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Modelling Movements Of Root Knot Nematodes Biology Essay

A system for monitoring movement of the free-living second stage juveniles of root-knot nematodes Meloidogyne spp. using digital image analysis is described. The method is based on the analysis of video sequences of movement of individual random nematodes encumbered with or without Pasteuria penetrans endospores. Software packages were used to grab video images, to process images and to monitor the movement of selected body part positions over time. Methods include the study of nematode locomotion based on (a) the geometric center (b) the centroid body point, (c) tracking of two or four selected body points and (c) tracking a rectangular shape area produced by the nematode’s body. Data showed that (a) the normal sinusoidal movement of nematodes is changed when individuals are encumbered with endospores of P. penetrans and (b) in all cases a significant greater motility was observed by nematodes without P. penetrans endospores attached.

Keywords: nematode movement, digital image analysis, motion analysis

Introduction

Pasteuria penetrans (Thorne, 1940) is a mycelial, endospore forming bacterial parasite of plant parasitic nematodes (Mankau, 1975; Imbriani and Mankau, 1977) showing promising results in a biocontrol strategy of root-knot nematodes (Meloidogyne spp.), (Stirling, 1991). The endospores attach to the outside nematode body wall (cuticle) of the infective stage, the second-stage juveniles (J2) of Meliodogyne populations (Mankau, 1980). After the J2 penetrates a plant root and begins to feed, the bacterium penetrates the nematode body wall and begins to grow and develop in the developing nematode (Mankau and Imbriani, 1975; Imbriani and Mankau, 1977; Sayre and Wergin, 1977). Eventually, the female nematode body becomes completely filled with endospores (Sayre and Wergin, 1977; Stirling, 1991). Each infected female may contain up to 2.5 million endospores (Darban et al., 2004), which are eventually released into the soil.

The potential of P. penetrans to control of root-knot has been widely studied (Gowen et al., 2008) including distribution, host range, and specificity. Successful parasitism depends on the attachment of 5-10 endospores per juvenile, which is sufficient to initiate infection without reducing the ability of the nematode to invade roots (Davies et al., 1988; Rao et al., 1997; Davies 2009). There may be little or no root invasion if there are greater than 15 endospores attached, inferring that endospore attachment will affect the ability of a J2 to locate and/or invade a root (Davies et al., 1988). Few attempts have been made to quantify the effect of P. penetrans endospore attachment on the movement of infective root-knot nematode juveniles (Davies et al., 1991).

Nematodes move by undulations or wave-like motions through dorsal/ventral contractions of the body (Buchsbaum et al., 1987; Storer et al., 1979) similar to an undulatory swimming motion of eels (Tytell, 2004) and as larval chironomids (Brackenbury, 2003). As one segment of the body contracts, it “pulls” the remainder of the body forward along the body in a head to tail direction (Brackenbury, 2000). There are no previous experimental data to model root-knot nematode movement encumbered with or without P. penetrans endospores. In this chapter a study using digital image analysis is made of the movement of the root-knot nematode (Meloidogyne spp.) and how this is affected when endospores of the bacterium Pasteuria penetrans (a naturally occurring nematode parasite) are attached to the cuticle.

Materials and methods

Nematode cultures

Nematode cultures (M. javanica) were maintained on tomato plants in the glasshouse and fresh second stage juveniles (J2) were collected from infected tomato roots using the methods described by Hussey and Barker (1973).

Preparation of Pasteuria penetrans endospores

A commercial product of Pasteuria penetrans (Pp) (Nematech Co. Ltd., Japan) was used in this study. Fresh J2 were encumbered with Pp endospores as described by Darban et al., (2004). There were three treatments; nematodes free of endospores, nematodes with 5-10 endospores attached were considered as Low Pp and J2 with 15-25 endospores as High Pp treatments.

Acquisition of the video images

Nematode locomotion was tracked with an inverted microscope (MICROTEC 200) mounted with a digital camera (Aptiva 3.2 Megapixel). In all cases a nematode’s movement was observed in water in a 9 cm Petri dish. Nematode movement was recorded in 30 second video sequences. The microscope magnification was x 100 for Figure 1, x 200 for Figures 5, 6 and 7 and the highest magnification (x200) for Figure 40. All video sequences showing nematode locomotion were observed on Movie Maker 2 (Microsoft software) before any further analysis.

Image extraction

Before analysis, images (frames) grabbed from selected 30 sec videos were obtained. A video decompiler (SC Video decompiler software program) was used to extract frames. A total of 390 frames saved in jpg format were obtained from a 30 sec video. Original images were 320 x 240 pixels or 3.3 x 2.5 inches.

Measurement of nematode movement

Measurement of movement (in inches) was performed using image analyzer software Scion Image for Windows (Scion Corporation, www.scioncorp.com).

Image processing and analysis

All frames were saved in a tiff format before importing to the Scion Image software package. For image analysis the 39 frames were aligned in ranks of 10 as the 1st, 11th, 21st and the 31st frame. When an image file (*.tiff) was imported to the Scion Image software program, measurements were performed with the Manual Area Measurement selecting the Measure command of the program. In order to understand the aspects of nematode body posture, measurements were taken of the body movement. For each frame, five measurements were taken; (a) tracking of the nematode geometric center; (b) tracking the nematode centroid body part; (c) tracking of two or four selected body points and (d) tracking a rectangular shape area produced by the nematode’s body. In detail, the measurements of the five above measurements are:

Nematode locomotion

Using the rectangular selection tool of the Scion Image Program and moving the mouse on the nematode image, all faraway nematode body segments were fitted in a rectangle shape in order to estimate the X-Y geometric center (using the measurement options Area, X-Y Center of the Scion Image program). With the geometric center (X-Y center of the rectangle area) it was possible to track the geometric point of the nematode body, or a very close area matching that point. Further, metrics were extracted to an Excel data spread-sheet and transferred to GenStat 7th Edition to create a scatter plot. The trends of two randomly selected individual J2/treatment movement directions are shown in a scatter plot.

Tracking the nematode centroid point and two or four nematode body points

The centroid points, of four random J2 per treatment were tracked using the Elliptical Collection Tool of the Scion Image Program following the procedure described above.

Using the Cross Hair Tool, and moving the mouse on the nematode image four equal-distance nematode body points (mean that the two intermediate points are 1/3 and 2/3 down the length), were marked and their X-Y coordinates were recorded for each frame and analysed in the Program Results window. The points were: 1 the head; 2 the esophagus; 3 the centre of the gut: 4, the tail. All data were extracted as X and Y values on the program Result window and exported to an Excel data spread-sheet.

Using these data it was possible to display the nematode movement, of the centroid body point and the relationship of four nematode body parts, or the relationship of the two intermediate (Ym1 and Ym2) nematode body points, t in all Pp treatments.

Moreover, the equation of nematodes movement based to the centroid point were obtained by fitting the data sets (X, Y values) to GenStat 7th Edition statistical program, a curve fitting system for Windows by using the Program CurveFinder command. Further, the equation of nematodes movement based to four or to two intermediate Ym1 and Ym2 nematode body parts were obtained by fitting the data using the Standard Curves command of the Nonlinear Regression Analysis in GenStat.

Tracking the nematode rectangular shape area

Using the Rectangular Selection Tool of the Scion Image Program and moving the mouse on the nematode image, we fitted all faraway nematode body segments in a rectangular shape in order to estimate the rectangular shape area, using the measurement options Area of the Scion Image Program. Extracted measurements were transferred to Excel and represented the different rectangular shaped areas produced by nematodes encumbered or unencumbered with Pp endospores.

An estimation of J2 motility

The locomotion of nematodes treated with low and high or without P. penetrans endospores were estimates based on the nematode wavelength (λ) and the distance moved over time. The body lengths of each nematode were measured using the Straight Line Selections Tool of the Scion Image Program and moving the mouse on the nematode image marked the nematode head and the tail each time. The same procedures were used to measure the distance covered by the nematode head over time t1 and t2 (frames 1 and 2) (up to 15 frames) moving the mouse from X1, Y1 (frame 1) to X2, Y2 position on frame 2. Data were exported to an Excel data spread-sheet as described above. The absolute body length of a J2 in this research is equal to a 105 pixels as presented in Figures 6 and 7 with a dotted line. Measurements were based on 10 nematodes per treatment and with 15 frames per individual nematode. The time between two frames in sequence was 11.5 sec.

Statistical analysis

Scatter line plots (Figures 1-3) were produced in MinTab 13th Edition statistical program and all other graphs were made with GraphPad Prism5 statistical program. Analyses were performed mainly in GenStat 7th Edition statistical program and in CurveExpert program.

Results

Nematode locomotion

Over the same time period, J2 without P. penetrans endospores attached can move further than those J2 encumbered with low numbers of endospores (Figure 1). That means that the body of a J2 without Pp endospores moves in a direction explained by a linear regression (r2 typically 96-98%). Attachment with P. penetrans endospores probably disrupts this natural behaviour.

J2 without Pp end point

J2 without Pp start point

.

Figure 1. Nematode travel position without P. penetrans endospores (solid circles) and with low P. penetrans endospores (solid squares, top). The arrows indicate the direction of movement (X, Y axis units in pixels). The nematodes without P. penetrans endospores move in a line explained by a linear regression fit y=a+bx with a correlation coefficients equal to 0.9868 and 0.9679 for the two random individual nematodes. Axis scales x, y are measured in pixels (200_250 pixels), value for a straight J2 body length is 10 pixels.

Tracking the nematode centroid point and two or four nematode body points

When data sets based on the nematode centroid body point were fitted with CurveExpert, the best equation to explain the J2 body movement without P. penetrans endospores (Figures 2.1a-2.4a) is the sinusoidal fit, y=a+bcos(cx+d) with correlation coefficients r1=0.9368, r2=0.9396, r3=0.9345 and r4=0.9090 for four random nematodes. When nematodes were encumbered with P. penetrans endospores there was no sinusoidal movement (Figures 2.1b-2.4b and Figures 2.1c-2.4c).

A J2 free of Pp endospores fits a rectangle shape with a forward movement* (figures 1-4a in a column)

A J2 encumbered with low Pp endospores fits in a smaller box with a slow movement (figures 1-4b in a column)

A J2 encumbered with high Pp endospores, fits in box with no forward movement (figures 1-4c in a column)

Box a

Box b

Box c

Figure 2.1a, t=0sec

Figure 2.1b, t=0sec

Figure 2.1c, t=0sec

Figure 2.2a, t=10sec

Figure 2.2b, t=10sec

Figure 2.2c, t=10sec

Figure 2.3a, t=20sec

Figure 2.3b, t=20sec

Figure 2.3c, t=20sec

Figure 2.4a, t=30sec

Figure 2.4b, t=30sec

Figure 2.4c, t=30sec

*Note that the grid lines show that there is a significant movement of J2 without Pp endospores compared to those encumbered with Pp endospores Figs 1-4b and 1-4c.

Figure 2. Nematode body wave formation presented as a rectangle shape movement over time. J2 were encumbered with Pp endospores column b (low Pp) and c (high Pp) or without Pp endospores column a. Arrows indicate the J2 speed.

Our simple tracking system for extracting data from the four or the two intermediate nematode body part points has shown that nematodes without P. penetrans endospores attached have a sinusoidal movement producing a double Fourier curve (equation 1, Table 1). This is represented in Figure 3A where the Ym1 line presents the esophagus and the Ym2 line the gut (R2 = 86.0, P<0.001) and in Figure 3B where the tracking points are the head, the esophagus, the centre of the gut and the tail (R2 = 78.4, P<0.001).

Based on the movement of the four body points, the best curve to explain our data is also the double Fourier curve. This is a compound of two sine waves as presented in Figure 4, one having half the cyclic period of the other.

Y = a + b*sin(2*pi*(X-e)/w) + c*sin(4*pi*(x-f)/w)

equation 1

Figure 3. Motion analysis and position of nematode body parts over time. Nematodes were not encumbered with P. penetrans endospores. Analysis was performed using GenStat Statistical Package based on (a) Ym1 (esophagus) and Ym2 (gut) data sets and (b) on four nematode tracking points (head, esophagus, gut and tail). Y axis, is in proportion to nematode body length which is equal (in this study) to 1.8. and X axis is in frames where 39 frames are equal to 30 sec.

Table 1. Estimates of parameters (w) for equation 1

Nematode body parts

estimate

s.e.

Head

40.17

3.88

Y1

34.8

1.06

Y2

32.68

1.22

Tail

7623

344.7

Head

Ym1,Ym2 & Tail

Figure 4. Motion analysis and position of nematode body parts (XY) over time. Nematodes were free P. penetrans endospores. Analysis was performed based on the Head, Ym1, Ym2 and the J2 tail data sets.

The observation that a nematode body produces a sine wave is further tested using the MotionPro software program ver. 4.4.2., by PDSofTec (www.pdsoftec.com), based on head region turns. The directions of head region rotation were observed based on nematode movement and displayed as a set of points (dots) in real time when nematodes moved (Figure 4).

With nematodes free of endospores we observed that the 2nd, 3rd and 4th body part follows the head movement. This does not happen when the nematode is encumbered with P. penetrans endospores at low or high density (Figures 2.1b-2.4b and Figures 2.1c-2.4c).

Tracking the nematode rectangular shape area

The analysis showed that the nematode without P. penetrans endospores produced a rectangular shape with a significantly greater area compared to nematodes encumbered with endospores (Figure 5). This was confirmed with the Movie Maker 2 software program where each nematode video was observed (Figure 2). We conclude that nematodes without P. penetrans endospores fit a rectangle shape with a strong forward movement equal to the rectangle shape in Figure 2 marked as box a, whereas nematodes encumbered at a low or high density of endospores could fit to rectangles equal to boxes b and c in Figure 2. There was little movement of J2 encumbered with high P. penetrans attachment and several times they were seen to collide.

Figure 5. Rectangle estimation results for J2 motion treated without (left) or without P. penetrans endospores (middle and right). The major (long) rectangular side presents J2 forward movement where the minor (short) presents the width of the sinusoidal J2 body motion. The value of two (2) in Y axis is equal to the value for a straight J2 body length.

An estimation of J2 motility

The measurements based on the nematodes locomotion shows a significantly greater wavelength (λ) and distance movement values for nematodes without endospores attached compared with nematodes encumbered at a low or high density of endospores (Figures 6 and 7 respectively). Nematodes encumbered at a high spore density showed insignificant movement (Figure 7) confirming observations shown in Figure 2 where nematodes’ faraway body segments can be fitted in a box with an insignificant or no forward movement.

Figure 6. Differences in J2 body length [= a nematode wavelength (λ)] during motion in treatments with or without P. penetrans endospores. Dotted line represents a straight J2 body length which is equal (in this study) to the value 105 in Y axis.

Figure 7. Distance moved by J2 with or without P. penetrans endospores (N=10) in 15 sequential frames (=11.5 sec). Dotted line represents a straight J2 body length which is equal to the value 105 in Y axis.

Discussion and Conclusions

In this paper we present a technique to track a plant parasitic nematode movement using a digital camera and an inverted microscope. Similar techniques where shown in Baek et al., (2002) and Cronic et al., (2005) where the authors used a microscope fitted with a camera and a videtaping (VCR) system to record movement of Caenorhabditis elegans.

Using free Internet software packages such as the SC Video Decompiler we extracted images (frames) from video files (.avi format) for further analysis. This is similar to Cronic et al., (2005) who took their data to a PC using a Matrox Meteor-II/Standard video frame grabber hardware and the Recognizer 2.1 software package.

Further, with the commercial software package Scion Image we collected data taking selected nematode body points. Similarly, Cronic et al., (2005) presented the same ideas for data extraction and processing in Matlab called Wormproc; they showed many C. elegans measurements and histograms grabbed at 13 points and from the centroid point of the body respectively. Greng et al., (2004) identified and tracked separately the head and tail movement of C. elegans. In our studies we employed the GenStat statistical program and the Standard Curve Routine, a tool of the regression analysis and we described effectively with the double Fourier curve the motion of four or two body points in nematodes without Pp endospores. Wallace (1958; 1959), Baek et al., (2002); Cronic et al., (2005) concluded that nematodes produce a sinusoidal movement. In our studies we showed that the nematode motion is a compound of two sine waves, one having half the cyclic period (have a period of 10 frames, as presented in figure 3), of the other (double Fourier curve).

A natural characteristic is that all nematode body parts follow the movement of the nematode head (Niebur and Erdos, 1991) and this is demonstrated. However this did not occur when the nematodes were encumbered with Pp endospores, probably because the endospores impeded forward movement. Moreover we show that J2 encumbered with high numbers of endospores show no forward movement, appeared disorganized by the Pp endospores suggesting that high Pp endospore numbers attached to the nematode cuticle have a significant impact on movement with a significant impact on locomotion (Vagelas et al., 2011).

The nematode rectangular shape area produced by a nematode’s body parts proved a very good estimator to describe nematode locomotion for nematodes without endospores and those encumbered with low and high numbers.

Nematodes without endospores move faster than those that are encumbered. Moreover those nematodes moved in a straight line in the same direction and covered a longer distance than those with endospores. Those nematodes pulse the body with a wavelength (λ) equal to a straight body position, probably this is a random walk with memory as suggested by Hapca et al., (2007). Wallace (1958) observed the same for Heterodera schachtii migration in soil and he concluded that the maximum speed of the H. schachtii J2 is attained when there is no lateral movement and each part of the body follows the part immediately in front of it.

Finally it can be suggested that this research could be improved with more emphasis on mathematics developing codes e.g. on the Matlab software package, study longer times of observation to get more waves and hence estimate parameters more accurately.

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