Mutant/mutation
The mutant lacks expression of B9 

Protein (function)
The B9 protein contains a 4-cysteine domain with a structure that is highly similar to the structure of 4-cysteine domains in the known proteins of the 6-Cys family and is identified as a 6-Cys-related protein. B9 is predicted to be glycosylphophatidylinositol (GPI) anchored. 

Phenotype
Normal numbers of motile salivary gland sporozoites are formed. While 30 wild-type sporozoites were sufficient to establish infection in all rats, even 1 × 10 B9(-) sporozoites were insufficient to establish infection in all rats.

B9(-) parasites formed abnormal liver stages (LS) and displayed increased cell traversal activity. The number of B9(-) LS parasites formed in HepG2 cells was 6% that of wild-type parasites at 24 and 48 h post-inoculation (hpi) of sporozoites. The average diameter of the B9(-) LS parasites decreased to approximately 80% that of wild-type LSs at 48 hpi. There was a decreased number of sporozoites entering the hepatocytes by productive invasion and reciprocally, an increased number of sporozoites that continued migration through the hepatocytes. Evidence is presented that B9(-) LS parasites develop in the nucleus of hepatocytes. Evidence is presented that sporozoites lose the capacity to switch invasion modes by disruption of either B9 or P52 (see also mutants RMgm-5267 and RMgm-5268). 

Additional information
To demonstrate that B9 is expressed in sporozoites, parasites expressing this gene as a FLAG tagged protein were prepared using a centromere plasmid, followed by immunofluorescent staining of the salivary gland sporozoites. The tag was inserted near the N-terminus of the protein following the predicted signal peptide (because the C-terminus portion is predicted to be cleaved by modification of the glycosylphosphatidylinositol (GPI) anchor. The B9 protein was detected in small particles in the cytoplasm and co localized with P52, suggesting that it is targeted to micronemes as other members of this family that are expressed at this stage.

From the paper: We also performed cell wounding and membrane repair assays to evaluate the cell traversal activity of B9(-) sporozoites . The number of HepG2 cells damaged by invasion of B9(-) sporozoites was approximately 3 fold higher than that of wild type parasites. These results suggest that the disruption of B9 impaired the switching capacity of sporozoites . More specifically, there was a decreased number of sporozoites entering the hepatocytes by productive invasion and reciprocally, an increased number of sporozoites that continued migration through the hepatocytes . This phenotype of B9(-). is similar to the previously reported phenotypes of P52 disrupted P52(-) and P36 disrupted P36(-) parasites

At 8 hpi wild type sporozoites were observed near the nucleus and inside the PVM, extending towards the nucleus of HepG2 cells. In clear contrast, very few B9(-) sporozoites were observed in the cytoplasm and UIS3 was not detected around them, suggesting that no PVMs were formed around them. Most B9(-) sporozoites were located in the nucleus and were in the process of transform ing in to the LS. UIS 3 was not detected around them. At 24 hpi wild type LS parasites developed into LSs near the nucleus of HepG2 cells At the same time, B9(-) parasites had transformed into LSs inside the nucleus of HepG2 cells and had undergone multiple nuclear divisions. At 48 hpi B9(-) LSs significantly increased in size compared w ith that at 24 hpi, but the progress of their nuclear division varied and their development was obviously delayed compared with that of wild type LSs. No LSs were identified in the cytoplasm at 24 and 48 hpi. An insignificant number of wild type LS parasites were located in side the nucleus of HepG2 cells and, similar to B9 (-) LS parasites, they had no PVMs and exhibited retarded nuclear division. 

Other mutants