expect that dominant populations would have a greater chance of being sampled multiple times. These sampling errors can result in low reproducibility between technical replicates (17.2 ± 2.3% for two replicates; 8.2 ± 2.3% for three; Zhou et al., 2011) . Microarrays, in contrast, interrogate all samples against the same set of sequences (probes), so that the same population is sampled each time. (ii) Relative abundance. Abundance of individual species will vary greatly within microbial communities. With sequencing-based approaches there will be a bias toward the most abundant sequences in the environment so that many of the obtained sequences will represent the most abundant species/sequences while possibly missing lesser abundant species/sequences. Microarrays are not affected in the same way since lesser abundance sequences will still hybridize to their corresponding probe and as long as it is above the detection limit, it will be detected. (iii) New sequence detection. One of the greatest advantages of sequencing is that new sequences are easily detected since any sequences in the sample can be sequenced (open system). Microarrays, in contrast, can detect only the limited number of sequences covered by the probe set on the array (closed system), as such, it is not able to detect new sequences. Some new microarray techniques have been developed to allow the discovery of new sequences. Capture microarrays have been developed, which use lower stringency conditions to hybridize or "capture" sequence variants Okou et al., 2007) . These captured sequences are then washed off and sequenced. An array with probes specific for viral families has been developed that uses the hybridization pattern to classify novel viruses (Wang et al., 2002; Ksiazek et al., 2003) . As such, microarray and sequencing approaches could be used to maximize the benefits and minimize the deficiencies of each.