In deeper sediment,

35–40 cm, the DGGE pattern contains fewer bands than the other two analyzed depths. Küntze and colleagues [20] recommended the combination of PCR for bamA, which gives an overview of the anaerobic aromatic hydrocarbons degrading microorganisms present in the studied material, with PCR for bssA, which is specific for toluene and xylene degradation – although this gene also seems to be involved in the degradation of some long-chain aromatic hydrocarbons (L. Andrade, unpublished data). In the current study, sediment samples from the three depths tested negative for bssA (data not shown). Samples were also similarly screened with PCR primers targeting assA, involved in anaerobic alkane degradation, and results were also negative. Our failure to amplify bssA and assA do not necessarily mean that anaerobic selleck chemical aromatic hydrocarbon-degrading microorganisms are absent from the Surui mangrove sediment; they may be present at abundances too low to be detected with the PCR protocol used. Alternatively, anaerobic hydrocarbon degraders possessing ass/bss sequence variants lacking homology to our PCR primers [18] or that employ degradation pathways altogether different to the ones tested here (e.g., carboxylation reactions [32] or the two-step selleck compound oxidation of methylene observed in the degradation of ethylbenzene

by a nitrate-reducing strain [33]) for catabolism of anaerobic hydrocarbons. PCR-DGGE analyses for dsr showed that the bacterial community profile in the top 5 cm differs from the two selleckchem deeper sediment intervals, which was also observed in DGGE analysis of 16S rRNA genes. Nevertheless, the similarities in banding pattern are large concerning sediments of the two deeper layers, while both change a little when comparing to superficial sediment. Similar diversity among dissimilatory

sulfite reductase sequences in deeper sediment layers was also observed by Fan and colleagues [34] who analysed dsrAB from the surface to 50 cm depth. They suggest that different surficial and deeper sediment SRB community structure is related to tidal variation, which makes sediment temporarily oxic, hypoxic or anoxic. Moreover, tidal inundation also transports sulphate from the sea to Phenylethanolamine N-methyltransferase the coastal sediment, which shows a high sulphate concentration in the first centimetres of sediment, but diluted in the freshwater presents a low concentration downward. Taketani and colleagues [35] also studied SRB community structure using DGGE and showed that SRB diversity decreases with depth in mangrove sediment, as well as revealing a drop in the relative abundance of SRB, in agreement with the qPCR results presented here (Figure 4). However they noted little variation in diversity in the first 30 cm of that sediment [35].