Inhibition of bacterial activities by solar radiation in nearshore waters and the Gulf of Mexico

Abstract

The effects of ultraviolet ( U V ) r a d~a t~o n on thymldine and leucine incorporation were evarmned In surface waters from the Gulf of Mexico and Santa Rosa Sound a mesotrophlc estuary In no] thwest Florida USA Whole dnd 0 8 ].[m flltered surface waters were incubated w~t h 3 H -t h y m~~n e and 14C-leucine in IJV transparent containers under natural solar radlatlon Solar radlation was either not filtered (samples exposed to UV-B UV-A and photosynthetically active radlatlon PAR), filtered through Mylar 500D (samples exposed to UV-A and PAR), or filteled through Acryllte OP3 (samples exposed only to PAR) I11 Santa Rosa Sound thymldine lncorporatlon was lnhlblted an average of 44 % relatlve to dark controls when exposed to unflltered solar radlatlon PAR contnbuted 23% to the total thynudlne ~n h i b i t~o n lvhlle UV-A and UV-B contributed 37 % and 39% respectively to total inhlb~tion L e u c~n e incorporation In Santa Rosa Sound was lnhlblted 29% by full solar r a d~a t~o n The malonty of the total l e u c~n e inhlb~tlon was d u e to UV-B (83%) whlle PAR only treatments showed leucine lncorporatlon rates 1 0 "~ higher than dark controls For the Gulf of Mexico expenments full solar radlation ~nhlbited thym~dine inco~polatlon approximately twlce as much as leuclne lncorporatlon However there were no consistent patterns In differences d u e to d~fferent wavelengths Both thymidlne and l e u c~n e incorporation were lnhlbited to a greater extent ~n < 0 8 pm filtered water samples than In whole water samples suggesting that the presence of primary producers may mediate the d e t~l m e n t a l effects of solar radiation on bacterioplankton Surface rvater was also incubated In s~t u wlth thymidlne at flved depths in UV transparent and darkened containers at 3 locations in the Gulf of b l e x~c o Total ~nhlbltion was 60 to 7 0 % at the surface and was evldent to 15 m Comparison with radiometric data and DNA doslmeters lndlcated that UV-B exerted the greatest effect In the upper 5 m vvhlle below that the lnhlbltion was most l~k e l y due to longer wavelengths Our results suggest that both UV and visible solar radlation can negatively affect bacterial metabolism and fallure to take Into account the effects of light may result In the overest~rnat~on of bacterioplankton production in surface waters KEY WORDS: Ultraviolet radlation . Bacterla Thymidine .

Distribution and turnover of dissolved DMSP and its relationship with bacterial production and dimethylsulfide in the Gulf of Mexico

“…All samples used for DMSP turnover and other rate measurements were collected on casts made in the early morning, 0600-0730 h, a time at which bacterial and phytoplankton populations are minimally affected by exposure to daily ultraviolet radiation (Aas et al 1996). At each station, four depths within the upper 100 m were sampled for rate determinations (see below).…”

Effect of solar ultraviolet radiation on bacterio- and phytoplankton activity in a large coral reef lagoon (southwest New Caledonia)

“…Indeed, it is frequently proposed that UV-R induces an increase in carbon release by phytoplankton. Aas et al (1996) reported a significant stimulatory effect of PAR and PAR + UV-A on BP associated with an increase in organic carbon release in coastal surface water of the Atlantic Barrier Coral Reef. In the same way, their bioassay experiments showed a significant increase in rates of bacterial secondary production, in the growth rates and cell volumes of bacteria grown in sunlightirradiated water samples (i.e.…”

“…Differences in BP, PPP and DPP among the various light treatments were assessed with the Mann-Whitney U-test. All results are mean ± SD reported at a 0.05 significant level (ns = non significant) of the afternoon can be considered as representative of the highest value, particularly since UV inhibition of BP is cumulative over the course of the solar day (Aas et al 1996, Visser et al 2002. Lastly, short-term measurements of UV-R photoinhibition can be difficult to translate to long-term ecological effects.…”

Differential response of planktonic primary, bacterial, and dimethylsulfide production rates to static vs. dynamic light exposure in upper mixed-layer summer sea waters

“…It appears that the ability to take advantage of dynamic light exposure may depend on the taxonomic composition and size structure of the phytoplankton community, their light history, and their nutritional status (Barbieri et al, 2002;Brunet and Lavaud, 2010;Helbling et al, 2013). Knowledge on the photoresponse of (bacterial) heterotrophic activity is much more limited, but a number of studies suggest that significant PAR-driven stimulation frequently occurs (Morán et al, 2001;Church et al, 2004), as does inhibition due to UVR (Aas et al, 1996;Kaiser and Herndl, 1997). There is mounting evidence that UVR resistance and photostimulation responses vary among bacterial phylogenetic groups (Agogué et al, 2005;Alonso-Sáez et al, 2006;RuizGonzález et al, 2012), which might be related to the occurrence of photoheterotrophic metabolisms in the ocean (Kolber et al, 2000;Béjà et al, 2000;Kirchman and Hanson, 2012) or to their interaction with other light-driven processes (see references in Ruiz-González et al, 2013).…”