Fig 4.

(a to d) Depth distribution of chlorophyll (solid line), PAR (crosses), density (closed circles), and the concentration (mean ± standard error, n = 3) of Labrenzia-like nosZ mRNA (bars; *, not detected) at stations 1 (a) and 2 (c). The corresponding depth distributions of nitrate (closed circles) and nitrite (×5, open circles) concentrations at stations 1 (b) and 2 (d) are shown in the right-hand panels. The additional dotted line shown in panel d is the oxygen saturation profile for station 2. (e) Electrophoretogram of nosZ RT-PCR products from the Arabian Sea isolate 4N grown in denitrification medium under an aerobic atmosphere (t₀) and following transfer to suboxic conditions for 30 min (t₃₀). Equal quantities of total RNA were used for the reverse transcriptase (+RT) reactions. The absence of contaminating DNA was verified in parallel reactions in which the enzyme was omitted (−RT). The mean concentration (n = 3) of the nosZ PCR product at t₃₀ determined by QPCR was 4.23-fold that at t₀. The lower band in each lane is a mixture of QPCR primers and the fluorescein-labeled nosZ probe.