Enhancement of marine bacterial growth by mineral surfaces' Gordon T. Taylor and Jeanne D. Gulnick Abstract: The effects of sorptive inert surfaces on growth of marine bacteria and metabolism, as well as partitioning of organic substrates, were examined in microcosms inoculated with bacterioplankton from a local salt marsh. Introduction of organic-free glass beads to a dilute seawater medium (tryptic soy broth) increased yields of ATP, a surrogate for bacterial biomass, by 187% within the entire microcosm (attached + free-living). Growth efficiencies (bacterial C /media C) were 30% for bacteria grown in microcosms with beads compared with 16% without beads. Surface enrichment increased rates of proteolytic enzyme activity and cell-specific [3H]leucine incorporation into protein by factors of 6.8 and 2.2, respectively. Scanning electron microscopy revealed obvious organic coatings on all beads after 2 h of exposure, but few strongly attached bacteria were evident, even after 40 h of exposure. Results support the hypothesis that mineral surfaces facilitate bacterial utilization of complex organic matter through physical-chemical processes that increase conversion efficiencies of labile substrate despite possible kinetic limitations. Furthermore, firm attachment by bacteria to these surfaces is apparently not a requirement to produce surface-enhanced activity. Key words: epibacteria, sorption, interfaces, hydrolytic enzymes, growth efficiency. Resume: Nous avons Cvaluk l'influence de surfaces inertes absorbantes sur la croissance de bactkries marines ainsi que sur le mktabolisme et le fractionnement de substrats organiques dans des microcosmes inoculks avec du bactCrioplancton provenant d'un marais salin local. L'introduction de billes de verre exemptes de matikre organique dans un milieu de culture ?i l'eau de mer (bouillon trypsique de soja) a augment6 le rendement en ATP reprksentant la biomasse bactkrienne, de 187% dans la totalit6 du microcosme (cellules libres + fixees). Les rendements de croissance (C bacttries / C milieux) Ctaient de 30% dans le cas de bactkries cultivtes dans des microcosmes avec des billes comparativement B 16% en absence de billes. Un enrichissement des surfaces a augmente les taux d'activitk de la prottolyse enzymatique et l'incorporation dans les proteines de [3H]leucine sptcifique B la cellule par des facteurs de 6,8 et 6,2, respectivement. La microscopie Clectronique B balayage a nettement rCv61C des enrobages de matikre organique sur toutes les billes aprks 2 h d'exposition, mais il y avait t*s peu de bactCries fortement attachkes mCme aprks 40 h de contact. Ces rksultats confirment I'hypothkse voulant que les surfaces minkrales puissent faciliter l'utilisation par les bactkries de matikre organique complexe selon des processus physicochimiques qui augmentent les efficacitks de conversion de substrats instables malgk la possibilitk de limites cinktiques. De plus l'adhkrence ferme des bactkries B ces surfaces ne semble pas nkcessaire pour obtenir une augmentation d7activitC par des surfaces. Mots cle's : epibactkries, adsorption, interfaces, enzymes hydrolytiques, rendement de croissance. [Traduit par la rCdaction] Introduction metabolism. However, to what extent the effects are positive or Numerous biological, geochemical, and biotechnological processes occur at interfaces between aqueous and solid phases, a realm distinct from either bulk phase that provides unique habitats for microorganisms. On a global basis, diagenesis of a significant portion of organic matter (OM), both native and xenobiotic, is controlled by its association with surfaces of sediments, soils, and seston and their indigenous microbial communities. It is known that the presence of sur- faces and their sorptive capacity for nutrients affect bacterial Received January 30, 1996. Revision received May 13, 1996. Accepted May 28, 1996. G.T. Taylor2 and J.D. Gulnick. Marine Sciences Research Center, State University of New York, Stony Brook, NY 11794-5000, U.S.A. Marine Sciences Research Center, State University of New York, Stony Brook, contribution No. 1028. Author to whom all correspondence should be addressed (e-mail: gtaylor@ccmail.sunysb.edu). negative depends on a variety of factors, including substrate composition and concentration, substratum composition and surface properties, aqueous ionic strength and pH, temperature, hydrodynamics, and microbial community composition (ZoBell 1943; Fletcher and Marshall 1982; Bright and Fletcher 1983; Samuelsson and Kirchman 1990; van Loosdrecht et al. 1990; Zheng et al. 1994; Taylor 1995). One set of conditions, such as small molecules sorbed to porous clay phases, may reduce the bioavailability of nutrients and produce negative surface effects for bacteria, leading to sorptive protection of OM (e.g., Gordon and Millero 1985; ashm man-and Stotsky 1986; Mayer 1994; Keil et al. 1994). Whereas another set of conditions, such as macromolecules sorbed to less porous clay or siliceous phases, may improve bioavailability and produce positive surface effects for bacterial metabolism and degrada- tion of OM (e.g., Estermann and McLaren 1959; Griffith and Fletcher 1991; Taylor 1995). In a dilute medium, such as most natural aquatic systems, organic matter can concentrate at the interface through adsorp- tion, which in turn can stimulate bacterial activity (ZoBell Can. 3. Microbiol. 42: 911 -918 (1996). Printed in Canada / Imprim6 au Canada Can. J. Microbiol. Downloaded from www.nrcresearchpress.com by SUNY AT STONY BROOK on 06/19/13 For personal use only.