The bacterium Sporosarcina pasteurii (SP) is known for its ability to cause the phenomenon of microbially induced calcium carbonate precipitation (MICP). We explored bacterial participation in the initial stages of the MICP process at the cellular length scale under two different growth environments (a) liquid culture (b) MICP in a soft agar (0.5%) column. In the liquid culture, ex-situ imaging of the cellular environment indicated that S. pasteurii was facilitating nucleation of nanoscale crystals of calcium carbonate on bacterial cell surface and its growth via ureolysis. During the same period, the meso-scale environment (bulk medium) was found to have overgrown calcium carbonate crystals. The effect of media components (urea, CaCl2), presence of live and dead in the growth medium were explored. The agar column method allows for in-situ visualization of the phenomena, and using this platform, we found conclusive evidence of the bacterial cell surface facilitating formation of nanoscale crystals in the microenvironment. Here also the bulk environment or the meso-scale environment was found to possess overgrown calcium carbonate crystals. Extensive elemental analysis using Energy dispersive X-ray spectroscopy (EDS) and X-ray powder diffraction (XRD), confirmed that the crystals to be calcium carbonate, and two different polymorphs (calcite and vaterite) were identified. Active participation of S. pasteurii cell surface as the site of calcium carbonate precipitation has been shown using EDS elemental mapping with Scanning transmission electron microscopy (STEM) and scanning electron microscopy (SEM).

The particular bacterium under investigation here (S. pasteurii) is unique in its ability, under the right conditions, to induce the hydrolysis of urea (ureolysis) in naturally occurring environments through secretion of an enzyme urease. This process of ureolysis, through a chain of chemical reactions, leads to the formation of calcium carbonate precipitates. This is known as Microbiologically Induced Calcite Precipitation (MICP). The proper culture protocols for MICP are detailed here. Finally, visualization experiments under different modes of microscopy were performed to understand various aspects of the precipitation process. Techniques like optical microscopy, Scanning Electron Microscopy (SEM) and XRay Photo-electron Spectroscopy (XPS) were employed to chemically characterize the end-product. Further, the ability of these precipitates to clog pores inside a natural porous medium was demonstrated through a qualitative experiment where sponge bars were used to mimic a porenetwork with a range of length scales. A sponge bar dipped in the culture medium containing the bacterial cells hardens due to the clogging of its pores resulting from the continuous process of chemical precipitation. This hardened sponge bar exhibits superior strength when compared to a control sponge bar which becomes compressed and squeezed under the action of an applied external load, while the hardened bar is able to support the same weight with little deformation. Video LinkThe video component of this article can be found at

Fiber configuration in sliver and the incidence of hooks in sliver and rovings have been studied, employing two different techniques. It has been established that during the drafting of sliver at draw frames, trailing hooks are removed preferentially as com pared to leading hooks. The direction of presentation of hooks in the ingoing material (sliver or roving) at the ring frame has been shown to have a considerable effect on yarn strength and evenness. For best results with carded yarn, the majority of hooks in the feed to the ring frame should be presented to the drafting system in a trailing direction, i.e., there should be an odd number of processes between carding and spinning.

The effect of various carding parameters on hooking and loading characteristics and on yarn quality has been investigated for a California 15/32 -in. cotton.Lickerin speeds and method of doffing the card web were shown to have no effect on the pattern of hook formation which is influenced mainly by cylinder and doffer speeds and the hank of the delivered sliver. These same factors also influence the loading on the cylinder and the coefhcient of transfer of fibers to the doffer. No clear-cut relationship between loading and hooking has, however, emerged. Increased doffer and cylinder speeds, at a constant carding rate, were seen to decrease yarn imperfections..

Hook formation at fiber ends and fiber disorder in the card sliver have been studied by using a fluorescent-tracer-fiber technique and Lindsley's method for measuring comb ing ratio. The rate of throughput at the card and the cylinder and doffer loadings have been shown to affect the proportions of the different types of hooks in the sliver. Other factors, such as the type of wire on cylinder and doffer, the action of flats, and the doffer comb speed, have been seen to have no influence on hook formation. Within the range of speeds investigated, the speed ratio between doffer and cylinder has little influence on hook formation. On the basis of the results obtained and the different hypotheses of Morton, it is suggested that the trailing and leading hooks are both formed at the junc tion of cylinder and doffer, but by different mechanisms.