Ultraviolet-B radiation and bacterial metabolism in coastal waters

Abstract

The impact of ultraviolet-B (UV-B) radiation on bactenal density and production and on extracellular enzymatic activity was investigated the northern Adriatic Sea. Samples were incubated in quartz bottles and exposed to natural solar radiation (0.5 W m-2) as well as to artificial UV-B (0.4 W m-2) sources. Exposure to artificial UV-B sources over a penod of 12 h revealed a constant decline in bactenal density to about 60% of the corresponding dark value. Total lipase and leucine-aminopeptidase activity showed a decrease to 38.8 and 21.9%, respectively, of the dark control; dissolved leucinearninopeptidase activity was significantly more affected (15.3 % of the corresponding dark value) than hssolved lipase activity (43.2 % of the corresponding dark value). Samples exposed for 6 h to artificial UV-B or for 4 h to natural solar radiation exhibited rapid recovery during subsequent dark incubation Following UV-B exposure (0.4 W m-2) bactenal density recovered rapldly from 74.6% to 84.1 %, lipase activity recovered from 64 % to 80% and leucine-aminopeptidase activlty from 53% to 7 1 % of the corresponding dark values dunng 6 h of subsequent dark incubation. Recovery of bacteria followng exposure to natural solar UV-B radiation with similar intensity was even higher. In these experiments bacterial density reached smllar values as in the dark control, bacterial production even exceeded the dark control production rates after 6 h of dark incubation following UV-B exposure. This difference might be attributed to photorepair induced by UV-A and to increased availability of dissolved organic matter due to UV-B mediated photolysis. UV-B radiation levels of 0 4 W n1r2 as used in this study are detectable in the surface layers of the northern Adnatic Sea up to 0.5 m depth for at least 3 to 5 h d -' during summer Thus our results suggest that microbial life might be affected by UV-B radiation and consequently also the carbon and energy flow in aquatic systems.

Diel variations in frequency of dividing cells and abundance of aerobic anoxygenic phototrophic bacteria in a coral reef system of the South China Sea

“…Our research area was a shallow coral reef system, and solar radiation was most intense at around 12:00 to 15:00 h (Fig. 1), when the growth of bacteria could be inhibited and photo-induced cell lysis could occur (Müller-Niklas et al 1995, Pakulski et al 1998). In addition, viral lysis of bacteria mainly occurs around noon to afternoon (Winter et al 2004), which might be another factor leading to a drop in AAP abundance at noon.…”

Effects on aquatic ecosystems

“…The equilibrium between UV damage and photorepair is governed by the passive movement of the cells within the mixing layer, where they are alternately exposed to high levels of damaging solar UV radiation near the surface and beneficial UV-A/blue light at greater depths. Other macromolecular components of the bacterial cells, as well as ectoenzymes responsible for the cleavage of external organic matter, are affected by solar UV-B radiation [55]. The bacterioplankton serve as food for heterotrophic flagellate picoplankton (-1 mm).…”

Diurnal variations in depth profiles of UV-induced DNA damage and inhibition of bacterioplankton production in tropical coastal waters

“…It has been suggested that heterotrophic bacteria are likely to be more susceptible to UV stress than larger organisms, due to their small size and short generation times (Häder et al 1995) and the absence of UV absorbing pigments (Karentz et al 1994). Changes in the growth of bacteria upon exposure to UVR have been shown (Thomson et al 1980, Herndl et al 1993, Müller-Niklas et al 1995, Sommaruga et al 1997. UVR may have both direct and indirect effects on bacterioplankton.…”