Marine bacterial organisation around point-like sources of amino acids

Abstract

To better understand the trigger for and use of motility in marine bacterial chemotaxis, specific (amino acids) chemical stimuli were used to test the effect on bacterial speed and reorientation. An assay system was developed to analyse bacterial behavioural responses to point-like nutrient sources (beads 10-40 mum). The marine bacteria Pseudoalteromonas haloplanktis, Shewanella putrefaciens, Deleya marina, the enteric bacterium Escherichia coli and an enriched assemblage of marine bacteria were used in the assay. E. coli responded to the amino acids (e.g. serine, leucine) in this assay in a manner similar to the classical capillary plating method, and accumulated near the attractants using biased random walks and maximum speeds of less than 30 mum s(-1). The marine bacteria travelled more than 100 mum s(-1) and reversed direction instead of randomly tumbling to reorientate. Marine bacteria also showed different chemotactic responses. The enriched marine community and P. haloplanktis were repelled by serine while leucine was an attractant for all three marine isolates. More importantly marine bacteria formed band specific distances (>20 mum) away from individual beads. The bands were composed of free-swimming bacteria rather than bacteria attached to the beads or chamber surfaces. The bands' formation time (25-180 s) and width (5-20 mum) varied depending on the bacterial strains and attractant. This variation in chemotactic responses by the marine isolates may reflect adaptations to specific ecological niches of bacterioplankton in the ocean. However, band forming ability by marine bacteria has still only been reported in experimental studies, nutrient coupling between nutrient sources and bands of chemotactic marine bacteria have yet to be detected in the natural environment. The fragility of the bands, a clear association between free-swimming bacteria and nutrient, indicates the difficulty and potentially sets limits for finding microzones of bacteria around particles in the open ocean.

Aqueous films limit bacterial cell motility and colony expansion on partially saturated rough surfaces

“…Simulation results show motile bacteria prefer to congregate at most favourable nutrient gradient consistent with experimental observations (Adler, 1966; Zhulin et al. , 1995; Fenchel, 2002; Barbara and Mitchell, 2003). High motility could potentially provide a means for rapid and uniform dissemination of bacteria in polluted environments (Witt et al.…”

Helical and rod-shaped bacteria swim in helical trajectories with little additional propulsion from helical shape

“…In addition to the familiar run-tumble mechanism seen in many bacteria, such as E. coli ( 32 ), H. pylori also tends to reverse its swimming direction, which has been related to chemotactic sensing and quorum sensing in earlier works ( 28 , 31 , 38 – 41 ). Such run-reverse swimming has also been seen in several marine bacteria that swim in highly viscous environments ( 42 – 45 ) and in Caulobacter crescentus ( 9 ). We were able to observe reversal events in both the helical and rod-shaped bacteria tracks swimming in BB10, as shown in Fig.…”

Bacterial tracking of motile algae

“…A heat dissipation ¢lter consisting of water in a container 3 cm thick was used to minimise the e¡ect of any temperature changes caused by the microscope lamp [6]. The video image was recorded continuously by a video cassette recorder with a frame speed of 24 frames s 31 (Panasonic NV-HS1000).…”

“…Typically, marine bacteria swim at much higher speeds, up to 400 Wm s 31 [11,12], than E. coli with maximum speeds of only 40 Wm s 31 [13]. Marine bacteria also exhibit a run and reverse strategy, which enables them to form tight ( 6 20 Wm wide) swarm bands around air bubbles or chemical attractants [4,6,14,15]. Based on this run and reverse behavior Luchsinger et al [16] developed a computer model, which showed that bacteria would be able to orient themselves around ¢xed point sources of nutrients in a shear ¢eld.…”

“…In previous studies the nutrient source was assumed to be either a stationary point source or a gradient [1,2,5,6]. Here, we examine the ability of bacteria to respond to a moving point source and explore the limits of manoeuvring by investigating the extent to which bacteria can follow a moving point source.…”