This investigation has assessed natural product antifouling performance of an isolated compound from a terrestrial source against marine biofilm forming bacteria, Cobetia marina and Marinobacter hydrocarbonoclasticus. Novel bioassay protocols using the hydrodynamic system and its well plate microfluidics capability were developed to test the in situ antifouling efficacy of the natural product against biofilm attachment under two shear stresses (0.07 and 0.3 Pa). The hydrodynamic results allowed for the first time the direct observation of the natural product influence on newly attached marine biofilms and the evolution of the antifouling affect with time. Biofilm attachment behaviour appeared to be markedly different in the presence of the natural product, illustrated by limited cluster and extracellular polymeric substance formation which suggests an interference of the bacterial attachment mechanisms. Ultimately, this is fundamental in developing greater understanding of the biofilm kinetics. These observations were confirmed using epifluoresence and confocal microscopy, with the additional corroborative data on bacterial cell integrity using the LIVE / DEAD nucleic acid kit.

Suitable in situ techniques capable of sensing for the presence of a biofilm on metallic surfaces are becoming increasingly necessary, especially in order to maintain seawater pipe system performance. This study has investigated the detection of aerobic marine bacterial biofilms using electrochemical impedance spectroscopy by monitoring the interfacial response of Pseudoalteromonas sp. NCIMB 2021 attachment and growth in order to identify characteristic events on a 0.2 mm diameter gold electrode surface. Uniquely, the applicability of surface charge density has been proven to be valuable in determining biofilm attachment and cell enumeration over 72 h duration on a gold surface within a modified continuous culture flow cel(lsa controlled low laminar flow regime with a Reynolds number ≈ 1).In addition, the potential for biofilm disruption has been evaluated using 500 nM of the nitric oxide (NO) donor sodium nitroprusside (NO is important for the regulation of a number of diverse biological processes). Ex situ confocal microscopy studies were performed to confirm biofilm coverage and morphology, plus the determination and quantification of the NO biofilm dispersal effects. Overall, the capability of the sensor to electrochemically detect the presence of initial bacterial biofilm formation and extent has been established and shown to have potential for real-time biofilm monitoring.

Photobacterium kishitanii is one species of luminescent bacteria. This bacterium is known to convert chemical energy into light; it glows in the dark with a visible peak wavelength (ca. 475 nm) that is easily recognized. Luminescent bacteria produce autoinducers and respond to this molecule to switch on the luciferase structural operon. Luminescence is, therefore, controlled by the cell-population density.

If bacterial cells are viewed as enzyme bags, substrates, such as oxygen or autoinducers, diffuse into the bags through a semipermeable cell wall and are catalyzed by the enzyme. Oscillation in the product concentration is often observed in systems where a semipermeable membrane separates the substrate and the enzyme. Such behavior is simulated using a reaction-diffusion model.

We have reported several characteristics of the luminescence from a bacterial suspension. For example, in a batch culture, higher initial bacteria density resulted in an earlier luminescence starting time [1]. Apart from such linear characteristics, we have reported an oscillation in the luminescence intensity both spatially and temporally [2]. We hypothesize that a group of bacteria behaves differently from a sum of single cells. The nonlinearity of the bacterial luminescence might be a key to understanding the phenomenon. In a previous experiment, we separated bacteria into small groups that showed similar characteristics, such as motility and adsorption activity. For example, bacteria separated according to their motility using a microfluidic device were proved to show different bioluminescent intensities for each cell [3]. On an agar plate, the luminescence intensity from actively dividing cells was less than that from mature cells [4]. In addition to this basic study to understand the oscillation in bacterial luminescence, reactors were designed to realize stable bacterial luminescence. In a PDMS cell, only the parts of the suspension that faced the wall were illuminated [5]. This result suggested that the geometrical symmetry of oxygen supply to the suspension helped maintain spatial stability without convection of the bacterial luminescence.

Here, we report the luminescence behavior of bacteria that adsorbed on material surfaces. In this work, we show experimentally that the bacteria adsorb on the inner surfaces of a polyethylene terephthalate (PET) or polystyrene (PS) bottle and start to emit light when a liquid broth is added. We also show that the luminescence from the suspension oscillates. Experimentally, using a self-made luminescence detector, measurement of luminescence intensity from well-stirred bacterial suspensions in the bottles of different materials (PVC, PET, or PS) was performed. After the observation of oscillation in luminescence, the bottles were washed three times using the same broth, followed by the luminescence measurement. Such washing and measurements were repeated, and oscillation was repeatedly observed. The chemical condition of adsorption on the surface was investigated using surface analysis methods, such as AFM or FTIR, and the material characteristics with regard to cell adsorption and oscillation mode were discussed.