Chief scientist, two board members exit Twitter

Defections at Twitter are mounting. Not only is Chief Scientist Abdur Chowdhury the latest ranking technologist to resign from the San Francisco-based company, but two key board members are also stepping down.

Fred Wilson and Bijan Sabet, two of Twitter's earliest investors, will be leaving at the end of the month. Twitter confirmed this to Peter Kafka at AllThingsD. In early August, Twitter announced that it closed an $800 million venture deal--the largest in history--led by Yuri Milner's Russian venture capital firm DST Global. This brings Twitter's valuation to $8.4 billion. DST also invests in Facebook, Groupon, and Zynga. In keeping with new social-media norms, Chowdhury, Twitter's former top ranking scientist, tweeted about his departure Wednesday. TechCrunch reported on his exit earlier today.

The news adds to a growing list of key staffers abandoning the popular microblogging service in recent months. Twitter co-founder Biz Stone retreated in June to work on a new startup with Evan Williams, Twitter's other co-founder; and four engineering product leads were apparently fired in late July. Media reports indicate that those departures were initiated by Twitter Chairman and Co-Founder Jack Dorsey, who's been busily ushering out all staffers who were associated with Evan Williams' and Biz Stone's core founding team.

Chowdhury and four of his engineers came to Twitter from Summize, a search engine Chowdhury helped co-found, and that Twitter acquired in 2008. Greg Pass, formerly CTO of Summize, joined Twitter as director of engineering and ops. He, too, left Twitter, in May. Now there are no remaining employees from Summize at Twitter, which may point to a change in how real-time search is handled going forward.

As Dominic Litten from Cleveland, Ohio, tweeted this morning:

"Now that everyone from Summize has left Twitter, (tcrn.ch/nZWdCK), can they get someone to make their search function useful?"

Ouch.