## 3 Results and Discussion  
### Growth of Sde 2-40, B. cereus, and Co-Culture on Agarose and Xylan  
Growth of _Sde_ 2-40 and _B. cereus_, and the co-culture of both strains were investigated. The maximum amount of protein biomass for _Sde_ 2-40, _B. cereus_, and the co-culture using agarose (2\(\%\)\(w\)/\(v\)) as a carbon source in minimal medium at 120 h was found to be 0.892, 0.0417, and 1.11 g/L, respectively (Figure 2A). The lag phase on agarose was slightly longer for _Sde_ 2-40 as compared to the co-culture. The degradation activity of _Sde_ 2-40 in co-culture increased as compared to the pure culture. To confirm this observation visually, a loop full culture from co-culture grown in flask was streaked on sea salt minimal media agar plate. The growth of _B. cereus_ appeared after overnight incubation but _Sde_ 2-40 was not visible until 20 h of incubation at 30 \({}^{\circ}\)C. However, _Sde_ 2-40 colonies appeared on agar plate after 20 h of incubation and rapid increase in agar degradation on plates could be observed as the time progressed (Figure 2B). _Sde_ 2-40 grown alone produced eumelanin and started to die after three to four days of incubation, as observed in earlier reports [3; 34]. However, the colony growth and pit size due to agar degradation by _Sde_ 2-40 increased in the presence of _B. cereus_ and eumelanin was not produced even after ten days of incubation. This indicated that _Sde_ 2-40 cells show active growth in the presence of _B. cereus_ (Figure 2B). Figure 2C shows the growth characteristic of _B. cereus_ on minimal sea salt agar medium. The agar degradation by _Sde_ 2-40 was found to be very low when grown alone, as the pit formed by the colony growth was small and it did not spread far into the surrounding agar medium (Figure 2D). Eumelanin production was also observed with the appearance of black colour in agarose containing minimal sea salt media broth for the pure _Sde_ 2-40 culture but not for the co-culture after 120 h (Figure 2E). This indicated that _Sde_ 2-40 cells do not die in the presence of _B. cereus_, but instead grow well. Similar trends for _Sde_ 2-40 growth were observed with xylan as the carbon source. The maximum amount of protein biomass for the co-culture from xylan was 1.00 g/L, as compared to 0.237 and 0.781 g/L for _B. cereus_ and _Sde_ 2-40, respectively (Figure 3). _Sde_ 2-40 and _B. cereus_ showed higher growth in co-culture. At this juncture, the exact nature of the interactions between _Sde_ 2-40 and _B. cereus_ are not known. Co-cultivation of various strains of lactic acid bacteria showed growth rate increase due to interchange of growth factors [24]. Provision of substrates for the enzymatic activity by a strain to another strain in co-culture can enhance growth  
Figure 3: Growth profiles of _Sde_ 2-40, _B. cereus_, and co-culture on 1% (\(w/v\)) xylan. Figure 2: Characteristics of _Sde_ 2-40 and _B. cereus_. (**A**) Growth profiles of _Sde_ 2-40, _B. cereus_, and co-culture on 1% (\(w/v\)) agarose; (**B**) _Sde_ 2-40 growing on sea salt minimal media agar plate along with _B. cereus_. Increase in pit size with increasing time is indicated by arrows; (**C**) Growth characteristics of _B. cereus_ on minimal sea salt agar media; (**D**) Growth characteristics of _Sde_ 2-40 where agar pitting colonies were turned black; (**E**) Pure culture of _Sde_ 2-40 produced melanin while _Sde_ 2-40 growing in co-culture with _B. cereus_ did not produce melanin. rate [39]. Growth-inhibiting products of one strain can be reduced by another strain and growth of co-culture companion can be improved [40]. Within or between different species, the reaction of microbes for existence of other cell types can be sensed [41]. Microorganisms in co-culture systems can interconnect through uninterrupted cell to cell interactions or via signal molecules in media [42]. The _Sde_ 2-40 bacterium can produce proteins containing many cadherin and cadherin-like domains. These domains help in protein-protein interaction and bind directly to bacterial cell surfaces [43].